Fairfield Circuitry - The Barbershop (gut)  [traced]

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Manfred
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Post by Manfred »

I know that the 1M resistor gives the impedance, so this should be good, right ?
Should I make the cap bigger, to let more bass through, or does it have another purpose in the circuit ?
100nF together with 1M gives a roll-off frequency of 1.6 Hz.

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snk
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Post by snk »

Thank you, Manfred.
The BarberShop is built, boxed, and running :D
I got rid of the SAG pot, added a "bass" switch, and an output buffer. Now it sounds great anywhere in my effect chain.

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G.Bisson
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Post by G.Bisson »

I built one on vero using WhiteKeyHole's schematic. Build notes:
Substituted J201's with through-hole 2N5457's. Overdrive and Sag controls works and sounds like demo videos, but I was experiencing excessive noise and hiss. Tried three different matched pairs that all were too noisy.
Substituted with 2N5458's doesn't produce any overdrive, just clear tube-sim tonal coloration. Sag doesn't function as expected, like others reported, the sound quickly gets quiet and cuts out all sound within a small turn of the knob.

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bc108
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Post by bc108 »

Going crazy with this one.
Built and suddenly, start to squeal and motorboating.
Unbox, tested everything everywhere.. Not ground, not bad pots.. what could go wrong? The main squealing "control" is the SAG pot/resistor. I assume something is wrong with Jfets at this time..

Any help?
Thanks!

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Manfred
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Post by Manfred »

How do you feed in the supply voltage?
with battery, plug-in power supply or other power supply unit?

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bc108
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Post by bc108 »

Manfred wrote: 01 Nov 2021, 18:59 How do you feed in the supply voltage?
with battery, plug-in power supply or other power supply unit?
I've used a regulated and filtered power supply w/LM7809. And tried a Dunlop DC-brick to check.
I'll keep looking around, J-fets w/6v at Drain without SAG pot, but I assume the trouble comes from there (potentiometers)

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bc108
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Post by bc108 »

Update: no matter how many times, and pots I put there.. still sounds like a metal detector or some kind of oscillation.
Could be the 2n2222?

Update 2: yep.. was the f*****g 2n2222. Used a KSP2222A instead.. the same thing.
Something I've discover and I don't know if is only my pedal.. but with volumen (I know.. I know.. TONS of output), gain and sag at maximum, it sounds horrible?

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Manfred
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Post by Manfred »

Skip the SAG circuit and feed the 9V directly to the collector of Q3 to see if the squealing stops.
How is the circuit built PCB, Vero or point-to-point?

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bc108
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Post by bc108 »

Manfred wrote: 02 Nov 2021, 03:11 Skip the SAG circuit and feed the 9V directly to the collector of Q3 to see if the squealing stops.
How is the circuit built PCB, Vero or point-to-point?
Yes, it skips. DIscovered a bad batch of 10k pots with it too :cry:
With the new KSP2222 it works. Just not good when volume and gain are at max: sag start to crackle and noise AGAIN. I think it is not normal.
What I'm missing here? Any voltage readings there, to check? Maybe some J-fet are screwed.. just checked with no SAG:

In: 9.08v
Q1
D 5.95V
S 0.25v
G 0.01v
Q2
D 5.79v
S 0.21v
G 0.0v
Q3
C 9.03v
B 5.8v
E 5.30v


I don't want to miss with the original circuit: but which is the function of the NPN transistor there, some kind of buffer?

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Post by ppluis0 »

bc108 wrote: 02 Nov 2021, 12:23 I don't want to miss with the original circuit: but which is the function of the NPN transistor there, some kind of buffer?
Yes, is an emitter follower to avoid load the drain of second jfet and have low output impedance.

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bc108
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Post by bc108 »



Bad pot?

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graybench
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Post by graybench »

New video for the barbershop is live.


This is a different version than the schematic earlier in the thread.
I thought the tone control would be the only update, but there's several changes.
Here is the schematic for V2, unverified but should be correct (pdf attached):

schem1.jpg

Parameters for the JFETs seems to be consistent across other versions.
Here are the specs for the transistors in this Barbershop V2:
Q1 (Fairchild J201): Vp=-0.87V, Idss=780uA
Q2 (Fairchild J201): Vp=-0.67V, Idss=510uA
Q3 (PN2222A): hFE=198

Enjoy!
Attachments
schem1.pdf
(16.32 KiB) Downloaded 247 times

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Post by Vurguuz »

Has anyone had a chance to verify the v2 schematic kindly posted by @graybench? Debating on which version to build..

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JonesXavier
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Post by JonesXavier »

hello! I designed a layout with this scheme from Barbershop v2 by Gray Bench, and it works great, nice overdrive, so good! Thanks to Gray Bench for the scheme. I used MMBFJ201 and 2n5551 (Others like 3904 will do).

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