Help with TS808 debug

[bancika]

I just finnished TS808 made with Torchy's vero layout, with keeley mods (4.7K -> 2.2K, 47nF -> 100nF, 51K -> 20K, and I didn't put additional clipping diode, just jumper instead) and of course it doesn't work
I tried audio probe and signal gets as far as pin 3 of 4558. No signal on any other pin or anywhere further..
All voltages are fine.
Any ideas where to look for problem.
Tnx

[bancika]

I found the problem: dead 4558.
Wow, I'm getting better, takes less time to make it work every time
Sorry for bothering, bye-bye

[dano12]

Isn't that a nice feeling? I remember spending hours trying to track down problems. Now I can do it in halves of hours

[SuperGeo]

I'm having a little trouble with mine

I have a simple question, when the gain pot is maxxed, the resistance between pins 1 and 2 in the OA should read about 551k? Mine measures about 366k. I'm have to crank my volume pot to make the effect output a little louder than the bypassed

EDITED: I'm using 500k for the 510k reisistors. maybe that's the cause of the low output?

[bancika]

Isn't that a nice feeling? I remember spending hours trying to track down problems. Now I can do it in halves of hours

yeah, great feeling

SuperGeo: I'm not sure, but on mine level pot is at about one third with volume equal to bypass volume. Check wiring twice, are you sure volume pot is 500K

[SuperGeo]

I soldered an 22nF where had to be an 47nF, in the feedback loop. Seems to be better now

SuperGeo: I'm not sure, but on mine level pot is at about one third with volume equal to bypass volume. Check wiring twice, are you sure volume pot is 500K

yeah I took it off and measured it has 500k but when on board it measures 360k

now acctualy it has a nice boost, but not that BIG as I was expecting. I wonder if that happens in yours too
Another thing that maybe confused be is that I'm using an Audio Tape for the volume control, making the unity gain past 12'o

[bancika]

it's not strange it measures less now, when you measure resistance in circuit have in mind that it's paralleled with the rest of the circuit.
It's little strange to lower 22nF, I guess it will further reduce bass. I put 100nF there.

[SuperGeo]

it's not strange it measures less now, when you measure resistance in circuit have in mind that it's paralleled with the rest of the circuit.
It's little strange to lower 22nF, I guess it will further reduce bass. I put 100nF there.

sorry I meant I fixed by changing it and putting the 47nF

I uploaded and audioclip with the bypassed sound and kicked in with Volume and Drive maxed and Tone 2o'clock
http://s48.yousendit.com/d.aspx?id=1SEL01TBGMGJ60Y71KDY29Q5TT

[bancika]

Here's mine
first is played bypassed and second with all knobs turned MAX.
http://www.storm-software.co.yu/diy/clips/ts_level.mp3
I'm not saying mine is normal, as I've said before levels are equal at about 1/3 of level. Can someone else check out those clips and compare with their builds?
Cheers

[SuperGeo]

WOW now I'm 100% sure that there's something wrong with mine

your clip made me turn down the pc speakers   


I already swapped the transistors, checked everything, shorts on the board... I'm not sure of why it distorts nicely but not having enough gain

I believe it's something wrong with the clipping stage, os something after is putting the signal down 

[bancika]

I can think of two things: bad IC or bad (misswired) Q2

[SuperGeo]

I swapped both transistor and CI and it's the same

audio probed and here my results

there's no volume loss in the emitter of first transistor, after the buffer.

from OA pin 1 to pin 5 there's a volume loss, but at the output, with all controls cranked, the volume is the same as the pin 1. So there' no volume loss from pin 1 to output.

there's nothing wrong with 2nd buffer too


well now I think the problem is at the feedback loop of the OA. I still suspect when measuring the resistance between pins 1 and 2, it goes from 0 to 366. It's strange because when I measure just between the pot lugs, I get the same results.

Reading the RG.Keen article, I found that maximum gain is when the resistance is at 551k/4k7, so I think that I'm not getting all the gain.

[SuperGeo]

voltages
IC:
1- 4.71
2- 4.90
3- 4.69
4- 0.00
5- 4.79
6- 4.79
7- 4.79
8- 9.61

Output transistor
E 3.28
B 2.83
C 9.63

Input transistor
E 3.28
B 2.83
C 9.63

[johngreene]

You wouldn't happen to be using germanium diodes in the feedback loop, would you?

--john

[SuperGeo]

no I'm using two 1n4148 diodes on it. 


would be nice if someone could confirm about the drive pot thing

[bancika]

I changed some resistor around gain stage: 4.7K with 2.2K and 51K with 20 so I'm not good reference, but voltages are pretty close to mine

[johngreene]

When you measure the drive pot "in circuit" you have to realize the diodes are in parallel with it. So, the meter measures resistance by running a small amount of current through the device and then based on the voltage, it can determine the resistance. So once the voltage builds up enough to break down the diodes, the corresponding voltage is the same as it would be for 366K.

If you want more level out of your clipping stage, add another pair of diodes or use LEDs.

--john

[SuperGeo]

thanks for the replies

once the resistance in the loop is right, Does the first opamp provides all the gain of the unity?

[johngreene]

Yes, unless you crank the tone all the way up. Then the second stage provides some high frequency gain. But the majority of it comes from the first opamp stage.

--john