All things G1176 - the new "repost" thread.

[Whoops]

Thanks for your reply. I've recorded three bits at unity gain with the output knob at three different positions:

After listening to the noise I think it's probably due to:

1) cold or cracked solder joint. So re-touch all solder joints, all really, from beginning to end

2) It could also be a malfunctioning transistor. After re-touching all solder joints, if there's still the crackling noise, replace transistors one by one.

After those 2 I don't have any ideas, maybe replace opamps, does your circuit uses any Opamps?

Anyway I think that point 1 and 2 will solve it

 

[gswan]

I could not load your sound files. Links did not work.
Is this with gain reduction disabled?
Did you measure the DC bias points of each of the transistors and verify?

 

[Whoops]

I could not load your sound files. Links did not work.

Try it in another browser.
I couldn't listen to them in Firefox, but they worked without any problems in Chrome

 

[gswan]

Try it in another browser.
I couldn't listen to them in Firefox, but they worked without any problems in Chrome

Chrome? No thanks. Google spyware is banned here.

 

[cprins]

I could not load your sound files. Links did not work.
Is this with gain reduction disabled?
Did you measure the DC bias points of each of the transistors and verify?

I just checked the files by clicking on them and run into the same problems with Firefox and Safari. It is however possible to download the files by right clicking on them...? Gain reduction was enabled in this case, but disabling it makes no difference whatsoever- as do any of the other settings. I will check/verify the bias points and report back.

1) cold or cracked solder joint. So re-touch all solder joints, all really, from beginning to end

2) It could also be a malfunctioning transistor. After re-touching all solder joints, if there's still the crackling noise, replace transistors one by one.

After those 2 I don't have any ideas, maybe replace opamps, does your circuit uses any Opamps?

Idem dito, will do 1) and 2) and report back. My build uses the 5532 at the input stage, but will first perform the other checks.

Thanks!

 

[sodastereo]

Sir, my suggestion is: insert sound and with a test probe touch the signal path, to find from what point the fault is, minimally, in the output pot, so you will know if the fault is in the pre or de stage. power.

 

[cprins]

Hi sodastereo, thanks for your suggestion, I will see if I can get my hands on a a scope. Meanwhile I have desoldered all BC107' s and they measure ok on a (cheap) multifunctional tester. When checking the voltages in the circuit against the voltages provided by gyraf there is a very significant voltage drop in the preamp and gain reduction control amp sections - see the attached file. Also, on some points the digital multimeter doesn' t measure any voltage at all or can' t get a steady measurement (blinking 0L). I' ve marked those with a Ø. I did retouch all solder joints, but this would seem to indicate a cold cold or cracked solder joint as suggested by whoops, or not?

 

[sodastereo]

Mother of God... what a big problem, there are different voltages at different points... my suggestion is: if you can remove the plate from the cabinet, do so, then take it out into the sun, or failing that, use the ceiling spotlight and look against the light as You can see these tracks, you have to see them clearly, if not, be patient, check that there is no short circuit on the tracks, if that is ok, check the value of the resistors, name of transistors (bc107) and of course their polarity.
For example, R:17,18, 62,69,70, and if the resistors and PCB are fine, suspect a transistor, I repeat, be very patient and don't despair, could you post good photos? quality and close?

 

[gswan]

Hi sodastereo, thanks for your suggestion, I will see if I can get my hands on a a scope. Meanwhile I have desoldered all BC107' s and they measure ok on a (cheap) multifunctional tester. When checking the voltages in the circuit against the voltages provided by gyraf there is a very significant voltage drop in the preamp and gain reduction control amp sections - see the attached file. Also, on some points the digital multimeter doesn' t measure any voltage at all or can' t get a steady measurement (blinking 0L). I' ve marked those with a Ø. I did retouch all solder joints, but this would seem to indicate a cold cold or cracked solder joint as suggested by whoops, or not?

One or more of your transistors is in the wrong way around. Until you get the DC bias measurements to be close to what they should be, your unit will be faulty. Are you really using those old tin-can noisy BC107's? If so then check the polarity carefully, the Emitter is the lead near the tab.
Did you check the hfe of the transistors being used in the GR amp section? They should be selected so they are >250.

 

[gswan]

Does the DC voltage on the base of Q5 change when you move the output pot? If so then C10 isn't working as a capacitor.

 

[gyraf]

I think there's something wrong with your measurements - you can't get 0V at the bases of most these transistors and then still have significant higher voltage at their emitters..

Describe your exact process of measuring - what meter, what setting, what reference point etc..?

/Jakob E.

 

[cprins]

Does the DC voltage on the base of Q5 change when you move the output pot?

Hi gswan, the voltage on the base of Q5 is always 0, irrespective of the position of the output pot.

I think there's something wrong with your measurements - you can't get 0V at the bases of most these transistors and then still have significant higher voltage at their emitters..

Thanks for chiming in as well Jakob! I only get a 0V reading at the base in combination with a positive voltage at the emitter at Q5. At the other transistors the digital multimeter is somehow unable to get a reading in auto mode. Those are marked with a Ø. The multimeter is a Fluke 113 and I use the ground supply 0 as a reference. I have redone the measurements of the problematic transistors in the manual mode and get the following values at the base:

Q4 2.42V
Q5 0.13V
Q12 2.20V
Q13 2.20V
Q14 0.54V
Q15 1.69V

I've focused on these for now because of the obvious problems with the voltages, but maybe it' s a good idea to re-check all other transistors manually as well...

One or more of your transistors is in the wrong way around.

One of the good things about the old and noisy BC107s is that they' re virtually impossible to reverse mount ;-) They are all hfe > 250. Would it be worthwile replacing them with a newer model? If so, what type would you suggest as a replacement?

don't despair,

Mother of God... what a big problem

That doesn't really help in order not to despair ;-) I had hopes that it would be possible to narrow down the problem but instead it seems to be growing larger to the point where I'm contemplating desoldering everything, check all components again and start anew...

Anyway, thanks a lot to you all for all your input so far!

 

[gyraf]

..would be easier to analyze if you write measured voltages into schematic and post a pic of that..

/Jakob E

 

[sodastereo]

The best thing would be to put several photos of good quality and size so that we can see it, sometimes there is an error that we overlook

 

[cprins]

Will do (updated schematic with voltages and photos)!

 

[cprins]

First couple of pictures… Please let me know if you need any additional pictures/angles. Power supply is on a separate board.

 

[gswan]

DC measurements around Q4 don't make sense. Your supply rail to these transistors has dropped to 10.4V?

On the underside picture I see a couple of places where there may be solder bridges. Check for these as this will cause the problem you are seeing. Check all traces running from Q4.

 

[cprins]

DC measurements around Q4 don't make sense. Your supply rail to these transistors has dropped to 10.4V?

On the underside picture I see a couple of places where there may be solder bridges. Check for these as this will cause the problem you are seeing. Check all traces running from Q4.

Will do tomorrow, thanks for checking!

 

[sodastereo]

ok, you should put a light under it, so you can see the tracks very clearly, use the sun or the light from your ceiling, or a flashlight, so you can see if there are unwanted bridges.
What I see, R84, is 1k, could it be wrong?
R11 560k? it's okay?.

 

[cprins]

..would be easier to analyze if you write measured voltages into schematic and post a pic of that..

See attached image...

On the underside picture I see a couple of places where there may be solder bridges. Check for these as this will cause the problem you are seeing.

I' ve cleaned up the PCB and checked the PCB against sunlight as suggested by sodastereo. The tracks seem fine however, see attached image of the area around Q4. Could the residual flux be part of the problem?

What I see, R84, is 1k, could it be wrong?

I' m using the original output transformer so that R84 on the PCB is not used. Instead I' ve soldered a 1K resistor across the terminal, see pic.

R11 560k? it's okay?.

It's 560K as prescribed, it' s the blue one nearest to the border in the attached picture.

Thanks again!