Author Topic: Low Gain, neutral dist/OD  (Read 4356 times)

Ben N

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Re: Low Gain, neutral dist/OD
« Reply #80 on: September 11, 2019, 01:35:21 PM »

GGBB

Re: Low Gain, neutral dist/OD
« Reply #81 on: September 11, 2019, 01:51:30 PM »
I don't have 6.8n or 2.2 n but I have 10n and 1n. Also I don't have B250k but I do have B50k or A250k. Will those substitutions work ok? Just for a quick breadboard layout.

6n8 is a high pass filter. Bigger means more bass/flub, smaller means thinner.

2n2 is a low pass filter. Bigger means duller, smaller means brighter.

A250k will work fine but adjustment will be crowded at the clockwise end.

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #82 on: September 11, 2019, 04:48:18 PM »
6n8 is a high pass filter. Bigger means more bass/flub, smaller means thinner.

2n2 is a low pass filter. Bigger means duller, smaller means brighter.

A250k will work fine but adjustment will be crowded at the clockwise end.
Ok, I'll try both options and go with what sounds better. Oops, I meant to say I have A500k. I'm sure it'll work more or less anyway.

GGBB

Re: Low Gain, neutral dist/OD
« Reply #83 on: September 11, 2019, 07:00:52 PM »
Ok, I'll try both options and go with what sounds better. Oops, I meant to say I have A500k. I'm sure it'll work more or less anyway.

The pot and the 100k below it act as a voltage divider off of the MOSFET output into the JFET configured as a standard volume control. The 100k sets the minimum gain level relative to the total resistance. So 500k will give you additional lower gain settings without changing the max gain (which is always max/total resistance). But the total resistance also forms the other half of the high pass filter with the 6n8, so change the total resistance and you also change the filter cutoff - more resistance means more bass/flub, less means thinner. If you change the overall resistance of that divider, you should also change the cap in the other direction by the same factor to compensate and maintain the same value for the low pass filter cutoff. So with 500k plus 100k, you would want to change 6n8 to 3n9 (math: 6n8 / ((500k + 100k) / (250k + 100k))).

You can also use your B50k (so as to keep the same taper) and change the connected 100k to 20k (substitute 22k or 18k) and change 6n8 to 33n. That should also give you close to the same result as original spec.

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #84 on: September 12, 2019, 04:45:28 AM »

You can also use your B50k (so as to keep the same taper) and change the connected 100k to 20k (substitute 22k or 18k) and change 6n8 to 33n. That should also give you close to the same result as original spec.

I have 22kr and 33n so I'll use this option. Cheers.

The LPF calls for 8.2k+2.2n=8.8khz. My options are:
13k+1n=12khz
22k+1n=7.2khz
1k+10n=16khz
3.3k+10n=4.8khz

I think I'll go for 22k+1n=7.2khz.
« Last Edit: September 12, 2019, 06:31:50 AM by Killthepopular »

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #85 on: September 12, 2019, 11:10:00 AM »
What's the deal with J201s? I'm checking the voltage of the j201 Drain and it's like it changes every minute for no reason. I've set up a voltage divider with 2 10k resistors. The output of that divider is 4.5v~. I connect it to my J201 drain. Check the drain voltage. 4.5v. Great. I check it again a minute later. 3.3v. What? Now it seems to be back at 4.5. Am I doing something seriously wrong or is this normal behaviour for jfets?

Wait. It's something to do with me touching the other legs with my multimeter probe. This seems to screw with the drain voltage somehow and drop it down to 3.3v. I swap to another one that I haven't checked in a while and it's at 4.5v again. Am I screwing with the latent charge of these transistors or something?

EDIT: Looks like I had set it up so that the resistor below the gain pot wasn't connected to the gain pot. The circuit seems to sound and work ok now.
« Last Edit: September 12, 2019, 11:22:22 AM by Killthepopular »

Sooner Boomer

Re: Low Gain, neutral dist/OD
« Reply #86 on: September 12, 2019, 01:26:52 PM »
A couple of things to think about, and save for future reference;

A good analysis of the Tube Screamer, including how the tone control section works, including frequency response graphs  https://www.electrosmash.com/tube-screamer-analysis

Presence/tone control based on the Big Muff tone stack; http://www.muzique.com/lab/tone3.htm      (all of Jack's stuff is worth reading)
Dan of 9 Toes
I'm not getting older, I'm getting "vintage"

PRR

Re: Low Gain, neutral dist/OD
« Reply #87 on: September 12, 2019, 02:12:56 PM »
> Am I screwing with the latent charge of these transistors

If the Gate is floating, no resistor toward Source, the FET state is unknown past history of charge.

FET/Tube Gates/Grids must ALWAYS have a known bias.

Rob Strand

Re: Low Gain, neutral dist/OD
« Reply #88 on: September 12, 2019, 05:04:33 PM »
Quote
The LPF calls for 8.2k+2.2n=8.8khz. My options are:
13k+1n=12khz
22k+1n=7.2khz
1k+10n=16khz
3.3k+10n=4.8khz

One thing about that circuit is the output impedance of the JFET stage needs to be included in the filter calculation.  As drawn that means anything for 0 to 50k!   A 50k there in series with the 8k2 is going to have more effect that the 8k2 itself.  In practice the uncertainty won't be as wide 0 to 50k.   A typical value might be 18k to 20k (that's not the expected range of uncertainty though).
« Last Edit: September 12, 2019, 05:11:20 PM by Rob Strand »
The mind often distorts without gain.

GGBB

Re: Low Gain, neutral dist/OD
« Reply #89 on: September 12, 2019, 06:58:56 PM »
The LPF calls for 8.2k+2.2n=8.8khz. My options are:
13k+1n=12khz
22k+1n=7.2khz
1k+10n=16khz
3.3k+10n=4.8khz

I think I'll go for 22k+1n=7.2khz.

If you have a spare 10k pot - you can use that with a 10n cap connected to the wiper and have an adjustable tone control.

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #90 on: September 13, 2019, 07:49:15 AM »
I like the peppermill more than I expected so I'll buy the parts and try it properly. I'll buy some parts for two other circuits I wanna try while I'm at it; ROG Eighteen and Fairfield Barbershop. Ordering now.

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #91 on: September 26, 2019, 04:58:31 PM »
Had another go with the peppermill with the proper components (no substitutions). It's cool but it sounds a bit transistory to me. Not really what I'm looking for.

Can someone help me with the pinout for the vp3203 on the barbershop? I can't find it with google.  Also, I notice that the tagboard effects version of the barbershop seems to omit q4, r11 and r10. Are they somewhat superfuous parts of the circuit?

http://4.bp.blogspot.com/-Roy4uUPtPQ8/T-oMZ3fHO4I/AAAAAAAABv0/0IPFOReE0QU/s1600/Fairfield+Circuitry+-+The+Barbershop.png




Rob Strand

Re: Low Gain, neutral dist/OD
« Reply #92 on: September 26, 2019, 06:08:00 PM »
Quote
Can someone help me with the pinout for the vp3203 on the barbershop? I can't find it with google.  Also, I notice that the tagboard effects version of the barbershop seems to omit q4, r11 and r10. Are they somewhat superfuous parts of the circuit?
You can leave those out. Probably a good idea to keep R10, maybe make it 100R.

The motivation appears to be polarity protection but that circuit is going to be hard to fry,
http://www.geofex.com/Article_Folders/mosswitch/mosswitch.htm

The mind often distorts without gain.

PRR

Re: Low Gain, neutral dist/OD
« Reply #93 on: September 27, 2019, 12:43:46 AM »
> pinout for the vp3203

http://ww1.microchip.com/downloads/en/DeviceDoc/VP3203%20B082613.pdf

Agree it isn't essential.

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #94 on: September 27, 2019, 05:03:51 AM »

You can leave those out. Probably a good idea to keep R10, maybe make it 100R.

Like this?




Ben N

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Re: Low Gain, neutral dist/OD
« Reply #95 on: September 27, 2019, 05:13:01 AM »
I like the peppermill more than I expected so I'll buy the parts and try it properly. I'll buy some parts for two other circuits I wanna try while I'm at it; ROG Eighteen and Fairfield Barbershop. Ordering now.
This is how it begins. Get away now, while you still can, I tell ya!
« Last Edit: September 27, 2019, 05:22:58 AM by Ben N »

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #96 on: September 27, 2019, 06:17:36 AM »


Out of interest, what is the function of c6 and r12? Most volume pots I've seen so far just have one of the pins as the audio output without any further components. Something to do with impedance or filtering low end?

Killthepopular

Re: Low Gain, neutral dist/OD
« Reply #97 on: September 27, 2019, 07:28:01 AM »
Fairfield seems to be working ok. Although there was a burning smell coming from my amp when I first turned it on... Maybe there's just an insane amount of gain available with the fairfield and something in the input stage of my amp was getting overloaded (marshall valvestate).

It sounds pretty cool although It still sounds pretty transistory. It's possible that I don't really care for the sound of transistors being overloaded. I think maybe the tone, once you get a certain amount of crunch, becomes a little too crispy, and I prefer something more muddy and squishy. It's like the sound is too hard, not enough give. Germanium fuzz faces sound cool but I guess those are a rather different beast. I love the sound of distortion circuits like the 250 and the DS1 but those usually aren't so good with the subtle breakup tones.
« Last Edit: September 27, 2019, 07:41:40 AM by Killthepopular »

Ben N

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Re: Low Gain, neutral dist/OD
« Reply #98 on: September 27, 2019, 07:32:54 AM »


Out of interest, what is the function of c6 and r12? Most volume pots I've seen so far just have one of the pins as the audio output without any further components. Something to do with impedance or filtering low end?
Decoupling and setting the output impedance.

Rob Strand

Re: Low Gain, neutral dist/OD
« Reply #99 on: September 27, 2019, 07:15:34 PM »
Quote
Like this?
That way is fine.

The topic of protection has come-up many times and I guess the consensus is these days is a Schottky diode in series with the +rail has some advantages (and some small disadvantages)
The mind often distorts without gain.