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Old 8th December 2008, 04:04 AM   #1
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Default Carver mk II modified audio amplifier

Hi there, new to DIYaudio, and I"ll get to posting soon (I usually hang out at CarverAudio).

I've been experimenting with Carver M-500, M-500t and M-1.0t amplifiers, and have developed a stable, reliable upgrade I call the mk II series.

see carvermk2.com for more information, and email me if you need more info.

Thanks,
Rich
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Old 8th December 2008, 05:04 PM   #2
anatech is offline anatech  Canada
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Hi Rich,
Good to see you. I was factory warranty for Carver in Canada for a while, until AC Simmons went down. I had sold my company by that time.

I've heard bits about your upgrades, and have some concerns relating to running the supply voltages higher - that's one thing I've heard anyway.

I find these amps are very reliable if they are serviced occasionally. Those lower tier filter caps have a rough life with the waveform they have to deal with. The larger 130V caps are one thing I have only rarely had to replace. Normally after a "tech" shorts out the triac in an attempt to defeat the protection.

So, were you in the service department, or engineering?

-Chris
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Old 8th December 2008, 06:38 PM   #3
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I wasn'y an engineer yet back then (I was still a kid) and it was a part time gig. I was in the USAF, and my boss, who worked at Carver, brought an M-500t in over Christmas break. He said anybody who could fix it could have the repair money. The service manual was only a schematic, but for some reason it made sense to me. He PCS'd a couple of months later and I got his job at Carver (inherited a couple of his 'boat anchors' too ;(
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Old 8th December 2008, 08:24 PM   #4
anatech is offline anatech  Canada
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Hi Rich,
The M-500t was possibly one of the prettier Carver amps. It looks fantastic in champagne gold. Those are the European models called "Bennytone".

Most of the early Carver service information was simply a schematic. A few later ones detailed how his circuits worked. I lost all my manuals, Carver included, when I sold my shop. I do have the modifications still, and a couple later products. The Lightstar product was a return to the drafting size paper with schematics only. I still have one output PCB with a hole where the feedback resistor used to be.

The Carver "Cubes", M-400 X, were more difficult to work on. I think that manual had a circuit explanation in it. Once you get used to working on them, it's only time and patience.

What did he leave you when you got his job?

-Chris
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Old 8th December 2008, 10:39 PM   #5
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Quote:
Originally posted by anatech
.....Most of the early Carver service information was simply a schematic. A few later ones detailed how his circuits worked. I lost all my manuals, Carver included, when I sold my shop.


Yes, the later manuals were much more descriptive re theory of operation.

Quote:
......The Lightstar product was a return to the drafting size paper with schematics only. I still have one output PCB with a hole where the feedback resistor used to be.
The lack of available schematics for Sunfire is what got me into this in the first place. When I got into re-building my setup, I ended up with 4 M-500t mk II, 3 M-1.0t mk II and 1 M-1.0t mk II opt 002.

I want to be able to work on my own equip, instead of paying $600 flat fees. Otherwise, I could have gotten away with a couple of Sunfire multi-channel amps

Quote:
......What did he leave you when you got his job?

-Chris
IIRC he had toasted a couple of M-1.0t's by shorting across the triac in an attempt to 'jump start' the power supply.

I guess I was at an advantage because, being a newbie to electronics, I wasn't 'ingrained' with common troubleshooting techniques and circuit behavior.

I really admire the triac controlled field coil design, and tiered rails, very clever
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Old 8th December 2008, 10:47 PM   #6
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Hi Rich,
Quote:
IIRC he had toasted a couple of M-1.0t's by shorting across the triac in an attempt to 'jump start' the power supply.
Oh god!!! Not wise at all!

-Chris

Edit:
Quote:
I guess I was at an advantage because, being a newbie to electronics, I wasn't 'ingrained' with common troubleshooting techniques and circuit behavior.
That was never proper procedure - ever! I use a variac with a shorted triac. You're safe up to about 40 VAC. You can troubleshoot faults with reduced voltages. I've found faults as low as 10 VAC input. Besides, the amp tries to come on. It cycles on and off by itself. These amps do everything to prevent further damage and even try to help you figure out the fault.
Quote:
I really admire the triac controlled field coil design, and tiered rails, very clever
That took Bob a lot of work to get right. The protection circuits are also part of the triac control as they shut the amp down. Anyway, getting the firing angles matched between cycles to prevent uneven firing was an issue in the M-400 products, and some newer too.
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Old 8th December 2008, 11:28 PM   #7
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Quote:
Originally posted by anatech
......That was never proper procedure - ever! I use a variac with a shorted triac. You're safe up to about 40 VAC. You can troubleshoot faults with reduced voltages. I've found faults as low as 10 VAC input. Besides, the amp tries to come on. It cycles on and off by itself. These amps do everything to prevent further damage and even try to help you figure out the fault.


Yes, a variac is the way to go, but as improper as it is, MANY techs have tried the triac jumper 'trick' only to end up with a pretty box of iron.

Quote:
.....That took Bob a lot of work to get right. The protection circuits are also part of the triac control as they shut the amp down. Anyway, getting the firing angles matched between cycles to prevent uneven firing was an issue in the M-400 products, and some newer too.
I saw that in some of the ECO's and TCO's re uneven firing angles.
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Old 9th December 2008, 01:35 AM   #8
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Hi Rich,
Quote:
Yes, a variac is the way to go, but as improper as it is, MANY techs have tried the triac jumper 'trick' only to end up with a pretty box of iron.
We went through hell with that in Canada. Because these mag coils draw so much current when fed 120VAC, we also sold many mag coils. That's even after advising the "tech" that this behavior was normal and that there would be no refund. Just plain hell. Then there were the "warranty shops" that had to be shut down due to destruction. Most were dealer service, but the entire province of Quebec ended up with no warranty shops. Must have been a cultural thing, 'cause they just would not listen.

I got most of the attempts to repair on my bench, some were pretty bad. That is why I'm so sensitive about untrained people getting into these amps. The rules have changed, as Bob Carver designed them.

Ever see a PM-1.5 that was plugged into 550 VAC? The arc from inside one of the power transistors cut through the top of the can. It also cut through the bottom cover plate over the outputs. I've seen a few where the arc cut the top of the can, but only one where the amplifier cover was cut also. Didn't fix that one. It needed ..... everything. Even the circuit boards were done. Case was marked up, so that amp was a complete loss. Poor thing.

Quote:
I saw that in some of the ECO's and TCO's re uneven firing angles.
Most were not that bad. Aside from some triac failures (blown fuses and popped capacitors), most just had uneven firing. Tickity - tick - tick - tickity .... on and on. They evened out under load. Once they went to transistor firing circuits and away from diacs, things were much, much better. Still, Bob had to go to great lengths to get that sorted out.

I think the protection/power supply circuits were one of the best. Smart shut down and reduced weight and heat as side benefits. It's just that they needed to use switching supply capacitors that could take those current spikes better.

Which brings me to another question for you. The use of small capacitors was done for a reason. You have increased the capacitance. Was that an availability thing, or towards something more material? This power supply was designed to work with lower capacitance than normally used as it had the ability to draw huge amounts of power from the AC supply when required. You did not have the normal tiny charge period that a normal supply has to deal with.

If your design is something you don't want to detail, then that's okay. You can always PM me as well.

-Chris
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Old 9th December 2008, 02:37 AM   #9
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Quote:
.......Which brings me to another question for you. The use of small capacitors was done for a reason. You have increased the capacitance. Was that an availability thing, or towards something more material? This power supply was designed to work with lower capacitance than normally used as it had the ability to draw huge amounts of power from the AC supply when required. You did not have the normal tiny charge period that a normal supply has to deal with.

If your design is something you don't want to detail, then that's okay. You can always PM me as well.

-Chris [/B]
I'm not keeping it to myself; the parts list is posted at Carveraudio.com, and I'll help anybody who wants to do it to their own amp.

The capacitance thing......I did this in two stages.

After researching datasheets (and these forums as a lurker) I came up with a preliminary parts list. Once everything was installed, I initially bumped the rail + 10 VDC, and got the following:

(m-500t)
Original:
RMS <0.15 THD
8-----283W
4-----332W
Dynamic
8-----387W
4-----474W
2-----412W

Mk II Stage I
RMS <0.15 THD
8-----373W
4-----410W
Dynamic
8-----410W
4-----702W
2-----947W

This showed a substancial increase, especially in dynamic power, where the original tended to sag. Next, it tickled the rail another +10VDC (the two tiers were 35 and 74, now they're 45 and 95), and put the highest capacitance I could fit into the dimensions available. I got the following:

Original:
RMS <0.15 THD
8-----283W
4-----332W
Dynamic
8-----387W
4-----474W
2-----412W

Mk II Stage I
RMS <0.15 THD
8-----373W
4-----410W
Dynamic
8-----410W
4-----702W
2-----947W

Mk II stage II
RMS <0.15 THD
8-----380W
4-----420W
Dynamic
8-----519W
4-----926W
2-----1145W
Bridged
8-----820W

Not much of an increase with a steady sine signal, but dynamic power was substantially raised again.

The higher capacitance was more of an empirical experiment than a calculated plan; Overall, increasing the capacitance yielded a 40W (with RMS signal) or so gain, so I kept them in.

I then took a non-contact thermometer to the heatsink center and found:


into 8R at full bore for 20 mins:-----120 F-----mag coil @ 125 F
into 4R at full bore for 20 mins:-----140 F-----mag coil @ 135 F

Stock unit

into 8R at full bore for 20 mins:-----115 F-----mag coil @ 120 F
into 4R at full bore for 20 mins:-----135 F-----mag coil @ 130 F

So at most a 5 or 10 degree F difference in heat dissipation; probably attributable to the increased voltage drop across the outputs with the same amount of heatsink.

While I'm doing a burn-in (I do 96 hrs into 1/4 power at 4R) I occassionally walk over and give her full boost. Into static 4R dummy loads (not reactive loads like speakers, but quieter I haven't been able to shut one down through thermal protect.

One owner is driving 4R Magnepans, and reports no issues with heat.

One Carveraudio member who demo'd a unit on his Carver ALS's was able to shut her down under thermal protect......they definitely won't drive Carver amazings. He was also comparing to his Sunfire (load invariant design).
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Old 9th December 2008, 03:11 AM   #10
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Hi Rich,
Yes, the increase in heat is due to higher voltages.

Shutdown. You have not modified the over current protection, so the original shutdown levels are at the original settings. A good thing in my book.

ALS speakers were always hard to drive, along with many other silly designs. I wouldn't worry about that. I had a Lightstar amp, that would toast those speakers. No point though. I had to sell that one as I couldn't justify keeping it. One of Carver's nicer sounding amplifiers.

My feeling is pretty simple on speakers. If they are hard to drive, they will never sound as good as they would have if they were designed properly. That hamstrings the speaker unnecessarily. Why do that?

You should measure the pre-driver case temperatures. The drivers and outputs are on heat sinks, the others are more critical possibly. You should (if you have the time) try your normal mod, but with the lower capacitance values. I don't think they will materially affect the sound with live music. Also, since the supply is regulated, the RMS values are a truer test I think. Here the Carver design should shine compared to a normal design. Of course, for a Caver winding out, you need a stiff AC supply. That may affect your readings more than the internal capacitance. Just a thought.

I am curious what test gear you are using. Professional curiosity since you are doing so much higher energy work. Keep in mind that most Japanese THD analyzers have internal HF loss between 30 and 40 KHz. Something that will go up beyond 500 KHz might be better. This is especially true for looking at commutation noise. I look at the residuals out of a THD analyzer triggered from the speaker out on a dual trace scope. You can see these glitches very clearly then. A purpose built spectrum analyzer is even better some times.

-Chris
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