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Changing timing crystal in a behringer reverb pedal

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Changing timing crystal in a behringer reverb pedal

PostPosted: Fri Sep 28, 2018 8:02 pm
by BillB
I am getting a Behringer DR600 (remarkably cheap on the website of a large UK vendor recently taken over by a larger German vendor...)

Basic room/hall/plate/spring and modulated reverbs (no shimmer), but it sounds pretty good:
https://www.youtube.com/watch?v=YQX7RzIfl2Q

However, all the reverbs sound fairly short, so I thought a mod might be fun:
https://www.youtube.com/watch?v=AxdfiXXcEQ8

This guy changed the 10Mhz crystal for a 4Mhz crystal and got longer decay times (presumably 2.5 times longer!). He mentions, and I would expect, some degradation of the signal (especially density), but given the low starting cost, I thought it might be a fun experiment.

So the question, to those who know these things, is: would it be practical to connect a few crystals (say 4/8/10Mhz) via a switch, or would (short-ish) lengths of wire interfere with the operation or loading of the crystal?

And would it be OK to have one common lead to all 3 crystals and the switch selecting their other lead, or would some form of double-pole arrangement be better?

None of it is expensive, including the crystals, but it would be good to have an idea of likely success...

Thanks for your thoughts :geek:

Re: Changing timing crystal in a behringer reverb pedal

PostPosted: Fri Sep 28, 2018 9:15 pm
by Sam Spoons
A good few years ago I had the bright idea of using a cheap digital photo frame as a lyric display. It worked fine, I just scanned the lyrics in as jpegs and I could scroll through with the button on the side. So I tried attaching a foot switch via a mini jack socket in place of the membrane switch with no success, even using a few mm of wire to bridge the switch did not work. I may well be wrong but I assumed that because the switch was passing digital data even the short link was picking up enough RFI to bugger things up.

So, it's cheap and swapping the crystal should work but the switchable mod may not. I would have thought the crystal was controlling sampling frequency and the delay time is determined by the system memory? Reducing the sample rate may increase decay time but, as you say, at a much reduced bandwidth/quality.

Worth a try if your soldering skills are up to it, you can always stick the original crystal back in it as flog it on ebay......

Good luck :)

Re: Changing timing crystal in a behringer reverb pedal

PostPosted: Fri Sep 28, 2018 10:03 pm
by BillB
Sam Spoons wrote:Reducing the sample rate may increase decay time but, as you say, at a much reduced bandwidth/quality. Worth a try if your soldering skills are up to it, you can always stick the original crystal back in it as flog it on ebay......

Thanks, Sam. At £22 inc postage I'm willing to give it a go - and not much worried about recouping anything. The YT videos do suggest that it should work, but until you hear it for yourself, with your own kind of material, you don't really know - guitar swells are the worst possible input to judge a reverb character! As you suggest, it should be reversible provided the solder pads don't get messed up.

However, I am thinking of taking it a step further and desoldering all of the pots, and potentially doing the same with my EM600 'Echo Machine', then mounting them in a new box. These units have a good basic sound - but the knobs are teeny and frustrating. I would really like to get them into a rack with decent-sized knobs for tweaking - oo-er, missus - etc. May need a set of new pots though - not sure if the behringer pedal pots are panel-mountable. I think they are just designed to sit on the pedal PCB.

So if anybody has a redundant/dead old 1u rack unit, suitable for taking about 10 knobs, that they would sell for £10-15, please let me know! I have some old rack gear which is nothing special (Alesis 3630, Zoom1201), but it works as intended, and I can't bring myself to gut it. :geek:

Re: Changing timing crystal in a behringer reverb pedal

PostPosted: Fri Sep 28, 2018 10:17 pm
by Folderol
Before doing this, try to find out the characteristics of the crystal. In particular its internal capacitance. This is usually part of the oscillator circuit itself and a radically different value might not oscillate at all. Ideally it should also be the same physical size, so it takes the same or a similar amount of energy to drive it.

There are also three legged types that are called resonators, they have two built in caps along with the capacitance of the 'crystal' producing the required overal delta form.

Finally, don't try switches, even 20mm of lead length can make the whole thing quite unstable. You may be able to find PCB sockets with the right pin spacing - or butcher a chip socket.

Re: Changing timing crystal in a behringer reverb pedal

PostPosted: Fri Sep 28, 2018 10:48 pm
by Wonks
Your sampling rate and therefore bandwidth will also suffer accordingly. I'm not sure whether that the anti-alias filter would work correctly as a result, or whether it too would be affected by the clock change. Normal bandwidth is just over 20kHz, so expect around 8kHz with a 4 MHz crystal.

I notice that the impedance with a single jack input is only 250k ohms. Not a pedal you'd want without a buffered pedal before it.

Re: Changing timing crystal in a behringer reverb pedal

PostPosted: Sat Sep 29, 2018 9:48 am
by BillB
Thank you both. I am expecting sound degradation, Wonks, but think it could be interesting.

Folderol wrote:Finally, don't try switches, even 20mm of lead length can make the whole thing quite unstable. You may be able to find PCB sockets with the right pin spacing - or butcher a chip socket.

Ok, good advice, Folderol, especially socketing the crystal(s). I noticed that the crystals on CPC had varying internal capacitiance, but the most common was 30pf. So on the basis that the guy on youtube’s just worked, I thought I would go with the law of averages and pick 30pf. Might the value be printed on the pedal’s crystal case, or would it only show the frequency?

Re: Changing timing crystal in a behringer reverb pedal

PostPosted: Sat Sep 29, 2018 10:25 am
by Sam Spoons
It will almost certainly have a component number which will help you find a data sheet.