Carver PM-2.0t Amplifier chat?

[CaptDon]

Anyone here working on or with the PM-2.0t series? I got a slew of broken
ones (all had power supply problems) from Clair Brothers years ago. Carver
made 3 special types of the PM-2.0t units and the 1250watt amplifiers were
classed as 1kw amps called CBA-1000. The Clair mod pushed the main switch
transistors to their bitter limit and they failed often. I have used a newer higher
rated transistor and turned down the peak switch current limiter a bit and mine
amps have been through hell and back and survive! 2 X 625 watts or 1250 mono
at 11 pounds is good even by today's standards. The CBA-1000M Monoblock with
the 14 added capacitors on the high rails is killer for sub woofer use. Very few
amps can keep up with sustained bass like these can!!

[redshift96]

Hi, tysm for posting this.  Hoping maybe you can help resolve a question about the monoblock version. 

Both versions are based on the Carver PM 2.0, afaict.  The original manual for the Carver PM-2.0t (not sure what the "t" represents) gives the output specs as follows: 

   465wpc @ 8 ohms; both channels driven

   600wpc @ 4 ohms; both channels driven

   450wpc @ 2 ohms; both channels driven

   1000w @ 4 ohms; mono output


That 2 ohm rating seems odd, but most folks familiar w Carver's mag field amps will never run them into a low-impedance load, so nbd.

But here's the question.  1200w total in stereo into 4 ohms, and 1000w total in mono into 4 ohms makes sense.  And Carver's factory monoblock amp has a single set of 2 output binding posts, with a choice of using either of the single TRS or XLR inputs.  Fine, no problem.

However, on the Clair Bros monoblock amps, it appears that they've modded the standard 2-channel amps as there are two sets of binding posts, and what appears to be spaces where one of the two TRS & XLR inputs have been removed.  So only one input channel, but what appears to be two output channels.

Clair rates their modified monoblock amps at 1000w.  I would assume that means 1000w TOTAL at 4 ohms into a single output channel, and that only one of the two sets of output binding posts are active.  But since the amps have been modded, and I have no idea exactly to what extent, I'm trying to verify the output capability of this amp.  And I'm puzzled that they went to the trouble of removing one set of inputs, but left two sets of outputs.  Surely this amp is not putting out two identical channels of 1000w @ 4 ohms, is it?

It's also puzzling to me that Clair didn't start with Carver's Monoblock version to begin with, since it has the obvious single I/O channel.  I'm going to post pix of the Clair vs Carver Monoblock front & rear panels if the site lets me.

Any chance that you can you shed any light on all this, having had them apart? 

I'm considering buying some of these for use with a set of very power-hungry 21" sub cabs that are rated for 800w @ 4 ohms.  And I'd really like to make sure there's plenty of headroom.  If that "monoblock" is only delivering ~600w to each of the two outputs, it will definitely not serve my purposes.  If it's delivering 1000w to a single output channel only, it could work well.  If it's delivering 1000w to TWO output channels, well... that would be fantastic.  But that strikes me as highly unlikely.

[redshift96]

Carver Monoblock:

[redshift96]

Clair Bros CBA 1000 Monoblock:

[redshift96]

A couple of additional puzzle pieces for anyone who may be interested.  The second diagram seems to suggest that once the amp is internally jumpered for bridged operation, the right and left red output posts are to be jumpered in order to drive a single speaker with the max 1200/1250w output.  But then I'm not clear on exactly what they mean in the last sentence about wiring the red posts in parallel.  Nor on what the rated output might be in each impedance config.  Grrr.

[CurtWash2]

YES, I have two cba 1000 amps that need repairing. Anybody here able to fix the?

[CaptDon]

Are your CBA-1000 amps mono block or 2 channel? CBA-1000 = Monoblock 1000wrms into 4 ohms, Output posts are internally hard wired together red-red / black-black, There are two 1/4" input jacks, only one is active the other is to physically support the preamp board. There is one XLR input, it is also active with pins 2/3 wired opposite of what you may expect. The inputs to both amplifier driver sections are hard wired in parallel, there is no 'bridged mono mode'. CBA-1000S is a normal 2 channel amplifier. 400w+ @8ohms, 500w+ @4 ohms 'both channels driven' rating. There is another oddball often thought to be broken as one channel has no low end, the CBA-1000M with built-in crossover components on the preamp board used for driving the Clair monitor wedges. Only one input is active and the unit is basically for a mono input driving a biamp'd monitor wedge. What is the malfunction with your units? 99% chance the switch mode power supply is dead. The over current shutdown threshold on the CBA units was set well beyond what the aged MJ100XX darlingtons could handle, They fail dead shorted. Sometimes the 'new' owners will put in a huge fuse (bigger than 10 amps) and wipe out the power transformer which is unobtainium for 20 years now. Tell me about your units. Thanks!!

[CaptDon]

B.T.W., the super tricked out and rare to find CBA-1000 units are built 'upside down' and have the power supply and bar graph on the left side. The later CBA units are like the home consumer version with power supply and bar graph on the right.

[CurtWash2]

The units have the one xlr input. They also say Clair/Carver 1000s. They are stenciled with markings low and high above the channel 1 and 2 knobs with a small metal toggle switch in the front panel between the pots. One of them says Hi-Tech serviced 2/1/2011 damaged sell as is. It does not power
 on. Neither does the other.

[CurtWash2]

Both of the amps make a pulsating squeal sound about once a second but will not power up. There are no fans running. So I also have a couple PT-1250 amps that work fine except one appears to have bad bearings or something hitting the fan. I have a third Pt-1250 that appears to be starting that weird once per second oscillation although it still works? So the PT-1250 amps are rated 625watts@4 ohms per channel. So technically speaking are they more powerful than the Cba1000s amps? Is it possible to bridge the cba1000s amps so I could use them one each to a cabinet with its own crossover? So if possible to repair the cba1000s amps can they do mono in bridged mono out? What output into 4 ohms?

[Audiorepair]

Both of the amps make a pulsating squeal sound about once a second but will not power up. There are no fans running. So I also have a couple PT-1250 amps that work fine except one appears to have bad bearings or something hitting the fan. I have a third Pt-1250 that appears to be starting that weird once per second oscillation although it still works?

The PM1.5 I believe does this squealing/fans not running thing if the power supply is adjusted too low.
I think the two are quite similar, or at least the PM1.5 I am familiar with is similar to the PM1200, which want +/-  124v on their  high rails to work properly.
The PT1800/2400 also have a similar adjustment required to run properly.

[CaptDon]

The PM-2.0T, The CBA-1000 and the PT1250 are all identical inside. See my post above, bridged mono IS NOT possible. The monobloc versions have the two amplifiers wired in parallel both on their inputs and outputs. There are soldered jumpers on the audio board as well as the output jacks. The Clair Bros versions were down rated by Carver to 1000 TOTAL watts rms as a more realistic 'continuous industrial touring duty' rating. The home consumer ratings totaling 1250 watts is a bit optomistic but again, the amps are the same inside. I believe the PM1.5 and PM2.0 are completely different inside with a huge weight difference. The pulse width adjustment must only be made under the correct test voltages and conditions. Dicing around with that scratchy easy to break adjustment pot while running on line power will almost instantly blow up the power supply!! If your units are chirping and not powering up the audio output transistors are probably failed shorted. The CBA-1000 monoblocs will always chirp 3 or 4 times until they power up because they have that huge 14 capacitor energy storage bank on the + and - 125vdc rails.
 

[elecdonia]

Check the DIYAudio forums, especially their “solid state” sub-forum under the “amplification” tab. There is a wealth of technical info there about everything Carver going all the way back to the earliest Phase Linear products. Repair, restoration, and modification are all covered.

[Audiorepair]

All these amps appear to share the same basic topology. 
The PM 2.0t has more output devices than the PM1.5 I am familiar with, and presumably a bigger transformer and a metal tray of extra caps, all adding to the weight.

I have repaired quite a few PM 1.5's and PT1800's, and it is surprising how many of them turned out that the only problem was the power rail adjustment was out.
Yes, you need to be careful adjusting this, I always spray the adjustment presets with De-oxit and excersise them well before actually performing the adjustment, but that is kind of true with any bias adjustment really.

But the amp being maladjusted can mean its outright refusal to power up in the first place.

It could of course also mean there is a short on the output devices or dead PSU caps or something, and trying to increase the PSU voltage could just make stuff go bang, so you really need to bear all this in mind at the same time.

[CaptDon]

Doesn't the PM1.5 at 21 pounds have a rather large power transformer with triac control on the A.C. input vs. the PM-2.0T which has a true push-pull 1Khz switch mode power supply (Hence the 1Khz whine they are noted for) with a power transformer that looks about the size of a 75VA 'control transformer' likewise being 10 pounds lighter and slightly more powerful? Isn't the PM1800 / 2400 with dual power cords really two PM-2.0T units in one bigger box?

[Audiorepair]

I told you I'm not familiar with the PM 2.0.
I had a quick look and it seems the power amps have the same topology, I didn't study the power supplies.

What I do know is that both the PM1.5 and the PT1800 can refuse to start if the power rail adjustment is out.


Which pretty much covers the PM2.0 too, it would seem.

[elecdonia]

…the PM-2.0T which has a true push-pull 1Khz switch mode power supply (Hence the 1Khz whine they are noted for) with a power transformer that looks about the size of a 75VA 'control transformer' likewise being 10 pounds lighter and slightly more powerful?

This is the first time I’ve heard of an SMPS operating in the audio frequency range. What is the core material for the PM-2.0T power transformer? Steel laminations, powdered iron, or ferrite?

I have SM and/or schematics for almost everything Bob Carver made, but never had a PM-2.0T on my workbench. I probably do have a schematic but that might not specify the switching frequency.

For the older triac-based 50/60Hz “magnetic field” Carver power supply circuits it is essential to get the conduction angles and durations to match perfectly for both + and - AC half cycles. The early M400 units used a diac which wasn’t symmetrical enough. Later designs used a more sophisticated circuit to control triac trigger timing.

I agree that adjusting the rail voltages perfectly and observing that they are stable is essential.

Slightly OT: I own a TFM-15 where the toroid power transformer failed as a total short circuit. It isn’t burned or overheated anywhere but now it is always a short. At first this fault was intermittent. The amplifier would work fine for weeks, days, or hours and then blow the mains fuse unexpectedly. It gradually got worse. I’ve been thinking of total power supply replacement with 3 +/- SMPS, each with appropriate output voltages. I think there is enough room for them after removing the toroid.

[CaptDon]

Electdonia, Yes indeed, you would be shocked to see the power transformer of the PM-2.0T. It indeed looks like a conventional E/I laminated core. From the physical size you would guess it was a 75 V.A. @ 60 Hz filament / control transformer. It does in fact switch at a 1Khz rate and the amps were known for an audible whine. There is even a nulling adjustment for it. The switching rate is R/C fixed at right around 1Khz and the power delivered is controlled by pulse 'on-time'. The control loop is 'current control' and not voltage control so the PM-2.0t / CBA-1000 / PT-1250 units are EXTREMELY finicky about their line power voltage and quality. The 'on-time' at no load is about 60us each half and can ramp up to about 440us each half. At 1Khz the repetition rate is of course 1ms. I was just thinking as far as core material cross section, I know it isn't a linear interpolation, however the 75V.A. @ 60Hz would be expected to interpolate as 750V.A. @ 600Hz or 1249V.A. @ 1000Hz!! It is interesting that these amps were rated 1250 rms watts (Total) And I have run them at 1KW RMS (total) into a dummy load for hours and the amps run barely more than luke warm!
Cheers mates!! Enjoy the music, even better, enjoy being paid to play it!!

[CurtWash2]

Ok so the two amps I have are Clair/Carver Cba1000s amps. The led meters are on the right of the front panel. The volume knobs are labeled low and high. There is a toggle mounted down in front between the volume knobs. Several questions: Does anybody here know the purpose of the small metal mini toggle switches?

Also who has worked on these specific families of amps with the noted power supply problems? As I mentioned above I have several PT1250 amps as well that do work. I have them rack mounted in a lightweight rack with Furman power conditioners and I have also used them with beefy battery back up units. So they get stable conditioned power.

I know some say all amps sound the same... But I find I prefer Carver and Crown amps over others. I have not tried the Carvers with subs but the Crowns are remarkable. I do have a pair of Jbl SR4733 cabinets I would like to use the cba1000s amps with. I thought there was some way I could get 1000 watts to each cabinet. The cabinets do have internal crossovers that are very good and it makes it easier not to hook up bass frequencies to the 2450 horn diaphrams by mistake. The Pt1250 amps when I had them out of the rack seemed lighter than the cba1000s amps. I bought the cba1000s amps online as is thinking that I would be able to possibly get them repaired or use them for parts.

[CaptDon]

You would need 2 of the monoblock amps, one for each cabinet if you want 1000 watts per cabinet. I don't repair these amps for the general public. I do sometimes buy dead ones if they are the upside down version with the LED's and power switch on the left and volume control(s) on the right and Clair logo on the faceplate. I think the mini toggle switch changes the amp between a single full range input with a hi/lo output for the Clair Bi-Amped monitor wedges to a single full range input with dual full range mono outputs (NOT bridgeable because both channels are in phase). You could verify that in a heartbeat with 2 full range speakers connected. I never had a use for the hi/lo versions and never bought or inherited any.

[CurtWash2]

So in some ways the ones I have are the least desirable. They are 20 pounds instead of 11 like pt1250, and the pt1250s are rated at 625 per side these 500 But I thought Clair turned them up? Confused.. I guess if driving two cabinets with the same signal that wouldn't be bad. But to get good coverage sing 2 cans per side you would need cabinets with 60 degree horns, or, line arrays or something? Idk.

[CaptDon]

Clair never 'turned any up'. On the CBA-1000 units they turned up the power supply fault current but in fact down rated a consumer 1250 watt amp to an industrial touring amp of 1000 watts. Basically however the guts are identical with two possible exceptions. 1 there is a resistor modification in the power supply to allow a higher switching current before being seen as a fault and forcing the amplifier to go through a restart cycle. 2 there is a tray of 14 capacitors I believe 470uf@150vdc each usually only found in the monoblock versions to support use as a subwoofer amplifier. All of my notes and statistics ONLY apply to the PM-2.0t (touring) the PT-1250 (these are the late production Pro-Touring units) and specifically the Clair special order versions known as CBA-1000 / CBA-1000M / CBA-1000S. The PM1.5 and PM2.0 are indeed completely different animals inside with the so called 'Magnetic Field' power supply and NOT the push-pull 1KHZ switched mode supply, hence the apprx. 9 Lbs heavier weight.

[CaptDon]

Those 'silver faced' amplifiers with a single fan on the back are based on the PM1.5 or PM2.0. The ones with the recessed black face are based on the PM-2.0t version just to eliminate confusion. They are very different beasts!!! I am 100% unfamiliar with the heavier PM1.5 and PM2.0 units. I had a few early on but ditched them for the lighter switched mode power supply touring units. Sorry if I misunderstood what units you owned or were modifying/repairing.