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RETICON SAD1024 CHIP QUESTION


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9/6/2000 7:32 AM
friday
RETICON SAD1024 CHIP QUESTION
I am working with a Ross Stereo delay that has a constant high pitched whine in the background.  
 
There are 3 Reticon SAD1024's (socketed!)inside. Are they the likely culprits? or is this likely a byproduct of having digital/analog in the same box?
 
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9/6/2000 3:52 PM
Anders Westerberg

Is the pitch of the whine changing when you turn the delay time knob?  
Is there any trimmers inside? If there is, you can probably adjust them to get grid of the whine to some extent.
 
9/6/2000 4:02 PM
Jay Doyle

I would have to agree with Anders. It sounds like a feedthrough problem more than a specific problem with the BBDs.  
 
I, too, have a Ross Stereo Delay but without the whine, I would try marking the trimmers and then adjusting them to see if you can get rid of the whine.  
 
The pedal is still all analog, SAD1024 are analog delay chips, they "hand off" the signal between capacitors and MOSFETs at a rate determined by the clocking device. It may seem digital, but it is analog all the way.  
 
FWIW,  
 
Jay Doyle
 
9/6/2000 4:46 PM
CJ Landry

I have had to replace many SAD1024's and some of them whined. Adjusting pots did not help. I had 2 known good SAD1024's and I used the substitution technique to resolve the problem.  
 
CJ
 
9/6/2000 5:47 PM
Jay Doyle

Wow! Really? I guess you would know better than me, you do a lot more repairs than I do.  
 
Sorry for the bad advice friday.  
 
In case your next question was where to find a new or good SAD1024 chip, I thought that R.G. had some.  
 
Otherwise, there are a few vintage parts dealers on the net that I have seen that have them, they are expensive though, and unfortunately I lost the bookmarks.  
 
Your next choice is to try and find an older delay and cannibalize it for the chip. The Commande series MXR Time Delay holds one in a socket, the old DOD analog delay is the predecessor to the Ross so I assume that it too holds three of them. I try to scoop these up whenever I see them as they normally go for less than the chips are worth, even on ebay!  
 
Thanks for the clarification CJ, again friday, sorry for the bad advice.  
 
FWIW,  
 
Jay Doyle
 
9/6/2000 9:18 PM
CJ Landry

I too have given bad advice and that makes you human Jay.  
 
Incidently, the MXR Time Delay uses a SAD4096 which is a dual SAD1024 in one IC package. Your best price for SAD1024's is RG. He has the best price I have found for these chips. I very much appreciate him for that!!  
 
I think I still have a SAD1024 that squeals. I know I marked it with a big red marker hoping that I find a circuit configuration that squashes the whine. I guess if I got clever (not to mention the time) I could build a filter to shunt the whine to ground, however, I am not sure if the whine changes with the delay rate. Even more trickyer (New word <:-) )  
 
CJ
 
9/7/2000 3:52 AM
Mike Irwin

I haven't had the luxury of having a lot of SAD1024's to put in my circuits. Do these have a failure mode where the clock signal can't be nulled from the outputs? Most flanger/analog delay circuits just tie the last and 2nd last outputs directly together and hope for a good cancellation of clock signal (this is OK if the clock signal never gets any lower than ultrasonic in frequency). The more elaborate circuits use a trimpot on the outputs which can be adjusted for best null (sometimes two trimpots for a single SAD1024). I hope people aren't throwing away good SAD1024's when a clock null trimpot is all that may be required to tame the circuit.
 

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