Simmons drum amp DA-50 low output

[nosaj]

I have a simmons drum amp it has low output . previously had none till I cleaned the line in jack. I can input .7vac 1k tone on the left drum/mono input
At IC1A Pin2 186mv pin3 184mv Pin1 output I get 280mv Pin8 I'm getting 14.86Vdc.
Does this even seem right or should I move farther down. Just mentally seems odd for such a signal drop from input to 1st IC.

nosaj

Output is ok at line in so its before there Im sure.

[Jon Snell]

The measurements are correct as it has a gain if about 1.5.
IC6a has a gain of about 3, so check what is there.

[J M Fahey]

On first sight it looks "broken" but Jon Snell has it right: checking gain resistors both input stages have stupid low gain, guess drum module output must be scary high.
Looks like a nice little drum module but I am amazed it does not include a Compressor Limiter, drum signals and waveforms are *extreme*.

So yes, what you measure is "normal"

To boot, each input has a stong highpass circuit, and also a passive mid notch, both *lowering* signal even further.

[g1]

Do you have an appropriate drum to test the drum inputs with? Was that the complaint?

[nosaj]

Do you have an appropriate drum to test the drum inputs with? Was that the complaint?

No I do not . Complaint was no signal. I cleaned Line in still no signal then traced signal to c13 where it stopped. Replaced that cap and now signal is low.
Signal is low on the drum input and the AUX input. I will check signal at 1c6 and report back.

Thanks
nosaj

[g1]

According to the specs in the user manual, the drum inputs are -10dbv relative to the line input.

[nosaj]

According to the specs in the user manual, the drum inputs are -10dbv relative to the line input.

So being dense. what am I supposed to be getting from your comment? There is no problem or I need to have a higher voltage tone at the input on drum or AUX as they both show -10dbv?

Thanks,
nosaj

[Helmholtz]

-10dBV means an absolute signal level of 0.32Vrms. Not a ratio.
If this is sensitivity, the input requires 0.32Vrms (or around 0.9Vpp) for full output.

[g1]

There is no problem or I need to have a higher voltage tone at the input on drum or AUX as they both show -10dbv?

The aux. and drum inputs are the same (spec). You said line in was good (?).
So at aux. or drum in, a signal 10dbv lower than what you used at line in should give the same output level.
Roughly, 1VRMS at line in, 315mV at drum in.

Wasn't suggesting there was no problem, just giving you some numbers to work with.

[nosaj]

Ok So I have a drum pad for it now. There is still an issue.
The Line in jack is indeed good.
Input .700Vac at DrumL Mono jack on IC6 I measure 1.6mv.

Jon Snell had asked for that measurement.
Thanks,
nosaj

[nosaj]

Would a tl072 work in this circuit to replace the 4558? I know they're similar but somewhere it was mentioned the tl072 is a jfet input. Wasn't sure how that might affect things If I needed to replace one as I don't have any 4558's on hand should I need one.

Thanksm
nosaj

[nosaj]

Ok i bit the bullet and replaced IC1 and IC2 with TL072 I had on hand. Amp works now.

nosaj