[sdiy] Rising Realsitic Electronic Reverb prices and the urgetomodify...

Mon Apr 28 13:44:08 CEST 2008

Another quick note on these, the "Stereo Synthesizer" is an elegant 2-stage 
notch filter. If you use 1% or 2% tolerance caps & trimmers in these notch 
filters, you can make the notches really sharp. And if you have two units 
you can make those notches come at 4 different frequencies (along with being 
able to have two different delays on the L-R "pseudo-surround" channels, 
even making one R-L if you wanted - only the '78s had these ouputs though - 
the '77 only had the sound field enhancer, which is pretty cool too, 
particularly if you're listening to an "overly stereo" album mix...)

I wish the LM1894 had caught on much more in other applications so that they 
would be more ubiquitous.
I'm still trying to make this group into converts over the compander system: 
you can run a small signal into the BBD input and add all the gain you want 
after the noise reduction. You have to use the input sound to control the 
filter via the sidechain (and you have to slam the gain on the sidechain if 
you don't use the summing amp) - but that's not too far from the same 
disciplines involved in complicated compressor/expander systems anyway.

Still, kudos to Paul Schreiber for convincing Tandy to go for a chip that 
needed licensing to use.

Seinfeld,
Anthony

>> Did you also design the Radio Shack Stereo Synthesizer unit?
>
> Wait. Do you mean the Archer Video Sound Processor? I buy those all the 
> time on eBay. I use every part. I even have TWO heavilly modded (of 
> course) units in actual use in a home theatre system ('78A's: the best 
> version for actual use, although the '77 has it's merits - like a full 
> steel chassis that works great for tube amps and a Reticon RD5106 and a 
> handful of 4136's and an LM1894 DNR chip, etc. etc...) and I have a 
> Pioneer receiver that has Dolby Prologic amongst other surround options 
> (because I'm still too poor for a full fledged 5.1 or 6.1 system...). It's 
> super-tweakable for a dork like me who instead of 2 or 4 good speakers has 
> 8 middling ones and a bunch of chip amps from car stereos. (Soone to have 
> a tube mono-block for my center channel and then maybe a stereo tube amp 
> blah blah blah...)
>
> I usually pass on the '78-NON-A's because they don't have the cool 
> JRC4558DD's (that's right TWO D's!) and the PCB is majorly kludged - 
> didn't think the grounding through ahead of time did we - with 2 DIFFERENT 
> BBD clocks??? Maybe if the price is super low. Good for an MN3007 and an 
> MN3006. The '78 was screaming for a redesign and I'm pretty sure that's 
> what the '78A is. So I buy those and the '77's.
>
> Counting the BBD chips I have it looks like I've gotten 8 or 9 of the 
> '78's in whatever incarnation and 3 '77's. Sometimes they go for a lot and 
> sometimes they don't. I always hoped I could keep 'em a secret so that 
> nobody would buy 'em, but they do anyways. I mean I get email 
> notifications and everything when one pops up on eBay. MN3011's too. 
> That's how I got two for $0.03. Dammit I just can't stop gloating about 
> that. Does it make you sick? What makes me sick is that since I have two, 
> my designs for them always end up totally Byzantine: a complete modular 
> synth just to run two brother-trucking multi-tapped BBD's!
>
> Did Radio Shack ever have a unit that used MN3011's? Or MN3005's? Or even 
> MN3205's for that matter???
> And why the hell didn't Pansonic make an 8-pin version of the MN3004??? 
> (Because I want to try replacing the MN3009's in my Roland MKS-50 and I 
> think MN3007's might be too big, but maybe not... maybe if I jacked up the 
> clock speeds I could get slide-whistle to go away?)
>
> Frasier,
> Anthony
>
>
>> Cheers,
>> Jeff
>>
>> -----Original Message-----
>>>From: Paul Schreiber <pschreiber at sbcglobal.net>
>>>Sent: Apr 22, 2008 9:37 PM
>>>To: anthony <aankrom at bluemarble.net>, Synth-diy at dropmix.xs4all.nl
>>>Subject: Re: [sdiy] Rising "Realsitic Electronic Reverb" prices and the 
>>>urge tomodify...
>>>
>>>Jeez, I designed this thing in 1980 and it won't die :)
>>>
>>>Paul S.
>>>
>>>----- Original Message ----- 
>>>From: "anthony" <aankrom at bluemarble.net>
>>>To: <Synth-diy at dropmix.xs4all.nl>
>>>Sent: Monday, April 21, 2008 1:13 PM
>>>Subject: [sdiy] Rising "Realsitic Electronic Reverb" prices and the urge
>>>tomodify...
>>>
>>>
>>>> Hi guys,
>>>>
>>>> So I have one Realistic Electronic Reverb: the greatest effect to use 
>>>> for
>>>> not quite what it was intended for. This booger is a great noisemaker 
>>>> and
>>>> lots of fun with it's slider controls. It's even better with a few 
>>>> tweaks
>>>> to the circuit: more gain and high-end roll-off to the regen path, 
>>>> 471pF
>>>> polytsyrene caps in place of the ceramic ones, JRC4558DD op amps in 
>>>> place
>>>> of the AN6550's, socket for the timing cap to play with different 
>>>> values,
>>>> adding 0.1 uF bypass caps here and there, and the latest greatest mod:
>>>> popping in a BL3208A (normal 8-pin!) from Small Bear and WOW! I've 
>>>> thought
>>>> about wiring 2 or 3 in series, the BL3208A being something like $3.75 
>>>> in
>>>> price. Next planned mod is making the "DEPTH" control into a true 
>>>> wet/dry
>>>> crossfader, which is a non-trivial task, but not impossible: I think a 
>>>> 1
>>>> uf cap and a couple 100kOhm resistors to put the bias in the right 
>>>> place
>>>> again and cutting the traces on the PCB and rewiring accordingly.
>>>>
>>>> SO I've been trying to buy another one on eBay for what I got my first 
>>>> one
>>>> for ($12.00) and it's been a daunting task. People are catching on to 
>>>> how
>>>> cool these are.
>>>>
>>>> I'm not one to care much for collectability in gear because I like to 
>>>> be
>>>> able to use my gear to the fullest. But I'm planning some more mods 
>>>> that
>>>> will actuall involve cutting into the unit and I'm beginning to wonder
>>>> whether I should. I wanted to add a DP3T selector switch to select 
>>>> between
>>>> various timing caps (if I can just find a good place on the front for a
>>>> toggle switch to go...), and adding some brass body contacts to bring 
>>>> it
>>>> (sort of) into the realm of circuit bending. I must admit that I don't
>>>> actually hold to the philosphy of circuit bending although I enjoy 
>>>> hearing
>>>> some of the results. I don't think wiring various contacts and 
>>>> capacitors
>>>> to the timing cap connections could be considered circuit bending in 
>>>> its
>>>> true spirit because they are not random bends, but carefully thought 
>>>> out
>>>> connections. Putting your fingers across the timing cap terminals is 
>>>> very
>>>> fun: it depends on the pressure exerted so it has a playability factor 
>>>> to
>>>> it: you can quickly (or slowly) descend into the realm of 2 second 
>>>> delays
>>>> and back again. With the increased number of stages in the BL3208A, 
>>>> it's
>>>> even better: repeats just go on and on without sounding like an
>>>> oscillation, but it'll oscillate too - and how!
>>>>
>>>> So I'm wondering: should I do it? I mean even when they're going at $40 
>>>> on
>>>> eBay, it's not like I'm talking about circuit bending an Ibanez FL9 or
>>>> something.
>>>>
>>>> Also, if anyone has DONE the wet/dry crossfade mod and would like to
>>>> share, I'd appreciate that a lot. Thanx...
>>>>
>>>>
>>>> Cheers,
>>>> Anthony
>>>>
>>>> _______________________________________________
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>>>> Synth-diy at dropmix.xs4all.nl
>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>
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