Carver amp, needs doc

Courtec

Member
2008-01-12 4:08 pm
Hello there in Ampland,

I was working in Holland with Carver professional amps for PA work. To my surprise i got a Carver Intergrated amp. Model MXC130. It's old and has some strange electronics. It looks that the amp has double power lines, and it could be one of the first amps with this tecnologi. it also has a board (very big) with something called Asymmetrical detector. I have no idea what that is.
The thing is broken and if any of the kind members could help me with a diagram, that would be great!
The step down power resistors are getting very warm (normal for this amp, so i read on the Internet) and apart from a broken amp, the electronics for the tuner and the selector is not working.

I'l keep the board posted!

Koert
 

boucivicsir

Member
2008-02-06 10:27 pm
same trouble mxr130 balance

i got the same amp.
wanted to know if someone had a trouble with balance?
mine's got a good left channel, but the right one is kind of -10db softer. if i put the amp in mono both side a 100% ok. just need a light. thanks in advance and sorry for the tread jack!

merci !!!
etienne
 

Courtec

Member
2008-01-12 4:08 pm
Carver MRX-130

Dear Etienne,
I would go for:
1.A lot of caps are dryed out after 20 years. check them.
2.The power supply +-15V van be a problem
3.Ceramic capacitors, resistors around opamps can be bad.
4.the circuit around IC401, 402 would be my first guess. There is the connection between a and b (mono) The probem must be found in this circuit or in front of it. After it's switch work and amp in.
5. Is the problem also with external inputs?
6. check and clean all connectors. In any case a good idea.

By the way, this amp has 2 power rails. 40V and 60V symmetrical.
The 60V is added when the output is at a certain level, about 35V.
Then a double transistor pair kicks in and gives 60V via diodes.
It switches the rail for both amps at once. It is shared electronics so to say.

Also strange is the triac for the transformer. With it you van regulate the power and, as far as i can see, it stabilizes the power. Very rare, I've seen only thyristors or solide state as a softstart for charging the power caps.

After all a nice piece of advanced electronics in that periode of time. It sounds... I will test it and compare it with my Canadian power amp, the Classé CA-400 on Dynaudio 2.5 speakers.


This one is working fine now.
 

Courtec

Member
2008-01-12 4:08 pm
Results Listening test and question

Hello dear members of the board,

And so i did compare the MXR130 with my own amp, a Classé CA-400.
In the mid frequency's its oke but mainly because the high is ss and the bass is weak, compared to the Classé

It's oke but not great.

But now technical, The amp has a triac in front of the transformer. The frequency is the normal 50 or 60Hz. It is regulated by a opto coupler which opens or closes the triac, with a potentiometer and it measures the 60V rail voltage.

Question: When i correct the voltage on the high rail (and the rest also) to 60Volt the waveform over the transformer is a half sinus. So the triac kicks in at 90 degrees. When i make the angle shorter (more u x i), the 60v voltage drops. (????)

I think the best way to get a stable voltage on the rails is a full sinus with big capacitors. With this you make the ripple under load much worse, apart from transients who enter the amp. Perhaps that is also one of the reason the amp sounds hard in the high frequency's.

Any suggestions about the meaning of this design?
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Koert,
You are playing with fire, and I mean that quite literally. Do not mess with the power regulator. BTW, the regulation of the DC supplies is much tighter this way. Far better than transformer with big caps. Large capacitors (over normal) is also a bad idea. The first mistake people generally make.

The design of this amplifier is actually advanced compared to many linear amplifiers today. There are multiple supply lines and there are transistors that switch the higher voltages in and out when required. They are called commutator transistors. There are commutator diodes to prevent the higher voltage from back feeding into the lower voltage supplies.
Asymmetrical detector. I have no idea what that is.
djk called it right on the money. Long explanation that djk summed up very nicely.
the electronics for the tuner and the selector is not working.
Low voltage regulator or bad solder joints. This amp has high raw supply voltages and you will get problems related to this that is normally not seen in the average receiver. BTW, this amp delivers it's full rated power easily. Don't let the light weight deceive you. Be very careful about what you read on the internet. I've seen a lot of nonsense out there.
1.A lot of caps are dryed out after 20 years. check them.
Yup, just like any other electronics.
3.Ceramic capacitors, resistors around opamps can be bad.
Not very likely at all. Red herring - ignore.
4.the circuit around IC401, 402 would be my first guess. There is the connection between a and b (mono) The probem must be found in this circuit or in front of it. After it's switch work and amp in.
Try and keep an open mind when troubleshooting. Electrolytic cap replacement may solve this fault.
Also strange is the triac for the transformer. With it you van regulate the power and, as far as i can see, it stabilizes the power.
This is the main power regulator and the reason the unit is light. Never, never, never - ever - short the triac and apply power to any of these units.
If you do, extensive damage will result.
This one is working fine now.
That's good news.

-Chris
 
there is a question .....

about all this id like to ask ..... ive seen this bob's amplifier once in my life ....... actually this was bob's dream to make he had in mind for a very long time and actually he was sleeping on it for years ....then digital technology made it possible ...... then later on got familiar with how sunrise newest amplifiers work ....

the question :
when this triac is active IE reducing "voltage across the transformer what you see in the triac out is a wave from between square and sine ...... its sine but with the edges chopped almost like square but only at the edges

how its possible for a transfromer to curry out this transformation since signal is not sinewave and the after that ? how its possible for bridge and capacitors to rectify that ?????

when i was a kid i tryied to make a tracking power supply using one dimmer and one center tap trafo 42+42 volts witha a diode bridge and two 10.000 mfd caps ......

my bridge was gone ( shorted ) the minute i turned the dimmer to 50% and then caps were boiling and goes on ....

is there something special about all this ?????
 

Courtec

Member
2008-01-12 4:08 pm
And i must agree Sakis. It puzzles my mind. The reason i spend time in discovering the ins- and outs of the powersection was the fact that it did start on a supply with a sinus wave form but not on a power inverter, a "thing" that is is common in a country where power, most of the time, is gone. The voltage out of an inverter is a block kind of thing. Very bad for filter capacitors and especially for a triac kind of thing. The reason it probably didn't start is a very small pulse for the triac and the bridge rectifier that is connected to an optocoupler. It simply will not start unless you touch it with a testcable. The solution i came up with is a 33K resistor parallel over the transistor in the optocoupler. The small current you create is sufficient for starting the triac. It has no influence on the behavour of the system, the voltage regulation works normal under all conditions.

But it still leaves the questions unanswered, about the depper thought of this circuitry. See attached file.
 

Courtec

Member
2008-01-12 4:08 pm
And i must agree Sakis. It puzzles my mind. The reason i spend time in discovering the ins- and outs of the powersection was the fact that it did start on a supply with a sinus wave form but not on a power inverter, a "thing" that is common in a country where power, most of the time, is gone. The voltage out of an inverter is a block kind of thing. Very bad for filter capacitors and especially for a triac. The reason it probably didn't start is a very small pulse for the triac and the bridge rectifier that is connected to an optocoupler. It simply will not start unless you touch it with a testcable. The solution i came up with is a 33K resistor parallel over the transistor in the optocoupler. The small current you create is sufficient for starting the triac. It has no influence on the behavour of the system, the voltage regulation works normal under both conditions.

But it still leaves the questions unanswered, about the deeper thought of this circuitry.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi,
The transformer is a special one that works on current. Carver called it a "magnetic field coil". It will saturate if you apply your normal mains voltage to it and probably destroy many parts. Never short out the triac.

The other neat thing about this system is that the amp will try to start with a fault, but it will never turn on fully and will generally not cause extra damage. This is very unlike the average amplifier in that normally a protection circuit will not restrict the power to the amplifier itself in the event of a fault.

Normal transformers do not like a waveform from a triac or scr circuit. Also, your dimmer probably output an asymmetrical wave form. There was a net DC running through the transformer core. An exhaust fan will suffer the same fate.

-Chris
 

Courtec

Member
2008-01-12 4:08 pm
Thanks Anatch
That resolves the question about the power supply, it's a current driven transformer. That explains why the thyristor kicks in at half a period. The current (and only current makes a transformer work)
will be regulated. And when i check the current with the scope, it's a kind of a rectangular. Although i think a current flow in this application is shorter in the transformer. And so the efficiency of the system might not be very good.
With other words, A regulated power supply with a high frequency (as in computers and modern amps) is a better technological answer.

But this is old... (the devil is old...)
 
another option

e mail bob ..... if there is any trouble i think that bob's people will be more than happy to help you .....

bob actually answered my mail in person about one issue .... not really importand what he said .... but i thing it was very importand that he simply answered my mail ..... one way or another i felt privilged to be able to say hello to a legend ....this what it is to me ..... a legend !!!!

here is the email of his secretery
"Sarai Fulton" <[email protected]>
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Koert,
Actually, the efficiency is pretty good. Losses show up as heat and those "transformers" idle cooler than regular power supply transformers. The entire amplifier was designed around efficiency.

With other words, A regulated power supply with a high frequency (as in computers and modern amps) is a better technological answer.
That's where the Lightstar was going. Higher frequency "down converters" to reduce heat. PWM determined the rail voltages. Like our industry, Carver product was advancing. BTW, I have seen more than a few inefficient high frequency switching supplies in power amps. Stewart was one shinning example of how not to go about things. It wasn't uncommon to see holes burned through the chassis and PCBs in those.

-Chris
 
thats why

i said that this amp was bob's dream - nightmare ...he was sleeping on it for years ......

after he made some models with this technology then digital electronics made possible his dreams and make what he calls track down converter resulting efficiancy of 95% or more .....

my first expirience repairing a sunfire amplifier claimed to be 2.500W per chanel with the transistors mounted on the botom of the case for hetsink .....

i said to my shelf THIS A JOKE !!!!!! then i relized that it was possible and working also !!!!!!

the amplifier had some broken pcb cause of shiping ....just some soldering and testing at 1R with almost 4 speakers connected per chanel prooved to play like hell !!!!!

bob !!!! a legend !!!
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi sakis,
my first expirience repairing a sunfire amplifier claimed to be 2.500W per chanel with the transistors mounted on the botom of the case for hetsink .....
That's where they are on the Lightstar series 1 also. The thing I had to keep telling people was that the AC supply was the limiting factor in power output.

Keep one thing in mind. Bob's "downconverter" technology is exactly what the new cutting edge regulators are right now. Switcher, followed by a linear regulator to deal with the hash. Today's switching ("D" class) amplifiers are like a switcher without the linear stage. I don't think you can produce better sound by not following the switching stage with a linear stage. Now think about how long ago Bob got there. I'm going to guess he played with class "D" before most others did, and passed it by. Good enough for a power supply! ;)

-Chris
 
much true my friend

all these years due to professional needs on my job i was mostly focused on power ..... then stable power .....then bit less power and more safety .....

now days i am working with rod's P03 its one amplifier that actually listen to for a month now the simplest thing you can never imagine ...and the truth is that i constructed my own pcb made everything by the book or better but the only thing i didnt do is messure the power ......ha ha ha ha ha

of course you dont expect like more than 40-50w from it but the blody thing plays so well .....

i think that what makes bob a legend is that no matter how strange the machines was ( regarding almost class d design in a time that nobody understood a word about it ) still .... he kept much of the quality from his amps ....

i havent touch a carver or sunfire since 2000 so there is not much to say now days ....also my expirience was much smaller ten years ago so there also not much to say about it...

its so njice to be here though ....share the thoughts of you .... bob .... others more qualified and goes on ...
 
mxr130 service manual

Here's the manual for for the 130 there are service bulltins for most of the problems I've seen in my searches might help someone, I saw the loud pop on turn of in the bulletins as well.

darn it's too big a file PM me and I'll email it to anyone that needs it