Has any one ever compared the fsh-1 to a clone?

[spiderman2812]

Hello all, I recently built the ggg fsh-1. Used all the recommended parts and stuck with a stock build. The filter works great but I compared the Sample hold feature to an original fsh-1 and it doesn't seem as pronounced as it is with the original. It doesn't seem to hold well or sample as well for that matter. Any ideas what might be wrong or is that just the way the clone is.
Parts list

2n3904
2n3904
bf245a
ca3080e
lm741
1m speed pot
10k linear trim
100k linear trim


Any ideas??

[Mark Hammer]

The FSH-1 samples a noise source in a stepwise fashion, and uses the sampled voltage at each of those points to set the resonant frequency of a filter.  While you'd think that noise is noise is noise, you'd be wrong.  For that very reason the DIY synth community and commercial providers have all kinds of noise source circuits.  A common instruction is to "select for noise" when choosing a transistor, because they're not all alike.  Part of the differences between them is the noise bandwidth and part of their difference is the noise amplitude.  What you want for a good S&H sound is something that provides lots of contrast for a more gurgly sound.  The transistor you select will do that by inserting lots of random spikes, such that there is a high likelihood that when the instantaneous voltage is sampled at this point it will be quite different from the instantaneous voltage sampled at that point.

Certainly, even if you pick an absolutely perfectly dreadful (noise-wise) transistor, the range of possible voltages is constrained by the setting of the 10k trimpot on the output of the op-amp used with the noise source.

The holding aspect is a function of having low leakage of the sampled voltage.  The sampled voltage is held in the .047uf cap between the two FETs.  Since they each provide an extremely high-impedance path, the charge stored in the cap has nowhere to go, and it sits there until a lower-impedance path is provided.  Of course, since no cap is perfect it won't sit there forever, but rather slowly drains off from the cap directly to ground.

The higher the capacitance value, the more charge is stored and the longer it takes to drain off.  The better the cap, the lower its leakage properties will be.  So, while there are a great many instances where cap type really doesn't matter, this isn't one of them.  For optimal performance, you will want the cap type with the lowest leakage possible.

Now, what cap type that is, I simply don't know.  But I'm confident that any of the true EEs around here can tell you.  My guess is that it's going to be plastic of some type.

[Paul Perry (Frostwave)]

For this circuit, polyester would be OK for the sample and hold cap. (mind you, I'm not an EE either).

[spiderman2812]

So I guess I should start at the transistor and check my voltages on the emmitter to or the pin of the ic to make sure I'm getting as high of a voltage as possible for noise. As for the caps I used xicon greenies for all of them. Any more input would be great from anyone who has come across this.

[Mark Hammer]

In some respects, maybe what you want to do is get yourself one of those free Fourier analysis software thingies from a site like hitsquad, and "measure" the spectral properties of the noise produced by the transistor.  Again, it's not the overall amplitude you care about, but rather the variability of the amplitude across those assorted spikes.  Stated another way, if you ran the best and noisiest device you could imagine through a compressor, squished the daylights out of the noise source, and fed that to the sample/hold section for sampling, your FSH-1, or indeed any similar sort of filter, would sound uninspiring....because the noise-source amplitude didn't vary that much.

[PaulCurtis]

I built a fsh-1 with my son. It didn't sample and hold all that well either. I looked at the noise circut with my scope and found that it really wasn't all that noisy. I went to the Radio shack and bought a package of 25 transistors for about three bucks. I auditioned each one for how much noise it made, there was a lot of variation. When I found one that made a lot of noise the pedal worked much much better. My recollection was that it was a transistor with a little more gain then the one called for in the parts list.

[Morocotopo]

Does the GGG layout have ticking in S/H mode? i built the Tonepad one and could never get rid of it, no matter what I tried... too bad, it´s a really cool FX, don´t you think?

Morocotopo

[DougH]

You like the sample & hold sound? Get a flanger that does step-flanging. It's basically the same sound and with the typical depth/feedback controls you can shape it as subtle or intense as you want.

I don't mean to rain on anyone's DIY-parade. The FSH-1 was on my "to do" list for years and years. Then I got a Line6 Liqui Flange to do flanger sounds and discovered the step function. Whoa! Cross the FSH-1 off the list... This is the same thing only better with more flexibility. And this flanger has a tap tempo too, although you'll never tap it fast enough to get the typical FSH "sequence" sound. (I would love a feature for "scaling" the tap similarly to the echo park's various tap modes.)

I believe the Digitech Hyper Flange may have the step function too, for an even more affordable alternative.

Something to think about.

[Pushtone]

Link to a mini-build report in the Pictures thread.

I mention the noise transistors I used and their results.


http://www.diystompboxes.com/smfforum/index.php?topic=36392.msg477668#msg477668

[soggybag]

I built two of these and had problems with both. You definitely need to choose the transistor for noise. I bought a pack 20 or so and tested every one. I found a few that produced some good noise and put these aside in a bag.

The trimmers make a big difference also. I was able to get a good sample and hold effect, but I was never able to get rid of the clock tick.

I should get back to these and see if I can get them to work.

[spiderman2812]

Hey thanks for all the input guys. A little more detail here. I used a 2n3904 for the noise tranny so I guess I should get a bunch and see which works the best huh? I never had the ticking problem but I did if it wasn't grounded right to the jacks but then it just ticked and didn't do anything. I'm real happy with it I just want to get the sample and hold to be a little more pronounced like the original one I have. It's nice to have one to compare it to though. Thanks any more suggestions?

[PaulCurtis]

I got rid of most of my ticking by twisting the power and ground wires together. When I was tracking the problem down I noticed that there was a spike on the ground. I was pushing wires around with my scope probe and I noticed that the ticking changed.  The way that I had it laid out was the wires from the voltage multiplier ran almost all the way acros the board. This wasn't the best thing I guess. After I twisted the power and ground I could still see the spike on the power and ground but it wasn't audible. I was going to try some smaller faster caps across the power, in parallel with the electrolitic caps that are already there.

[WormBoy]

I use a 2n2222 for noise, but I found that most of the ones I tried introduced a soft but noticable whine in the sound (interestingly, different trannies can whine at a different frequency). Luckily I found one that didn't whine and produced a nice S/H. I also tried BC338's which were quiet but too "wild" for me. Whine and LFO ticking where noticable also in the filter setting and in the bypass (Tonepad PCB). Shielding the in/out wires cured the bypass, and I'm now simply shorting the LFO when it's not needed, so it only ticks in S/H mode (where it does not really hurt that much as it is in rhythm with the steps of the filter). Still, I think it shouldn't tick at all, so I might try some of the other tricks posted.

[Morocotopo]

Just to set the record straight, mine (Tonepad PCB) only ticks in S/H mode.
In filter mode not at all. I took all the usual steps to avoid it (shielded cable, etc). In S/H mode, with the feedback control at  minimum, the ticking is almost inaudible, it gets more pronounced when the feedback control is advanced.
Might be worth to try what you people suggest...

Morocotopo