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## Help me understand the Micro Vibe

Started by jlo, June 30, 2020, 08:53:36 AM

#### duck_arse

that antonis, he's too hard.

jlo, observe the non-invert in of U2-2 [2 small for my eyes] - there is a 100k resistor to bias. this sets the stage input impedance. now there is two other 100k resistors feeding signal into that (+)in - so, what happens [to those original signals] when you have a 100k series feeding a 100k-to-ground [what the input impedance looks like]?
can you counts to 34.

#### antonis

U2-3 if you use magnifier tool..
"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..

#### jlo

Quote from: duck_arse on July 02, 2020, 10:43:43 AM
that antonis, he's too hard.

jlo, observe the non-invert in of U2-2 [2 small for my eyes] - there is a 100k resistor to bias. this sets the stage input impedance. now there is two other 100k resistors feeding signal into that (+)in - so, what happens [to those original signals] when you have a 100k series feeding a 100k-to-ground [what the input impedance looks like]?
You mean U3-2?

#### duck_arse

I have no idea.

you can quote me.
can you counts to 34.

#### jlo

(R18 + R9 + R8) is in parallel with R20?   So the net resistance is 66.6k.   So the voltage coming out of U3-1 is 0.398 of its input?

#### antonis

Quote from: jlo on July 02, 2020, 01:04:19 PM
(R18 + R9 + R8) is in parallel with R20?

Who knows..
(Hard enough, Stephen..??)

"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..

#### jlo

Im clearly confused.  Is the input signal divided into wet and dry paths and then mixed at the end like the Univibe?  If so I can't see where the two separate paths are.  I thought the signal split at U1-1 output.  Wet going through the various phasing stages and the dry was going through R18 going L to R on the schematic and then mixed into the + input of U3-2 along with the output of U3-1.

#### antonis

#27
Quote from: jlo on July 02, 2020, 05:38:21 PM
Im clearly confused.

You're not the only one..

Last attempt: Are we talking about dry/wet mix or about R22 right leg signal attenuation..??
"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..

#### jlo

In the univibe circuit, the input signal is split.  The wet path undergoes phase shifting and is mixed in with the dry signal in chorus mode.  In vibrato mode, the dry signal is not mixed in.  Micro Vibe only has chorus.  So does it have the same architecture of splitting the signal and mixing the two at the output?

#### ElectricDruid

Quote from: jlo on July 02, 2020, 06:33:01 PM
In the univibe circuit, the input signal is split.  The wet path undergoes phase shifting and is mixed in with the dry signal in chorus mode.  In vibrato mode, the dry signal is not mixed in.  Micro Vibe only has chorus.  So does it have the same architecture of splitting the signal and mixing the two at the output?

If it has chorus, then yes definitely it splits and mixes. The difference between "chorus" and "vibrato" modes is whether the dry signal is mixed in. If it is, then you have chorus (dry signal + modulated "wet" signal") or if not vibrato (just the modulated "wet" signal).

#### jlo

Quote from: ElectricDruid on July 02, 2020, 06:48:40 PM
Quote from: jlo on July 02, 2020, 06:33:01 PM
In the univibe circuit, the input signal is split.  The wet path undergoes phase shifting and is mixed in with the dry signal in chorus mode.  In vibrato mode, the dry signal is not mixed in.  Micro Vibe only has chorus.  So does it have the same architecture of splitting the signal and mixing the two at the output?

If it has chorus, then yes definitely it splits and mixes. The difference between "chorus" and "vibrato" modes is whether the dry signal is mixed in. If it is, then you have chorus (dry signal + modulated "wet" signal") or if not vibrato (just the modulated "wet" signal).

Right so then where is the dry signal path?  I thought it was from U1-1 output across R18 and then mixing just after R22 into +input of U3-2?

#### ElectricDruid

https://postlmg.cc/N5BSZtvx

Yes, you're right. R18 takes the output from the input buffer U1-1 to the output mixer U3-2. Interestingly, it's a passive mixer into a non-inverting op-amp, instead of the (perhaps more common) inverting active mixer. Not that it makes a huge amount of difference when this is a phase shifter circuit - phase is going to get scrambled either way.

#### jlo

Quote from: ElectricDruid on July 02, 2020, 07:37:44 PM

https://postlmg.cc/N5BSZtvx

Yes, you're right. R18 takes the output from the input buffer U1-1 to the output mixer U3-2. Interestingly, it's a passive mixer into a non-inverting op-amp, instead of the (perhaps more common) inverting active mixer. Not that it makes a huge amount of difference when this is a phase shifter circuit - phase is going to get scrambled either way.
So thats a different path that Antonis is describing.
Quote from: antonis on July 02, 2020, 02:59:47 PM
Quote from: jlo on July 02, 2020, 01:04:19 PM
(R18 + R9 + R8) is in parallel with R20?

Who knows..
(Hard enough, Stephen..??)

#### PRR

Quote from: jlo on July 02, 2020, 06:56:41 PMRight so then where is the dry signal path?

That's what I see too.

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#### antonis

Making things clear now you can see that both signals (Wet & Dry) are divided on R18/R20/R22 junction..
"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..

#### jlo

Quote from: antonis on July 03, 2020, 07:36:52 AM
Making things clear now you can see that both signals (Wet & Dry) are divided on R18/R20/R22 junction..
Ok so now revisiting the gain structure.  Are both wet and dry signals halved and then combined before tge U3-2 input?

#### antonis

It depends on paricular point of view..

"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..

#### jlo

Quote from: antonis on July 03, 2020, 09:58:00 AM
It depends on paricular point of view..

#### duck_arse

Quote from: antonis on July 03, 2020, 07:36:52 AM
Making things clear now you can see that both signals (Wet & Dry) are divided on R18/R20/R22 junction..

thanks antonis - this was the point I was trying to drive at.
can you counts to 34.

#### ElectricDruid

Quote from: jlo on July 03, 2020, 09:54:34 AM
Quote from: antonis on July 03, 2020, 07:36:52 AM
Making things clear now you can see that both signals (Wet & Dry) are divided on R18/R20/R22 junction..
Ok so now revisiting the gain structure.  Are both wet and dry signals halved and then combined before tge U3-2 input?

Yes. For both wet and dry, you've got a 100K/100K divider, so the level is halved. And then the amp provides some make-up gain. 150K and 118K (118K?!? Seriously? I don't believe it) gives 150/118+1 = x2.27, so there's a very slight boost overall.