QSXM2 problem

[zayance]

Hi There!! First post, and new member, so Hi to everybody.

I'm having a little prob with a finished QSXM2 unit.
The build is made going with the schematic values, all resistors double checked and correct value in the correct position, all BC550/560 in the right position etc..., and the SSM's, i used DIP sockets all the way (i know it's bad  :-P).
I use a Lab power supply to feed the board just for checking purpose, so +/-15V, and all seem to be ok with no IC IN, i mean no smoke or shorts or whatever.
The LED H1 lights up, not H2 tough...

Here are the probs i have so far, maybe just a stupid thing?

First the DC servo checking procedure found on "Build Instructions" don't get me to nowhere, i mean, applying a positive voltage at pin 6 of IC1 gets me a positive ( some +0.4 mV or so iirc) at TP1, and applying a negative gives me a negative (-0.55 mV iirc) at TP1, and not the contrary as you mention.
Tried to lower the values of resistors R27 and R28 and it didn't change nothing, i used a 68K in there, same same, i toought going with the schematic the basis will be just fine, a trimmer might have been easier for tweaking this actually, might try that.

Just for curiosity i tried to pass that and insert IC's since the voltage Pins seem to be just fine.
I used OP07 all the way, and the SSM's.
With all OP07 installed and no SSM's i get a 30mA load on each rails +/- , and when inserting both SSM's i have the minus rail failing at about 13V with about 100mA, and the positive voltage steady at +15V but 180mA???

Also when all IC's are in place H1 turns off, just for info.


Anyway hope i was clear enough, and any clarifications is appreciated.


Thanks a lot!

[peranders]

You have 1 pcs. SSM2210 and 1 pcs. SSM2220 in the prepreamp? The current is 800 uA?

R16-R17 mounted and the value 15/4 kohm? R18-R23 not mounted?

Input shorted?

Voltage drop over R26 and R31?

Voltage drop over R12 and R13?

[zayance]

Hi,

Thanks for the help.

You have 1 pcs. SSM2210 and 1 pcs. SSM2220 in the prepreamp? The current is 800 uA?

Yes 1 of each, and no, positive rail goes to about 180mA, and negative to about 100mA when both are installed, take them out and all is fine, well no short and current draw is back at 30mA on both rails.

R16-R17 mounted and the value 15/4 kohm? R18-R23 not mounted?

Yes R16 and R17 mounted and beeing 15K each, that's right? EDIT: wait a minute, you wrote 15K/4, so i should have fitted about 3.7K there???  :|
R18 to R23 not mounted.

Voltage drop over R26 and R31?
Voltage drop over R12 and R13?

R26: - 0.7V
R31: +1.33V
R12: - 2.7V
R13: +2.55V

I had noted on my schemo (back then) and when i read the description of the pre and build that:
R13 should be 4.6V
R9 : 5.65V
R7: 0.4 to 0.5V

That's right?


Thanks for the help again, appreciate.


T.

[peranders]

3.3 or 3.9 k is a suitable value. Four times the current should create the same voltage drop.

[zayance]

Well i guess i missed that info somewhere :(, but that makes sense, hope the SSM's were ok with that...

Now here are the readings i have:

R6: 0.37V
R7: 0.44V
R8: 5.7V
R9: 5.7V
R12: -4.73V
R13: 4.67V
R26: -1.1V
R31: 2.4V

My Positive rail is at 0.2A, while my negative is at 0.1A, that's still same same, and doesn't look right, should be about 0.1A each rails no?

Oh and H2 is on, but not H1

Thanks

[peranders]

I recommend that you identify correct current/voltages with using my measurements.

[zayance]

Yes that was going to be my next move anyway, now that the Emitter resistors are good.

Will keep posted.


Thanks.


T.

[zayance]

Allright, finally got back at it, and found the current draw prob.
Along the way of the build i had used tulip pins (from DIP8) for making exchange of components easier on the input side,
but ommited to add R2 (1K)
So after that all seem to be "fine" but a couple of measures are still off compared to yours:

Pre-Amp Left Channel, MM-mode, BC550C and 560C in all positions except SSM's, OP07 as DC Servo and no input Bias Servo, Input not Shorted.

All values until here are good: Red is what i get

R28: 3.65V ------> 14V
R29: 0.8V --------> 0.8V
R30: 3.62V ------> 14V
R38: 834mV -----> 2V
R39: 834mV -----> 2V
R42 to R47 : about 325mV ----->550mV

I tried the DC Servo check again after correcting , meaning injecting a positive voltage at Pin 6 of IC1 don't get me a negative voltage but a nearly 0V positive and vice versa, while your instructions says positive gives negative and vice versa, maybe just a typo??

H1 is ON, H2 is OFF

It passes Audio but all distorted, crackling and muting audio etc...


Thanks again if you can be of any help to clarify things

[peranders]

Can you short the input. What is your output voltage?

2 volts over R38, R39 is normal if you have "B" type BC's

Voltage out from IC1 is +14V?

Are both channels the same?

[zayance]

Can you short the input. What is your output voltage?

Input shorted i have about -2mV at preamp out.

2 volts over R38, R39 is normal if you have "B" type BC's

I use CG's

Voltage out from IC1 is +14V?

Well now checking back after you asking, i get 8V???? Right channel is at 10V (I lowered R27 to R30 on the Left channel, not on the right for testing purpose)

[peranders]

2 mV at the output looks good. J2 is not on I'll hope?

[zayance]

No J2 is on MM.

Audio test was passing, but the sound was bad, meaning a lot of dirt, crackling, muting etc... weird behaviour

EDIT: BTW shouldn't all LED on board be ON? I have only H1 ON, H2 is off.

[zayance]

Well no idea why it passes audio but so badly, crackles, distortion like, and muting signal on low levels etc....


Thanks for any clarifications if this speaks to you? I tought maybe some bad wiring, but here it's pretty light in terms of cabling, beside the power of 2x PSU feeding each channels...


T.

[zayance]

For now i leave this aside, no real time unfortunatly, tought it would go smoothly, and i need to check where is the signal getting this dirty,
for now it's a failure, tried a couple of things, but nothing changes, horrible audio signal tottaly unusable as is.


Thanks anyway.


T.

[peranders]

I recommend you to print out the schematic in A3 if you can and start to measure all DC voltages in order to see where you have the problem.