Carver amp, needs doc

[Courtec]

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

[toddyaudio]

Sounds like the MXR130 receiver, I don't think I have the service manual for that one but I will check. I may have a parts unit on the shelf if you need something specific.

[djk]

"with something called Asymmetrical detector. I have no idea what that is."

FM tuner mono-blend circuit.

[boucivicsir]

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]

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.

[boucivicsir]

wow thanks! i will check that as soon as possible... i will let you know for sure thanks again!
Etienne

[Courtec]

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]

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

[sakis]

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]

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.