SR-101 Pioneer Spring Reverb - diyAudio
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Old 16th January 2009, 02:14 AM   #1
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Default SR-101 Pioneer Spring Reverb

Okay - so I bought this thing on eBay listed as broken for $10 + $15 shipping from this really really nice guy - he sent me a broken Altec 1589B preamp with it for free without even telling me about it!

I'm a beginner in audio electronics, I have built a number of pedals and hundreds of low voltage circuitry of all sorts. I decided I want to build a tube amp in the near future, and then I found the Sr-101 on eBay - it seemed like a perfect thing to get. Cheap, introduction to tube electronics, 60's vintage effect!!!, and it's been noted for a great reverb, and amazing tube sound with reverb bypassed.

Annnyways. I got it, and obsessed over it for a day - first thing I noticed was a broken connection to one of the reverb tanks. I fixed it immediately. Then I tried it out - the reverb didnt seem to work on either channel. So I took it apart and spent a day or so checking internal connections, analyzing the schematic, etc. Then I realized that the schematic I found online has one huge difference from the one in the manual for the SR-101.

Since it is a stereo reverb unit for stereo systems, it is meant to be hooked up with a L/R input, going to L/R outputs. Wellll, apparently they decided to make it so the reverb sound from ONE input mixes with the OTHER signals clean output, and the reverb from the OTHER signal goes to the FIRST channel clean output. So it was working perfectly all along. And I wasted an entire day to realize it XD

The schematic is below - the highlighted wires are the ones I was talking about. On the schematic I found online (before I knew i was getting the manual with the unit) the red wire goes to the same final triode as the clean signal does. On the actual unit, however, they go criss cross like you can see...


So here's my problem. I figured, hey, thats easy to fix for mono, just switch the two highlighted wires and presto you got two seperately driven/modulated signal paths. Buuuut hey it didnt work. At all. Both channels would no longer output either the clean signal or the reverb.

Can someone enlighten me as to why this doesnt work? And perhaps point me in the right direction towards rewiring it for mono input/output?

Thanks alot!

And I HAVE to mention, this unit sounds absolutely DELICIOUS. It really brings out the mids and can make ANY amp sound utterly amazing. The reverb is verryy nice, but it needs quite a bit of space between it ad the amp to prevent feedback. I'm pretty much in love with this thing.
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Old 16th January 2009, 05:26 AM   #2
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Probably should have mentioned that I'm using this for guitar!

Is there no edit button on these forums?
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Old 18th January 2009, 11:26 PM   #3
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Old 21st January 2009, 12:23 AM   #4
jjman is offline jjman  United States
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Looks to me that the paths you're pointing out use some of each channels input signal to reduce the output of the other channel. This since the signal is being fed into the cathode of the other side which would be out of phase assuming both signals are identical. On the other hand, I guess this is also/actually negative feedback from the output of one channel back to the input of the other. So perhaps this is a way of expanding the stereo effect by reducing frequencies that are common to both channels. A "wide" effect in addition to the reverb ?

For mono, maybe just use one side? Not using the other side will prevent the negative feedback and all should be ok ?
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Old 21st January 2009, 06:39 AM   #5
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Thanks so much for your reply -

However, it works now. I really don't have any idea what was wrong with it. Today I decided to just try the mod I made before again and see what happens (a whim) and... it worked. I am 100% sure I made the same change in connection the first time around - It's only two wires and I could see where I had soldered them!

Whatever - I suppose it's just one of those unexplainable things.

Now I got to figure out where to stick a couple o' 1/4" jacks on it...
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Old 22nd January 2009, 02:23 AM   #6
JandG is offline JandG  United States
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Location: Washington State
I am intrested in this set up. I bought the JVC version of the pioneer long agao, but never got it working because of no schematic & yes I want it for guitar. What other effects are you running ahead of your amp & what amp are you running..? I think I will look for the reverb you are now useing. I am ctually very intrested in any other comments you may have on this device. I do NOT like digital device for electric guitar.
J & G
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Old 25th January 2009, 05:31 AM   #7
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I've never heard of the JVC unit your describing, and I couldnt really find any info about it online either... Is it pretty much the same as the SR-101?

Do you have any idea whatsoever what could be wrong with it? I think I saw in my googling that it was tube... You sure all the tubes are still good, and the tanks are intact (transducer wires, etc), caps don't need replacement...

As for my setup, I have only really been using it straight into the amplifier, (mostly my thrift store $25 Fender 85!), just for testing it as I messed with it. It sounds perfect just by itself...

I would definitely look for the SR-101. It's a simple unit overall and easy to troubleshoot, and the modification I made to fix the weird channels was a no-brainer (provided you don't have the stupid unexplainable problem I had) Having just added the 1/4" jacks today and put it back together, I was playing with it all day today and I even tried it as is was meant to be used, with a stereo. Couldnt really understand why you'd stick a reverb unit on your stereo system but as I did it I realized it is quite entertaining and can make some songs sound really atmospheric and interesting!

Not exactly something I would take to a gig, however, unless you were just using for the tube sound. If you did use it for reverb, you'd have to be real careful with it - it can feedback very easily especially at high volumes and is very sensitive (SPROIIINGGGG) to movement. For home & studio, it is wonderful.

No digital for me, either! I have never heard a single digital verb (or any effect, for that matter) that has appealed to me in the slightest. Amen

Good luck with the JVC, please tell me how you like that unit! Perhaps you could post a pic too, im interested to see what it looks like!
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Old 25th January 2009, 07:09 PM   #8
JandG is offline JandG  United States
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I will post pic of the JVC Nivico later on. I been searching for a 101 after seeing your post & will keep looking for 1 to come up. The JVC is in a condition, that I really need a schematic I think. Someone has been in there, namely me back when I thought I new what I was doing & definately did not..*s* Now as is well & could do it easily if not boched up. I have a Valco made Airline w/ leather handle & all that needs a reverb front end. I love this thing & payed only 20.00 for it & only had to recap PS. When this Airline is dimed & pushed a little w/ Xotic BB pre pedal,..only pedal I own for a reason.. most suck IMO.. this one definately does not if used properly, been thru a bazzlion of them ...I suspect the only digital reverb that would make me happy would be a 2k + rack mount by that famouse reverb company, since that is not going to happen ever, I must go the next best & do real spring tube driven, My Soldano has tube driven spring reverb & it is special also, but I tell ya. I would probally sell the Soldano before the little Airline. I love it. Tone like no other. I am a SG guy that has only 2. a SG standard & P-90 jr, & maore strats than I will ever need & they do not get played much. The SG was made for me & perfit fit allround. My LP's hang collecting dust as I love the way they sound, but my forearm hates them & allways will. So no go. I have noticed the little vinatge SE amps have hit the roof on prices & no longer can good Airlines & such be had so cheap,..maybe I'll find another at garge sell or something. Let me know anything else about how the little sr-101 does for you on a simple amp. Is it over the top ...? or does it controlable.. I had a old Danelectro reverb that was way over the top & only good for specialized music, ..very specialized.
Thanks J & G
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Old 25th January 2009, 07:42 PM   #9
Join Date: Oct 2005
Location: Central Florida
That reverb looks quite like the type gibson used back in the sixties. The tanks are higher impedence than the fenders and last time I looked were still available. You could cook up a reverb unit for the road pretty easily with pretty simple circuitry. I built several units back in the nineties, great airy clean sound, totally different than the fender sound. Look up the ampeg v4, I think it also used a similar circuit.
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Old 27th January 2009, 04:05 AM   #10
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The impedances on the tanks in the SR-101 are 1.5k and 2.2k. You can get accutronics replacements with the same specs if they need replacing, but the place they go in is quite narrow - you might have to chop off the tabs at the bottom of the tanks if you were to mount them in the SR-101.

The reverb can definitely be over the top, and is on most of the dial except for the first 20 degrees or so - in that range, it is wonderful. It can go from real short, atmospheric reverb to a wall of sound - I was pretty surprised at the range it has. It's quite controllable. it definitely sounds it's best with it giving just a slight amount of reverb to flesh out your sound. There's also the option of using a different tank for each channel if your willing to spend the money - then you could get two very different ranges and sounds from the same unit. Maybe even mount a switch on the front to switch between...? (I may even want to do that, now that I think of it... my second channel tank ain't sounding near as good as the other anyways...)

I have not really heard much about airline amps before, despite absolutely adoring their guitars. I wish I could find something like that! My fender 85 isn't the greatest (in fact, it sucks pretty bad ), but it does the job. I usually play bass, so my guitar equipment is kind of **** but I plan on fixing that real soon - Getting together the parts to build a 60's style VOX AC30 with a couple o' mods. I can't wait to get that baby running! Also working on a VOX starstream-style teardrop guitar. (im a sucker for VOX) I made a vow to myself to never buy new equipment - either gonna get lucky with something vintage or make it myself!

Like Bill said, theres also the option of making your own - theres tons of simple solid state spring reverb unit schematics on the net (like this one), as well as tube (though more difficult & costly to build).
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