ampeg micro cl head schematic reqd

[blindboybenton]

Good morning to you all

I have a ampeg micro cl head, with an odd sound fault. a sort of very slight distortion / Decay after a note it played

I know the fault is in the power amp, clean signal out of send, Headphones distortion

Hoping somebody will have a map. i read a post about it on here

hope you are all busy,, I know i am

Blindboy

[J M Fahey]

It smells of crossover distortion.
Of course, don't adjust it out by ear (I have seen people recommend that ), easy way to burn an amp, wait forn the schematic or exact instructions.

Just to do something meanwhile:

1) check what the power transistors are. Bipolar? MosFets? What code?

2) are emitter/source ballast resistors visible?
What voltage drop across them? (We are expecting millivolts there)

3) scope the output, either to check the existence of crossover *or* the other possibility, some output instability.
Not that common but I have seen it before.

In any case, if you hear something, it must also be visible on the screen.

4) just doublechecking: have you tried that head with other speakers and those speakers with other head?

5) would not be surprised *at all* to find that power amp matches other Ampegs out there, compare what you see with a known example same era.

After all I suspect main difference with others is only cosmetic, milking the SVT cash cow to death.

A customer bought one, thinking he was buying "a true SVT, just packed in a smaller case"

[J M Fahey]

...

[DrGonz78]

I am pretty sure this is the correct schematic for that amp. Hope it comes in handy.

[J M Fahey]

Thanks Dr Gonz

Weird, what a non-Ampegish design, second this day not matching what's expected.

Very low end Korean.

I'm starting to suspect that Companies now not only are fully in investor's and accountants hands, who couldn't care less, but also are losing aging Tech staff and replacing them with non Music oriented types.

This and the earlier Peavey "Backstage" make me think of Oriental OEM makers, who will build whatever is ordered at low cost, being asked by Marketing Account managers: "just make for us a ******* amp, xx Watts, this is the look you must copy, feel free to complete (electronics) details yourselves".

As in Orange amps, where the product is *anything* , as long as it's wrapped in Orange Tolex and has a white faceplate with words replaced by cartoonish symbols.

Oh well, customers think they are getting the real thing.

Just last week a Customer was happy because he bought a "Hiwatt" , actually a Maxwatt series SS Bass amp ... "the same as Pink Floyd used to use"
After a weak attempt at explaining the realities of life to him, I shut my mouth and sold him the speaker cabinets he needed.

All I would earn would be losing a sale plus his eternal hate.

Oh well.

EDIT: there is no bias control visible, at least on the schematic.

Anyway, measure voltage drop across R121 and R122 (we expect a few mV there, probably 20-30 mV or so) and post it here.

If 0mV or way too low, you can add a trimpot to make it adjustable.

As is, in theory you'd need 4 "diode drops" for biasing, although that tends to be alittle too high, so a little less is usually preferred, but here resistor string hints at ~3 1/2 diode drops, usually resulting in underbias and crossover distortion.

As usual, a couple gut pictures would be interesting.

EDIT: IF it were an SLM/Ampeg/Crate design they would have fitted their ubiquitous opto limiter , none of that here.

An SS amp, even more if underpowered (100W into shoebox sized 2x10") simply is unusable without some for of compression/limiting, unless farting means "Bass sound" to user.

And: 2k2 and 10k input mixing resistors?
What were they thinking?