Bad Stone build report

[RickL]

I finished this up this week using the layout here: http://topopiccione.atspace.com/

I used LF353's for the dual op amps, TL074 for the quad and a 4049 for the inverter chip.

At first I couldn't get the clock to sweep the filters. The manual sweep worked fine, as did the feedback and color switch. After some fiddling I found I could get the clock to sweep by either shorting pins 5 and 6 of the quad op amp or by adding an extra diode, oriented the same way from the junction of D1 and R46 to pin 13 of the quad. The sweep is a little abrupt, particularly noticable on slower speeds.

It sounds great! Better than my original Bad Stone I think. The speed goes way up into ring mod territory, the phasing is lush even with the feedback control backed off, the color switch acts as a dry cut to give vibrato.

I wish I knew why I couldn't get the LFO to work without modding it and I would like to even the sweep out a bit but I can certainly live with it the way it is. I'd be interested to hear others experiences with this layout and/or an explanation of why the fix(es) I found worked.

Rick

[Jason M.]

I haven't built it yet, but have been following the threads about the Bad Stone.

Try a LM324 for the quad. It may be critical for the LFO. Many designs use a LM324 for the LFO.
There was a thread not too long ago about the benefits of using that particular chip for LFOs.

Also, some have noticed a difference in sweep when using a 4049 instead of the 4009 for the inverter.

It's good to hear that the layout is verified and sounds good.
Thanks for posting you build report.

J.

[Zero the hero]

Thanks for showing your interest in this project!!!!!!

I've solved the issue in my unit and I removed the yellow box from the Bad Stone page. It was a fault of mine... just 2 off-board connections reversed...
I switched to a IR3702 made by Sharp but I didn't noticed any substantial difference in the LFO.
I had your same problem with the LFO: what transistor did you use? At first I placed a 2N3904 but the phasing was stuck. Then, using a high gain 2N5088 helped a lot, allowing the LFO to move the filters.

[puretube]

Zero: can`t see the LFO curve... does it look like a "M*c D*nalds"-sign
turned upside down?
(that`d be a hypertriangular, aka hyperbolic...)

[Zero the hero]

Why can't you see the pic in the "pics and clips" section?
I've uploaded the piturec into another server:
http://utenti.lycos.it/offramp/EHBadStone.osc1.jpg

[RickL]

I used a 2N5088 for the transistor.

One thing I have noticed is that when I first turn it on the LFO won't sweep the filters. I have to switch to the manual sweep then switch back to automatic before the filters are swept.

Still hoping someone will pop in with some analysis of why my mods worked.

[puretube]

information lost...

[RickL]

Yes, I do have a little single channel scope that I use occationally. I'm out of town until late Sunday so I won't be able to take a look at it until then at the earliest. I didn't realize traces of the LFO had been posted. When I finally get the chance I'll compare them to what I see on mine and post again.

One small thing that I forgot to mention is that when engaged my BS is a little lower in volume than when bypassed. I tried temporarily connecting the input of the circuit to the input jack when bypassed (as if it was not TB) and the volume difference went away. The gain of the circuit was obviously designed to allow for the loading caused by non TB.

I solved it by tacking a trimpot across the resistor to ground on the first op amp and adjusting it down until I got the same perceived volume engaged and bypassed. A better way would be to temporarily replace that resistor (4k7 IIRC) with a pot, adjust for proper volume and replace with the nearest standard value resistor after measuring the pot out of circuit.

[Zero the hero]

I used a standard electrolytic capacitor for c13 instead of tantalum.
Tonight I'll do more tests on my unit, including changing c13/c10, the IR3702, the diode and the trans.
I'll post my results later.

[RickL]

I used a 1uF and a 0.47uF cap in parallel to get 1.5uF, both non-polarized. I can't imagine that the particular cap type could make any difference barring reversing the polarity on a polarized cap.

[puretube]

my concern was: leakage...

[Zero the hero]

I used a 1uF and a 0.47uF cap in parallel to get 1.5uF, both non-polarized. I can't imagine that the particular cap type could make any difference barring reversing the polarity on a polarized cap.

Try a 1uF electro polarized: that's what I had before getting a 1.5uF Tantalum. Yesterday I changed this cap and it seems that the LFO is less noisy. It could be just and impression... it was very late yesterday when I did this mod... :oops:

[puretube]

ooops - wrong button