Studying deep blue delay circuit. A few question want to ask.

[nguitar12]

Hi everyone recently I am studying the principle behind deep blue delay circuit. I have a couple questions want to ask.

1. I notice that the gain is make up by 2 at input buffer and turn down by 0.54 at output buffer What is the advantages doing this?
2. Regrading to the gain setting resistor. What is the different between high value couple (eg 180k/360k) and low value couple (eg 10k/20k)?
3. Are C16 and C20 cutting the high frequency of the signal. If so why to do this isn't that it will affect the guitar sound? If not what is their function?
4. What is the function of R6? Can it be omitted?

Thanks for your help.

[duck_arse]

the pt2399 makes lots of digital noise. if you put twice in clean, then halve it out, you also halve the noise made in the chip by half. so, less noise.

180k will be looking at a guitar, maybe, so you don't want to load the input too much. but the 10k/20k are being driven by the boofy output of the opamp, it doesn't care what you load it with. [?and lower value resistors equals lower thermal noise?]

the caps in the feedback loops are selected so as to be effective above the guitar usable freq range. work it out with 1/2*pi*R*C.

R6 will isolate the output of the opamp, in case it is short circuited by something. it can be omitted.

[bluebunny]

if you put twice in clean, then halve it out, you also halve the noise made in the chip by half. so, less noise.

That's a bloody good point, duck.  Hmmm...  "Bloody Good Noise Reduction".  Nope, that a cuss-word.  Let's drop an 'o'.  "Blody Noise Reduction".  Sounds daft.  How about an anagram?  I know: "Dolby Noise Reduction".  Nah, it'll never fly...   

(as you were...)

[duck_arse]

I don't think "dobly" is being used.

(no cussing!)

[bluebunny]

Wasn't he in Harry Potter?   

[Kennt82]

The highs being cut is part of this pedal's character. It's meant to emulate tape delays and have the 1st repeat  be "warm".  There is a project for a Wampler delay that's  very close, but with a tone control over that part.