FSH-1 Maestro Filter / Sample and Hold (Tonepad)

[niggez]

Hi, some questions to the FSH-1 filter build from tonepad.com . The switch for the s/h / filter, is it supposed to be a momentary switch? Im confused by the way its depicted in the schematic below the layout!
I have some spare bf245b n channel fets, i read about people using 245a's. Are they likely to be compliant? From looking at the datasheets they are only slightly different, but my guess is the "operation data" (don tknow how to put this) is probably too different? I have never built anything requiring standard fets, so i dont really know what a standard fet is.
My guess would be bf245a is a standard fet? But I really cant say, and last time I asked the salesman in the electronics place, he sold me big buz11 fets. I guess those arent useful since theyre huge.

Hehe...Google just directed me to the tonepad site before opening the layout, where a little note sais: Fets are bf245a i love google.

[oldrocker]

The S\H switch isn't momentary.  It is to select sample and hold or filter (auto wah).   As for fets I used MPF102's and they worked.  I'd say socket them and try some different fets to see what works best.

[soggybag]

I don't think the FETs are too critical. I think I used J201s or 2N5457s.

You do need to choose the noise transistor carefully. I think this is the 2N3904. If you have a scope. Wire it on a breadboard in the same configuration used in the FSH-1. Probe it with the scope and look for transistors that put out a large noise. You'll see a definite difference between transistors.

I put the noisiest ones in a bag and marked them. They can be useful for other projects.

I also found that adjusting the trimmers and can help minimize noise from the clock.

[niggez]

Thanks for the advice. I got started yesterday, but I'm going to get some J201's /MPF102's or BF245A's, i think this might be a problem. I couldnt find more info on the specific difference, but there was a thread on an audio forum (hifi), where someone was building some kind of device (i know this is vague  ) where the BF245B's couldnt be used instead of the BF245A's. So just to be sure, I'll get some of those tomorrow.
I socketed all the fets/transistors, so that wont be a problem.

[oldrocker]

I have also used 2N5952's with success although they have to be installed 180 deg from the MPF's.

[niggez]

Hey...i did find some j201's and got it working. I'm onto the sample and hold resistor now, something strange i noticed. I've been trying out a lot of 2n3904's and some 2n2222's. Also some BC XXX npn. Strange thing i noticed, most of the metal can-type transistors give me sample and hold, but only when the "chassis" of the transistor is grounded, as in, I'm touching it. When i let go, no sample and hold. Same is true for all plastic-package transistors...bizarre.
Right now I'm trying c33740's and its goin wild can recommend those definately. I think they are similar BC817 or BC337.
HOw did you set the trimpots? Havent figured out that yet.
When in S&H mode, is there supposed to be constant s&h noise? I think the clock is ticking in S&H and that tick is s/holded.
And, what exactly does the 100k trimmer set?

[niggez]

I went through a box of electronic garbage i bought on ebay a while ago - big assortment of used transistors. I found some I like, the markings are not readable, but they work great 
Although i still dont understand exactly what the 100k trimmer does. What does it adjust soundwise?

[niggez]

I swapped the 10k for a multiturn - can recommend that definately. Its so much easier to adjust and get the best out of your noise transistor.
It's the 100k trimmer thats giving me headaches. If I'm not mistaken it somehow adjusts the filter range? I just can't seem to find a position where the up and down parts BOTH function properly.
And just when i think I've found one - it seems like its impossible to avoid the screaming treble.
Any advice? Everything, all controls etc, work, it seems like its just the trimmer...how did you set it?

[soggybag]

I don't think the 100K trimmer effects the range of the Envelope filter. It only effects the range of the Sampled voltage. So it is completely out of the circuit when in the S&H mode.

The only control that has an effect in S&H mode is the Rate and Resonance. And the two trimmers.

[niggez]

Strange...I could swear it changes the filter range on mine! But maybe its just that everytime i open and close the back cover i move the knobs a bit, unintentionally. But I#m going to double check that.

[niggez]

I am 100% sure now, the 100k trimmer definately effects the filter part of the effect. It changes the range when turning itk... could that be an error on my behalf? If i turn the trimmer while playing, it's basically like rocking a wah.
Theres no ticking for me, only while sample nad holding a little bit. Only problem that has strangely come up (wasnt there at first) is a high pitched whine when the effect is activated, in both filter and s/h mode. It disappears when i remove the noise transistor, but i don't think its because of a faulty transistor. I tested several with different trimpot settings, and the high pitched whine is still there, very faint, but its always present. Hm..... 

[rvargas]

I just finished a build of this pedal, and I got a little ticking.  It turned out the 100K resistor at the output node wasn't properly soldered at one point.  That took care of it.