Pioneer SR-60 Reverb - Modifications Help

[ilcaccillo]

Hello,
I have a Pioneer SR-60 unit and although it says "Reverberation Amplifier" it's actually a Delay, it uses a MN3008 BBD delay chip.




It would be great also to be able to change the Delay Time and the Feedback level.

here is the schematic for the unit:






https://i.imgur.com/JVhDN9V.jpg

The schematic is a bit confusing to me because of all the switching going on,
I need help from you guys.
How do you think I could implement a control the Delay feedback and change the Delay time even if Limited??

Thank you so much

[ilcaccillo]

This is the datasheet for the MN3008 Delay BBD chip:

[dmeek]

I'm just guessing a the resistor and pot values, they would be a good place to start

[ilcaccillo]

Thank you so much, i will try that out today and let you know.

[ilcaccillo]

Hello Dmeek,
I tried your suggestions and spend a little bit of time tweaking the values so that the Pot control ranges was nice,
here are the values after trying it out:





For the FEEDBACK, I liked a 51K resistor with a 200K Log pot in series, it gives a good range between few repeats and it goes into Oscillation in the full rotation.

On the DELAY TIME, this one is tricky.
The problem is with longer delay times there's a constant High Frequency whine pitch note that goes down in pitch and it's quite present.
I suspect that that high pitch note or noise is also there on the stock delay time but at an higher pitch above the hearing range.
Slowing down the delay brings that note into the audible range and it's quite irritating. (after the pot reaches around 70K)

Do you know any solution for this?

Thank you so much for your help, I had great fun today trying your suggestions

[dmeek]

The high pitched whine is the clock frequency. Unfortunately the only solution is to roll off the high end at the output which might leave you with a
3 KHz bandwidth at long delays. A sharp cutoff filter is best. 12dB/oct minumum, 24dB/oct or more would be better.

[ilcaccillo]

The high pitched whine is the clock frequency. Unfortunately the only solution is to roll off the high end at the output which might leave you with a
3 KHz bandwidth at long delays. A sharp cutoff filter is best. 12dB/oct minumum, 24dB/oct or more would be better.

Thank you, I guess it's fine, I will use it with faster speeds most of the time anyway. If I want to go slower I can EQ the FX return in my DAW.
I will use this for mixing music, and do a send from the DAW to the unit.
As the high pitch frequency it's stable after you set the slower time I can also you a notch filter on the return to the DAW to attenuate it.

Thank you so much for your input and help.

[ilcaccillo]

What mod would you advise to have a MIX pot, so I can have Completely Dry on one side and Fully wet on the other?

I can cut the L+R Dry signasl by lifting R41 and R42, but I've been thinking a MIX Pot might be more flexible.

Thanks