AD3208 delay trimpots+o-scope

[newbie builder]

My AD3208 delay from GGG is done (using their PCBs and the ICs from the group buy here on DIYstomp) and working, all I need to do is find the sweetspot on the trimpots. I've got an o-scope and signal generator, but it looks like GGG's new website won't come up on this computer so I don't have the text needed to see how I should go about setting everything up (i.e. what kind of signal to send, where to measure from, etc). So if anybody has some advice on working with a scope on delay pedals, it'd be much appreciated.
Thanks!

[markm]

I set mine up by "ear"......I trust what my ears hear!! 
I may have it saved somewhere in my computer, if GGG isn't up by this evening, I'll try and get it to you -or-
If the circuit-sheriff doesn't mind, I could probably post it here......temporarily of course! 

[newbie builder]

I trust my ears too, but no matter how I've been setting those damn things I'm still getting some distortion. Maybe I'll try some new chips in there (since I've now got MORE than plenty....I ordered thinking that about 40% would be good based on comments made by Analog Mike and Keith of BYOC about the first runs of the chips, but they sorted out those issues so now I've got way more than enough) and just tweek it some more. Just feel like I should be putting the o-scope I have to use since it's not too often I have a legitimate reason to use it!

[rmo]

From GGG, via google cache page:

Trim Pots and Circuit Checkout

Looking at the PCB layout, you will note there are 5 trim pots. What are they for?

The 500K trim pot near the top of the PCB adjust the maximum clock speed. If you have an oscilloscope, set it so that 10 kHz is the maximum clock speed. If no scope is available, set it to its midpoint and listen for clock noise in the repeats when set to maximum delay. If there is any, adjust the trim pot for a faster clock (shorter maximum delay) speed until it is no longer audible.

The other 4 trimmers (all 10K) adjust each BBD audio output balance and bias voltage. Looking at the PCB and viewing left to right, the trim pots are:

BBD2 Balance--BBD2 Bias---BBD1 Balance?BBD1 Bias

If an oscilloscope is available, the trimmers can be set exactly for the lowest distortion. Start at the first BBD, use a 1 Vrms sine wave test signal, and adjust the first BBD?s bias and balance for the best signal to the input of the 2nd BBD. Then repeat the process checking the output of 2nd BBD.

For most people I am guessing that no scope will be available, so in that case set both balance trimmers to their midpoint, and also set both bias trimmers to their midpoint. At this point, hopefully the bias is close enough that the delay signal will pass. If not try moving both up, then both down, the one up and one down, then the opposite, and some combination should allow the delay line to work. Once bias setting are found that produce delay, set each bias to the midpoint of the range that still allows the delay signal to pass. If you experiment you will note that too high and the delay stops, also too low and the delay stops.

[newbie builder]

Exactly what I was looking for, thanks! I'll have to give it all a try later today.

[coxter]

One question. I am using Visual Analyser as my scope, it works pretty fine.

When in the circuit do I touch with the probe to set the trimpots?

When i set the trims by touching pins 3 and 4 on the BBD to get a clean sine wave
but it sound like crap when combine together (as an effect), ie blatty farty delay
Maybe cos its not a real scope, its Visual Analyser...

So my guess is that it wont bias right with my scope so i used my ears instead.
I get a reasonably clean delay sound. But it just distorts TOO EASILY, I can't stand it...
No matter where I set it its just distorts when I play hard. And it distorts when I play low strings
even if i pick lightly, Low freqs just distorts the repeats

Can anyone offer some help? Or correct me if i'm doing anything wrong with the scope

[coxter]

Bump! really need help on this..

[coxter]

nobody can help?

[Paul Perry (Frostwave)]

BBDs in general don't have a very wide operating range.
You have to have enough gain to get above the noise - but then overloading is likely.
Notice how many commercial BBD applications have NE571 companders or similar.

[coxter]

Opps, so sorry, I didn't spell right...

i wanted to ask for where on the board do I touch my scope with to get a proper reading?
Because it sounds crappy with I set the bias with my scope touching pins 3 and 4


I know about the companding issue. is there any way to set the compander to "compress" harder?