No sound from TS808

[Brynngar]

Hi everyone,

I recently built a TS808 clone based on this layout:
http://4.bp.blogspot.com/-_SfO_0LxRdA/UyRV5uYYWeI/AAAAAAAAGSY/dbNm95s5ScQ/s1600/Ibanez+TS808+compact+with+clipping+switch+Rev2.png

Now that I finished it, I get no sound out of it.
What I've done so far:

-checked for solder bridges (couldn't find any)
-checked the transistor and IC orientation (correct)

Notes:
Since my pcb was only 19 holes in width, I had to solder the outgoing wires on the left in one hole with the other components there,
which shouldn't have any effect though...
The IC I used is a TL072, the transistors are both 2N3904

I couldn't find any "expected" voltages for a TS808 anywhere, but here are mine:

Q1 & Q2:
C: 9,4
B: 2,73
E: 3,23

IC:
1: 4,68
2: 4,74
3: 4,59
4: 0
5: 4,67
6: 4,69
7: 4,69
8: 9,4

From what I've seen so far this looks plausible at least..

Here are some pics, hopefully someone can find something 

[balkanizeyou]

at a first glance the IC voltages look fine, but the transistors' ones don't - the base should be one diode drop ABOVE the emitter, not below - maybe you mistakenly used 2n3906 (PNP) transistors instead of 2n3904 (NPN)?

[GibsonGM]

+1, the voltages for base and emitter are way off....look at the 2 transistors, be sure the part and pinout is correct, as well as the components around them.    Both bases should be connected to Vref by a 510k resistor, and the 10k's are coming off the transistors to ground. 

Once you get all that to check out, if you still have an issue you'll probably want to make an audio probe. 

[Brynngar]

The transistors are 2N3904, I checked again. The 510k and 10k resistors are also in the right place, I'll re - check the whole layout again later, mayber somewhere on the way something else went wrong.
At leats it's nice to know that there is an error that could be fixed 

[GibsonGM]

Oh, anything will work if we connect the parts right!  

The voltages on base and emitters of Q1, Q2 should be just about REVERSED, which is odd.  You would expect the emitter to be about .7V more negative than the base, not the other way around.     How's that ground the 10K is attached to?   
Did you actually check the VALUES of resistors?  Can be hard to tell as the film type are blue.  A magnifying glass is a useful tool, ha ha.

[Brynngar]

I checked the resistor values and the are what they should be. The ground is.. well connected to the ground  Indeed odd, that the values are switched.. for both transistors 

[R.G.]

You may be running into a secondary problem with your meter. The IC pin voltages are about right, so that means that the reference voltage generator is producing the correct voltage. If your meter is itself not a very high input impedance, it may load down high impedance points and produce a misleading reading.

For instance: Q1 is fed 4.5V through a 510K resistor to its base. If the base-emitter voltage drop is 0.6V, and the emitter is sitting at 3.23V, then the "true" base voltage is 3.93V. The emitter is loaded with a 10K resistor to ground, so 3.23V/10K = 323uA flows in the emitter. the base would be getting (4.68V-3.93V) = 2.8uA, and the effective current gain would be 323/2.8 = 115, which is very reasonable for the 2N32904.

IF that is true, then why does the base read 2.73V? It MIGHT be the meter. If your DMM has an input impedance of 10M, then the meter reading at the base makes the 510K into a 510K/10M divider, and the 4.68V on the input side of the 510K is turned into 4.68*(10M/10.51M) = 4.45V. But if your meter has an input impedance of only 1M (and some of them do), then the 4.68V becomes 4.68* (1M/1.51M) = 3.099V. That 3.099V then runs through a source impedance of the 510K and 1M in parallel, for a base voltage of 337K, and the base current through that equivalent resistance drops the base voltage some because the meter is loading down the reference through the 510K. We can only estimate the effect, because with only one meter, we can't measure the base and emitter at the same time. If the base only needs 2uA because the emitter voltage and current is lower now, then 2uA through 337K is a voltage drop to the base of another 0.67V, and the effectie base voltage is 3.099-0.674 = 2.43V. This is suggestively similar to what you read, although not a perfect match.

So - it might be your meter messing with the base voltage reading. Obviously, that's not the entire problem, just a red herring. (https://en.wikipedia.org/wiki/Red_herring)

What kind of meter are you using?

[Brynngar]

I found the mistake!!!

The right 1uF cap was not placed correctly... the lower leg was connected to pin8, not pin7, thus the signal didn't reach the level pot.
Thanks for your help anyway, I really appreciate it!
wooho 

[GibsonGM]

Good deal! It's usually something simple like that.   Enjoy the 808!

Nice intuition, R.G., absolutely...I didn't think outside the box back to the meter, ha ha...it would be worth it for Bryn here to determine his meter's resistance...

[Brynngar]

Regarding the multimeter, I have a PeakTech 1070. I looked up the manual etc. but couldn't find the input inpedance yet,
but I'll have a look at it! Never actually spent a thought on the MM messing with the readings.. 

[TejfolvonDanone]

Regarding the multimeter, I have a PeakTech 1070. I looked up the manual etc. but couldn't find the input inpedance yet,
but I'll have a look at it! Never actually spent a thought on the MM messing with the readings.. 

Just for the record it's in the manual under section 3.1. It says 1MOhm if my german knowledge serves me well.