AMZ Son of Tube Screamer, buffers

[ANDYEFFECT]

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AMZ SON OF TUBE SCREAMER, BUFFERS 
 
hello my friends, first I would like to know something. 
 
I set up " AMZsonTS " yesterday, and I looked at two mistakes schematic. It helps if I am wrong. 
 
1) C2 connects the ground (the schema is for Vr) 
2) it lacked a 10k after R4 for Vr. 
 
now I would like to know more on, not to use entrance buffer and exit of TS.   
 
I use key 3PDT. which the sound difference in not using buffers? 
 
Thankful. 
André

[Melanhead]

hmmmm ... no the schematic is correct, I've built one and it sounds great.

Not sure technically why C2 is connected to Vr but the 10K after R4 doesn't need to be there as there is not dc blocking cap. I beleive Vr travels through from the other opamp stage.

I'm sure Jack will pipe in ....

[ANDYEFFECT]

hmmmm ... no the schematic is correct, I've built one and it sounds great.

Not sure technically why C2 is connected to Vr but the 10K after R4 doesn't need to be there as there is not dc blocking cap. I beleive Vr travels through from the other opamp stage.

I'm sure Jack will pipe in ....

yes more because C2 connects Vr, original it connects the ground. which the difference? 
 
thankful

[smank]

There is no difference to connect C2 to Vr or ground, because a capacitor blocks the DC.

[Eb7+9]

technically there is a difference, and you gotta wonder why they originally designed it this way ... the impedance of Vr as a "source" is frequency dependent - ie it's not an ideal AC ground (frequency constant) as you'd get by using an op-amp or emitter follower following a resistor divider ... it's specifically "not great" at low frequencies depending on the ratio of circuit/source impedances ...

this kind of Vr source is ok in a high Z environment, like if you were using it to reference the + input of op-amps, but here it will have a non-idealizing effect causing the gain in that stage to drop slightly at lower freq's ... my analysis says the poor AC ground manifests itself more dynamically, ie at the clipping edges where the diodes turn on/off ... it's not a huge deal but there is a difference ...

jc

[smank]

>> technically there is a difference ...

The circuit obtains Vr from a resistor divider with a equivalent resistance of 5K (R8//R9), filtered by the 47uF capacitor (C8).
This small circuit is "charged" by the input resistance R1 (470K, so this effect is totally negligible...) and by the current from R2 (4,7K).
We can note that:
1) R2 value is similar to the internal resistance of the RC filter realized by R8//R9+C8
2) C2 value is totally negligible compared to C8 value
3) the frequency corner of an RC filter composed by a 4,7-5K resistance and a 47uF capacitor is around 1 Hz (!)
we can say that in the audio frequency (from the AC point of view) Vr is like ground.

[ANDYEFFECT]

yes more for you all....    Melanhead , smank  , Eb7+9 ,

which the difference among TS with buffer and TS without buffer? 
 
I use key 3PDT in my project.

[smank]

Sincerely I've realized only TS copy with transistor buffers (I've used PCB available on the web without mods...).
Theoretically you can design the TS without the buffers, bBut it's possible that this buffers can warm slightly the sound (I don't know if we are able to understand this effect...).
You can try both the solution.
Consider that if you do some mods to the original circuit, probably their effect on the sound is more invasive than the buffers.

[johngreene]

hmmmm ... no the schematic is correct, I've built one and it sounds great.

Not sure technically why C2 is connected to Vr but the 10K after R4 doesn't need to be there as there is not dc blocking cap. I beleive Vr travels through from the other opamp stage.

I'm sure Jack will pipe in ....

Actually the tone control works differently without the 10k after R4. It is rather lopsided without it.

--john

[Melanhead]

oooopppssss .... was thinking of the one I built without the tone control .... 

[amz-fx]

I set up " AMZsonTS " yesterday, and I looked at two mistakes schematic. It helps if I am wrong. 
 
1) C2 connects the ground (the schema is for Vr) 
2) it lacked a 10k after R4 for Vr. 

There are no mistakes....

1) Vr is effectively ground for this purpose
2) the 10k makes no difference with the sound at all.

Best regards, Jack

[ANDYEFFECT]

I set up " AMZsonTS " yesterday, and I looked at two mistakes schematic. It helps if I am wrong. 
 
1) C2 connects the ground (the schema is for Vr) 
2) it lacked a 10k after R4 for Vr. 

There are no mistakes....

1) Vr is effectively ground for this purpose
2) the 10k makes no difference with the sound at all.

Best regards, Jack

thanks