Ampeg Micro CL distortion

[Jewellworks]

And as a side note, yes I have to agree the gain structure of this amp is totally backwards. And it's also aggravating that the effects loop is after the master volume. If I turn the amp down, it adjusts what is feeding my effects. And in my case, it's a compressor. So that doesn't help... Its fine if you leave it up all the way, all the time, but that's it.
I bought it for it's form factor. But if I ever sell it, I'm getting a Fender Rumble 200 instead.

[doxy]

Thank you very much Juan. I feel lucky to have found this forum and your comment. However, the harmonic distortion problem has not been solved yet. A sound like vibration is heard while playing. What can I add to the circuit, do you have any suggest for this problem?

[doxy]

Juan. Thank you for your knowlegable and generous input. I will follow your advice. Yes, it does seem to sound better depending upon the instrument used. I did not trace yet, but you are suggesting the clipping is in the preamp?

So, regarding the output stage, the rails are +\- 48 vdc...what is the max p-p output voltage to exoect with a clean input signal? (I will try driving the power section direct).

Did you solve the harmonic distortion problem? Which way did you follow?

[JPM-Electronica]

Good morning guys, I tell you that I was looking at the post, I was able to solve the crossover distortion, replace C106 (original value 220pf) with a 680pf one and everything works perfect.
Also I add that this amp came with burned out outputs and were replaced by KTB688 by 2SA1943N (toshiba) AND KTD718 by 2SA5200N (toshiba).

I hope this helps you. Greetings from Argentina!

[JPM-Electronica]

Good morning guys, I tell you that I was looking at the post, I was able to solve the crossover distortion, replace C106 (original value 220pf) with a 680pf one and everything works perfect.
Also I add that this amp came with burned out outputs and were replaced by KTB688 by 2SA1943N (toshiba) AND KTD718 by 2SC5200N (toshiba).

I hope this helps you. Greetings from Argentina!

[Vicus]

The micro cl that came in my shop had a problem with a woofer (now solved) but the amp is not clean. The current in the emitter resistor of the power transistor was 0. I tdid ry to increase it by lowering R134 but not solved the problem. With the oscilloscope no visible distorsion.
Does increase C106 reduce the bandwidth of the amp? Also the first stage is a second order high pass filter and R24 and R25 is not the imput impedance (it contribute but it's not the only).

[mikeydee77]

Enjoyed studying this old thread over the last two weeks while working on a raspy micro CL. Amp is on good condition but little use and understandably. It sounds terrible rather like a torn speaker.

Lowering the gain as Juan mentions did help a lot but still the raspy distortion persists. The rasp is mostly present when playing bass but with a sig gen at 440hz it shows up as a little higher frequency oscillation on the crest of the signal. The distortion is present at speaker, line out and send. But when you remove the speaker load the distortion disappears and the output is clear. When you connect headphones it also is clear in the cans presumably because of the reduced load.

Injecting at the fx return is bad too but slightly less understandably. All of this makes it confusing when trying to diagnose if pre or power amp issue. Once you accept that this is a design issue then one can relax in to it more.

The suggestion of JPM really helped though. Changing c106 from 220 to 680pf makes the amp sound like a bass amp, not a great one but something more usable.

Just wanted to share my experience on this and hopefully save someone else's time.

Unbelievable that ampeg didn't have a listen before sending out...

[Arohana]

Re: Ampeg Micro CL distortion.

Yes, it is due to an inherent vice. The design and execution of this amp is detestable because it *causes* unmusical distortion to occur at any gain level.

To those who suggest irrelevant causes and non-solutions: please stop.

There is no readily available solution. I have discussed the issue with Ampeg's nearest licensed tech. He cannot get parts from the manufacturer. His advice was to sell it as scrap.

[g1]

Re: Ampeg Micro CL distortion.
To those who suggest irrelevant causes and non-solutions: please stop.

There is no readily available solution. I have discussed the issue with Ampeg's nearest licensed tech. He cannot get parts from the manufacturer. His advice was to sell it as scrap.

Did you read post #30? Did you try the mods and find that they did not work? There are no special parts that you need to get from the manufacturer, just standard capacitors and resistors.
If you did not try the mods, don't tell people what they can and can't discuss.