SL 3505

[Perry Babin]

Does the ±15v remain constant when the amp clips?

If so, post the DC voltage on the first two 1266s and 3198s in one of the channels. If the voltage is difference when the amp is clipping, make a note of which pins change.

[mekaiver]

It has +- 13.2VDC for the opamps. The first two transistors have voltages as following:

A : Pin 1,2 21.5VDC
Pin 1,3 0.5VDC
Pin 2,3 20.8VDC

C : Pin 1,2 21.5VDC
Pin 1,3 0.5VDC
Pin 2,3 20.7VDC


So do the others. And they dont change while clipping. The sound itself reminds me the sound of some bigger d-class amps ive done, when some of the diodes have been broken, literally. Then there has been that kind of crappy sound.

[mekaiver]

May i just skip all that crossover/filtering/opamp junk and feed the signal into some of the transistor bases? If still crappy, somethings wrong with the amp, if OK, then somethings wrong in the preamp section/opamps.

[mekaiver]

Well, found the last opamp in the signal chain before transistors. Unsoldred the cap between the opamp output and the transistors base(some resistors remained in the chain) and put the signal straight into the first pair of 1226/3198 base. The same crappy sound. Inserting the signal to the other pair on transistors bases makes the output louder but not less crappier. Maybe thats normal, its just such a crappy amp that this is the normal output sound of it. Thats how its supposed to sound

[Perry Babin]

You need to post the voltage on those components with the black probe on one of the non-bridging speaker terminals.

[mekaiver]

First ones

A : Pin 1 0.5VDC
Pin 2 -20.9VDC
Pin 3 0VDC

C : Pin 1 -0.5VDC
Pin 2 20.9VDC
Pin 3 0VDC

Second ones

A : Pin 1 0.5VDC
Pin 2 -21.4VDC
Pin 3 0VDC

C : Pin 1 -0.5VDC
Pin 2 21.4VDC
Pin 3 0VDC

No change when clipping.

Output transistors are A1726/C4512. Is +-21VDC normal to drive them? Lack of amps?

[Perry Babin]

There doesn't seem to be a problem with the voltages you posted. The output transistors don't require any minimum voltage.

Is the signal clipped at the output of the op-amps that drive the transistors you've just checked?

[mekaiver]

Well as i stated before, i dont think the clipping is the problem,because at the moment its not clipping anymore. But the sound is still not normal. Did you listen to the file i uploaded?

Lets start from a blank sheet. I have an amp that has a dirty sounding output. Powersupply transistors seem okay, output also. Every channel sounds like that. The only thing that seems to be wrong is one 555 chip which runs damn hot. Its not the opamps fault, cuz when i insert the signal to the bases of the first 1226/1398, it still sounds bad. So it might be somehow related with the powersupply(all channels sound awful) or its somehow connected with that hot 555.

Have u ever heard something like this? I mean if u listen to the clip. What might it be?

Somethings wrong with the feedback?

[Perry Babin]

If it's audibly distorted, it should be visible on the scope. Using a sine wave input, post a photo of the waveform.

[mekaiver]

sl3505.jpg:


Couldnt get a clearer image, but the ones circled are not the scopes fault, i have seen a clear sinus there, so thats the amp.

http://imageupload.org/en/file/220281/sl3505.jpg.html

0.2V/dev and with a 4 Ohm load.