Vero Layout Help

[comfortably_numb]

I designed this distortion based on the distortion+ with much help from this forum.  The layout I created matches the following schematic with some adjustments in values, plus power filtering and protection. 

I've double checked my layout (except for pot wiring) and the only problem I see is (potentially) with the placement of R6.  On the schematic, the signal goes through the feedback loop and on through C6.  This mean that the output of the opamp is connected to C5 and R6, but that C6 is connected only to C5.

Is there a problem with the way I've laid it out?  Will R6 interact with C6, or is this okay?  I've found a very simple way to adjust this on the layout if need be, but I wanted to make sure that it was necessary first.  I've seen many layouts where things seemed to be connected in slightly different ways than they are shown on the schematic, and I assume this means that some things are important and some things are not.

So is this important or not?

[burnt fingers]

I'm not the expert here but I think that cap should be paralel witht the resistor and make the same connections as the reistor.

Scott

[Gilles C]

First, I would suggest you to identify the parts on the schematic to make it easier to work with.  Having 2 or 3 resistors or capacitors with the same value would make it very easy to make a mistake, and even harder to debug.

Second, I'm quite sure C5 should be always connected  between the pins 2 and 6 of the IC when used because of the job it does. (it is a feedback capacitor to reduce the gain to unity at DC). And the other pot/resistors and cap are used for the gain and some freq shaping.

I will work the way you connected it, but then, something could be different. Try to follow the schematic the first time you try a circuit.

Please correct me someone if I'm wrong...

Gilles

[DuncanM]

C5 should be always connected  between the pins 2 and 6 of the IC when used because of the job it does. (it is a feedback capacitor to reduce the gain to unity at DC).

I may be wrong but I thought it was there to get rid of RF by offering a low impedance feedback path to high frequencies...

Anyhow, I reckon the circuit should work but at maximum gain with a 22pF cap it will be rolling off at 5.5kHz (500+820k) and at minimum gain it will be rolling off at 8.8kHz (820k only).
Going across the 820k resistor would avoid the frequency shifting and using a 10pF as per the drawing would up the rolloff frequency to 19.4kHz (if that really bothers you....).

The circuit as drawn with the frequency shift might be interesting though.

[DuncanM]

I spotted an error - your +9V line goes to pin 6 of the IC on the layout and it goes to pin 7 on the drawing....

[Gilles C]

C5 should be always connected  between the pins 2 and 6 of the IC when used because of the job it does. (it is a feedback capacitor to reduce the gain to unity at DC).

I may be wrong but I thought it was there to get rid of RF by offering a low impedance feedback path to high frequencies...

Anyhow, I reckon the circuit should work but at maximum gain with a 22pF cap it will be rolling off at 5.5kHz (500+820k) and at minimum gain it will be rolling off at 8.8kHz (820k only).
Going across the 820k resistor would avoid the frequency shifting and using a 10pF as per the drawing would up the rolloff frequency to 19.4kHz (if that really bothers you....).

The circuit as drawn with the frequency shift might be interesting though.

Well, I wanted to add that it was also making the opamp more stable, but you already added a good point there. Sometimes, I do things without remembering exactly why ...  I must be getting old

[comfortably_numb]

The feeback cap IS in parallel with the 820k resistor, only through the wiper of the 500k pot.  So the feedback resistor is the sum of the 820k resistor and half (sort of) of the drive control.  This way less resistance change is needed for gain change, which means less low end loss at maximum gain.

Thanks for pointing out the +9V power error Duncan.  That would have been perplexing for a while! 

Also, I'm planning on auditioning the 22pf and the 10pF to see which I prefer.  The 22pF was a suggestion by Mark Hammer, who seems to be well respected here.  Thought I'd at least give it a shot.  I DO want the circuit to roll out some high end with additional gain, as additional gain means additional hiss.  However, I do have a tone control post diodes, so that may be sufficient.

Back to my original question however - How will the feedback resistor R6 interact with the output capacitor C6 as is in this layout (ignoring the error to opamp powersupply)?

Thanks everyone for your input!