Tube Amps / Music Electronics
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|4/17/1998 12:38 PM|
||electro harmonix The Clone Theory- Help|
This pedal (did) chorus, flange and vib. It was sitting around for a while without use. My biggest complaint was the 60 cycle hum. Now that it doesn't work at all does anyone have any suggestions on the problem or a place where I can get a schematic? When you plug it in and turn the volume up on the amp the effects are heard in the background, but no output sound. I've checked the likely, solder joints and connections with no sucess. It is a clone does anyone know what it is copied after?
Thanx for any help mark g
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|4/19/1998 6:31 PM|
Any time you have an older analog time-delay device, the first place to check after looking over the solder joints, is the trim pots. As has been mentioned in this forum numerous times (a testament to the truth of what I'm saying), the trimpots on the inputs and outputs of delay-line chips need to be set just right, or else nothing comes out, and often these things drift over time.
There are usually two trim pots. The first sets the bias level of the signal going in to the chip. Bucket-brigade device need to receive a signal "riding" a certain DC level or else they can't do their job. At their heart, BBD's are simply a sequence of teensy capacitors, with FET's connecting them. A clock alternates between making some FET's conductors and others insulators, so that the charge in the capacitor gets transferred to the next one in line. If the charge to transfer is too small, or gets held for too long, there is simply nothing left over to transfer. This is why (inoring bandwidth issues), BBD's are limited in the length of delay they can be used to produce, have such mediocre signal-to-noise specs, and need the bias voltage. If it's off, you get nada.
The second trimpot is a balance control. Many (though not all, as far as I know) BBD's can be configured as two parallel devices. So, the Reticon SAD-1024 is configured as two parallel 512-stage devices (maybe one is 511 stages, but we're splitting hairs here). When run in parallel mode, any audible clock signal can be balanced out by combining these two "channels" at the output, since the clock signals are out of phase, and consequently cancel each other out. This removes some of the noise and grit from the signal. It is the less critical of the two trimpots, and many manufacturers will simply stick in two equivalent summing resistors to substitute for a trimpot, living with the consequences of imperfectly matched parallel signals. If the second trimpot is absent, and you're fussy about noise, you can always wire up a trim pot in place of the two summing resistors.
How do you know when the trimpots are set right? The easiest way is to simply stick in as decent a signal as you can into the device, and gently rotate the bias trimpot until you get the clearest signal coming through. You should hear it change from being absent, to VERY iffy and distorted, to mildly distorted, to clean, and back through the cycle as you continue to rotate the trimpot. Most people advise setting it to the midpoint, for starters, and tweaking a bit to the right and left to see how it responds. If you can send the effect output to an amplifier you can listen to through headphones, that will probably sharpen the accuracy of your by-ear adjustment.
I hope this restores your box to its glory.
|4/19/1998 7:36 PM|
I gave the trim pots a little twist. I do hear a change in the noise ratio but with different setting I still haven't come up with any sound from the input signal. Thanks for the pot info, if I get a signal I will have a good idea on how to adjust it and clean up the output.
|4/20/1998 2:35 PM|
The "clone" aspect of the name simply referred to the idea that a chorus involves the illusion of several identical copies of the original signal. I haven't seen the schematic, but I do believe it is an SAD-1024 based device (correct?) in a "Small Stone" style box, with one pot and one slider switch. I have old ads from the early 80's showing it with a price of $50, give or take a few bucks.
As with most EH delay-line devices, there is a lot more in the way of control possible than is provided for by the panel-mounted controls. Thomas Henry (Jack Orman's collaborator, who I'm surprised has never visited this site in any obvious way. Tom's a sharp cookie.) had a very nice article back in 1979 or 80 in DEVICE, on modifying the Deluxe Electric Mistress by bringing some of the trimpots up to panel-mount pots for better control. I suspect your Clone Theory has a single speed control and a colour switch (correct?). On the board, however, is the potential for balancing out dry and wet signal, providing variable resonance, changing the sweep depth and sweep range (i.e., begin/end delay-time).
Your indication that altering the trim-pot produces a change inn what you hear, could be seen as a good sign. If it isn't diagnostic, then you may need to consider replacing the BBD. RG Keen has SAD-1024's, and the Matsushita/Panasonic chips (MN3007, 3027, 3005, etc.) can be gotten from a variety of major supply houses.
What happened with the hum you describe? Did it go away? Is it still there? Does the clone theory use batteries? Does it have a compander chip (NE570 or 571) in it?
|4/20/1998 8:54 PM|
The clone theory does 3 functions, chorus, flange and vibrato. Outboard it has a bypass switch and one dpdt switch which changes between the chorus/flange voicing. there are 3 pots: 1st is from chorus/flange to vibrato (color), 2nd is rate, and 3rd is depth. It is AC only-no battery.
As for the hum, it's a problem that the AC is not filtered as good as it could be (like a bad wallwart). It does have a MN3007 chip, CD4047BE RCA927, MC1458P, and RC4558N CO24. If one of these chips were bad, would I still here the effect in the background? When you change the pots (outboard) You can hear the effect changing (depth,rate and color) basically the pedal noise while sitting idle. I have seen a lot of EH schematics around but none for the clone theory. I haven't had alot of spare time yet to dig deeper but it looks like I'll have to. You've given me a lot of good info so far and I've got a better understanding of the pedal.
|4/21/1998 6:49 AM|
I have worked on a couple of these and the one I had used a SAD1024 for a BBD.
60 cycle hum could be lots of things. Sounds more like DC at the output jacks instead of 60 cycle hum.
Try touching all of the opamps and see if any of them are hot. If they are replace it. If they are not, it is going to be difficult to troubleshoot without a scope. Ron Neely has schemos for this pedal and for a few bucks he could send one to you.
|4/21/1998 2:54 PM|
Thanks Guys for the info
I found Ron Neely's web site and I'm sending off a email to him for some info and availablity of a schematic of the clone theory.
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