Carver TFM-xx Amplifiers

[cknepper1]

There's a YT video of a guy repairing one of Bob's large mag field amps. It's pretty interesting to watch the tear down and troubleshooting. You can easily see how Carver was thinking 'outside the box' in the design. Once the technician got the schematics and familiarized himself with the kind of unique circuitry that was used, the thing went together in short order. Very powerful in the scheme of things.

Super cool! Thank you. Now I have something to watch when I get home tonight besides the doom and gloom of the Earth coming to an end....apparently. lol

 

[oldsysop]

There's a YT video of a guy repairing one of Bob's large mag field amps. It's pretty interesting to watch the tear down and troubleshooting. You can easily see how Carver was thinking 'outside the box' in the design. Once the technician got the schematics and familiarized himself with the kind of unique circuitry that was used, the thing went together in short order. Very powerful in the scheme of things.

xraytonyb has very good videos

 

[cknepper1]

I though Amir had an old Carver amp he could test.

That is what I was hoping for. It seems He has or has access to...well...everything!

 

[Digital Mastering System]

I've had three Carver products in my life. I really like my TX-11a tuner. The FM is great, but the AM section is unusually great.

Carver once made (or sold) a car head unit. I liked the design look, but it was pure crap electrically. Died very soon.

I have just bought a C-2 preamp on ebay with missing knobs and not really working for like $40. I had looked over the schematic and thought it was a good unit to chip roll since it's mostly opamps - discrete transistors only in the phono preamp, and is full of 741 style scheiss. I successfully installed OPA1656s and modified the power supply with LT3045/94 regulators for super low noise. Installed new Alps volume control. Cleaned things up, got new knobs, and recapped. Changed the output muting FETs to a reed relay and modified the headphone amp. It sounds pretty good now, but when I was checking it out I noticed the tone controls were a little odd. The bass sort of works as expected, but the treble only boosts, and not cut. WTF?
So I examine the schematic more closely around the tone controls. WTF! This design could never work. I LTSpiced the schematic. Works just as poorly in simulation as in real life. I think the point of the non-functioning design was to use the same audio taper pots for the tone controls as is used for the main volume; but man this is stupid. The tone controls really don't work as tone controls. It's effectively a passive design, even though 4 opamps are used. Setting the controls flat is pretty hard to do and as I said before, the Treble doesn't cut. (Luckily there is a 'flat' switch to bypass the silly circuit.)
I ordered replacement linear pots that should fit and then I'll replace this circuit with a Doug Self Baxandall; proper tone control circuit.
I can't imagine how this design ever made it out of the lab. Did no one ever test the tone controls?
I don't suppose Carver himself had much to do with this embarrassment, but it doesn't speak well to the organization around that time ('86).

One thing the TX-11a and the C-2 share is the annoying front panel color and lettering scheme. Vaguely gray lettering on a vaguely gray panel. It can barely be read with a flashlight at the critical angle. Give me high contrast black on white, or white on black. Backlit --- something better ... sheesh.

So is Carver 1 or 2? Take your pick. I'd say both.

Who else has seen really poorly or incorrectly designed electronics in the audio world? I'd like to hear some stories.

P.S. The C-2 schematic is available from HiFiEngine if you're curious.

 

[Wes]

The Sunfire Theatre Grandee pre-amp is another one that craps out and cannot be repaired - don't ask me how I know this...

 

[cknepper1]

The Sunfire Theatre Grandee pre-amp is another one that craps out and cannot be repaired - don't ask me how I know this...

It is rare to not be able to repair something...at all...ever! I'm dying to know, what the hell broke? lol

 

[Lavawood]

I recently had 2 15’s refurbed, they measured 20% over spec. All caps were good. I only needed power supply relay repair and meter rebuilds.

 

[cknepper1]

I've had three Carver products in my life. I really like my TX-11a tuner. The FM is great, but the AM section is unusually great.

Carver once made (or sold) a car head unit. I liked the design look, but it was pure crap electrically. Died very soon.

I have just bought a C-2 preamp on ebay with missing knobs and not really working for like $40. I had looked over the schematic and thought it was a good unit to chip roll since it's mostly opamps - discrete transistors only in the phono preamp, and is full of 741 style scheiss. I successfully installed OPA1656s and modified the power supply with LT3045/94 regulators for super low noise. Installed new Alps volume control. Cleaned things up, got new knobs, and recapped. Changed the output muting FETs to a reed relay and modified the headphone amp. It sounds pretty good now, but when I was checking it out I noticed the tone controls were a little odd. The bass sort of works as expected, but the treble only boosts, and not cut. WTF?
So I examine the schematic more closely around the tone controls. WTF! This design could never work. I LTSpiced the schematic. Works just as poorly in simulation as in real life. I think the point of the non-functioning design was to use the same audio taper pots for the tone controls as is used for the main volume; but man this is stupid. The tone controls really don't work as tone controls. It's effectively a passive design, even though 4 opamps are used. Setting the controls flat is pretty hard to do and as I said before, the Treble doesn't cut. (Luckily there is a 'flat' switch to bypass the silly circuit.)
I ordered replacement linear pots that should fit and then I'll replace this circuit with a Doug Self Baxandall; proper tone control circuit.
I can't imagine how this design ever made it out of the lab. Did no one ever test the tone controls?
I don't suppose Carver himself had much to do with this embarrassment, but it doesn't speak well to the organization around that time ('86).

One thing the TX-11a and the C-2 share is the annoying front panel color and lettering scheme. Vaguely gray lettering on a vaguely gray panel. It can barely be read with a flashlight at the critical angle. Give me high contrast black on white, or white on black. Backlit --- something better ... sheesh.

So is Carver 1 or 2? Take your pick. I'd say both.

Who else has seen really poorly or incorrectly designed electronics in the audio world? I'd like to hear some stories.

P.S. The C-2 schematic is available from HiFiEngine if you're curious.

That sounds so completely messed up it is hard to believe that there wasn't some kind of reason for the goofy build on that receiver. I believe you. It sounds like one of those things when you aren't there during the design process the decisions made can not be made sense of at all. But if you are there during the design process all of those decisions made make complete sense because you and your team are making decisions to solve issues as they arise. Knowing the pros and cons of each decision as you make your way through the process.

I work in the heating and air conditioning industry. I have literally run into situations like you describe here when you stand back and look at a design and think, "How in the hell could someone think THIS was a good idea?" I have then actually met some of the folks who made those "stupid decisions" and had the opportunity to ask them why they did what they did. And...sure enough...there was a logical reason to go with the bad decisions on several of those occasions.

That being said....sometimes the answer to the question "Why did you design it that way?" was "Whoops.....we didn't realize we were causing the problem you are describing." (The OBVIOUS problem!) lol I actually had Japanese engineers flown to America from India to fix the (OBVIOUS and HUGE!) problem during a recent stint with this kind of thing.

So it's hard to know how that receiver got designed so strangely. Was it engineers being educated beyond their own intelligence? ....sound like it to me. lol Like you said, however, I'm not sure if that was Bob's design or His engineering team. I have heard those receivers were legitimately amazing.

Also...sounds like you got that thing purring like a kitten after getting yourself stuck down a rabbit hole initially. Way to recover!

 

[Wes]

It is rare to not be able to repair something...at all...ever! I'm dying to know, what the hell broke? lol

dunno for sure but the pattern of progressing failure matches exactly the main PC board dying - which is a common problem with that particular piece of junk

 

[Digital Mastering System]

That sounds so completely messed up it is hard to believe that there wasn't some kind of reason for the goofy build on that receiver. I believe you. It sounds like one of those things when you aren't there during the design process the decisions made can not be made sense of at all. But if you are there during the design process all of those decisions made make complete sense because you and your team are making decisions to solve issues as they arise. Knowing the pros and cons of each decision as you make your way through the process.

I work in the heating and air conditioning industry. I have literally run into situations like you describe here when you stand back and look at a design and think, "How in the hell could someone think THIS was a good idea?" I have then actually met some of the folks who made those "stupid decisions" and had the opportunity to ask them why they did what they did. And...sure enough...there was a logical reason to go with the bad decisions on several of those occasions.

That being said....sometimes the answer to the question "Why did you design it that way?" was "Whoops.....we didn't realize we were causing the problem you are describing." (The OBVIOUS problem!) lol I actually had Japanese engineers flown to America from India to fix the (OBVIOUS and HUGE!) problem during a recent stint with this kind of thing.

So it's hard to know how that receiver got designed so strangely. Was it engineers being educated beyond their own intelligence? ....sound like it to me. lol Like you said, however, I'm not sure if that was Bob's design or His engineering team. I have heard those receivers were legitimately amazing.

Also...sounds like you got that thing purring like a kitten after getting yourself stuck down a rabbit hole initially. Way to recover!

Well, I still haven't got the parts for the redesign. It will happen soon.

 

[CDMC]

I will throw in my two cents. Bob Carver is a talented engineer. His Magnetic Field Amplifiers were nothing magical, they just used multiple rail voltages to reduce consumption and heat. They are called Class G. They always sounded fine to me, and with the exception of the M400 cube have been reliable. There is company, Nelion Audio, LLC, that performs rebuilds (new caps and any needed repairs) and upgrades to increase their reliability and power for reasonable prices.

The Sunfire amps were great. While the tracking downconverter is a neat design, others use them now (Class H). Emotiva uses such a design in their Differential Reference amplifiers. I acquired a used Sunfire Stereo for $700 nearly 20 years ago to use temporarily while having an Adcom 5500 upgraded by Stan Warren (the other half of PS Audio). The Adcom came back, was hooked up, pulled back out and the Sunfire stayed. More power, better sounding (in my flawed sighted testing, but I will say I expected the Adcom to sound better, many will say I didn't let the Adcom break in long enough since I only gave it a few hours), cooler, and had the cool, but useless, Joule storage gauge. Last year I spent about $400 to have Bill Flanery recap the Sunfire and continue to use it as my amplifier for my Magnepans.

Bob is also good about supporting prior products. When Sunfire went away, he set Bill Flannery up with all the information so he could have his own shop doing repairs. He did so previously with another company when Carver went under (long after he left).

 

[anmpr1]

Bob is an example of a guy who (in Kenny Rogers' words) knew when to hold 'em and when to fold 'em. In his youth and middle age you could see it in a drive for market share. My impression now is that he's just happy building small batch amps he can sell to a select clientele who are interested in that sort of thing.

I'll always honor his --I mean Miss Hologram's memory.

 

[Speedskater]

Because the Carver solid-state amplifiers had a very unusual power supply (to say the least), technicians would totally destroy the amp when they used some conventional test & repair techniques.

 

[Count Arthur]

There's a YT video of a guy repairing one of Bob's large mag field amps. It's pretty interesting to watch the tear down and troubleshooting. You can easily see how Carver was thinking 'outside the box' in the design. Once the technician got the schematics and familiarized himself with the kind of unique circuitry that was used, the thing went together in short order. Very powerful in the scheme of things.

Having watched that, isn't that triac doohickey, pior to the power transformer, making it operate in a similar fashion to a switch mode power supply?

 

[Speedskater]

Having watched that, isn't that triac doohickey, pior to the power transformer, making it operate in a similar fashion to a switch mode power supply?

While it's high tech and low budget, it's very different than a SMPS. It switches transformer taps as demand increases or decreases.
Bob Carver knew how to do more at less cost.

 

[Count Arthur]

If you watch at around 28 minutes in, the triac is on the primary and used to "pulse" the input to the transformer, not on the secondaries or the subsequent different voltage rails.

Also, see part 2 at about 24 minutes:

 

[Speedskater]

I just checked the TFM series schematic and it not similar to the Silver 9t.
No triac in the primary.

 

[Panelhead]

My beginning in better quality audio was a Carver 400M. Purchased a NAD 1020 preamp and the Cube from a dealer in Shreveport in 1981.
A year later drove past an Altec factory in OKC and there was a Sale banner visible from 1-40. Stopped in and was the happy owner of a pair of big two ways.
The Cube stayed in heavy use until around 1990. Those big Altecs and the Cube lacked the cred of friends Magnepan, 801F, big JBL, and others. But none played as loud and clean.
When the red lights on the front of the Cube started to dance the sheetrock would start to cry. Still worked perfectly when sold around 1993.
Carver was publically traded for a while, NY I think.
A friend had the Auto-Correlator preamp and Cube. Drove five foot tall JBL’s. He was disappointed in the preamp. He felt it was hype, but big and pretty. I thought my 150.00 NAD was a better preamp. Later purchased better (more expensive) gear.

 

[Sal1950]

The Cube stayed in heavy use until around 1990. Those big Altecs and the Cube lacked the cred of friends Magnepan, 801F, big JBL, and others. But none played as loud and clean.
When the red lights on the front of the Cube started to dance the sheetrock would start to cry. Still worked perfectly when sold around 1993.

Sounds like you had a lot of fun,
My type of guy.

 

[RichB]

I had a sunfire cinema grand signature and it was a solid amp that needed repair. it was fixed by a repair shop run by Bob‘s girlfriend (I think).

I still have a 200 WPC 5 channel amp driving a system with Revel M20’s and C20. That will 20 years this summer. I have no complaints.

- Rich