Pioneer SR-101 Stereo Tube Spring Reverb Mod

[TromNek]

( I like you folks here at GroupDiy so I figured I would post this here first )

I recently got into modifying a stereo tube reel to reel (philips el3536) to use for a guitar amp. I love it and want to add a stereo spring reverb to it.
So I picked up a Pioneer SR-101 to mate with it.

I repaired the unit to work but I want to get a higher mix of the dry signal into to output.
What are your thoughts ?
Here's the schematic ( it's a little weird in that channel 1 dry goes to channel 2, I'm going to install a dpdt switch to change that ) .

For channel 1 input;
Reduce R27 to increase dry signal ?
Increase R19 or R21 to reduce wet/reverb signal ? ( the reverb signal is really too strong )
Combination the the above ?
Other thoughts ?
Am I too stupid to be attempt this ?


thanks,
TromNek

 

[rock soderstrom]

Am I too stupid to be attempt this ?

No, not at all.

This Spring Reverb is always pretty wet at the outputs from my point of view. As such, it is well suited to be looped into an aux path on a mixing console, for example.

If you want to use it in front of a guitar amp, you need a variable mixer stage per channel, see Fender 6G15. Maybe you have enough current reserves in the power supply to include a 12AU7 mixer stage for both channels? Or you rebuild the output stage, analogue to the 6G15.

Another idea is to loop the reverb in parallel, as is done in many Fender amps via a mix resistor that allows you to control the amount of reverb, see Fender Princeton Reverb for example.

I wonder what R27 and R28 are doing? Negative feedback over everything or is this really a wet/dry mixer? But why from the other channel, more choas for the reverb signal?

 

[TromNek]

First I want to experiment with it in it's intended use for home stereo as a first stage after a tuner or phono and before the the pre-amp and power amp of the receiver. Thus the desire to get a better mix of dry and wet.
So, I'll try something along the lines of the Princeton Reverb amp (thanks).

I wonder what R27 and R28 are doing? Negative feedback over everything or is this really a wet/dry mixer?

Pretty sure it's the wet/dry mixer. That's why I was thinking to decrease it's resistance value to increase the dry part of the mix.
Less voltage drop over R27 leaves more voltage going to the cathode of V4b.
Is that correct ?

But why from the other channel, more choas for the reverb signal?

That's what most people think. But I believe the design intent was a 'conceptual' idea that you hear the reverberation of the Right channel on the Left and visa-versa.
I plan to put in a dpdt switch so I can do same channel dry, opposite channel dry, or no dry signal at all.

This Spring Reverb is always pretty wet at the outputs from my point of view. As such, it is well suited to be looped into an aux path on a mixing console

Ultimately, this is kinda what I want to do with it. Again along the lines of the Princeton Reverb design.
I'll gut the mechanics out of my stereo tube reel to reel (philips el3536) I'm using as a guitar amp, to make room.
And wire this reverb unit into it.

I'm still trying to figure out where in the reel to reel signal chain to put it.
The switch network in those reel to reels is really hard to figure out and trace.

 

[Tubetec]

All you want is 100% wet signal out of the reverb and find a way of blending that back in with direct sound from the pickup on a seperate input .
The idea of using these devices for hifi died out long ago , my advice ,dont bother .

Post up the schematic of the tape deck so we can have a look ,
what speakers are you using ?
Your gonna want a decent pair of 8,10 or even 12 inch speakers if you want anything more than a bedroom practice amp .

 

[TromNek]

Your gonna want a decent pair of 8,10 or even 12 inch speakers if you want anything more than a bedroom practice amp

It's a single ended EL84 so only about 4 watts, using the stock speakers right now.
Mainly use it at home and mic it to record.
I've taken it to a couple open mics, they microphone into the PA (when I want to do stuff with stereo tremolo).

Here's a schematic of the tape deck and switch chart.
Right now I'm using if in PA mode (SK6 shifted left ) which disables the Treble Control and the Main Volume.
Guitar -> StereoTremolo (EH SuperPulsar) -> Microphone Inputs

I'd like advice on modding the RadioPhono inputs for guitar (so I could use the microphone inputs for microphones).



There is a Line Out (Linien-ausgg)
Note: "nur bei Aufnahme wirksam" (only effective for recording), those gain pots also work in PA mode

I think? I would hook the reverb unit up between points 14/114 and 16/116, right before the B5 gain stage.

 

[Tubetec]

Id say just get rid of all the components at the grid of B1 ,
try 1M resistor ,should work fine .

I guess yeah if your miking it up it could work in a live situation .

 

[TromNek]

Here's a schematic with the switches set to Record at 3.75ips
It's a lot easier to trace through this one.

 

[TromNek]

I uploaded a few pdfs to google drive

Service Chart has a nice easy walk through of the circuit in different operating modes.


Service Manual in german