Adding PreAmp to 20 Watt Class-A Amplifier

[@jatza07]

Best channel on the YT, yet sometimes challenging to understand and follow :)))) But I love it. Thanks Eddie!!!

[@KissAnalog]

Thank you Very much! I appreciate you! I'll work on making this more KISS;)

[@keithmaddox1469]

Looks like your having way too much fun. hehe... good on ya. I haven't played with a turntable for forty years or so. I guess now they are putting the equalization in the turn table itself? That's a really nice build Eddie. Watching your videos caused me to order some modern BJTs to replace some of my stock of very old ( a few germanium ) transistors and break out my old amplifiers and their schematics. I found I needed some more non digital time:) I mean, you know... any idiot can count to one. Keep it up - love the videos.

[@KissAnalog]

Well - we have to admit, every great PWM controller has some logic gates in it;) I'm glad you decided to come back and get grounded;) I am curious about where germanium is these days...so maybe I should play a bit.

[@versace885]

Hi Eddie, another nice video. I really enjoy your tutoring. Thank you.

[@KissAnalog]

You are very welcome! I appreciate you!

[@adityamody8942]

cool build, love it.

[@KissAnalog]

Thank you! Cheers!

[@ats89117]

Nice video. Are you concerned that any error in offset from the zener diodes used to reduce the rail voltages will cause a DC offset in the input to the power amplifier? That's a beautiful box by the way. I guess it was part of the kit?

[@KissAnalog]

Thank you and great question! No, I'll have to share an updated schematic so you can see. The box is separate. I'll make sure I get a link to it;)

[@mosfet500]

Hi Eddie, hope you're feeling better. Zener's are noted to be noisy, I'm wondering if the noise went up on your amp between them plus the added gain? This is why I don't like these low power amps, they sound good with certain types of low dynamic range music but you're always struggling to get headroom out of them, add to that the poor efficiency and you're basically running a couple of hundred watts to listen to music. Did you redo the THD? I forgot to tell you I have a new way of making power supplies. Since these Chinese board houses give you 5 and 10 boards for $5, I decided to make my supplies full wave and just piggy back boards if I need more filtration or the power goes up. This way I can use the same design for several apps. I just did this with my CNC power supply that is 30v - 10a. My small amps only need one board but on this I used two. Running full means that even with two boards I'm only using 4 diodes but with less voltage drop than a bridge. Works great!

[@KissAnalog]

Thank you - I appreciate you! Yes, I am doing much better;) There is a fair size cap in parallel to the zener, so I don't think it changed the distortion. I'll do a full batch of testing on the final product to see how it performs. I know what you mean about the dynamic range.

[@johnshaw359]

My power amp has 2 gain settings, 23db for 2V balanced and 29 db for 1V single, so it seems you got that right 140mv from a source is "not so good". Learning a lot from your power amp project.

[@KissAnalog]

Thank you John! That is helpful and I appreciate your feedback!

[@MichaelBeeny]

I have used these little pre amp boards many times on my channel. Looks like yours is OK with it's 30 pf cap, but hundreds were made with the wrong value cap in the same place giving a HF roll off above about 8khZ. It proves that the makers never test such things. I'm sure you will love it's sound, or should I say LACK of sound. AB test will show no apparent changes in the sound stage, just gain, which is what a preamp should do. Gain, nothing else added.

[@KissAnalog]

Thank you Michael - that's great feedback. Do you have a link to one of your vids?

[@MichaelBeeny]

@@KissAnalog Hi Eddie, as requested here is the link, this is a follow up video but is the one you show kzbin.info/www/bejne/bGizYmuwgZaKjJo an earlier video where I first find this component fault is here, almost the same but this one is for a single supply rail kzbin.info/www/bejne/rIuYiayOd5d1i5I keep up the good work, more audio please.

[@HillsWorkbench]

Yeah, I'd like to see at least one Volt RMS out of a Line Out. Wondering if that preamp card should have gone into the turntable instead.

[@KissAnalog]

Great comment;) The turntable has two outputs, and one has the EQ, but why they didn’t bump the gain up a bit more is a little strange. I think it was meant to have a pre-amp, and the non EQ is for a preamp with the EQ. But, if you add the EQ with gain, why not make it 1 VRMS? :)

[@Margarinetaylorgrease]

You're description is for the next video.

[@KissAnalog]

Did you see the little pre-amp I added to the box?

[@Margarinetaylorgrease]

@@KissAnalog "I will show what adding capacitance to the power supply will do for ripple reduction. This video title is; 20W Class A Amp meets Big Capacitor. There is a playlist for this 20 Watt Class A Amplifier (see below). It is titled 20W Class-A Amplifier meets Big Capacitor."

[@aurthorthing7403]

You should check into building a small form factor bass guitar amp. Look at what Phill Jones builds.

[@KissAnalog]

Thanks! That sounds interesting;)

[@SamichHunter]

Does you friend's turntable need an RIAA compensated pre-amp, or is that done in the turntable electronics? I ask because I did not see anything but a normal amplification circuit in the pre-amp and in the channel boards themselves.

[@KissAnalog]

Great question! His turntable actually has two outputs and one is for the EQ out, but only puts out 140mV.

[@aurthorthing7403]

Where did you get the preamp board?

[@KissAnalog]

Thanks for reminding me;) I just added the links below the video.

[@aurthorthing7403]

@@KissAnalog thank you. I have been looking for inexpensive replacements for onboard bass guitar preamps. They are way too proud of them. But this may be a good candidate with a few or no adjustments.

[@DazzaDirect]

@KissAnalog #KissAnalog my understanding is that there are two main types of phono cartridges ceramic and magnetic and there is also inside the group of magnetic cartridges two types of magnetic cartridges , Moving Magnet (MM) and Moving Iron (MI) cartridges and that they are based on which part moves and the cartridges type stylus abrasive between en.wikipedia.org/wiki/RIAA_equalization standards and en.wikipedia.org/wiki/Magnetic_cartridge i see they mention 35dB, i dont understand logs but if 3dB is a doubling 35/3 would mean a gain needed of 11.6 constant which seems close to the gain of 10 you mentioned tbh i have only worked with magnetic types and they only output up to around 6mv and they need gains of 200 -250 so the turntable must be ceramic cartridge based or have preamp elsewhere i would think i found this article www.vinylengine.com/turntable_forum/viewtopic.php?t=30431 very interesting in talking about the wide variation of ceramic based cartridges and there is science around the abrasive stone too, thanks for taking the time to make this video very interesting and enjoyable you make great videos that get me thinking and asking questions ;-]

[@KissAnalog]

Thank you @Dassa Direct! Good info - I'll check out the links - thanks. Another way to look at db is for every 20dB you have a 10x gain;)

[@Margarinetaylorgrease]

@@KissAnalog I'm looking at this and going "no, 10db is 10X power" then I realise (after google) you're doing amplifier gain and I'm doing speaker power.

[@dennis2494]

doesn't the preamp need RIAA EQ for hooking up to a turntable

[@KissAnalog]

Great Question! The turntable has two outputs, and one of them has the EQ.

[@dennis2494]

if the turntable has a pre amp out it should conform to the RIAA curve then as long as it has adequate amplitude or gain that is the one to use with your amp

[@KlaweKlapki]

when playing music it will be less than 140mV

[@KissAnalog]

Thanks for that. It is true, most times that will be enough, but I did want it capable to go full volume;)

[@mindgate1818]

He's just spending too much time with his 8bit.

[@KissAnalog]

Sorry about that - are you getting tired of the 20 Watt amp? ;) I have spent a lot of vids on this without many others in between... But I'm making up for it;)

[@coldfinger459sub0]

Sounds like there’s two more big projects to add to this amplifier. A dedicated component phono preamp’s for a turntable Nelson Pass design ( Pearl phono pre-) And a dedicated preamp another one of Nelson Pass designs something like the front end for the BA-3 Or if you really wanna go all out bells and whistle‘s amazing pre-amplifier design by Zen Mod Who is very well known and respected by Nelson Pass. (Iron Pumpkin) You could look it up on the forms at DYI AUDIO Remember there is a synergy between different components matching them together. To get that perfect gain in that perfect impedance matching. Of course there’s a lot of discussion on DYI AUDIO about what are the best preamplifiers that match with your alpha amp

[@KissAnalog]

Thanks for all the great feedback! I will have to find a nice pre-amp to build;)