MXR Delay Ebay boards

[blues123]

Hi Guys,

Anybody tried one of these:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=3768382328&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

Just wondered if they still have "the sound" with the change from the analogue to digital PT2399

[Melanhead]

Hi Guys,

Anybody tried one of these:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=3768382328&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

Just wondered if they still have "the sound" with the change from the analogue to digital PT2399

Hmmmm ... nope but would be interested in hearing the answer.

[Mark Hammer]

Just wondered if they still have "the sound" with the change from the analogue to digital PT2399

These boards have been discussed before.  In view of the dearth of replacement BBD delay chips for them, the use of a PT2399 seems like a reasonable approach to achieving the same delay time.

The thing to remember is that a lot (though not all) of what people associate with "warm analog sound" is really the filtering around the delay chip, and not the chip itself.  The filtering, in turn is intended to make up for the shortcomings of the BBD chip.  It's a bit like a woman swooning over the "sexy slouch" of a cowboy, when in fact the sexy slouch is a joint product of having been born with one leg shorter than the other and having busted a hip at a rodeo.  One person's flaw is a virtue is someone's eyes, I suppose.

In any event, the critical thing about whatever "tone" the old green MXR Analog Delay box had was its use of a tracking filter.  The filter used the same sort of switch-based system/design found in the MXR Envelope Filter, except in this case the master clock driving the switches was the same one driving the BBD chip.  So, as you increased the delay time by slowing down the clock, you also lowered the rolloff frequency of the filter.  In this way, the unit would adjust the tone of the delay signal in a manner proportional to the time delay selected, achieving the most usable frequency response for that delay setting.  Other units of that era (and since then) would pick one corner frequency for the filter and leave it at that.  Occasionally it would be something that kept clock whine at a blessed minimum at all delays but dulled things a bit too much at shortest delays.  Occasionally, it would be something that gave nice bright slapback delays, but let a little too much clock whine sneak through at the longest delays.  The MXR approach aimed to deliver the best at each end of the delay spectrum.

Why am I telling you this?  Because while the PT2399 is a good delay chip, and is easily coaxed to give decent sound, it likely does not work off the same clock as the filter system on the board (unless they've come up with some workaround).  I don't think it would be impossible to have a separate clock adjustment for the switched filter network, and in some respects it might even yield more tonal flexibility than the original had.  But will it necessarily sound *exactly* like the original in terms of how the filter tracks the delay time?  I strongly doubt it.  I'm not saying it will sound bad.  It might sound great.  But if your goal is to "nail" an original MXR Analog Delay pedal for cheap, this purchase will sidestep that.

[nero1985]

i built a Rebote Delay 2 and it works amazing, it distorts a little bit and sounds like the Eddie Van Halen's delay, and im really not too crazy about digital circuits but in this case its worth it!

[Dirk_Hendrik]

In any event, the critical thing about whatever "tone" the old green MXR Analog Delay box had was its use of a tracking filter.  The filter used the same sort of switch-based system/design found in the MXR Envelope Filter, except in this case the master clock driving the switches was the same one driving the BBD chip.  So, as you increased the delay time by slowing down the clock, you also lowered the rolloff frequency of the filter. 

I ran into this config in a Ross delay as well and wasn't exactly pleased with it. At max delay time the cutoff is at approx. 1 Khz which is really low. The request for that ross was to brighten it up. I declined since switched capacitor filtering is not a field in which I have much experience.

[Stompin Tom]

My friend has a ross delay, and I agree that it did strange things to the signal... I'm not exactly sure if it's related to the tracking filter, but I suspect it is. It cuts out a lot of the low end in the original signal, and the delays are pretty muddy! It sounds pretty good if you run it stereo with the delayed signal going to a different amp, but is pretty useless running it mono... step on it, and your signal is all gone.

[blues123]

Thanks guys and in particular Mark for all that valuable info. You have certainly given me a few things to consider.
If I do go ahead, I will let you know how it goes, as I do have access to the "real thing" for comparison - not mine unfortunately:(
Thanks again
Steve UK