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RAT project

Started by rangermaster, March 02, 2021, 10:58:35 AM

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rangermaster

Thanks fo rall the replies! helps me a lot.

So correct me if i'm wrong..

1. I can leave the R10 10k resistor out of the PCB.. no need to jumper the connection ? (not really useful in this schematic i understand)

2. reversing 4n7 and 1k doesn't matter or change the sound and value on the end of the line.

3. Opamp IC is in this PCB wired correctly to get the best bias/values

thanks again.

trying to learn that's all.

GGBB

Quote from: idy on March 04, 2021, 10:46:28 PM
So the extra resistor was there to help the LED switching find a good path to ground if the volume was all the way up?

Sort of yes - the switching circuit not the LED itself. Look the green section. Q2 operates as a power switch for the diodes-resistor-LED string between Q2 source and ground. When pedal is engaged (FS2b flipped right as shown), Q2 gate is biased high via R13 to +9V - JFET is therefore "on" so +9V supply at drain flows through drain-gate to LED. When bypassed (FS2b flipped left), gate is now connected via 10k R15 to ground and therefore biased low. 100k volume pot alone wouldn't bring bias low enough. With gate biased low, JFET turns off and supply to LED is stopped.
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GGBB

Quote from: rangermaster on March 05, 2021, 12:09:32 AM
Thanks fo rall the replies! helps me a lot.

So correct me if i'm wrong..

1. I can leave the R10 10k resistor out of the PCB.. no need to jumper the connection ? (not really useful in this schematic i understand)

2. reversing 4n7 and 1k doesn't matter or change the sound and value on the end of the line.

3. Opamp IC is in this PCB wired correctly to get the best bias/values

thanks again.

trying to learn that's all.

Yes. Leave R10 out - not jumpered - that would ground the output signal.
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rangermaster

So i got it working but there is a lot of squealing/oscillating noise when the gain pot is turned up...

I checked every part and every wire(short wires) but it all looks fine. I also tries replacing the opamp but that doesnt work either.

Does anyone know how to fix this ?

rangermaster


GGBB

Keep some distance between the circuit input and output wires. Clean up their solder joints. Shielded wiring for the input specifically might help.


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idy

Special attention to the foot switch; wires close together there can do it. Some folks wire the 3pdt so the "in" and "out" side are on the outsides and the LED is in between...

rangermaster

#27
Thanks guys. I will creat some distance between the wires.

I did wire the switch this way.. like i always do with these switches.



Also the gain pot does not really do what it should do.. it tapers a little from 0 to 2 and then the gain stays the same....

GGBB

Quote from: rangermaster on March 11, 2021, 02:39:48 PM
Also the gain pot does not really do what it should do.. it tapers a little from 0 to 2 and then the gain stays the same....

What kind of pot did you use? Linear taper or log?
  • SUPPORTER

percyhornickel

I have build some rats and they all works great, even oce I changed a bit the last bufer to use a npn transistor insted the Jfet.

I have the pcb design just to print and etch..   ...the regular rat and the mod rat for NPN or Jfet use.

2N5457/2N5458/BF245 works perfect

BC547/2N2222/2N3409/2N4401/2N5088...   ...any pnp.

Saludos
P.H.

rangermaster

The pots are B100k. Linear

antonis

Quote from: rangermaster on March 11, 2021, 03:22:52 PM
The pots are B100k. Linear

Only for Asian & American suppliers..


Taper         String      Asia (common)   Europe   America   Vishay
Linear          LIN                B                   A            B           A
Log / Audio  LOG               A                   C            A           L
Anti-log        -                   -                    F            C           F
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

ElectricDruid

Quote from: antonis on March 11, 2021, 04:09:37 PM
Quote from: rangermaster on March 11, 2021, 03:22:52 PM
The pots are B100k. Linear

Only for Asian & American suppliers..

Taper         String      Asia (common)   Europe   America   Vishay
Linear          LIN                B                   A            B           A
Log / Audio  LOG               A                   C            A           L
Anti-log        -                   -                    F            C           F

I've lived the majority of my life in various places in Europe, and I've never seen a Log "C" pot or an Anti-log "F" pot. Basically everything I've seen follows the Asian/US pattern: A=Log, B=Lin, and if you can find it C=AntiLog. That's the standard, and Vishay are just having a laugh. Dunno what they were thinking.


GGBB

Quote from: rangermaster on March 11, 2021, 03:22:52 PM
The pots are B100k. Linear

That's the problem - they need to be log especially the gain pot.
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antonis

Quote from: ElectricDruid on March 11, 2021, 05:49:38 PM
I've lived the majority of my life in various places in Europe, and I've never seen a Log "C" pot or an Anti-log "F" pot.

I'm away from my junkbox but I promise you some revealing photos tomorrow Tom.. :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

duck_arse

Quote from: antonis on March 11, 2021, 06:07:49 PM
Quote from: ElectricDruid on March 11, 2021, 05:49:38 PM
I've lived the majority of my life in various places in Europe, and I've never seen a Log "C" pot or an Anti-log "F" pot.

I'm away from my junkbox but I promise you some revealing photos tomorrow Tom.. :icon_wink:

.... popcorn ......
You hold the small basket while I strain the gnat.

rangermaster

Ok.. so after isolating the wires and put them away from each other no change.

I have read that changing the 30pf cap can solve this. It should tame the opamp ?

What value should be best? And does it effect sound?

antonis

30pF cap is considered as "compensation capacitor" and it affects op-amp's Slew Rate..
(the smaller the cap the faster then slew rate and vice-versa..)

By raising its value you'll make op-amp respond "slower" for high frequency harmonics..

For 9V supply, 30pF cap and Slew Rate 300000 (taken from dadatasheet) the frequency limit is at about 5.3kHz so I don't think your squealing issue is comensation cap value..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

rangermaster

#38
Ok now i'm really confused.

Dunno what else it could be

I changed the pots to 100k log.

antonis

Quote from: rangermaster on March 31, 2021, 05:54:58 AM
Dunno what else it could be

Try to use a much bigger value cap (470pF say) instead of 100pF feedback cap..
(the one in parallel with Gain pot)

You might lose some high frequency gain so proceed to lowering its value untill squealing point just appears.. :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..