Carver PM1.5A - Bridgable?

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi AltheaToldMe,
They are bridgeable, but watch your speaker impedance and your AC supply impedance. Practically speaking, the amplifier will probably run into trouble due the poor AC line regulation.

Now for one last question. Do you have any idea how much power you are dealing with in normal stereo mode???? How about in mono-bridge mode? You will run out of AC power before you run out of Carver power. Your speaker(s) may offer themselves up to the fire god. Most woofers will not be able to handle the full output from a Carver in normal mode for very long, not unless your AC supplies are drooping badly.

Last point. If you are really going to do this (recommend that you don't), the old filter caps may give up the ghost. You had better have that amp serviced properly before you embark on this idea.

-Chris
 

djk

R.I.P
2001-02-04 4:23 am
USA
On 10mS tone bursts at 8R in stereo, a PM-1.5 can put out in excess of 200V peak-to-peak.

This implies 400V P-P bridged.

At 8R in bridge mode on bass the collector bond wire for the outputs could fail (25A peak rating).

I might try it if driving a 16R load that can handle in excess of 1.2KW on program material.
 

AltheaToldMe

Member
2008-01-08 10:56 pm
Thank you for the quick replies!

As they are bridgable, can you clue me in as to which two speaker binding posts result in the bridged (mono) configuration? There is not information about this on the amps themselves.

I'm aware of the power of these puppies, but I love to have tons of headroom. I am using a set of Infinity SM125's right now, but have a set of Paradigms inbound.

I am using a line conditioner by PowerVar to power the units. Hopefully this will temper any AC irregularities that may come about.

Thanks again for the sage advice!
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi AltheaToldMe,
As they are bridgable, can you clue me in as to which two speaker binding posts result in the bridged (mono) configuration?
The two "positive" speaker terminals.

I'm aware of the power of these puppies, but I love to have tons of headroom.
You already have excess headroom. I don't think any amp sounds good in bridge mode. This effect varies with the amp. Remember that your damping factor just got cut in two, and that is not the entire reason for the difference in sound.

I am using a line conditioner by PowerVar to power the units. Hopefully this will temper any AC irregularities that may come about.
That is the very worst thing you can do! Do not run these Carvers through anything. Use really good quality outlets rated at 20 amps minimum. Wire each amp directly to the breaker panel directly, and on the same phase. Nothing ever gets put between a high power amplifier and the AC supply.

Think about this. Carver amps chop up the incoming AC waveform. What possible good would anything do here? All that will happen is that your voltage drop will be much worse if you use any conditioner no matter what that manufacturer says about them.

-Chris
 

AltheaToldMe

Member
2008-01-08 10:56 pm
Points well taken. I really appreciate the advice.

While I am still here, do you have a listing of the specs for the PM 1.5's? I'd love to know.

Also; What would be a couple of good tip for PM on these. Anything in particular to pay attention to as far as components reaching end of life?

I'd like to buy you a beer for your help. Perhaps wine?
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi AltheaToldMe,
I think it was rated at 450 WPC into 8R. I never bothered trying to remember that stuff. Besides, the power is so high that it doesn't matter and the ability to deliver that amount of power hinges on the AC supply at those levels. I'm pretty sure the specs are out there. I can tell you that the supply rails were spec'd at 125 VDC, plus and minus. I normally set them for 118 VDC as they tend to creep up over time. That should send chills up your back.

The filter capacitors on the first two tiers will be degraded by now for sure. There are some resistors that tend to overheat on the power supply PCB as well. Standard solder joints and the fan bearings need lubricating. Blow the dust out. The rest depends on how hard a life it's lead. You may or may not have other thermal problems.

Lastly, these are different amps than most. You need a real Carver technician to work on them. People who are only sure they can fix them will cause damage.

Well, I'm in Canada. So it's a long way to fire a beer, but thank you. Why not send some $ to the site instead. It will go to help more people.

-Chris ;)
 
I'm with Chris on this one - don't even think about trying to use carvers in bridge-mode!

you'll just end up with dead speakers and possibly dead carvers.

I don't agree with the power conditioner discussion.
Here in the UK, our mains frequency is 50Hz, the carvers were designed for 60Hz operation.
The result over here is that the power supply runs out of power a little early so we don't use them on bass bins.
There is no thermal sensor in the transformer windings so the amp is prone to overheated windings - smoke and a smell of urine !
The chokes between the inlet and the triac are a little on the flimsy side so the carver 'carves up' the mains.
(you get a dimmer-type buzz picked up around the system).
We're using industrial triac surpressors (30A choke in a can with class X and Y capacitors) wired back-to-front (like you would on a washing machine, because the interference is generated on the load side).
we use 1 per amp - its a little bulky but stops the famous 'carver buzz' dead.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi AudioSystemsEng,
Here in the UK, our mains frequency is 50Hz, the carvers were designed for 60Hz operation.
I can't see that happening. What is more likely is that the added resistance from this ....
We're using industrial triac surpressors (30A choke in a can with class X and Y capacitors) wired back-to-front (like you would on a washing machine, because the interference is generated on the load side).
is causing the line voltages to sag badly when the Carver attempts to grab a ton of current.
There is no thermal sensor in the transformer windings so the amp is prone to overheated windings - smoke and a smell of urine !
The reason the transformer might smoke is the - voltage drop created by the filter!!!! Carver amps have very good amplifier protection, but it wasn't designed to be used with high resistance power supplies. When the voltage drops, the regulation circuit requires the amplifier to draw more current (just like a standard switching supply) to compensate.
The chokes between the inlet and the triac are a little on the flimsy side so the carver 'carves up' the mains.
The chokes are not going to deal with the chopped sine or distortion. They are there to filter out RFI. I can't say as I've ever really noticed them actually.
The Carver power supply uses a "transformer" designed to work on current pulses. It will saturate on a normal sine wave input.

-Chris
 
Hi Chris and anyone else who's interested in Carver,
I put my post in here so that people can benefit from the practical experience that I and other large users of carver amps have.
As with all internet forums, wikis and blogs, the reader should try to gather as much information from as many sources as possible and make their own decision of the validity of each piece of information.
I do agree with you that high power amps benefit from the lowest possible mains source impedance, and in an install situation, this should be strived for. However, who on earth would install carvers in 2008?
Its not very helpful to the reader for you to chop up posts and insert comments out of context. If you want to write a constructive post, then please leave other posts alone.
For example, when i said the transformer is prone to overheating, this happens regardless of the supply condition, whether hard wired to the distribution board, or on the end of a 50m feed at a festival. Amps such as the EV P1200 range have a thermistor built into the transformer that will turn the amp down if it is in danger. I did not make a link between using a filter and overheated transformers.
I included my comment about the mains frequency because as the mains frequency increases, the minimum core volume decreases, as bob's brief was to keep the weight as low as possible, it is quite likely that the core volume is a little low for 50Hz operation. We believe this is the reason why the amps will not drive sub-bins in this country (again, under a variety of supply conditions). I think its important to share this information so that anyone in the UK who is considering buying an amp such as a PM1.5 to run their bass system doesn't waste their money.
Finally, i must pull you up on your understanding of my comments about chokes. Maybe i didn't explain myself clearly. We (most of the large production companies in the uk that still use carver) are using Low impedance filters to reduce the amplitude of the triac switching passing back down the line where it can be picked up by by sensitive equipment in the system. This is most likely to happen in a touring situation, where the whole system will often be star-fed from a mains distro rack which is on the end of a long cable (don't forget about the distance between the venues outlet and the sub-station).
For readers that are unfamiliar with the carvers power supply, it consists of of a type of switching power supply, operating at line frequency, on the PM1.5, (although the PT2.0t uses a conventional push-pull switch-mode supply operating at the ridiculously low frequency of 1kHz!). The transformer in the PM has a large core volume which allows it to store pulses of magnetic energy. Unlike a linear transformer, the pulse transformer core is magnetised to saturation. The pulses are created using a triac which is fed through an opto-isolator from one of the secondaries. This is how regulation is achieved. The switching of an inductor causes high voltage spikes that travel back down the line to the source. Most of the carvers that appear in second hand lists over here have already been 'modded' by concert sound or brit row to include an extra mains filter squeezed next to the fan. This can be easily identified by the 8mm mounting stud visible on the under side of the amp, we prefer to use an external filter which is larger and has a lower impedance.
It is a compromise, but the other option is for us to get rid of our carvers, which would be a shame because their such a nice amp for touring (an of course, haviing the service centre in-house is a benefit too ;-)

I should mention one other useful mod to the PM1.5's (which have a single fan).
The fan speed increases as the mean output amplitude increases, this is a useful side effect of the way the mains transformer is regulated. However, if the amp is driven hard continuously, then a thermal sensor switches the fan to high speed mode (by bypassing a resistor). There is also a fan speed switch on the back of the amp that switches out another resistor. The result is the fan can be over stressed if the amp is run hard - ie at max into 4 Ohms from a compressed audio source (we're talking about DJ's here).
Although there is a 1 Ohm 3 Watt series resistor to limit the current going into the fan motor, I'm receiving a lot of amps where this resistor has failed open circuit too late, so the fan motor has been killed. The original fan motors are getting hard to get in the UK although they are similar the the motors used in model racing cars.
We have been fitting a 24V 5W zener across the motor to limit the voltage across it (at the expense of the 1 Ohm resistor, but i'd rather replace that than a motor).
Many of the ex-rental PM's in the UK have had the so-called 'double fan speed mod' - the resistors in series with the fan (2x51R/1W, if i remember correctly) have been reduced. - this will over stress the fan. The correct way to improve cooling of amps is to properly design fan cooled racks, or use an amp room (not the beer cellar!).
...or just don't thrash your system ? .. Nah, too obvious !

Thanks for reading
J
 
I really would like to tip my hat to all you folks that have the knowledge to teach neophytes like myself some interesting stuff. I also appreciate you folks taking the time to answer my questions.

I have decided not to bridge the amps, but to install one in my exercise room instead. I also have taken the time to install an isolated ground receptacle for each amp (much like a hospital receptacle) with a barrier ground as well as the main ground. I have eliminated the small amount of hum I was experiencing.

Thanks again to all you kind folks.....Much appreciation!

For all of you thinking about buying one of these amps….Do it. The sound is unbelievable and it has devastating amounts of reserve power.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi J,
I was attempting to answer and / or correct some of your points. There was no attempt to take them out of context at all, but rather to clarify the points being made.

If you want to pound Carver amps through a sub-standard AC supply, fine. There will be trouble. Understand that those amplifiers were not designed to be used in that way. Other makes of amplifiers are better suited for that as they do not draw sudden peaks of current to the same level a Carver does.

The AC regulation circuit is more complicated than you explained. It senses all the supply voltages together. Some of those sensing resistors will overheat over time. Their values will shift. The core is not normally operated in saturation either. That is a fault condition and it draws tons of current when that happens.

Practical experience. It's only worth the knowledge that backs it up and is plagued with inaccurate information. Never forget that anyone can write whatever they want - in print or on the internet. Reading from every source available is a good way to get something wrong. My post was an attempt to clear up what I see as errors, and to possibly help you out with something that appears to be misunderstood. It's that simple. There was certainly no attempt on my part to attack you. So I guess I'll have to say, if you wish to be helpful. only write things that you know first hand to be fact. Hearsay generally results in smoked amplifiers. For what it's worth, I'm reasonably familiar with these amplifiers and their design.

To illustrate that point, we had problems in North America (can't say about the rest of the world) with roadies using Carver amps for mid / high duties only. That's because they are very light. Someone started the story that these amps didn't operate well on sub duty. Problem is that the commutator hold up time was set up for bass or full range. As a result of this "knowledge", several amplifiers were damaged. It turned out that these amps work extremely well full range and sub duty. That's as long as your AC supply meets the requirements of what you are doing. Normal amplifiers are protected by line sag (that limits their power output). The opposite is true with a Carver amplifier.

The one thing you are correct about is that the odd one burns. I have seen only a couple over many years. Usually as the result of a tech shorting out the triac and plugging the amp in.

Core size with these "transformers" doesn't really matter that much going from 60 Hz to 50 Hz. The same energy is stored and depends on the power requirements.

About the fan. The best mod might be to go with a standard "muffin" type fan with two speeds. They are easier to get and may last longer. These amplifiers were not designed to be operated in the manner that you just described. I can not understand why you guys did such a fancy work around when the other fan styles are more efficient. By your own admission, you do not really require a multi speed fan.

Those amps are so old now, you guys should be using a newer design anyway. Something better suited to what you are doing with them. In other words, I agree with you that no one should be installing those in a professional application these days. They are now more of a liability than anything else now. Like a car with a million miles on it.

As for your noise problems, you should have been filtering you signal level stuff, not your amp racks.

-Chris
 

djk

R.I.P
2001-02-04 4:23 am
USA
The power supply in a Carver amplifier does not like sagging line voltage. As the internal DC voltage sags (driving a heavy load) the conduction angle on the triac is increased. When the conduction angle starts looking too close to a sinewave the transformer will overheat and the windings will burn.

There exists a factory mod to limit the maximum amount of conduction angle (but I no longer have access to it).
 
I'm with Chris on this one - don't even think about trying to use carvers in bridge-mode!

A 3db gain at the expense of the amplifiers and possibly the speakers. Not good reasoning at all in my opinion.

I won't consider bridging ANY amplifier unless I run an impedance sweep on the speakers it would be driving. An 8 ohm nominal rated speaker can have its impedance dip to 4 ohms at low frequency and this doesn't play right with a bridged amplifier needing a 8 ohm minimum load.
 
totally ! -
i wish more ppl understood that 8 ohms nominal is not 8 ohms at all frequencies...
i have a client at the moment who is obsessed with trying to "get more power" by running his bins at 2 ohms :-(
i've explained several times about the loss in the output stage, the loss in the cables, the fact that the imedance will drop to 1 ohm just below resonance - to no avail :-(

so i guess i'll be seeing this amp i've just repaired back here again
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi J,
Sometimes you just can't win with some people. I wish you luck with him.

I'll bet his installation would sound much better with twice the amps and a 4 ohm load on each. I suspect that most amps may go into current limiting with his idea. Therefore, more power if he splits his load up. Definitely more impact on transients the right way.

-Chris