Problem with VCF - faulty 2SC2291 ?

[Holyver]

Hi,

I'm building a x0xb0x (kit from x0xsh0p.de), and when testing the VCF as described in the build manual, i get nothing at the resonance pot.
After reading around on this forum, I started investigating Q22 (2s2291). Unfortunately, I don't have a transistor tester, but I do have a diode check on my multimeter.
I notice that I don't get any continuity between base and the right hand side emitter. Between base and the two collectors the voltage drop is symmetrical.
So (readings with a diode checker):
E-C-B-C-E
0.618V - 0.591V - base - 0.590V - Nothing

Voltage readings (Cutoff max, reso min, again E-C-B-C-E):
11.21 - 11.73 - 11.71 - 11.72 - 4.50

Can I conclude from this that the 2S2291 is defective, and should try the BC337-pair-trick to see if I can get my filter to work?

Thank you in advance for any advice!

[reinvantveer]

Hey Holyver,

I'm building a x0xsh0p.de kit as well, just working on the VCF right now. I'm reading 11.33 volts on both outer pins of Q22, pretty close to the 11.2 volts from the analog section voltage reference on http://forums.adafruit.com/viewtopic.php?f=12&t=12453). Maybe this isn't helping, but I am unclear on what your output of 4.5 volts means.

I have my Q22 soldered in (sorry, I'm not going to pull it :) but I have about 3.5 Mohm between base (+) and the outer right pin (-), and about 20 Mohm to the left (-) respectively. switching polarity on these readings (- on base) gives me no conduction on either side.

Is this any help?

[Holyver]

Thanks for your reply.

I went on and tried two BC337 transistors in place of Q22 (after reading this: http://forums.adafruit.com/viewtopic.php?f=13&t=39226), and since then, the voltages were indeed much more as expected. So the 2291 must be defective.
Meanwhile I have completed everything else, and the x0xb0x is working perfectly, only with a temporary alternative for Q22. Soundwise, I have nothing to compare with, so I can't tell how much the sound is off compared to a x0xb0x with a real 2SC2291 at Q22.
I have contacted x0xsh0p.de for a possible replacement...

On a side note: if you're using the (beautiful) aluminium case, the big 2200µF capacitors in the power section should not be soldered in standing up, but lying down. Otherwise, it's impossible to assemble the case. While typing this, I realise you're probably past this point already, but I'll leave it in for any other future readers.

[substyler]

On a side note: if you're using the (beautiful) aluminium case, the big 2200µF capacitors in the power section should not be soldered in standing up, but lying down. Otherwise, it's impossible to assemble the case. While typing this, I realise you're probably past this point already, but I'll leave it in for any other future readers.

woopss... you had no printed hint in your kit? kits with aluminum housing should (normally) have a sheet with the instructions for the alu-housing.
I'll tell Andy to put that sheet in every kit ;)

[Holyver]

No printed hint at all unfortunately :-)
With a little improvising everything worked out, but maybe I'll put in some new caps in that spot one day. Is there a digital version of this sheet around?
Does it also mention something about the the big selector knobs that come with this case not fitting the rotary switches?

Still waiting for a reply from x0xsh0p.de about the 2s2291 though :-(

[substyler]

No printed hint at all unfortunately :-)
With a little improvising everything worked out, but maybe I'll put in some new caps in that spot one day. Is there a digital version of this sheet around?
Does it also mention something about the the big selector knobs that come with this case not fitting the rotary switches?

yes, the wing knobs must be drilled to 6.35mm to fit the encoder shaft. (I have always used a 6.4mm drill, works fine)
let me see if I can find some instruction sheets and I'll send them to you.

best,
Sub

[Holyver]

Thanks substyler!

Meanwhile I've received an answer from x0xsh0p.de, and they included a link to a zip-file with the construction manuals and hints, so you don't have to look any further. Would have been easier to have had these from the start of course, but hey, all is good now.
They will also send me a new 2SC2291, hooray!

Greetings!

[substyler]

They will also send me a new 2SC2291, hooray!

great :-)