Ego Driver no Gain

[Marshall Arts]

Hi there,

I have build the ego driver according to specifications with the following parts:
OA1154 for D1
500 kA Pot for Gain
100 kA Pot for Vol

For testing, I did not use a footswitch yet, but simply hooked it up with a battery (so, no bypass at this point in time, which should not be a problem).

Problem: Vol, Gain and Tone Controls are working, but the signal is way to low (basically like the input signal, no overdrive at all). The diode clipping switch does not change anything in sound. In fact, when I remove the Diode D1, nothing changes either...

What I tried:
- As said above, removed Diode D1 - no change
- Changed orientation of D1 - no change (of course, given, that it seems to be irrelevant, whether the diode is in there)
- Removed D4 and D3, no change.
- Checked soldering (see images - I removed the pots again for a cleaner view on the soldering side of the PCB)
- Checked IC (TL082, took it out and put it in again, sound stopped when I took it out)
- Checked Orientation of Elkos and transistors, LEDs and Diodes
- I use metal film resistors and Wima Capacitors for the rest of the build

Slowly running out of ideas - would be great, if somebody could send some help (and motivation ;-)).

[Marshall Arts]

P.S. I should mention, that I trusted the handwritten labels of the vendor on the resistors and did not check the value for each resistor (based on the stripes on the resistors...). Maybe, if somebody is quick in reading these patterns, that would be a (even if not very likely) source of the problem.

[oldhousescott]

C2 and C5 should both be 220pF according to the latest build docs. It's hard to tell for sure, but it looks like you have 22nF in at least one of those spots, maybe both. I would expect 220p to be a mica or ceramic cap, although it's possible you could have a 220p box mylar cap. If in fact you do have 22n in those places, that's going to kill a lot of the signal in the mids and highs (make those stages unity gain actually). Your resistors look correct, best I can tell, and your soldering looks fine.

[madbean]

Yeah, you are using 100x the value for C2 and C5. Get a couple of 220pF ceramics there. Also, your C1 is 220n, not 22n. That's okay, just swap one of the 22ns you are using for C2 or C5 into C1.

[Marshall Arts]

I am not sure - it is labelled WIMA 0,022. Isn't that correct?

[marmaliser]

0.022uF = 22nf or 22000pF

[oldhousescott]

As Brian said, that's a 22n or, stated another way, 22000p cap, 100 times the value specified for those positions. Replace them with 220p caps and it should start working properly.

[Marshall Arts]

You guys rock, thanks a lot. Will order some and send an update. BTW - Great PCB, top notch quality!

[Marshall Arts]

I double checked my order, the one I ordered was this one: http://www.musikding.de/Passive-Bauteile/Kondensatoren/Folienkondensatoren/Wima-FKP2/FKP2-220pF-630V::1775.html

Could it be, that the one I put in C1 (labelled "220") is actually the one I am looking for (so, the value is written on it in pF)?

[marmaliser]

IIRC the PF value WIMA's do have the writing in PF on them. Because they are rated 600v they are quite big.  SO i think you are right the 220 in C1 is actually the 220pf ones you need.

[Marshall Arts]

Could be right, I will check. I found this item here: http://www.ebay.com/itm/WIMA-Polypropylene-Capacitors-FKP2-220pF-100V-6PCS-EACH-EXTRA-ITEM-0-50-SHIP-/110747804879, which might be a good hint!

[Marshall Arts]

OK, I swapped the caps, C1 C5 and C6 seem to be right now. It sounds much better, more bass, more mids. BUT: still not a lot of gain, basically like a boost, but not an overdrive. Bridging D1 does not make a difference, switching to LED-diodes neither. What can I do next? Measure voltage at specific points? Would the help you guys to further guide me?

Best,
Matthias

[Marshall Arts]

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