Tonepad BMP questions.

[stuznu]

I have recently completed a BMP as per Tonepad Gran Mango diy etched pcb and BOM.

No modifications or changes have been implemented with the only variation being the use of two 10k resistors in place of a 22k which was not available at time.
When plugged in there is no audible difference to the output regardless of any adjustment to the volume, tone or sustain knobs.

Voltages at transistor pins are listed below:

Q1    E=0.033v     B=0.586v     C=7.89v

Q2   E=0.033v      B=0.586v     C=7.89v

Q3   E=0.026v      B=0.572v     C=7.51v

Q4   E=0.176v      B=0.727v     C=8.21v

From the experience shared by other BMP builders on this forum and other diy websites, it appears that transistor collector pin voltages are usually approx. 4.5v. If this is the case, are these collector pin voltages too high? I have also found that voltages that are similar as in Q1 and Q2 are a symptom of a resistor issue. If this is the case; is it the resistor/transistor issue causing the malfunction or possibly off board wiring.

The off board wiring was done as per tonepad wiring for 3DPDT bypass switching.

Any help or suggestion is appreciated.

[antonis]

I'm not sure if you use the "traditional" BMPi transistor numbering but I'm sure that none of your BJTs is properly biased..

Maybe you have to check resistor values (and ratio) on last transistor voltage divider and feedback/base resistors on gain and input transistors..

[duck_arse]

can we see some photos of your build, and what transistor type number did you use?

[edit :] which of the three versions did you build? if the triangle values version, test all your 390k resistors are actually 390k. if green russian, do the same for the 470k resistors.

[stuznu]

Sorry about the oversight - I used 2N5088 transistors. Unfortunately, I am still having difficulty with attaching pics.

[antonis]

<off topic>

For 2N5088 better try 12-15k collector rersistors (less gain, more "warm" sound and negligible current consumption rise..)

(off topic>

[stuznu]

Q1 - Q3 has 12k to collector,

Q4 has 10k

[duck_arse]

so what version is your build? what do your resistors measure? it seems all your transistors voltages are off by similar amounts, which suggests a resistor value common to each stage is the wrong value/different to what the circuit expects.

or all your transistors are backwards, would be another guess.

is your problem with the images in the taking of them, or the understanding of the posting of them? (they need to be 'hosted' somewhere on the interwebs already, then you link to the image in your post, using the image button.)

[stuznu]

I built the Russian, and as per the components diagram all transistors are correctly placed. I will check resistors again - although i measured each one twice with DVM before installing and soldering.

I dont understand how to post pics - or how to host on what you call interwebs??

[duck_arse]

take your photos. then, find an image hosting site on the web. imgur is one that causes no problems for browsers, and (might still be) is anonymous if you don't want to start an account. there are other* hosting sites as well.

you uplaod your image to their site, they provide you a link, sometimes they'll resize images on the fly and give a link to each size**. you copy their link, then paste it between the tags provided by clikking the image icon, just above the typing window.

done. you can tryout the method in the "testing" post area if you like. you can also "preview" before you post, just to see. get to it!


* I shall not mention their names, they all cause browser problems due to crap code.

** please consider other users, and don't post mega sized pics. some people (I hear) look at this site on their telephones.

[stuznu]

Thanks. I will give it a try.

[stuznu]

Improved images posted o imgur

http://imgur.com/a/LtfGS

[hymenoptera]

Those collector voltages are twice what they should be. As if some ground connect somewhere isn't what it should be, either wrong resistor, or just open somewhere. Using multimeter, check that all ground connections, both on the PCB and off, all have a low impedance path to negative terminal of the battery snap or DC jack.

Linking to several similar threads, Tone Pad Big Muff Pi with no distortion, only clean sound, but these guys have very different voltages, I'm just cross linking for future debugging.
http://www.diystompboxes.com/smfforum/index.php?topic=97987.0
http://www.diystompboxes.com/smfforum/index.php?topic=92265.0

[antonis]

I think that you have a complicated problem...

First, there is a major biasing problem (most likely common to all transistors..)

Second, with these collector voltage values you should have a huge "uni-directonal" distortion (positive collector waveforms should be almost totally clipped..) but you've said that:
<When plugged in there is no audible difference to the output regardless of any adjustment to the volume, tone or sustain knobs> so something also happens with ON/BYPASS mode...

[hymenoptera]

so something also happens with ON/BYPASS mode...

Agreed. And need better pics to help diagnose. Pics of the wiring would help.

[stuznu]

BMP off board wiring pics posted

http://imgur.com/a/1FBuI

[hymenoptera]

It's hard to tell with those blurry pics, but it looks like one of the input jack terminals has nothing soldered to it. Is the pedal "always on"? In other words, did you purposely not follow the instructions on wiring the on/off (ring/sleeve) connections and just wire it up as "on" all the time?

If you indeed tried to follow the standard wiring instructions, then I think you made a boo boo on the input jack.

Also, if you're having trouble with the camera focusing, try holding the pedal further back. It looks like it focused on the carpet just fine. I'm guess it's a cell phone so there's probably no focus settings. If it's not a cell phone, then either manually focus it, or switch to auto focus. These photos are almost unreadable.

[duck_arse]

just for fun, can you switch off power, and measure the resistances around the Q1 stage? from ground to base, from ground to emitter, and from base to collector, and base to V+.

just for fun, mind. and please, post the results.

[stuznu]

Thanks hymenoptera I will check the tonepad off board wiring diagram again.

As per duck's request.
resistances around Q1 listed;

Ground to base=87.5k
Ground to emitter=2k
Ground to collector=84.5k
Base to collector=89.4k
Base to +ve=134.6k

[duck_arse]

ground to emitter should be no more than 390R in your version. how come it reads 2k?

[stuznu]

Cleaned the board with isopropyl alcohol and brush and inspected with magnifying glass. Found a solder web between legs 470pf cap and 10k resistor. Corrected that, but no obvious change to transistor voltages.

Also retested transistor to ground resistance without power and found no change!

Will keep looking...

Thanks for the suggestions - drew my attention to soldering fault.