Gristleizer Problems

[tomas1808]

Hi,

For my 2º build I decided to give the Gristleizer a shot.  Etched my own board (using gaussmarkov's layout) and assembled it. Didn't work first time, but after reading jacobyjd's build report I realized I too had placed TR2 incorrectly (layout is very misleading), then it worked just fine. Well.. almost :

First of all I can't manage to set up the Triangle. Every time I try to set it up I end up with kind of Semi Ramp Up instead of a smooth triangle. I tried setting the trimpots to about every possible combination without getting any triangle. I suppose I did something wrong. Has anyone managed to get a perfect triangle???

Then, in square mode, I cant get that choppy On-Off effect at maximum depth, I don't know if the depth section is unable to get to that deep or if there is some kind of leakage of the input signal. What distance should input and output cables be apart? I'm sure there was another user with the same problem.

Unsurprisingly I'm also getting some ticking, not only in square mode, but all four. Any tips?

Thanks!

EDIT:

[Taylor]

On my build using the board I designed, I was able to get a good triangle. If the photo you posted is the closest you can get to triangle, it's definitely not right. I also had no problem getting a very hard chop. What did you use to derive -9v? It seems like you may have a problem with your voltages if you're not able to get full depth.

[tomas1808]

I'm using the Bipolar 9V Power Supply at gaussmarkov.

Measured the PS with a DMM:

Input: +9.71v
Positive Output: +8.67
Negative Output: -8.45

Shouldn't I be getting equal measurements on the outputs?

Regarding the depth I am getting quite a hard chop but it does not go completely silent. Maybe I'm demanding too much. Does yours go completely silent?

Thanks for the help man

[Taylor]

It's been a while since I used it, but I'm fairly certain it went completely off, yes. But I wasn't scoping it, just listening, so maybe not.

[tomas1808]

Anyone ? 

[PRR]

> Anyone ?

Post a LINK to the plans you used or lazy gits like me will just ignore the mystery question.

http://gaussmarkov.net/wordpress/circuits/gristleizer/
http://gaussmarkov.net/layouts/gristle/gristle-schem.png

IC1 IC2 are a now-obscure but perfectly fine RAMP generator with about 99% duty rising and 1% fall. Scope the output of IC1 at pin 6. (I do NOT trust your sound-card "scope"; such things can overload and distort a +/-7V wave all out of recognition, may also null "subsonics".)

> Has anyone managed to get a perfect triangle???

There is a trick. The basic shape is ramp. This is fed to TR1 which is a modified "Cathodyne". Cathodyne has a "flaw": when you overdrive it, the input feeds to the plate through the grid-plate diode and comes out inverted. Also works with a BJT. The "shape" control offsets the ramp so that half +/- of it overdrives TR1 and is inverted. When just-half, the output is a fairly good triangle. The part values appear reasonable. I'm too lazy to find a matchbook and confirm them until you verify that part-values are correct. (Analysis is pointless if you have brn-blk-yel where should be brn-blk-org, or you don't have TR1's Base lead in the right hole.)

> layout is very misleading

Explore this. The schematic I linked to seems correct, at least well-thought. Many-many-many errors creep-in along the way through layout, layout reading, and part-stuffing. Cross-check your understanding of the layout with a what-goes-to-what and what-value from the schematic.

[tomas1808]

Fixed!  Thanks Paul!

As you suspected the problem was at TR1. When I bought the parts I was not aware that I was given a mixture of regular 2N3906 and 2N3906-C. The C version has a different pinout. Swapped the transistor with a regular one, tweaked the trimpots, and now I have quite a good triangle:



Also thanks for the "Cathodyne" trick explanation. (I was able to confirm it by tweaking the "shape" trimmer while using the scope. )  It's good to understand how the circuit works.

Regarding the depth, is there some part that controls the maximum depth that I may be able to tweak?

One last thing, I found out that I get the best depth when I increase the bias knob to the "clipping zone". Is there some way increasing the bias without getting distortion that soon? Upgrading IC's? Input gaint control?

Thanks!