Outsider Mono Power Amplifiers

[hifiboy]

Hi,

anybody who know the outsider mono power amplifiers from the beginning of the eighties with a negative output resistance (adjustable)? I have the problem that both amplifiers get very hot (oscillations..?), so that I have to switch them off after a few seconds after switch on. Anyone having the schematics or service manual?

hifiboy

[jacco vermeulen]

I'd try to contact Manfred Baier at Omtec, Mr Baier was the one who did the Outsider amp designs untill the Outsider Team fell apart in the mid 80s.

[hifiboy]

I did so already, but he is not very helpful. Doesn't want to give away the schematics. Given the bad reputation he has, sending him the amps is no option.

[jacco vermeulen]

Shame.

I've never had a close-up look see inside the Outsider endstufen, but the circuit and parts choice/quality will likely not differ a great deal from the Omtec Class A models from the mid/late 1980s.
The trimpots at the loudspeaker return inside the amps, that set the additional feedback for the negative output impedance, are more than likely semi-open Piher PT models and you can be sure that those need replacing after 25 years.
With both amps experiencing the same problem, your assumption that the trimpots are causing the mono blocks to oscillate seems a good guess.
The trick with a second (but positive) feedback path from the loudspeaker return makes the amps susceptible to oscillation.
Easiest would be to take the trimpots out alltogether and connect the loudspeaker direct to ground to see if they're the ones causing the heat-up.
Setting the trimpots will require a signal generator, a scope and a dummy load, the reason why the amps have to be opened to adjust them.

The Outsider circuit will be easy enough to reverse engineer.
Posting some interior/exterior pictures of the pretty glass-top classics would be appreciated.

[hifiboy]

Before changing them it is probably better to clean them. I want to avoid to dismount the whole amp, because all the inputs/outputs of the PCB are soldered.

I have all the necessary equipment for the adjustment of the positive feedback. But how do I need to adjust it?

hifiboy

[HVfanatic]

So I want to "repair" Mr. Baiers reputation: I have the Omtec line amp. I was the second owner.The preampdied for some unknown reason. I sent it to Mr.Baier. I got it back a few month later, fully upgraded to V2 version. He made it without charge.

In my opinion this is exceptional customer service. I also own the antares and the CA25.

I love this quality products (especially CA25 and antares) and would always buy them again.

No rip up, outstanding built quality, fairplay in any respect.

Send an emal to Mr.Baier, I'm sure he will help you.

Regs, Dirk

[hifiboy]

Finally the monos are running again after going a little deeper in the amplifier design . Push-pull class A coupled with small positive and negative feedback. Can be certainly improved with better capacitors and a regulated power supplier for hum and ripple rejection. It seems that's the same amplifier as the CA-60 from Omtec built until today with some improvements.