Carver M-400 Part 2: Putting the Smoke Back In!

[@banjoperator]

back in the eighties, i was a club DJ, we ran the m400t through a pair of lascalas.. now when the heat really climbed in the summer in the booth , there would be an overheat condition occur, but a service tech told us that that was one of the improvements for this model, there was a temp. protection built in as a mod, i tended to believe him, when the amp shutdown due to heat, when it cooled down it would fire up again, no issues.. below a room temp of 100 degrees f it would run all day and have no issues running hard at night when it would be cranked to almost full power for 6 to 10 hrs straight.. this was an awesome amp , wish i had had one of my own .. still do.....

[@ronp5615]

I am so happy to see this video. I am the original owner of a M-400t and it's companion C2 Preamp. I bought them both in 1985 at the Gramophone in Birmingham, MI and used them to DJ while in college occasionally. I had a party once driving a pair of Cerwin Vega D9's and D7's with a Kenwood amp on the 7's. It was incredible. The B&O RL 140's I used with them for ages did not fare so well. The cube has some issue and needs some love though :-(

[@leekumiega9268]

I was using a Kenwood monster receiver the Super Eleven ,it really looks impressive with every feature you can imagine with excellent specs and 125 watts, BUT when I got new Ohm Walsh 2 speakers they did not sound nearly as good as they did at Tech Hi-Fi with the Kenwood. I then got a used Carver MXR 130 receiver and my speakers came to life , better controlled /tighter bass ,sweeter midrange and highs ,wider sound stage and I heard things on my records and CD's that I never knew were there. I could not wait to listen to my entire collection to hear what I was missing.

[@gingerbaker1]

I was in the top end stereo retail store in my hometown many years ago when the Carver salesman walked in with a big Cheshire Cat grin on his face. He had a demo prototype of the first cube amp in his hands, and he was tossing it up and down and catching it like a volleyball. It was brushed aluminum with Sharpie markings on it for the power level numbers. He asked the owners what sort of component he had here, and the absolute last thing they thought it was was an amplifier. At the time, the king of stereo power amps was - I think - a Bose, which was a huge thing with a gigantic heat sink that you could fry eggs on, and which weighed IIRC at least 60 lbs. They were pretty shocked when he said it was an amplifier, but they were hooked when he asked them how many watts did they think it put out. They guessed something like 6 watts? 10? 20??!? When he said 200 watts their jaws actually dropped and their mouths stayed open. They really did not think he was being serious. So, he suggested they try it out. They did so immediately, hooking it up to their big Dahlquist speakers which IIRC were known for being pretty inefficient. The salesman said, select some music with a good bass workout. So, they put on a stereophile quality recording of the 1812 overture through their best turntable, and when those cannons went off everyone in the place was hooting and hollering. I ordered one on the spot. It lasted only about 4 years before needing repair, and then blew again several years later. I gave it to a friend of mine who liked trying to fix equipment, and eventually bought a Carver A550x THX which has been absolutely stalwart now for decades. Say what you will about Carver the man or the company, but they were the first to offer the common man affordable high-powered audiophile-quality amplifiers. Tony - you made that Cube look beautiful on the inside, and I bet it will last a LONG time. Really enjoy your videos, your thoughtful explanations, the care you take with the equipment you repair, and your personality really comes through. Which is a good thing. :)

[@leekumiega9268]

I have heard similar stories where the salesman suggested they compare it against much more expensive amplifiers , they laughed at the suggestion until they heard it and like in your story their jaws dropped.

[@leekumiega9268]

Roger I got to thinking why your amp did not last, Did you run it close to it's rated power for an extended period ? That would certainly explain why it died as the heat sink was not adequate to dissipate the heat generated when running on the high power rail for extended periods of time as it was meant mostly for musical peaks . I got a used Carver MXR 130 receiver that while I play it loud I don't do it all day long and have not had any problems with it after 30 years of use.

[@njphilwt]

Tony... Excellent work. I really enjoyed this series. Thanks for posting it!

[@wirenutt57]

Very very interesting video series with the Carver M-400s. I own two Carver M-400t amplifiers that I haven't run in years. I used them in a DJ setup driving Klipsch Lascala speakers. I could make ears bleed at 500 paces if I so desired. I was never left wanting for sound pressure levels, no matter the venue, including a large party I performed at once in a park where they had something like 10 acres to use. I had the second amp just as a backup, I didn't run them simultaneously. I still have all the equipment in storage. I should get it all out and make sure it all still works. If not, Tony is gonna get to work on a "t" model if he can find schematics!

[@mdzacharias]

Wow. What a great job. The only one of these I ever tried to work on was about 1986. Failed. Sent it back to Carver.

[@intothevoid9831]

I would just like to thank you for all the excellent content, especially for such unusual and hard to repair items! Will be donating to you soon.

[@2574mcu]

I always wanted a Carver setup. I remember around the late 70s or early 80s seeing the ads in high fidelity and Stereo review magazine.

[@honestaquarian1]

I've had two M400t's and one M400 and currently own an M400a for over twenty years (and it still works) The later "t" versions were modeled after a Mark Levinson amp. I cannot recall which one.

[@cocosloan3748]

You are such a hard working guy-they should appretiate you repairing this..You really take care of every small thing-like all should!

[@tinkmarshino]

nice star wars type start.. I do not know enough to even begin to play with these things.. but I do know enough to be totally entertained by those who do.. thanks this was interesting.. to know someone can put the magic smoke back in once I have let it out is a good thing..

[@toltec13]

Bob Carver's Cube! They were badass when they came out and even today they kick ass!!!

[@larryb.lindsay2366]

I built a set of 4 very high end speakers for a quad system powered by two of the M-400 when they were popular. For the day an incredible sounding system

[@InssiAjaton]

Great presentation up to “regular listeners’ alley”. You might have mentioned that the transistor power dissipation numbers are given as totally unrealistic ones, where the case temperature would be fixed to 25 degrees C. That would be possible in a lab with water chiller cooled heat sink or “infinite heat sink”. For practical heat sinks, you need to watch the DERATING GRAPH. In the case of 2N3055, the graph gives 115 W at below 25 degrees, then just 95 W when heat sink is at 50 degrees, 80 W at 75 degrees and so on. Finally, at 200 degrees heat sink temperature, the allowable dissipation is 0 W, or nothing at all. As to component voltage (and current) derating, way back when I saw a magazine article giving highlights of a MIL Handbook of component reliability and required design practices. While I have never seen the actual book, I memorized the basics from that article. In short, you should plan to use components at 70% of their maximum voltage as well as 70% of their maximum current. The product of these two, or as independent number (just like the transistor), the power should be limited to 50% of the data sheet given (unrealistic) maximum. Those practices should give the operational margins to achieve the military required system life time.

[@VernGraner]

While I watched this video, the entire time I was playing the audio through my own Carver Cube 400 here on my desk! 😁 Thanks for keeping vintage tech like this alive! My only quibble is with all the work you did to make it sound right, I am bugged you didn't fix the metering! 🤦‍

[@diabolicalartificer]

Thanks for the explanation of how these work - clever stuff.

[@OldTechFan]

Tony, It looks like your meter deflection is fine but the bottom led on the right side is burned out. Really nice work. Preserving a piece of audio history.

[@MrBrymstond]

The transistors sit really close to the resistors which probably cook the transistor, maybe bend them back and away from the resistor.

[@garybevis8691]

Hi Tony, amazing series on these Carver amps. Great work you do, I have been catching up with past videos of yours while following you currently as well. I am the proud owner of a Pioneer SA 8800 and I plan on recapping the old girl someday soon. It still sounds AWESOME, but I bought it new in 1978 (I was a Jr. in HS) and think it is time to recap. I just wanted to thank you for the videos and some great insight into these marvels of electrical engineering from Japan. I also noticed you using Probe Master Probes. I recently discovered them and I cannot say enough good things about Probe Master. I think if you have not done a review of them you should do so and soon. I am going to get a their 500 MHz scope probe for my Tek TDS 520A after seeing the quality of their DMM test probes I am a new advocate for them. I own Agilent and Fluke test probes and the Probe Master beats both at 1/4 the price. Great work on the videos and repairs Tony, cheers and good health to you and yours.

[@dwoodog]

I remember seeing these new in the store. I think there was a 500 too, that one was a more traditional shape with analog meters.

[@justsumguy2u]

Some of Carver's designs were cool, but he used the cheapest parts he could get away with. This one really blew up in grand fashion

[@leekumiega9268]

As I posted to another person the early ones did have reliability issues and other bugs that were fixed as production continued ,then they could last many years until the caps eventually dry out as all electrolytic caps do.

[@Dyaxxis]

Ah I see! You did put the smoke back in... in the form of that sweet classic soundtrack! Anyways, great work as usual!

[@BobPegram]

I kinda, sorta recognized it, quite happily! What is it!?? I want a copy of my own! Thanks in advance

[@BobPegram]

The Song I mean!!

[@Dyaxxis]

"All of You" - Don Felder, Heavy Metal Motion Picture Soundtrack

[@1matdad362]

WOW.... HEAVY METAL SOUNDTRACK FOR TESTING!!! TWO COKED OUT ALIENS DRIVING A SPACESHIP AS I REMEMBER??

[@rogermarcoux8029]

Damn that was a great video! I learned a lot from your detailed review. As a Bob Carver fan from the phase linear days I coveted my first M400 and C4000. Currently have a M400t that needed some love (leds don’t work and I feel it requires some re-capping due to sound issues). I now have a better appreciation for the amount of work involved. But I think it may be worth it after watching the video and seeing how you made it dance . As an old TV repair guy I am almost itching to tackle it but not having the bench hardware you have it’s not going to happen. With your obvious experience would you know where I might find someone who could take on a repair such as mine (note that my m400t does work)? Would you think it’s worth the investment? Thank you again for the videos, subscribed and eager to watch more. R

[@Chrissy4605]

I applaud you at knowing your skills and limitations. I am gearing up to start my own repair business.

[@leekumiega9268]

Since it works all you really need is a ESR meter to check for bad caps (in circuit), replace them , then all you need is a high power dummy load from E-Bay (2 8 ohm 200watt resistors attach them to a huge heat sink) , a volt meter to tweak the pots as shown on this video.

[@MrBrymstond]

Yes, I've done the same with electrolytic caps higher the voltage and capacity. Good idea

[@PecanPie1102]

MikesRadiorepair and 12voltvids also has a channel and might have hard to find IC's from his collection. 👍another great vid and a pleasure to watch.

[@Internutt2023]

Great videos on the repair of this unit! I would like to know what PN's you used for your Triac and Diac replacements, as I've come across 2 "for parts only" units on Ebay and I am looking forward to getting music out of them again.

[@widecast]

There is a small glass diode on the amplifier board that appears broken. Looks similar to a 1n4148.

[@davidgriffin79]

What filter capacitor replacements did you use? The reason I'm asking is that I'm going to re-cap a Madrigal Audio Labs Proceed Amp 3 (effectively a Mark Levinson amp); the problem is the Chem-con 21000 micro farad/75V used in the amp are snap-ins and not available any more. The Chemi-con replacements available now (some 20 years after the amp was built) are 22000 micro farad screw in types and much too big to fit in the case in any orientation. I've found some Cornell Dublier 21000 micro farad/75V capacitors which I can jerry rig in using 10Amp wire and laying them flat, but their insanely expensive £33/$45 each (I need 6). I'm therefore curious what you use when re-capping a quality amp.

[@JOY_INK_DOT_ART]

43:30 this was teslas idea on how to service electricity to the entire city and even counrty by using that therum it also would keep repair men safr when changing out the transistors he was brilliant

[@rb89509]

I know I'm very late to the party but, I bought an M400a back in the early 80's? Carver had this coupling device that let you run it off the speaker outs on your receiver and then let you use the low level RCA's into the M400a. I wish I still had it, it never gave me any trouble. It would make a pair of Cerwin Vega D9's scream. But like an idiot, I sold it on ebay around 2009 for next to nothing.

[@danishnative9555]

Carver Cube. I sent one of these to Goodwill moons ago. All that Magnetic Field hype promotion did not do Bob Carver well. That being said, I still have my Phase Linear 400, GAS Thaedra preamp into JBL L220's. Working combo. I have one Carver stage amp with balanced inputs that use real authentic 2SD555 output devices. I might salvaged it for it's devices, if the Phase Linear 400 ever fails (again).

[@curtislucka9954]

Great Carver rescues! How did you get schematics. I have several subwoofers that I inherited. Would like to restore and use.

[@PSKResearch]

Wow that thing was really fried. Did someone spill a drink down it or something? I used have one of these for my mobile/road DJ system. The idea was to keep it as light & small as possible but still sound good. Never problem for years driving into 4 ohms per channel for almost twice the power. I kept a small fan blowing up the bottom so it wouldn't get too hot though.

[@1959Berre]

I've been sitting in front of my PC since I knew (!) part two was about to show up any minute.

[@BobPegram]

Great Job! When you play the 400 over the big Kipschs, tell us if it still lacks some impact in the bass. I assume that's what you meant in your remembered description of the 400's sound. Then after playing the 400 and the Silver 9Ts, what do you hear as the differences? I heard how clean the 400 was; on dinky but properly equalized laptop speakers! It's amazing to hear that! However, even with my and your hearing being similarly degraded by age, you're there, you'll get more, especially more bass!

[@randomrepair1680]

I could be wrong but I think the biggest difference with the t model is the RC network at the output. Hopefully you can find the schematic, but u will see what I have here.

[@giuseppebeppe_tv8257]

Hi Tony, very good work ! a question: have you matched the power transistors ( NPN with PNP ) for nearly equal gain between them?...thanks, bye from Italy....

[@giuseppebeppe_tv8257]

@Phil Allison Thanks indeed for your reply....bye....

[@anastigmatix4119]

Hanging out there like a big mazza ball, Tony !??

[@TY-ob7fz]

Hi Tony. What an interesting series, the Carvers. The poor design makes for fun watching when you probe and jump into full repair mode head on -pun intended ! Is incredibly to see many of the repairs you’ve made when many would had given up long long before. As you mentioned long before these amplifiers don’t sound much louder than the 100 watt amps or even the 80 watters in terms of decibels, especially for the current they’re capable of drawing. Again poor design when they’re capable of avalanching so easily without much protection as evident of all the components replaced. Much happier with my Pioneer any ole day. Thank you for take the time to post this and again making an interesting series. Ps. Hope family is doing great !!!

[@edifierbass7821]

One way to test its reliability, is to crank it up play 5 songs with heavy bass if it survives means its ready to Rock.. like the way it should.. anyway nice video educational.. thanks

[@MarkTillotson]

I have a sneaking feeling those caps were sold as +100/-50% tolerance and were all 1200uF to start with!

[@andrewhall6221]

Exactly my thoughts.

[@jeffd9133]

Great video, but, I would like to know what was wrong with the meters?

[@trickyrat483]

Great video. Ps. Audio sounds great. :)

[@HAL4400]

Cool video!!!

[@gordonmacfarlane4348]

Great video, lovely restoration but a horrible sounding amp when I had one in my system years ago

[@Roflcopter4b]

What does "horrible sounding" mean exactly? Did it hum? Did it hiss? Was it highly distorted?

[@gordonmacfarlane4348]

@@Roflcopter4b .Bright , lean , and no bass

[@leekumiega9268]

@@gordonmacfarlane4348 You must of gotten a defective one as some of the early ones had reliability issues and other bugs that were eventually resolved .

[@busboy48]

I have a working M400-will you refurbish it for me to get another 10 years of life??

[@stefanmansson6734]

Very hissy sound in this video. Check the level of treble next time you record, Now I saw you fixed the problem. Excellent!

[@nicholasroos3627]

The VTL5c3 opto is available from cabintech. 5$ a pop mind XD

[@TheDefpom]

What is the cap tester you are using? What test frequency is it using?

[@michaelhaiden6718]

Hook it up to a set of boss 901'1s

[@niemandalkidson7018]

Thx!

[@johnsweda2999]

why don't you use Polly film caps like muse when replacing electrolytics.

[@machintelligence]

Those capacitors are strangely similar. Could they have been mislabeled or a result of defective manufacturing? I am not a capacitor expert.

[@marcwilliams5567]

Currently trying to find a M400a or M400t. Any suggestions outside of eBay?

[@glasstronic]

Very cool. Class G...Ahhhhhhhhhhh... ;-)

[@garybrockie6327]

My brother had one of these!

[@bulwinkle]

How does such catastrophic failure occur? Is it the result of aging components, mismatched load impedances or something else?

[@russellhltn1396]

Unless there's an insulating cover for those back transistors, all it would take is for something conductive to come in contact with those cases. I'd figure out some kind of cover before sending it back. I've seen covers that fix over the TO-3. That might be a place to start.

[@editorjuno]

@@russellhltn1396 -- Yes, those are common and should be dirt cheap.

[@marcwilliams5567]

I'm in the Indianapolis area. I'm having a hard time finding a electronics tech to work on: Carver M 400t Dynaco PAT 4 Pre Amp Dynaco SE 10 Equalizer Any help locating a tech would be appreciated.

[@bryfar6178]

If your still looking for a Carver tech try Deltronics in Woodridge IL. Their an authorized Carver repair shop. Just got my M400 & C4000 back form them.

[@marcwilliams5567]

@@bryfar6178 thx I am still looking.

[@stevesmyth4982]

Twelve hefty output devices would give 500 Watts into 4 Ohms but that mains transformer looks no bigger than 250 Watts rating.

[@rymburg]

Where did you find those 4000uf 80vdc caps

[@johnrotten4613]

I used the Epcos in mine as they fit all the parameters.

[@dontcare563]

The question is why would you want to rebuild/repair this amp? This was a very early Carver product and known for its cheap price and high power for the time. Its not exactly an audiophile grade amp although I'm sure it sounded fine. I'm sure these repairs weren't cheap with lots of time invested.

[@eddevito3282]

As an owner of this amp, I would ask, why do you say it is not audiophile grade (it is)? And if you can make the case it isn’t (you can’t), why would it matter if it “sounds fine”? Indeed, it produces an identical signal for a given input to a Mark Levinson amp of the same era, as you would know if you have any knowledge of the brand. But the answer is, these (and its successors) continue to be in service by the hundreds, are continuously deemed worthy of rebuild (a quick tour of KZbin or Carver forums will validate that) and and continue to be in demand on the vintage market because of the ground breaking design. As for mine, I am the original owner, it has never been opened, it has been in service almost continuously, and it functions perfectly.

[@dontcare563]

@@eddevito3282 Sorry but not even close. IMHO but if it makes you happy and sounds good to you then why do you care what others think.

[@eddevito3282]

Dont Care It has served me well. In answer to your original question, It’s eminently worthy of a rebuild for the reasons mentioned. I had asked why you don’t deem it audiophile grade (to be clear in comparison with other amps of its time). You havent answered, because you can’t.

[@leekumiega9268]

@@eddevito3282 You are absolutely correct in what you said , There was a story that went around where the Carver sales rep wanted to compare it to much more expensive amplifiers ,the people at the high end store laughed until they heard it then their jaws dropped. You said yours have never been opened all ,electrolytic capacitors dry out and or leak electrically and or physically and should be replaced at this age, A service rep can check them in circuit with an ESR meter . Good preventive maintenance before something blows due to bad caps.

[@anastigmatix4119]

I suspect it boils down to which country club one belongs to.

[@gingerbaker1]

Beware the deranged tribble! :)

[@keithchristie4678]

Do you want to try your luck with another one? I have an original that hasn't seen a/c for 20 years. Bought it new in 1982. Should still work but I'm sure the caps all need replacing. Let me know!!! By the way, the fuzzy wind screen is known as a "dead cat". 🙀

[@leekumiega9268]

The Carver site has authorized service places listed ,give them a call for recap price estimate.

[@harbselectronicslab3551]

Take the wind sock of the mic.....unless its windy in your shop it serves no purpose at all.....just slip it off and keep it for outdoor shoots.

[@loudsubwoofer8492]

great job! very interesting. now, when i watch videos like this i always wonder what is the final complete cost. i have a system over 35 yrs old and so far no problems, but eventually it will need service and it would be nice to get a ballpark figure of what i might expect to pay for a repair. just wondering.

[@leekumiega9268]

It is the labor that can get expensive ,the electrolytic caps eventually dry out on all old equipment and they cost (depending on quality) anywhere from a few dollars for a pack of 10 for small ones to over 10 dollars each for really large ones depending on where you buy them. You can go to the Carver site and there are authorized service places listed that can give you an estimate.

[@russellhltn1396]

I would not consider it "class H" just because it has a regular to regulate the supply voltage. It would only be class H if it used the input signal to modulate the regulator. I highly doubt that's the case here because the regulator can only adjust on each half of the 60Hz power line. Far too slow to track the input signal.

[@bulwinkle]

New mic ok but sibilants hiss slightly.

[@ImTheDudeMan471]

Mine says, Carver M 400 "t" ?

[@leekumiega9268]

The T means transfer function which means it has modifications to sound like a much more expensive amplifier. read the Carver challenge . www.stereophile.com/content/carver-challenge

[@grhinson]

DON'T CROSS THE STREAMS! IT WOULD BE BAD.

[@williamstaten8102]

The only people who wound know what a Tribble is, is Trekkie's lol. Of course a channel like this and being a Trekkie probably goes hand in hand.

[@DAVIDGREGORYKERR]

I prefare PWM amps