DH Echo problems

[jrc4558]

Hey everybody!
For reference - http://www.generalguitargadgets.com/index.php?option=content&task=view&id=85&Itemid=113

I've assembled all the components and I get clean signal through P1... The delay channel (controlled by P2) however produces high pitched hiss and loud crackling noise. I checked the traces, nothig seems to be shorting, voltages are withi expected levels, the cirquit is powered with two 9V batteries...
I doubt about the RAM chip orientation. I assumed that pin one is indicated by a triangle printed on the top of the chip. Chips are from Smallbear. Thanks, Steve!

Has anybody here succesfully built this circuit or encountered relatively same problems? Need your help.

[Dean Hazelwanter]

Hi...

I'm not sure what brand of RAM you're using, so I'm not sure if the triangle is over pin 1. Is there a little notch in the center of one end, as in the 1st placement diagram on GGG?

I would check for shorts again - there is a trace that runs between 2 pads, between the RAM and delay chip that are close.

You can try using an audio probe at pins 2 and 4 of the delay chip (input and output respectively), but I'm guessing that there is a problem in the delay/RAM section, not the audio path. Check and recheck component values, traces etc etc etc. It's always the things that I know I've checked, that turn out to be the things that bite me in the butt!

[jrc4558]

Its the one from Steve at Smallbear, marked in two rows as follows:
row 1 - M41256PP 12B
row two - tiny triangle beside my 'supposed' pin one,
then WE34B  18686

On to checking for shorts! Thanks for your help!

[jrc4558]

Ok! Got it working! A question, however...
How was the fidelity of the repeats on your prototype? Mine are quite muddy and there's some hiss coming through, too. Would really appreciate your answer. Thank you.

[Mark Hammer]

I have happily built one that you can see right here: (the white sloped-front 4-knob thing below the orange pedal in the upper right.

The fidelity is NOT the greatest, but that's more the chip than Dean's design.  I inserted a couple of impromptu lowpass filters to trim unneeded treble from the delay and recirculation signals and it sounds decent.  Not a DL-4, but decent.  More treble, you say?  Yup, more treble.  Long echoes don't have to sound crisp.

As you can see, R8 (82k) runs along the side of the board. I simply split up that 82k value into a couple of series resistors that added up to the same value, and ran small caps from their junction to the ground connection on the edge of the board.  I forget the specific values, but whatever nails you 3khz-4.5khz bandwidth will work fine.  This also has the benefit of trimming progressively more treble off the successive repeats for a more natural sounding decay.

R6 (10k) can also be "subdivided" into a few smaller value resistors with caps to ground for lowpass filtering.  Here you can probably aim for something in the 5khz neighbourhood.  The crucial partis the regen loop, because, as you can see from the diagram, it is a wholly analog path that simply taps the output and feeds it back to the input for A/D conversion all over again.  Whatever quantizing error existed the first time gets committed all over again...and again...and again.  The lower the bandwidth on the recirculated signal, the less quantizing error and other audio crap accumulates.  Plus, whatever hiss there is in the digital path is also reduced.

[jrc4558]

Mark, I get a fit of Freudian castration anxiety every time I see this photograph of your arsenale...
Thanks for the tip though... I am currently moving into the delay's domain, the only thing holding back is the $(@&%^ Ring Frobnicator, which seems to be a curse/karma/indulgence of mine for the past several months...
So far I'm just looking for something that will give me a double-track kind of sound w/o excessive noise and, ideally, single 9V supply, although my rig can accomodate another bipolar-powered effect. I'm leaning towards the Rebote delay, but just wanted to give the DH delay a shot, since its nice its know your options. Next one will be the PT-80 delay, and after that I should have enough comparison do settle on the best sounding one.
My band has suddenly decided to become another one of those 'best-of-all-time-progressive-rock-bands-that-will-make-Gentle-Giant-sound-like-Rolling-Stones' kinda band, so I have to have this double track 70's sound in my rig, hehe...
Anyways, thanks for the info and make that picture grow! I adore people who box most of their DIY effects.