Mysterioso Jr: gated/fizzy distortion

[Bucksears]

Got my Mysterioso board last week (thanks Brian!) and did the board this weekend, the rest of the wiring tonight.
All controls work, bypass works, but I'm getting that 'misbiased transistor' sound when I play with any gain. The buffer/reactive switch seems to work.
All parts are correct and I triple checked the copper side for any unintended solder traces.

Anything else I can check?

[jkokura]

Do you know how to audio probe? That may help you find the source of the problem.

The only things I think of without more data or pics is that you've got either a poor soldering joint or a faulty part. I'm not %100 familiar with the build. I wish I could be more helpful.

Jacob

[madbean]

Buck,

We may need some voltages off the 4049 in order to proceed. Did you do any sub for the transistor? Also, maybe double check the value for R18 and verify that it is 120R. Oh, and make sure you are using the UBE (un-buffered) version of the 4049. Let me know what you find.

[Bucksears]

Thanks Brian.
I'll see about measuring the 4049UBE (it is that model).
R18 is definitely 120R. I did have to 'double up' on the 390k resistors (270k + 120k) and I think the .0033uF caps I used were quite old and may have fried one of them.

I've got those parts on order and should have them tomorrow or Friday and will replace those as well.

[Bucksears]

Ok, I replaced the .0033uF caps, the 2.2k and 390k resistors with singles (I had added resistors together to reach those values previously).
Still getting the gated/fizzy sound - triple checked all the wiring and it's correct.

Here are the 4049 voltages:

1:   7.12V                    16:   n/a (keeps increasing mV)
2:   2.64V                    15:   2.5mV
3:   2.64V                    14:   7.12V
4:   2.65V                    13:   n/a (keeps increasing mV)
5:   2.65V                    12:   2.4mV
6:   2.65V                    11:   7.12V
7:   2.65V                    10:   2.4mV
8:   1.0mV                     9:   7.12V

[Bucksears]

Here are the TL072 voltages:

1:   4.5V               8:   9.12V
2:   4.5V               7:   4.5V
3:   4.5V               6:   4.5V
4:   .8mV              5:   4.5V

Thanks!
Buck

[madbean]

Here's the readings off my reference build:

TL072
1- 4.42
2- 4.42
3- 4.38
4- 0
5- 4.37
6- 4.42
7- 4.42
8- 8.89

CD4049UBE
1- 7.16
2- 2.9
3- 2.84
4- 2.75
5- 2.84
6- 2.84
7- 2.85
8- 0
9- 7.16
10- 0
11- 7.16
12- 0
13- 0
14- 7.16
15- 0
16- 0

MPF102
C- 8.89
B- 2.29
E- 0

Interestingly, I used a SignalFlex PS which apparently only puts out 8.89v. Never knew that. But, it's close enough for referencing.


Looks like there is something going on the right side of your 4049. Your grounding isn't quite right....esp considering the minute readings off pin4 of the TL072. Check the grounding plane for continuity and for bridges. Re-melt the solder on the pins that are off, too. I think this will be an easy fix.

[Bucksears]

Wow - thanks Brian.
I'll check mine out tonight - I didn't measure the J201, but will do that.

Does it make a difference using J201 vs MPF102 (or 2N5457)? I know that they have different amounts of gain when used in stages (ala Box of Rock, BSIAB II, etc), but didn't know if that mattered in the buffer portion of this circuit.

Thanks again for everything,
Buck

[madbean]

The pin-out of the J201 might be different than the MPF102. I mislabeled my post above as CBE, rather than DGS, too. I always seem to forget that the MPF102 is a JFET !

[oldhousescott]

Does it make a difference using J201 vs MPF102 (or 2N5457)?

All three have the same pinout and the buffer is a source-follower type operating at a gain of (slightly less than) one, so any of those choices should be fine.

[Bucksears]

Ok, I think I've narrowed it down quite a bit. I got out my MM and started connection/beep-testing around the board. (black connector to ground, probed with the red connector).

The only thing out of whack that I've found is the area on the PCB where the input wire connects to board and also connects to R1/C1/one leg of the B/R switch. (lower left on the PCB)
That little 'island' is connecting with ground somehow - I double-checked my soldering in that area and it's fine, so it might be the wiring. I'll unwire/rewire the footswitch and input/output jacks this weekend and see if that resolves it.

Thanks again,
Buck

EDIT:
Scratch that above post - I was probing while the in the 'off' footswitch selection. It's wired for the input to go to ground that way; need to ground probe again with the footswitch 'on'.

[Bucksears]

Update:
I have verified that only the things that should be connecting to ground are. For some reason the middle lug of the volume pot was connecting to ground. Even after I unsoldered the wired from the middle lug, when I tested continuity to ground, it was there. I think I'm just going to wire it straight to the footswitch rather than the board-to-footswitch.

Tried different 4049UBE IC's (why is the notch on one end, but the 'dot' at the other?), and even a 4049UBCN and got the same fizzy results with both. Those minute voltage readings are still occurring to ground on the IC's, though. I think I'm going to shelve this one for a while and come back to it later. It's one of the few projects I've ever had a problem with; I've built it twice now: once from my own PCB and once from Brian's. Both had the same problem. I'm sure it's something small, but I'm starting to obsess over it a little to much.

Thinking about trying the Krankosaurus in the meantime. I'm looking for something to nail that AC/DC 'Shoot to Thrill' drive sound. My modded BSIAB II at lower gain/higher volume can get pretty close, but want to try a different circuit before I build another BSIAB.

[madbean]

Buck,

Any chance we could get some high rez pics of the top and bottom of the board?

[Bucksears]

I'll see if I can get around to that tonight after mowing the lawn. The pads on the solder-side are quite close together; I might see if I can just put it on my scanner and get a better image.

Photo of the top-side shouldn't be a problem.

Thanks,
Buck

[Bucksears]

This may sound lazy and more trouble than it's worth in the end, but what if I started clipping the parts that connect with ground one at a time until the ground reads ZERO volts?

That will at least rule out those parts.