syn

Yamaha R100 analog in and out mods?
« on: September 11, 2020, 11:18:56 AM »
Hi

        I just got this vintage box, and thought it would be nice to upgrade / mod the analog part a bit.   First of all, is really +/-5V all that is needed - I was thinking of upping  the audio power rails to  +/- 15V  or  no need for that ? Then, I wanted to introduce balanced input and output  for getting it to interface smoother with my mixers balanced  connections and for the last to replace 4558 with OPA 1612 on both input and output .
Are Q108 and Q109 muting transistors, can I ditch those as well? I got quiet of a sonic improvement by ditching muting transistors from my vintage Emu-1820m  outputs.
Any ideas are most welcome. Shematic attached.
« Last Edit: September 11, 2020, 11:46:29 AM by syn »


syn

Re: Yamaha R100 analog in and out mods?
« Reply #1 on: September 12, 2020, 02:36:19 AM »
To balance the input I'm thinking  about  avoiding  the input stage as it is altogether. Than I'd use  THAT1246 (-6dB)   straight to the input level pot at r105 - c108 junction  (lift the c108 "input" leg and connect a wire from the THAT1246 output to it) .
Output would need another gain stage to bring  the level up to  +4dBu  (around 20db of gain is needed) .
Opinions?

JohnRoberts

Re: Yamaha R100 analog in and out mods?
« Reply #2 on: September 12, 2020, 09:46:26 AM »
Hi

        I just got this vintage box, and thought it would be nice to upgrade / mod the analog part a bit.   First of all, is really +/-5V all that is needed - I was thinking of upping  the audio power rails to  +/- 15V  or  no need for that ? Then, I wanted to introduce balanced input and output  for getting it to interface smoother with my mixers balanced  connections and for the last to replace 4558 with OPA 1612 on both input and output .
Replacing the 4558s with modern equivalents shouldn't hurt. You could reconfigure the input stage to be differential with a 3 circuit input connector. I wouldn't mess with 5V rails, it looks like a lot of the ICs are 5V, that is not the weakest link in that audio path.

Maybe drop down the value of the series output resistor lower than 1k. Try 100 ohm, or even 50 ohm, and use a similar value in the - output leg to impedance balance them using 3 circuit output jacks.
Quote

Are Q108 and Q109 muting transistors, can I ditch those as well? I got quiet of a sonic improvement by ditching muting transistors from my vintage Emu-1820m  outputs.
Any ideas are most welcome. Shematic attached.
Yup you can just bin the muting transistors... may get turn on/off clicks/pops/thumps. Those muting transistors are specifically designed for the application but can still add detectable distortion to large signal swings. Note the NPN mute transistors are operated backwards with the collector to ground, that delivers a smaller saturation voltages when muted.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

syn

Re: Yamaha R100 analog in and out mods?
« Reply #3 on: September 12, 2020, 01:38:44 PM »
Replacing the 4558s with modern equivalents shouldn't hurt. You could reconfigure the input stage to be differential with a 3 circuit input connector. I wouldn't mess with 5V rails, it looks like a lot of the ICs are 5V, that is not the weakest link in that audio path. 

Great, thanks a lot for this idea. Would this do the trick ?


syn

Re: Yamaha R100 analog in and out mods?
« Reply #4 on: September 12, 2020, 01:45:42 PM »

Maybe drop down the value of the series output resistor lower than 1k. Try 100 ohm, or even 50 ohm, and use a similar value in the - output leg to impedance balance them using 3 circuit output jacks.


That is great but I still need about 20db of gain at the output in order to reach +4dBu.

JohnRoberts

Re: Yamaha R100 analog in and out mods?
« Reply #5 on: September 12, 2020, 02:34:07 PM »
You could consider leaving it stock and building an external bump box to balance and level shift.

Back in the day there were commercial products for interfacing between +4 dBu pro gear and -10dBV semi-pro...  You might may find an old used one. Or roll your own.

JR 

Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.


 

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