Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hold  [schematic]

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Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hold  [schematic]

Postby grrrunge » 18 Mar 2012, 21:05

I've been building the Maestro FSH project from tonepad during the last couple of days, and i thought i'd share my findings so far:

First off, there's a lot of people rambling on about the circuit being prone to ticking noise from the LFO bleeding through to the audio path, and some even blame it on the layout from tonepad.
I built mine from the latest document version available from tonepad ( Rev.2, 2008: http://www.tonepad.com/project.asp?id=50 ), and it's noisefree. If the 10K trimmer is not adjusted properly, there's ticking noise though ;) I strongly advise to use multi-turn trimmers for this build!
Also - the 3K3 resistor going to pin 7 of IC3 can be lowered to 2K. I read on DIYSB that it decides the pulsewidth being sent to open Q5, and that it just needs to be of big enough value to let Q5 open. It's supposedly a step on the way to less tick ;)

Secondly it's not necessary to use BF245A's as Q2, Q5 and Q6. I tried tossing 2n5457's in there instead. It raised the output volume from the circuit considerably and added some clarity (probably perceived clarity because of the added loudness?)

I put a BC560 in Q3 instead of a 2N3906, and it seems like it's harder to push into overdrive at higher resonance settings than the 2N3906.

Speaking of transistor choice for the noise source, there's quite a few mentions of BC338's as a good noise source over at tonepad, so i ordered a bag of 100 from Tayda, so we'll see how it goes :) So far i'm not overly impressed with the 20-something 2N3904's i've gone through. whoismarykelly (Montgomery Appliances) mentioned 2n2222's as a good noise source somewhere as well, and he's got a good sounding sample on youtube as well ( http://www.youtube.com/watch?v=4TFX_dYJlHg ) :) I'll have to try those too… I'll keep you guys posted.

The datasheet for LM13700/LM13600 says that the difference between 13700 and 13600 is that the built in buffers in the 13700 performs better in the audio range than the 13600. I've only got 13700's so i haven't got anything to add to that. Anyone else?

Overall this circuit performs very well, but the "stock" project definitely has room for improvements :)
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby pedalgrinder » 19 Mar 2012, 11:56

thats some great feedback on this circuit as the ticking concern did run through my mind but you have assured me my thoughts were true it really can't be that bad if adjusted correctly thanks for sharing this info. Much appreciated :thumbsup
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 31 Mar 2012, 17:33

grrrunge wrote:there's a lot of people rambling on about the circuit being prone to ticking noise from the LFO bleeding through to the audio path, and some even blame it on the layout from tonepad.
I built mine from the latest document version available from tonepad ( Rev.2, 2008: http://www.tonepad.com/project.asp?id=50 ), and it's noisefree. If the 10K trimmer is not adjusted properly, there's ticking noise though ;) I strongly advise to use multi-turn trimmers for this build!


I've tried a couple of different op-amps for the oscillator part (IC3 in tonepads layout), and the choice of op-amp here is crucial!
When i first built the circuit, i just tossed in a couple IC's from my "scrapyard", and everything was fine. After fiddling around with the transistors quite a bit, i went on to try out different op-amps.

I ended up keeping the JRC1458 i first used for IC3. Using a TL072, TL082 or JRC4558 resulted in a massively ticking circuit, and let through a high pitched squeal that seems to originate from the noise transistor, as the squeals frequency changed with each tested transistor.

The 1458's datasheet says that it's a low-power consumption op-amp, so maybe there are even better alternatives for this IC in the realms of Low-power consumption op-amps?
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 01 Apr 2012, 12:12

I ordered a bunch of TL062, LM358N, and KIA358P's from tayda today, just to see if they perform as well as - or better than - the JRC1458.

I have ended up using a 2SC1815 for noise. I got good overall results with those. From a bunch of 100 i had 60 useful and 20 good ones. the last 20 pretty much stayed in the same resonant spot all the time.
BC550's works well too though it seems to be either/or. Some works good and some doesn't work at all.
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby chicago_mike » 10 May 2012, 02:47

I am building 2 of these right now and am trying to find ALL the damned info I can. :D

Thanks for this post! I dig this pedal, but wish it wasn't quite so finniky with the fets and the ic's.

I have 5532's in mine and I think I need to take them out.
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 10 May 2012, 05:13

chicago_mike wrote:I am building 2 of these right now and am trying to find ALL the damned info I can. :D

Thanks for this post! I dig this pedal, but wish it wasn't quite so finniky with the fets and the ic's.

I have 5532's in mine and I think I need to take them out.

The 5532's are fine for everything but the oscillator. That's how I built the two I've made so far, and they sound awesome! ;)
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 10 May 2012, 05:21

chicago_mike wrote:...but wish it wasn't quite so finniky with the fets and the ic's.

By the way, IMO the only tricky thing for me was to look up in the datasheets and find the major difference between the op-amps i swapped in place of Q3 ;) Now you don't have to.
The JFET's were easily substitutable with 2n5457's and i suppose other similar JFET's will work just as well.
chicago_mike wrote:I have 5532's in mine and I think I need to take them out.

If you got squeals and ticks all over the place, you know what to do... :thumbsup
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby chicago_mike » 10 May 2012, 06:34

Well I'm getting the S+H. but the filter is not opening up. I'll double check all my solder joints tonight.

Hmmmm.... :hmmm:
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby chicago_mike » 10 May 2012, 06:38

I've got J201's in mine right now. he only other fets I have lying around are some mpf102's. I'm not too sure if theres a huge difference?

But I can always swap them out..the fun of diy.

Just wondering what would be stopping the filter from opening.. :hmmm:
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby rrroo » 10 May 2012, 08:09

my fsh is quite weak. the filters do not respond very well and it seems to lack gain. there is a significant volume drop when you put the effect on. it propably needs more gain in the input section. how could i do that? I used lm13700 instead of 13600 does that matter?
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 10 May 2012, 14:06

chicago_mike wrote:I've got J201's in mine right now. he only other fets I have lying around are some mpf102's. I'm not too sure if theres a huge difference?

But I can always swap them out..the fun of diy.

Just wondering what would be stopping the filter from opening.. :hmmm:


Have you tried adjusting the trimpot for the envelope filter mode?
Also, are you using multi-turn trimmers?
Did you use the tonepad layout, cause i can definitely confirm that as working ;) If not- let's see what you've got...
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby chicago_mike » 10 May 2012, 19:55

Ohh...I thought both trimmers were for sample+hold. :slap:

I bought 2 Tonepad v.2 boards. I said screw the etching with these guys. LOL!

Okay, after lunch, imma go check it out. :D
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 10 May 2012, 20:14

chicago_mike wrote:Ohh...I thought both trimmers were for sample+hold. :slap:


After checking out the schematic again, it seems like you're right... I was sure the 10K was for tuning the random filter mode and the 100K was for tuning the envelope filter mode :oops: Maybe someone else could enlighten us both a bit here?
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 10 May 2012, 20:18

On secon thought, the functionality of the envelope filter is very dependant on the "range" setting. Have you tried playing around with that one?
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby chicago_mike » 10 May 2012, 20:28

Oh yeah..I have it maxed out, and Im using an active bass with high output. Nada.

Ill do a double check soon.
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby p_wats » 10 May 2012, 20:44

I loved my FSH-1, but it quickly got replaced on my board by the Snow White Auto Wah I built. That said, I want to box it up again...thanks for reminding me!
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 10 May 2012, 21:40

chicago_mike wrote:Oh yeah..I have it maxed out, and Im using an active bass with high output. Nada.

Ill do a double check soon.


That control doesn't get maxed out. it determines the area in which the filter moves. If you have it turned all the way up, try fiddling around somewhere around the middle. The resonance should be cranked though :) That way you'll hear it right away, when the filter starts moving...
Also try sweeping through the range pot with the up/down switch in both positions. The range setting that makes awesome swooshing sounds on the up setting, makes almost no sound on the down setting and vice versa.
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 10 May 2012, 21:42

p_wats wrote:I loved my FSH-1, but it quickly got replaced on my board by the Snow White Auto Wah I built. That said, I want to box it up again...thanks for reminding me!


No problem ;) I got onto the project via a friend, who wanted one built. Now i can't understand why i hadn't heard about this beauty a long time ago...
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby chicago_mike » 16 May 2012, 04:16

This is wierd.

I have a 1458 in IC3, and a JRC4558 in the other IC socket. I get the S+H, but No filter still. I tried a TL072, but then I got nothing at all...and its a working 072. :hmmm:

Im gonna try to get a few ore 1458's and my FETs are MF102's. I didnt use J201's as I first thought. Cant easily get the 2n5457's or whatever other people use.

I may swap the noise tranny too at some point, but the S+H is working, just the filter is still not doing a damned thing.
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Re: Maestro FSH-1 / Oberheim VCF / Tonepad Filter/Sample/Hol

Postby grrrunge » 25 May 2012, 07:34

chicago_mike wrote:This is wierd.

I have a 1458 in IC3, and a JRC4558 in the other IC socket. I get the S+H, but No filter still. I tried a TL072, but then I got nothing at all...and its a working 072. :hmmm:

Im gonna try to get a few ore 1458's and my FETs are MF102's. I didnt use J201's as I first thought. Cant easily get the 2n5457's or whatever other people use.

I may swap the noise tranny too at some point, but the S+H is working, just the filter is still not doing a damned thing.

Tayda has 2n5457's relatively cheap, and shipping is dirt cheap as well. Just make sure you don't order above the import tax limit for your country, and you'll be off with 50 2n5457's for less than $10 ;)
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