LM1875 IC audio amplifier board kit test and review

Low priced solder together chip amp kit from eBay. Is it any good? You might be surprised!

[@user-bu9rj5sf3u]

Low cost, high power, small chip with good sound quality. Impressive.... Thanks.

[@seans1102]

It's funny I bought this kit to practice soldering and expected it to be garbage. I also bought two 24v regulated supplies for an lm1875. Thanks for the review.

[@freddiebell2813]

I can say from personal experience, the entire line of Texas Instruments IC audio chip-amps, LM class is awesome. I've been home hobby DIYing these chips for 20 years. If you breadboard them, keep the connections as close as possible, use better than average resistors and caps, good power supply/transformer, adequately cool, you WILL get amazingly, unexpected audio-sound straight into those beautiful speakers you would not test the finished board with. I started low years ago, then advanced to the LM3886. Try it, you'll be amazed if you're a newbie.

[@AndrewSosa]

I'm new to this stuff and I want to build my own Bluetooth amps with Texas chips for Portable speakers but I have no clue on how to wire them could you help?

[@funkytransport]

"better than average resistor"... em OK...

[@jetsam8073]

I bought two of these from that river store place, built them up, stuck them in a box, connected them to my audio interface and a decent old dual bench supply I have. They work great; I'm using them right now. I have one problem I don't know how to fix: they almost always don't start up correctly on powering on. I guess they get stuck in some power blowing oscillation; not sure. I get no sound, and the voltage is low, current high but not too high. I need to touch the non-isolated heat-sink on the chip of one channel to make the amp go "schquwreeEEeEchhhChttts...." Then it starts working... Thanks for the recommendation. It's a fun project, and it sounds great powering some inexpensive thrift-store bookshelf speakers, originally from a decent set of home theater speakers. I enjoy your channel a lot. I don't always have the time or ability to follow everything; your long amp series is pretty complex, but I've learned a lot from your videos. So thanks... Make more, please. :)

[@logotrikes]

Hi John, with regard to the 10uf coupling cap, can I use motor-run caps? (I think they're metalised polyester). I can get em cheap at 400v even though that's overkill. Otherwise I'll just use suitable polyester or polyprop caps, rated at say 50 or 63v. Cheers, Martin

[@bluesman608]

Thanks for your videos, John! I am really learning a lot from you and ordered four of these kits. I built one and powered it with your virtual ground and a 19.5 volt laptop supply. Weird thing - The voltages read +/- 9.63 V from the supply but once connected to board, they become lopsided! -13.3V and +6.2V. The amp worked initially so I put it in an iPhone box with a 8 Ohm speaker to use with my laptop. After a couple months it began distorting sometimes. Today I built a second kit with an LM1875 from Mouser. Again, lopsided voltage. It is as above without speaker connected and -17.76V and +1.83V with the speaker. Any idea how to fix? Also there are two 10 Ohm resistors but schematic shows a 10 Ohm and 1 Ohm. The 1 W resistors measure 1 Ohm. Weird.

[@GaryGolbraich]

Hey John, I decided to order few of these boards. I thought buying from DigiKey resistors and caps and using them instead of the questionable supplied ones. But I am getting confused as to which voltages, materials, tolerance and value should I get from DigiKey..,. Is it possible that you list which capacitors and resistors are recommended assuming all the components to be replaced ?

[@erlfram]

What is the breadboard-thingy at 9:02? Something clever to turn stereo into mono sound? In that case, do you know if something like that can be bought of the shelf? (ebay)

[@xaenon]

I would guess that your LM1875 chip is a 'factory second' - something that was not cosmetically up to QA standards, but still functional, possibly sold to a distributor or wholesaler at a deep discount rather than scrapping it

[@williamstaten8102]

Got a few of these kits. The boards seem really well made, better than most OEM stuff. My soldering iron seems magnetized, it also charges caps while soldering them in.

[@1pcfred]

Check to see if your soldering iron tip is grounded. It should be.

[@IliyaOsnovikov]

John, have you found these boards separately? I would like to build a power rail splitter with LM675 on this board. But it seems like that the most of these kits are sold now with some lower quality PCBs.

[@alvin10388]

Thank you for this info,I just bought one, should received soon. what Ac power required for this board

[@FreshLemunz]

Quick question. Are you ever going to review the LM3886 board? I have heard they are good for HiFi but want to see your thoughts on it. Thanks.

[@teohchiawei]

which board are you referring? is it on internet?

[@tightirl]

hey john I got a similar kit to the one you have in this video but I cannot for the life of me get it to produce any noise or anything really. I'm wondering if I did the power supply wrong or am misunderstanding? I used a ~19 volt laptop supply and a separate equal voltage lab bench PSU hooked up to give me dual rails. I tried to build the circuit on my own with my own parts as a proof of concept and have seen this video many times so I am pretty familiar with the component layout so I'm pretty sure that's ok...Do you have any advice as to where I should look first? Also, assume I am totally ignorant because I am.

[@andreasolsson451]

Can you explain what happens if you use a lower/higher voltage psu? I'd like to come up with a good battery powered amp and was considering using 4x 4v batteries to get 16v (I think this is the minimum?) Thanks

[@shrek477]

There's an electronics magazine in Australia called Silicon Chip, and the December 2004 issue had a project called Schoolies Amp which is where the design for this amplifier section came from (it also had a power supply). They've also published some other good DIY amplifier projects (including the Ultra-LD series), for which they sell the PCBs on their online shop. And the more recent projects are often available as full kits at the local electronics retailers in Australia.

[@DasAntiNaziBroetchen]

How do you know the magazine was first, and not some chinese seller?

[@RexxSchneider]

@@DasAntiNaziBroetchen Because it's not in the Guinness Book of Records for the first time that a Chinese seller created an original circuit instead of ripping off somebody else's work.

[@sultanmahmud6267]

which circuit would be best for 20V 3amp power source (laptop adapter) and how many speaker i need .plz let me know.

[@caspartech3893]

Hey John, Do you have a schematic for a pre-amp with 3 band eq and gain or volume? I would like to build this amp as an on-board practice amp for my guitar pedal board. If it sounds good enough, I may utilize it for small venues. Thanks for the awesome videos. Chad A Sparling

[@JohnAudioTech]

Check Elliot Sound Products site. He has tone control opamp schematics. I straight feed my amplifiers (no preamp or tone controls). I can see the need for a guitar amp, however. I plan to look at opamp filter circuits at some point.

[@teohchiawei]

please share

[@seans1102]

Guys Im looking to add a amp for bass duties to go along with this amp are the tda 7293 enhanced boards any good for that other than the power aspect? I plan to use them at 8 ohm loads so still plenty of power.

[@amitghosh6966]

I have an Lm1875 chip with packaging similar to Tda2030A and 2050 that is two scoops on both sides (slightly upper than the authentic one) but no other similarities as in the Tda20xx chips. Is it the good chip ?

[@gkdresden]

@JohnAudioTech, I am a little bit puzzled by the input filter of this chip amp. Especially, the function of the 10 Ohm separation of the input ground from the output ground is not clear for me. Could you please explain this for me?

[@RexxSchneider]

It's to increase the channel separation when a pair are used as a stereo amp.

[@KarlAdamsAudio]

Nice little kit. I'm not surprised you don't see distortion on your scope's FFT, though - with an 8-bit ADC you get approx 48dB of dynamic range, so the minimum level of THD you could possibly see would be around 0.4%, something you're unlikely to see in a solid-state amplifier that's not being driven into clipping.

[@JohnAudioTech]

I tested this once by making a tone with a built in harmonic to see if it would show up. 1.0% and 0.5% were clearly visible on the FFT. 0.1% is lost in the noise floor. I never calculated were the cut off would be, so this makes sense. I'd like to get a spectrum analyzer or a distortion analyzer but these are currently out of my reach. There is some debate at where distortion can start to be perceived in music but most agree that under 1% should be inaudible (in most cases).

[@thomaslapsley7867]

Hi John, I brought and soldered the LM1875 kit together and I'd like to but this in a cabinet. Can you make a recommendation on an inexpensive power supply for this LM1875 audio amplifier board? I understand the board requires a two-rail power supply of +25VDCand - 25VDC. I looked at a transformer with a full wave rectifier that would put out the voltages, but those transformers are expensive. Any ideas would be appreciated. Thanks, Tom

[@themouseisinthehouse]

Hi! Would this be able to power a 125w PA Speaker? And maybe loud enough for a band(with drums)? I'm planning to use it for keyboard or acoustoc guitar. =)

[@JohnAudioTech]

It depends on the sensitivity of the PA speaker. If the speaker was rated 98db @ 1w, you could get around 111db at 20 watts. If that is good enough depends on how loud the rest of your band is and where you play.

[@caspartech3893]

Hi John. I found a CT transformer, but it has 3 input leads and, of course, 3 output leads. label says: Primary 115/230VAC to 24VCT. Will this work for this application?

[@JohnAudioTech]

That might be good for 15 or so watts into a 4 ohm load if the tranformer is large enough. Do you know its current rating? If not tell me the core size and I can estimate the current rating.

[@sanjoy2521]

Please publish a video on Lm1875 at Single supply taking readings on different supply voltages.

[@trainzntrainz]

Is it normal, that my amplifier became 2 times more quieter, after replacing those 100uF 50V with 220uF 50V Nichicon FW's? I am rebuilding a soviet AB class amplifier, and I have put two of these boards in it. I guess it's time to give it a new preamp stage?

[@DasAntiNaziBroetchen]

I'm not an expert, but that doesn't seem right. I replaced audio caps on my amps with equivalent voltage and capacitance Nichicon audio caps and noticed no difference. Did you measure all parts to make sure the capacitances and ESR are where you expect them to be?

[@marekbax513513]

Hi may i have question ? how I can control bass or make bass more powerful on this board with LM1875T. Thanks

[@JohnAudioTech]

Do nothing to the board. It is meant to boost the voltage and current of the signal to drive a speaker with a flat frequency response. If you want more bass, use a preamp circuit with bass boost.

[@25830]

Hi John, I've commented before and I have to say that yours is hands down my favorite KZbin electronics channel! I watch pretty close to all your videos and I always learn more every time I watch one! This particular video I've watched quite a few times and because I'm pretty much electronics illiterate, I pick up more tidbits of useful info every time I watch it! Thank you for taking the time to do these vids! I purchased and built the stereo version of this kit recently. And I actually just finished it a couple of days ago. It sounds fantastic! I didn't use the supplied ICs that came with the kit, I ordered new ones from Digikey to be on the safe side. The only issue I'm having is when I power the amp on or when I power it down, there's a slight audible snap in the speakers. Not a big deal, but a little annoying. Can I add a cap and/or resistor somewhere in the circuit to eliminate these snaps? Thanks again, John for all you do!

[@JohnAudioTech]

Thanks for the kind comment! I'm glad you bought new ICs because they are now supplying counterfeit chips with these kits. I had another question today about power up/down thumps and clicks plus some in the past. I think I'll do a video on it because there are many scenarios and solutions for it.

[@25830]

Excellent! Thank you. John!

[@IsraelLopezMascorro]

Hello, what are you using as sound input?

[@Berkner80]

Never built one. Is it better to buy a kit like this your first time? I’ve soldered components before but never built an amp before but looks fun.

[@danilocruz4265]

hi john i really love your videos.that schematic i believed is from silicon chip and the pcb lay out

[@Tbonyandsteak]

Just bought 4 pieces due to your recommendation, they also claim to have S/N ratio up to 105 db, Very good!!. My old Marantz amplifier has just a little over 90 db. Having a kitchen speaker project, this is just perfect for that. Really like the simplicity of that board, easy to understand.

[@looseralexa7841]

Where to buy lm1875 full kit?

[@audiotechlabs4650]

For me John, these videos are very valuable! I want to to know about these low power audio amps and I don't have the time to research what's out there, thank you so much! Will this chip run on less voltage, say 9 volts or maybe 12 volts? I know the power out put would be lower, but does it have a minimum threshold voltage? Here goes another small amp! Thankz

[@JohnAudioTech]

9 volts is too low but 12 volts could work. It requires a split supply, so 12v is actually +6 and -6 volts. Power supply voltage vs. output power is an exponential function, so expect to get only about a watt or two at such a low voltage.

[@iblesbosuok]

I always put a 100nF film cap in parallel with 47uF electrolytic cap. Gives additional stability. Cheers from Indonesia

[@rich1051414]

Lowers the ESR. I always use good low esr panasonic FM series caps and on the scope, i can see very little if any improvement doing that, but yeah, it can't hurt, especially if you are unsure about the ESR of the electrolytic. Don't put ceramics in the signal path though :)

[@kurtvisti]

Hi John, Love your channel! With a proper power supply these kits sound great. To achieve best sound quality which of the components do you suggest changing to a more “reliable quality”? Would you change any of the components values?

[@JohnAudioTech]

I would change all the passives (caps & resistors) to known good brands. This is no guarantee that the sound or reliability would actually be any better but would make me feel more confident knowing that better parts were used.

[@kurtvisti]

JohnAudioTech I’ll do that...assemble an extra stereo-version with non-ebay components for a blindtest.

[@jakepeterson5199]

Hi John, nice work as usual. Subscribed awhile ago on different account and always enjoy your videos. I've been wanting to build a lm1875 amp for awhile and finally getting around to it. Do you have a video on designing the power supply for it? I've built bipolar supplies before but was wondering if the lm317 and 337 would handle the current of the 1875 if I built 2 mono blocks? Could I view it as 3 amps of handling current? 1.5 for lm317amps and another 1.5amps lm 337 together?

[@JohnAudioTech]

Hi Jake, Why use regulators? Power amp stages normally don't need them.

[@jakepeterson5199]

I just wondered if it would improve the circuit at all. Maybe improve power supply noise rejection, and protect chip against voltage spikes. I know most people just use a large amount of capacitance to filter but have also seen people suggest a regulated supply is better, some even suggest the sound may be slightly improved so just curious. I'm also am trying to decide if I should build two mono blocks to separate signals more and prevent any cross talk. I also have two of the same power transformers which will only handle one channel each.

[@caspartech3893]

Also, do you have advice or a direction on finding inexpensive speakers which are very efficient?

[@JohnAudioTech]

Efficient speakers that cover the audio spectrum and sound good tend to be quite large. PA speakers can be quite efficient. It's all relative and depends on exactly what you want. For myself, I left the loud booming bass for a more accurate sound reproduction.

[@DuyPham-123]

Can I use DC power supply with this board ?

[@tjbrison]

As usual great video. i would love to know how to connect 2 of these modules to give stero output?

[@RexxSchneider]

Just mark one as the left channel and feed the left input into its input and take its output to the left speaker. Then mark the other as right channel, feed the right input into it, and connect the right speaker to its output. You can use the common input ground wire as the ground input for both left and right modules.

[@adryanyork3581]

Question for you from a DIY new be. Could you hook one of these boards for each speaker and run them from the left and right output of a bluetooth board? or, would it not be worth the hassle? Great Vids mate, keep up the good work. Cheers .................my answer was at the bottom of the comments haha................ Ta

[@seans1102]

John are you saying that one cap needs reversed to be ok for dc? Im going to be using ac to dc power supplies.

[@JohnAudioTech]

The input cap will work either direction. I was just pointing out that it was marked on the board backwards from the schematic.

[@SciPunk215]

I'm seeing kits for the LM1875T on eBay. It looks the same. Not sure what the T means.

[@logen85]

Hi! I think I saw you recommend a power supply for this in one of your videos..? Is there a schematic available for this?

[@JohnAudioTech]

Here is a video discussing an audio amp power supply. You would have to use a lower voltage transformer for the LM1875. kzbin.info/www/bejne/g2GXnHWtfKmCn8k

[@logen85]

@@JohnAudioTech Thanks! :)

[@reynolds087]

How do you control the output volume of this board? Is it controlled by the input signal level?

[@JohnAudioTech]

Yes. You would need to add a volume control to the input.

[@amitghosh6966]

I have questions- 1. Which type of work input capacitor is better for audio amplifier ? Ceramic or Metal film ? 2. If I want to use two numbers of lm1875 boards like this to make stereo , how should I connect the grounds to reduce noise and oscillation ?

[@JohnAudioTech]

1. metal film. 2. treat each amp as separate unit. Power supply ground is the only common point.

[@ggieo63]

Could this circuit handle higher input wattage or does it need to be a rca level input?

[@JohnAudioTech]

It is line level. For higher levels, use a resistor divider to lower the level.

[@Tbonyandsteak]

Btw wondering if you can implement a filter to an active into this circuit, since you already have that 10 uf in the signal line. The advantage with that is that you save a lot of components in the signal way. You could take a 1 uf instead of the 10 uf to a high pas filter to a treble speaker. You gain transparency with lesser component in signal way.

[@johncoops6897]

Of course you can add a filter onto the input. The vlue 1uF is not relevant however, since the impedance (resistance) across the input terminals is nowhere near as low as across a speaker coil. You wouldn't save ANY components doing it that way... a filter is a filter, no matter how you cut it. So, you save a inductor and capacitor in the crossover, but add a capacitor and resistor onto the PCB. For active crossovers, you are better to use a Preamp that incorporates those parts and functionality

[@Tbonyandsteak]

@@johncoops6897 Hi, and thx. Reason for speculating on this is doing a 6 db crossower, preamp already, 6 channels to 6 speakers, have some really good tweeter that can handle low frequencies. So, but since they are quite expensive it might be a good idea to add another filter on them that is one octave lower, just for protection. So it does have preamp already, although this amp only needs 600 mvolt acording to John. Yeah 6 db have pro and cons, some swear to it, while others do not. Depends from were you are looking at it. Since I value Transparency high on my list, this is my choice. Man, In my experience many producers over speculate feedbacks and adjusting components with make tons of it in the system. Due to they are infected with demands and stats. My old Marantz amplifier was a beast at it. When I bought it sounded terrible, compared to the previous amp that I had, a Luxman. I got the recommendation to cut all feed back in the input section, HUUUGE EFFECT. There were tons of component in the input line. I just cutted them off, all of them were short cut's components, so I did not even needed to rewire anything. It turned from a sound like a transister radio to sound like an actually high end amplifier with a very natural transparent sound. And no nothing came unstable, when it is in the signal way at the input section at the input terminals. Just think about it, when ever adding a resister, a coil and a capacitor, you removing information of the sound. And it all sums up or rather remove away. When it become complex you have no way at all knowing what it does to its sound information. Especial short cutting components, taking the life out of the music. Sound is many things and very fragile, terms like Transparency, natural, dynamic, details and colors of the music shows that and how does the component handle that in its frequencies range.??? I know not many knows this, since this is only discussed in hifi forums and magazines. So do not be too theoretical about it, make it simple. Cant be highlighted enough. Simplicity is key to brilliance ~~Bruce Lee. Best amp I ever heard had no feed back at all.

[@TheGazLab]

I have a transformer here 12-0-12, any good to power this? 0 to ground?

[@JohnAudioTech]

Yes that would work if it can supply enough current. I don't know your knowledge of power supplies, but you need a rectifier bridge and a couple filter capacitors to make a split DC supply to power the board.

[@MrSamu1]

Hi john, really good videos you have on this channel. Could you make a video where you explain how you do the powertest. what frequency do you use and maybe show what are you feeding in. Many times that part stays little bit unclear to me. Ps. i like most vids where you explainings analog circuit and how to calculate right component values that's just something that is not done enough here in youtube. keep up the fantastic work. Pps snickers is a awesome electronics lab cat.

[@JohnAudioTech]

Thanks Samuli! I might make an updated video on power testing. I did describe it in one of my early videos. I can't put the link here because YT seems to think links are spam.

[@MrSamu1]

JohnAudioTech whats the name of that vid?

[@JohnAudioTech]

"Audio amplifier power measurement and power supply repair"

[@rangerdoc1029]

Did you ever find a source for just the PCBs? If not, I'm thinking of making some.

[@JohnAudioTech]

Someone sent me bare PCBs. I don't know where they are from but apparently they are out there.

[@neogeo106]

thanks for the review

[@bluesman608]

Apologies if someone already asked, but how do you calculate the thermal resistance (C/W) needed for the heat sink? I want to make sure I get the right value when I order heat sinks.

[@RexxSchneider]

You first need to know the maximum temperature rise allowed for the semiconductor junctions. For the LM1875, the thermal cut-off will operate at 170°C for a single event, or at 150°C for repetitive temperature rises. So assume you want to limit the maximum junction temperature to 150°C. Then determine the highest ambient temperature you can allow. Let's say 30°C as an example. So the maximum temperature rise is 150° - 30° = 120°C. Next work out the maximum power dissipated in the chip. Without any load. the chip takes a supply current around 100mA. If you use ±25V supplies as in the video, you'll dissipate 50V x 0.1A = 5W quiescent, which means you are always going to need a heatsink. The datasheet gives graphs showing power dissipation vs power output for various supply voltages , but for ±25V supplies delivering 20W into 4Ω load will dissipate 32W internally, or about 19W if driving an 8Ω load. Driving a 4Ω load, to dissipate 32W with no more than a 120°C rise, you need a junction-to-ambient thermal resistance of 120°C / 32W = 3.75°C/W. The chip has an internal junction-to-case thermal resistance of 2°C/W and the TO-220 package has a case-to-heatsink thermal resistance of 1.6°C/W using a mica insulator and heatsink compound. That leaves just 3.75 - 2 - 1.6 = 0.15°C/W for the heatsink, which is impractical. If you electrically isolate the heatsink, you can leave out the mica insulator and mount the tab directly to the heatsink reducing the case-to-heatsink thermal resistance for the TO-220 package to 1°C/W. That means you need a 3.75 - 2 - 1 = 0.75°C/W heatsink, which is still pretty big. Driving an 8Ω load would require a total thermal resistance of 120°C / 19W = 6.3°C/W. So using a mica insulator, you would need 6.3 - 2 - 1.6 = 2.7°C/W heatsink. That's quite feasible. Sorry for the long reply, but it takes some explaining. Hope it helps.

[@bluesman608]

@@RexxSchneider Thanks Rex. This exactly what I wanted to know. Very kind of you to take the time to explain it.

[@pepeluis670]

Thanks for the explanation, I would like to know how many Amps is the power source recommended for this small amplifier to operate?

[@RexxSchneider]

Given that the maximum rms voltage into a 4Ω load before clipping was measured at 8.44V rms, the peak positive or negative voltage would be around 8.44 x √2 = 12V. That shows that the peak current would be about 3A from either rail. Some of that could be sourced from the power supply filter capacitors (at the expense of supply ripple and slightly reduced power), but the average current will still need to be at least 2A. Driving an 8Ω load would need around half of those values. One caveat is that a loudspeaker is a complex load and sometimes represents an impedance less than its rated value at certain frequencies.

[@pepeluis670]

@@RexxSchneider Thanks for the information, hugs

[@BeetleJuice1980]

can we use just +12vdc ?

[@verifier6764]

Hi.. Is it possible, to connect two of those to play in stereo..?

[@DonatoGreco]

yes, one for each channel

[@isoguy.]

John where have you and your fab videos gone? There are more than 24k people who have subscribed.

[@SciPunk215]

Love these videos. I'm getting motivated to get back into electronics. Is this a mono amplifier? If I wanted to make a stereo amp I'd need two of these?

[@JohnAudioTech]

Yes it is mono. There are stereo versions available but I have not evaluated those boards. I'd go dual mono using two of these boards because I'm not confident in the layout of the stereo boards from what I can tell just by looking at the posted pictures.

[@2davydo]

A while back I ordered a 2 ch stereo kit. It was just the board only. It even had the power supply section built right onto the board. all that was needed was a ac power source. IE. 24v center tap Xformer. Was like 4 or 5 bucks on flea-bay. The board quality looked good. But who knows. I still need to source the components and assimble it

[@saadman920]

I want to make a passive low pass filter at input stage. is there any compulsory that I have to use ceramic cap only? can i use electrolytic cap? should i use a high impudence or low impedance resistor in the filter?

[@JohnAudioTech]

Depends on the pole frequency of the filter. Film caps can be used. Ceramic caps come in low values and work with high frequencies well.

[@saadman920]

JohnAudioTech for a low pass filter at nearly 200hz cuttoff R1= 220ohm c1= 2.2uf for 219hz cuttoff. :) im using an electrolytic cap. would it be a problem? and please tell me how effective this passive filters are,i never made or tested one, i'll do it on tomorrow.

[@jishusingh8361]

I would really like to know the purpose of the 1M ohm resistor in the input stage, the tda2050 is similar but doesnt need the 1M ohm resistor. The rod elliot design doesnt have one (this: sound.whsites.net/project72.htm ) and there has been reports of oscillation. Please do reply. Thank you.

[@JohnAudioTech]

The resistor assures that no charge remains on the input coupling capacitor. It is a good design choice to have it but it is not necessary. If you add a volume pot, there is no reason to have it at all.

[@jishusingh8361]

Thank you so much, really thanks for the knowledge. So let me get this straight no need for the 1M resistor if potentiometer is used? I would also like to point out that in your video (this one) the schematic does have the 1M resistor before the input capacitor. Also, please do forgive me if I am annoying you but I would really like to know : sound.whsites.net/project72.htm this would work right? thank you.

[@eatdrinkwineguy]

Hey John. I have a couple of these kits on your recommendation with verified authentic LM1875 chips bought from Digikey to replace what might be fake chips. I know this has been asked before in maybe a slightly different context but do you think changing up to better quality (Elna/Nichicon) and more suited (ie polypropylene vs electorclytic) components would have a great difference on the final sound??

[@JohnAudioTech]

I can't say for sure. I'm populating a couple of these boards using all components I bought from DigiKey and should be authentic. I can't say for sure that the parts in the kit are bad or fakes or not. I did decap one of the LM1875 chips from the kit and it had a full sized die meaning it is probably authentic.

[@eatdrinkwineguy]

Well it would be interesting to see in a video if you compare them to see what the results are. I think I will just put one together with some replacement caps and see. Thanks again.

[@eatdrinkwineguy]

Thanks for that. I have new components on the way so will be making a little amp at home with these. Out of interest I have looked at the schematic from the LM1875 datasheet and the schematic from the kit they provide and there are a few differences in values but also in design. Looks like mainly at the input stages of the amp and particularly at the negative feed back and nov-inverting stage. It looks like it is missing an RC high pass filter? Does that sound correct when comparing? I have used a great site from Circuitbasics (lm3886 amp) and he has a thorough explanation of values and layout which has been pretty awesome - www.circuitbasics.com/ - this is what I base my question on. Not sure what difference some of these changes in layout makes if any. I am pretty green with this sort of stuff but am trying to get a better understanding how it all works. Maybe could be interesting to compare the schematics and how they are different and are better/worse if they even are. Just be interested to hear your thoughts regardless. Thanks again for your response.

[@caspartech3893]

Hey John! I know I am posting a lot on this video, but Man!!! I am very excited about this design. My next question: Power? A 24VDC wall wart or is there a small design for an AC to DC power supply? I would like to enclose this thing in a small wooden box and have it all self contained. Any suggestions??

[@JohnAudioTech]

No problem. This amplifier requires a split supply with a positive voltage, common and negative voltage (three wire). You can make one with transformer that has a center tap secondary, full wave bridge and a couple filter caps.

[@caspartech3893]

Thanks John!!

[@edwardboghosian2299]

John: I already have a DC power source about 25 v. but it has three wires coming from it. What would I do with the third wire(common, I assume) with this board since it has a two wire input? You mentioned in your presentation about putting in an additional capacitor or upgrading. What capacitance and temperature would you suggest? And, what is the wattage of the resistors? Thank you.

[@JohnAudioTech]

You need a bipolar supply for this amp which means a common lead and a +12v lead and -12v lead. Okay if the supply voltage is higher, such as +18v and -18v. I checked the capacitors and they are okay to use as is, but you could upgrade the two larger electrolytic capacitors to 220uf 25v 105c low ESR types.

[@teohchiawei]

They gave you the schematic?

[@galabpopov]

Hi John ,I've seen this and the other vids few times for info. I saw in another video that you had changed some bits on this board.Can you please tell me ,apart from the input cap and the large ones which other parts/values need upgrade. I have the big caps swapped for 470uf 50v sounds good but it seems a bit quiet with +-30v supply and smartphone source.Does it need higher voltage line input or that is the normal output with this setup.Can"t reliably measure the output ~ 5v ac into 4ohms with multimeter. I get. At max source volume. Also, do tickle your ears with some Tda 2030 stereo diy kits single and double supply versions-i find them fantastic for $3-4. Low power but make me smile every time running the bookshelfs. Long one ,sorry. Please keep up the excellent educating videos. Best Regards.

[@JohnAudioTech]

Part values are good, I'd just get them from a supplier that doesn't sell counterfeit parts. The headphone output jack from a phone or music player doesn't have enough signal voltage to drive the amp loudly. You would need a preamp.

[@Dinkleberg96]

Nice video! So let me get this straight.... I read the comments because I not sure about what kind of power supply it requeres. It is a 3 pin AC transformer? Like: "12v - central tap - 12v" ? Or it requeres a symmetrical power supply?

[@Bob_Lob_Law]

Ricardo Reis A 12v 3amp switch mode power supply will do. Don't bother with transformers, those are relics of the past.

[@cantinasongband]

difficult to find the same boards you got. the ones I ordered from ebay just came and the boards are not as nice. the PCBs are green and have smaller copper traces. They have the same layout as yours even down to the backwards input cap though

[@pepeluis670]

greetings, do you have any insulation between the ic and the temperature sink?

[@JohnAudioTech]

Unless the heat sink is isolated, you should use isolation between the IC and heat sink.

[@pepeluis670]

@@JohnAudioTech Thank you, please recommend me a link to buy a power supply module for this amplifier?

[@Ostfriese777]

The price of this kit is in Germany at 1,70€ at the moment. That's a joke. Because this tiny chipamp is anything else, but not a joke. I ordered 2 kits half a year ago ( as they were @ about 5,70€). 3 weeks waiting, 30minutes soldering and you got a wonderful sounding little amp.The psu is +/- 25V and I put a hand full 2200µF/35V capacitors for a smooth DC in it. The LM1875 drive two 2-way Sats with a 130mm Gradient W130 AL 8 and a Monacor DTM104/8 25mm tweeter. A TDA7293 prallel kit powers a closed little sub with a Mivoc AW 2000. It's my 1st diy audio attempt and I'm convinced. It's much more I ever dared to hope I'd get. Now I'm totally infected with the diy-virus and I'm reading much about active crossovers & dsp ;) ... . John, keep up your excellent work! I love to solder while you are explaining all these new things for me :). abload.de/image.php?img=2xlm1875-tda7293-satrmuuet.jpg abload.de/image.php?img=siebunglm1875komplettzluae.jpg

[@johnnytheangel1]

hi john, what would I need for this amp to put a guitar into it

[@DonatoGreco]

you need a DI that converts the high-Z guitar output impedance to a much lower impedance output to get enough signal at the ampli input. the DI also pre-amplifies the signal to LINE level, the optimum for an ampli input.

[@uK8cvPAq]

Nice find! Have you ever had a bad experience with an amp because it didn't have the RC low pass filter on the input?

[@JohnAudioTech]

Yes, I had an amp burn up it output snubber (RC network on the output) because of HF oscillation due to feedback on the input. The filter might have stopped this from occurring.

[@Cyberpunk-cq7wm]

Could you recommend a power supply for stereo setup? I must say I am quite intrigued by this cheap little kit.

[@JohnAudioTech]

If you mean a ready made supply, look for a +25/-25 volt dual supply of at least 2 amps for 8 ohm use or a +18/-18 volt 3 amp supply if you will use 4 ohm speakers.

[@Cyberpunk-cq7wm]

Thank you sir!

[@gkdresden]

@@JohnAudioTech I'd recommend not to exceed +15/-15 V for 4 Ohm speakers. Otherwise the LM1875 could get very hot. I use +12 / -12 V supplies for LM1875 / TDA2030 / TDA2050 at 4 Ohm loads.

[@saadman920]

why it says lm1875 and tda2030? are they have same pinouts? and what is the formula for calculating RMS?

[@JohnAudioTech]

Yes, the same pinout for TDA2030, 2040 and 2050 ICs. RMS voltage is the product of the peak voltage times the inverse square root of 2 (.707).

[@saadman920]

JohnAudioTech thanks a lot :)

[@seans1102]

What amplifier build are you planning on doing im curious? Also thanks for the reply.

[@JohnAudioTech]

It will be a simple two channel stereo amp using a couple of the boards. It would have a volume control and power supply all put in a nice wooden case.

[@adryanyork3581]

looking forward to it.

[@Tbonyandsteak]

Have to say about the board, the soldering points are very small and the copper very thin. The boards comes in different qualities. Those I bought can not take any stress at all. Recommend to glue the connections terminals

[@madmahi]

I want a calculator like that. Could you please tell me the make or model of that?

[@JohnAudioTech]

It is a 40 year old model, Radio Shack EC-380.

[@NikoMidi]

i bought this but it has a v-, ground, and v+, how do i hook it up

[@JohnAudioTech]

It requires a split supply with a plus voltage, negative voltage and common (3 wire supply).

[@terencekaye9948]

Hi John,, Where can you buy original LM1875 chips?

[@JohnAudioTech]

Mouser or DigiKey.

[@jorgefilipe9106]

I am about to order a Mean Well 150W SMPS which has two V- and two V+ outputs (18V), is it possible to use it with this amplifier? How should I connect V- and V+? thanks

[@JohnAudioTech]

Yes that would work well. V- goes to v- and so on. 150 watts is overkill unless you will power 2+ boards with it.

[@jorgefilipe9106]

Thanks! Where should I connect the ground? To the ground of the power supply marked with earth symbol?

[@SimpleEnough2k9]

The ground should go to a black terminal, potentially marked as G or GND or something like that. Do not plug your equipment to the earth ground. The earth ground is used on the high voltage side 120V/220V only. If could can't find the proper place to connect it, give use a link where we can look at your PS manual. That will be easier to direct you adequately.

[@jorgefilipe9106]

@@SimpleEnough2k9 Sorry for the late reply. I have busy with work. This is the link www.meanwell.com/productPdf.aspx?i=420

[@nsraju-nk4by]

Hi jhon..as per your openion for this amplifier board 4 ohms speakes stereo how much power to be needed ?? 12 v,18v ,24 v ??

[@JohnAudioTech]

Go no higher than +18/-18v dual supply with 4 ohm loads

[@nsraju-nk4by]

@@JohnAudioTech thank you

[@nsraju-nk4by]

@@JohnAudioTech thank you

[@RMORENO75]

Do you happen to have a link so to purchase that board? Great review.

[@JohnAudioTech]

Several sellers have the same thing. Search using "LM1875 board" and you'll see plenty.

[@RMORENO75]

JohnAudioTech The reason I asked for this one was for the reason you liked it. Just for the board. Also do you have an email?

[@RMORENO75]

Can you scan the board for me. One of my providers is a prototyping plant. They could source me the board and if interested I can send some over to you.

[@rich1051414]

www.amazon.com/SODIAL-LM1875T-Channel-Stereo-Amplifier/dp/B075XH3MQ7/ref=sr_1_13?ie=UTF8&qid=1535046446&sr=8-13&keywords=LM1875T This is the exact board

[@neosandi6]

www.ebay.com/itm/20W-LM1875T-Mono-Channel-Stereo-Audio-HIFI-Amplifier-Board-Module-DIY-Kit-V3Q1/283016875265?hash=item41e51ecd01:g:r94AAOSwJ~9bKoyu

[@KarlsLabReport]

What are those speakers you are using and where to get some?

[@JohnAudioTech]

These are speakers I built myself.

[@hrlego6450]

I tried putting 2 of these in parallel on the same power supply for 2 channels. The 10 ohm resister blew up. I will try 22 ohm.

[@cukedaddy]

The first thing i thought was the caps and transistor looked used.

[@cubanman2009]

What is the the voltage required 12v or 24v ?

[@JohnAudioTech]

It requires a split polarity supply of +18 and -18 volts max for 4 ohm loads or +25 and -25 volts for 8 ohm loads.

[@theaddies]

I really enjoy your videos. I am trying to emulate this test with the LM1875. I believe I have everything connected correctly, but I don't get any output signal. Reviewing your setup in the video it seems like you are doing something on the input side. I simply have a stereo jack coming out of my phone to serve as the input. Will this work? I can see the music on the Oscilloscope but there is simply no output signal. I am using a split supply voltage of 30V from my lab power supply. It is correctly measuring +15V and -15V. I am muddled up as to what I might be doing wrong. I would very much appreciate any advice you might have. Oh, and hello from Ohio. I live in Stow near Akron. Thanks.

[@JohnAudioTech]

Hi Andrew, You can use the signal from your phone to test. It should appear on pin 1 of the IC after passing through the input components. If you are using the kit, be careful of the values of the resistors. The color code on blue can be hard to read and the 3 digit, 1 multiplier means different colors for a given resistor value than the typical carbon types. (it is easy to put in the wrong value). Relative to ground, be sure -15v is on pin 3 and +15 is on pin 5. Output pin 4 should be close to 0v with no input signal.

[@theaddies]

John, many thanks. Your hints sent me in the right direction. I measured the signal at pin 1 and found nothing. I then proceeded backwards towards the source and i have to say what I found was embarrassing. I write it here because, well, everyone makes mistakes. When I connected up the input capacitor I failed to notice which holes were input and output. I ended up connecting the capacitor to 2 input holes. Once I fixed that all was good. I do have one additional question. In the video you mentioned that the input capacitor should be a film cap. I replaced the 10 uF capacitor with a 2 uF film capacitor. What would be the appropriate value of this capacitor. I looked for 10 uF film capacitors and that seems to be a big value for those capacitors. Thanks again. Andrew

[@JohnAudioTech]

@@theaddies Glad you found the problem. 2uf is near perfect. I don't know why they used 10uf. It is way overkill.

[@theaddies]

@@JohnAudioTech John, my testing continues of my LM1875. It seems that I am getting perhaps 9 Watts into 4 Ohms and 12 Watts into 8 Ohms before clipping. The supply voltage is about 27V. I am using the parts that came with the kit, but I do have some authentic LM1875s that I bought from digikey. I am using a heat sink but nothing nearly as big as the one you used. The temperature of the LM1875 seems to reach about 90F or so. I am testing at room temperature. Do you have any thoughts as to why the output is so low? Thanks in advance.

[@JohnAudioTech]

@@theaddies Be sure it is not your source signal that is starting to clip before the amplifier. Headphone output sources may not have enough voltage to drive the amplifier to clipping. That is why I use a preamp. Why you get less power from 4 ohms could be the power supply can't deliver the current the amp needs.

[@kmahes8169]

sound test?

[@kevinlivingston9563]

I wonder if the chips were inexpensive due to the scratches and everything. Maybe still authentic?

[@JohnAudioTech]

One seller listing that same kit said something about the IC being used. Possibly the ICs were in some product that production was canceled. The left over boards were stripped of the more costly parts. For fast assembly, power ICs are often clipped to the heat sink and removing the clip caused the scratches. Well that's my thinking anyway. There are companies around that resell recovered parts.

[@evieanindyaputri610]

good audio, very detail

[@snaprollinpitts]

great video, thanks

[@DuyPham-123]

Can I use battery with this board ???

[@JohnAudioTech]

You'd need two batteries, one for the positive rail and one for the negative rail. You'd have to use a double pole switch to control both rails at the same time.

[@cameronl62]

I just ordered a pair to play around with.

[@JesemanuelRamirez]

is this a stereo amp? if not, could I use 2 of these to make a stereo setup? if so, how would one go about doing that

[@JohnAudioTech]

You would need two of these for stereo. You could use one power supply or two (one for each board).

[@JesemanuelRamirez]

JohnAudioTech and how would one split the channels to each board? is there a video that explains this setup if so I would love to see it.

[@Heimbasteln]

Just connect one channel to one amp... Dont buy these kits if you dont even know how to do that

[@eatdrinkwineguy]

Why not? Isn't that how people learn? Get on Google, watch a few vids, read some articles and give it a go. Make a mistake or two and see if you can get it working.

[@mitchwil4180]

Myles Thomson That is until you burn your house down with a bad soldering job...

[@mirur2158]

This old AMD heatsink :-)

[@chriskniss9405]

I've soldered my LM1875 kit together but noticed that I may have the 10uf cap backwards compared to yours in this video. In one of your videos you mention that this board is mislabeled, but not an issue. Should I resolder this cap the other way?

[@JohnAudioTech]

No, you can leave it as is,

[@dhakshinamoorthy2931]

Respected sir, I need the pcb schematics and pcb files ..can you support please

[@VIPINSAINI_20]

He doesn't have it

[@ashishjain2219]

John audiotech travolta, i was looking for info for my first DIY boombox. after so much scroll troll and scrible drible i finally found use full info on your channel (hence subscribed) and now i am not able to find components relating lm1875 (its a tough world) but no issues i will pull through somehow. i am going to use some old sony 4.5" 25w full range speakers with some tiny 8 ohm ones, please tell how to add up a little more bass to final output. i feel it can be done. you, sir, are my only hope for now. Let there be light...winter is coming

[@ashishjain2219]

previously i was looking forward to this one www.circuitbasics.com/build-a-great-sounding-audio-amplifier-with-bass-boost-from-the-lm386/ but then i realized it is very low powered for my application...

[@JohnAudioTech]

Thanks for watching and I hope your project works out.

[@poptartmcjelly7054]

The chip included in the kit looks alot like the K174YH14, those are vintage soviet-made chips, the chip you have must be a vintage one salvaged from somewhere, the nichicon caps must be salvaged as well.

[@brunobassi2440]

K174yh14 = tda2003

[@amitghosh6966]

What should be the size of heatsink (in inches) for this IC ?

[@DM-kf1bt]

The heat sinks on the reverse of the chip are completely different