Maestro filter/sample&hold problem

[toneless]

Hi.
It is the second time i'm trying to make this effect and it
doesn't work.
When the effect is on i'm listening my guitar signal but it doesn't
have any filter or sample&hold effect.My pots do nothing,too.
Only the upper trimmer work (it changes the frequency of the signal)
and there is some hiss in the sound.
I've used CA3080E and LM741 for the ics and BC239(in place of MPSA5172),BF245C for the fets and everything else like the schematic.
I've double checked all the pinouts.
Perhaps the iCs are bad or the onboard dpdt is oriented wrong,when i
replace it and play with the cables i listen some funny noises but
nothing near the impressing sound a Maestro can produce.

Ps.It seems that i don't have much luck with anything that has a CA3080
in it.I've tryed Dyna Comp,Ring Frobnicator etc and none worked:(
I 'll try again though...

Thanks
Nick

[toneless]

No luck with the Maestro yet...
I noticed that if i have the 10k trimmer maxed and play a note i hear
a repetitive sound that gets slower or faster when i turn the speed
pot.
Anyway after a lot of hours trying to make this thing work even the batterys get tired...they are less than 8.2v now.

nick

[smoguzbenjamin]

Use a wallwart Does the sound improve when you max out the 10k trimmer and get worse as you turn it down? In that case maybe you can try adding a series resistor... :?

[Zero the hero]

This stompbox is supposed to be a battery sucker, so that's right that your batteries died soon...
It's not easy to set the trimmers, I noticed I had the same problem when I've built mine unit, that is hiss sound and no response from both trimpots.
I suggest you to set carefully both trimmers.
Don't worry, I've built a ring frobnicator too with no result...

[ExpAnonColin]

OTAs are for sure very hard to get right.  Connect something to the wrong pin and you've fried it...

-Colin

[Elektrojänis]

I'm not too sure about this but BF245C might not be the best possible fet for an effect powered from 9v battery (that one seems to use two though). Check this geofex article: http://www.geofex.com/Article_Folders/fetmatch/fetmatch.htm

BF245C should be quite close to that BF244C mentioned in the geofex article in this respect (at least if I'm reading the datasheet correctly). BF245A could be better if you can get them. My local suplier has BF256A and that has worked fine on my prototype cabsim so it might work on other 9v stuff too.

This is only my non-educated speculation though as I have never built that maestro S&H filtter pedal nor anything even remotely like it.

[toneless]

I found those number in the data sheet but they don't tell much to me.
BF245A   Idss= 2-6.5mA
BF245C   Idss= 12-35mA
Those are the only markings that are not the same between the two.
It seems that nobody has BF245A trans around here...

I changed all the trans and ICs and the effect still doesn't work.
All the traces are clean and i measure the right voltages...

The sound pass through but it is unaffected and now only the upper trim works and pots do nothing,too.

[toneman]

i'm thinkin there should be another fet after the 2nd 3080.

Check out the Oberheim SEM filter module.
the ASM-1 uses same type filter.

also, thought U had to reversebias the noise transistor, Q4,
to get noise.  In the schemo, emitter&collector hooked to supply
pos and neg.  Put pos on emitter, gnd to base.  Leave collector
unconnected.

just get it working as a filter first.
then, make S&H work.

tone

[Elektrojänis]

I found those number in the data sheet but they don't tell much to me.
BF245A   Idss= 2-6.5mA
BF245C   Idss= 12-35mA

This seems to be different too:

VGS gate-source voltage ID = 200 mA; VDS = 15 V
BF245A -0.4 -2.2 V
BF245B -1.6 -3.8 V
BF245C -3.2 -7.5 V

It is the value that is discussed in that geofex article (if I understood correctly). If you want to experiment with it and can't find that BF245A, check if they have BF256A. It should be similar (to BF245A). You could also check if they have other fets mentioned in that geofex article to have low vgs.

But anyway... It might as well be something else that causes the problem.

[toneless]

I suppose i'll have to make a new cleaner board and buy new parts:(
The problem is that everything i want very bad it never works :evil:
I'm not very experienced with stompboxes but i've made a lot more complex effects(except everything that has a CA3080 in it).
I can only find CA3080E around here and i hope this ic is not the problem.

Thanks
Nick

[Paul Perry (Frostwave)]

I can only find CA3080E around here and i hope this ic is not the problem.

Nick

Rest assured, that isn't the problem. CA3080E is cool.

[toneless]

I'll try to take a look for "cold" solder joints and replace the trans with other types...and i'll use a power supply with +- 12v.
I suppose the problem might be aroun 2N3906.

Nick

[ustompsteve]

I have made a few of them using a layout which I have posted at http://www.ustomp.com.

For the noise transistor I ended up using an MPSA18 the others weren't noisy enough.

You might try that. Which schematic did you use?

--Steve

[toneless]

I used the schematic from www.generalguitargadgets.com.
Perhaps i'll try your board if i can't fix this one...

I tryed 2N3904 and 2N2222 for the noise transistor but i don't think that this is the problem because neither the filter work.

LM833N is 741 right?

Nick

[ustompsteve]

LM833N are dual op-amps. Same idea, but the 741 is just a single op-amp in one package.

So when you put the switch to the env-filter position you don't get anything either?

--Steve

[toneless]

I can hear my signal on both positions of the switch but it is unaffected.
When in the filter position the 100k trimmer works and when i play and turn it it sounds like a manual filter but the filter pot do nothing.

Nick

[swt]

i've build it and it's working fine. The fets that you chose won't have enough gain or swing to make it work, you shall look for bf245A. that's what i 've used. I also have lm 3080 instead of ca3080. What schem did u used??.