Maestro FSH Project - Part subs, will they work?

[Kevin Mitchell]

I would like to throw one together this weekend; Tonepad project FSH1

From my research I believe I could possibly substitute all of these parts for what I have on hand. Please validate/ explain any possible issues. I'd really appreciate it. Redrawing the schematic to breadboard is giving me a headache so I'm hoping the Tonepad layout will work as is with such substitutes.

Okay;
MAX1044 for a LT1054 (Charge Pump/voltage inverter)
BF245A for 2n5457 (FET)
LM13600 for LM13700

I'm 90% sure these are pin-to-pin swapable and will show identically/exact results to the original BOM. Anyone please chime in! 

Thanks!

[Govmnt_Lacky]

MAX1044 for LT1054: Possibly. As long as the current draw from the circuit does not exceed the mA limit. The 1054 can go up to ~50mA... maybe even 100mA. Also, the MAX chip will fail if you put in 10.0000000001VDC

BF245A for 2N5457: Check the pinouts. I believe you might have to turn it 180 degrees.

LM chips: You can sub these. No issues

[blackieNYC]

The noise transistor, with the open emitter, is a very difficult pick.  Could try anything. I pull out the pedal and try to get that working right, then I put it away again.

[Kevin Mitchell]

The noise transistor, with the open emitter, is a very difficult pick.  Could try anything. I pull out the pedal and try to get that working right, then I put it away again.

You mean Q1 with the base open? The BOM said chosen for noise. I have an abundance of npn transistors so no fear.

BF245A for 2N5457: Check the pinouts. I believe you might have to turn it 180 degrees.

You're right about that. Easy fix. I've read they share similar/practically the same specs minus the pinout orientation.

About using the LM1054, from what I can tell it does have the same pinouts as the MAX1044, they are just described differently. I'll be sure of it before I give it a shot.

Thanks guys!

[Govmnt_Lacky]

About using the LM1054, from what I can tell it does have the same pinouts as the MAX1044, they are just described differently. I'll be sure of it before I give it a shot.

Keep in mind that the MAX1044 has the Frequency Boost option. The LT1054 does NOT. If you use the LT1054, you will have to cut the trace between Pins 1 and 8.

[blackieNYC]

Base open. Didn't look.
The trade-off there seems to be a deep rich random modulation vs. popping. Some claim to have nailed it right away.  When I reach the spot in the trimpots where the modulation starts to sound good, it's already popping sharply. Literally sounds like a person saying "pop".  I tire of him.

[Kevin Mitchell]

Keep in mind that the MAX1044 has the Frequency Boost option. The LT1054 does NOT. If you use the LT1054, you will have to cut the trace between Pins 1 and 8.

That's what I had to check out. From my understanding the original stompbox ran off 2 9-volt batteries. I'm guessing one was for the reversed polarity parts of the circuit. So as long as I get my 4 rails (+8, +9, -8 and -9) it should be fine. LT1054 should do the job. I was worried what the boost pin getting +9v is doing to the circuit and if going without it would compromise something. But I don't believe it would.

Instead of boost, the LT1054 has a "FB/SD" pin. Any ideas on this? Should I ground it or leave it disconnected?

[Govmnt_Lacky]

Instead of boost, the LT1054 has a "FB/SD" pin. Any ideas on this? Should I ground it or leave it disconnected?

I believe that if you want to use the LT1054 with this circuit you will want to lift Pin 1 from the socket. This way, V+ is only getting to Pin 8.

[Keppy]

2N5457 will work. The one in the oscillator is a simple switch, and the one in the filter is biased with feedback to minimize differences between FETs. Check the pinout as others have said.

I've used an LT1054 in this circuit with no need for the FB/SD pin. Just cut the trace between pins 1/8.

13700 is, if anything, better for this circuit. The only difference, quoted from the datasheet:

The output buffers of the LM13700 differ from those of the LM13600 in that their input bias currents (and hence their output DC levels) are independent of IABC. This may result in performance superior to that of the LM13600 in audio applications.

[Kevin Mitchell]

Thanks for the info! Very helpful.

I should have asked this in the original post; would 1N4148 diodes work just as well as the 1n4001 in this circuit?

[PRR]

>>> noise transistor, with the open emitter
>> Q1 with the base open?
> Base open. Didn't look.

The difference is 0.5V breakdown.

Perhaps 7.0V collector-base, 7.6V collector-emitter.

In 9V-only work, we have little to no headroom from breakdown to battery, we strongly prefer the collector-base connection.

At 18V, should be zero difference. The collector-base voltage and impedance and hiss way-dominate the base-emitter junction's contribution.

Q5 should be a high threshold voltage part or hiss-peaks will pop-through the FET switch.

Q6 is a buffer and a low threshold voltage part (or a TL07x) may be best.

[Kevin Mitchell]

Bumping my last question before I build the board. Please review schematic in 1st post.

Would 1N4148 diodes work just as well as the 1n4001 in this circuit?

If not the 1n4148 then how about 1N34A like diodes?

[Keppy]

4148 is fine. 1N34A is less good, but only because they're germanium and might be a little leaky. They'd probably still work though. Almost any common diodes will in this circuit.

[blackieNYC]

Q5 should be a high threshold voltage part or hiss-peaks will pop-through the FET switch.

Q6 is a buffer and a low threshold voltage part (or a TL07x) may be best.

Hey Paul -
Q5 and Q6 are BF245s (no TL0s - ?)  I'm hijacking this with my popping problem. Are you saying another FET for Q5 or Q6 could help?  A higher Vgs for Q5? (the BF245 is -8, the J201 is -40)         I've tried many Q1 transistors.

[Keppy]

Don't forget about the .15uF cap attached to CV. That should slow down current changes in the filter circuit. If your value is off, it could contribute to popping, and increasing it above .15uF might improve things. Same goes for the .05uF between Q5 & Q6.

If your circuit is popping on the frequency changes, check your cap values attached to CV and between the FETs. If your circuit is popping between frequency changes, that's when I'd look at the FETs.

[Kevin Mitchell]

The circuit has been near complete for a while now. Just haven't had enough time to finish it up!

Quick question; I'm short on 220uF caps, could I substitute these with 470uF? They're for the voltage inverting section and I'm not sure if increasing this value would throw anything off.

Might try anyways. Though knowledge is power. Thanks guys.