Problems with my Fender Blender - suggestions?

[ethrbunny]

I ended up with a PCB for the Fender Blender due to an ordering issue. I put it together over several sessions. This evening I stuck all the pots, jacks and whatnot onto it and plugged it in. At first blush it didn't have any effect on the sound at all. Turning pots did nothing. I was getting a clean signal through it but no fuzz to speak of. NOTE - there isn't any switching or bypass-ing done to the circuit at this point. This 'clean' signal passed through the board.

Rechecking the wiring turned up a missing lead from the 9V rail to the input jack. (**) When I connected this lead all the sound went away. Now I get nothing. Turning the trimmers produces no change.

I checked the orientation of the electrolytic, diodes and transistors and they appear ok. The 9V rail is happily at.. well.. 9V. No anomolous heating.

With nothing plugged into in/out the transistors (2n5089) read (from L to R on the schem (in V))
#: (E, B, C)
1:4, 2.5, 2.5
2:~0, ~0, 9
3:3, ~0, 4
4:0, 0, 1.5
5:0, 1, 5.5

Here is the schem from Fuzz Central. You can see the 9v lead to the input jack in question.

What should I look at next? I'd appreciate pointers on debugging. This will turn out to be a trivial build error but I can't find it yet.

Ive read the FAQs everywhere I can find 'em.


(**)I guess these stereo jacks are used to switch battery operated effects on / off. Since I always use a power supply I'd like to get rid of them. Is there a standard work-around? Something such that I can use mono jacks on both ends? What if I connect the 9V directly to the 15K resistor and then the input lead to this junction?

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[ethrbunny]

Re-searched the forum and found this:

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=14543&highlight=fender+blender

My question - does there need to be something in the input and output in order to test a box like this? do I need a frequency generator?

[R.G.]

My question - does there need to be something in the input and output in order to test a box like this? do I need a frequency generator?

No. The voltages are read with no signal into/out of the box. Signals would throw off the DC measurments.

[ethrbunny]

Crikey. I must have something majorly wrong.

[ethrbunny]

The saga continues:

A few of the pots weren't wired to the board properly and are now fixed. I disconnected the 9V lead to the input jack and now Im getting a tone from the board. The pots seem to be working ok save that the tone is rather faint. When I rotate the 'blend' knob the plain signal is much louder than the distorted signal. What would cause this?

I rechecked all the transistor voltages and they seem way screwy (based on the comments from the earlier post).

[R.G.]

I rechecked all the transistor voltages and they seem way screwy (based on the comments from the earlier post).

It would be a great help if you'd write the voltages down and post them.

[ethrbunny]

It would be a great help if you'd write the voltages down and post them.

Right. Of course.

#: (e, b, c)
1: 0, 0, 2
2: 4, 2, 9
3: 3, 1, 4
4: 1, 1, 1
5: 0, 0, 5

(My meter is analog)

At this point I can get a 'fuzzed' signal from it that responds to the pots. Unf its about 25% of the volume that it should be. As I rotate the 'blend' control I can hear the original signal coming through with the appropriate volume (much louder as the case may be).

I tried using an 'audio probe' but to be honest, I don't have a clue what Im listening for. I don't hear the octave effect that I would expect either.

Thank you for any help on this.

----------------
Life on the steep part of the learning curve.

[R.G.]

Sorry, took me a while to get back.

Those are the voltages I need, but I need them measured to the nearest tenth of a volt as opposed to the nearest volt. Will your meter do that?

[ethrbunny]

Sorry, took me a while to get back.

I appreciate any feedback you can give me.


Rats. Unfortunately I can't really get a more accurate reading. Its an analog meter with a small display. I need to upgrade but Im a bit nostalgic about it :roll:. Mostly I use it to find open / short circuits. Ill take another crack at it and post something closer to the truth.

Can you tell *anything* by these readings? Is the trend that C > B > E? (based on the older post about this circuit). I am getting at least part of the signal back out. Hopefully its something poorly soldered and not an incorrectly etched board.

[R.G.]

OK, I'll make some guesses..

#: (e, b, c)
1: 0, 0, 2

Very hard to say. The emitter should be up at a fraction of a volt, the base 0.6V above that. The collector should be higher than either, and it is, but 2V is awfully low.

2: 4, 2, 9

Q2's base is tied to Q1's collector, so it has the same voltage, and it's collector is at 9V, OK. But its emitter is higher than its base. That means that it can't be working as a linear amplifier. Even more important for your purposes, it's higher than anything it's hooked to except its collector. So Q2 has problems. Bad connection, solder thread or short, something like that.

3: 3, 1, 4

If this stage is working properly, its base is tied to 3.6V by the 150K and 220K base resistors, and we see it's at 1V. Some problem with the resistors or a short, possibly? If it's working properly, the emitter is at 3V, which it is, but the collector should be at 6V, and it's at 4. Problems here with hookup?? Soldering?

4: 1, 1, 1

One of the dead giveaways in debugging is that when things that are not supposed to be at the same voltage are at the same voltage, they're often shorted. However, a resolution of 1V doesn't let me say that for sure here. The circuit is supposed to have the emitter at maybe 0.8V, the base 0.6V higher, and some substantial voltage on the collector, maybe 3V to 6V. That's not the case, so there's a problem with the soldering, or connections here.

5: 0, 0, 5

Can't tell. With a resolution of a volt, you could be reading a fraction of a volt on the emitter and 0.6 higher on the base, which would be right, and the collector at 4.5V, which would be good. This one could be working right.

That's about all I can do with them. Hope that helps.

[ethrbunny]

Ok. Let me try to do better.

fr = fractional -> greater than zero but not by much
#: (e, b, c)
1: fr < fr, 2
2: 4, 2, 9
3: 3, <1, 4
4: <1, 1, 1.5
5: fr, .5, 5.5

I went back and rechecked the color value of each resistor to make sure they were correct. I used a flashlight and a meter to look for shorts as well.

Im going to show my ignorance here (try not to cringe) - why shouldn't the collectors for q3 and q4 be at 9v? Is it because they don't go to ground and there is an unknown resistance inside the transistor before the current gets to ground? Im trying to apply my rudimentary understanding of ohms law here. The 10K going into q4 should have all 9V across it. Yet you say it should be 3-6V.

Thanks for your help on this.