Modifying Tascam 488 with post-fader direct outs
« on: May 02, 2020, 10:49:57 PM »
Hi all. Has anyone here modded their Tascam 488 for post-fader direct outputs on each channel? Or maybe had someone else mod theirs? The reason I’m asking is there’s a guy on eBay who does the mod and he told me in a message there are no active electronics, but when I tried the mod myself, the impedance mismatch made it useless unless you plug into a hi-z input. I came up with a circuit to make the impedance line level, but I’m just wondering if anyone else has tried this mod with any success.


john12ax7

Re: Modifying Tascam 488 with post-fader direct outs
« Reply #1 on: May 02, 2020, 11:16:28 PM »
Do you have a schematic? Often mixers will have a buffer after the fader.  If you take the signal after this fader it should be fine. The loading problems come from taking the signal straight from the fader (before the buffer).

Re: Modifying Tascam 488 with post-fader direct outs
« Reply #2 on: May 03, 2020, 01:02:45 AM »
Do you have a schematic? Often mixers will have a buffer after the fader.  If you take the signal after this fader it should be fine. The loading problems come from taking the signal straight from the fader (before the buffer).

There are several buffers after the fader, but they come after the pan and after the “assign”, which sends the signal to one of four busses and those of course have their outputs already. I made a capacitively coupled emitter follower directly from the fader wiper and it works well.

PRR

Re: Modifying Tascam 488 with post-fader direct outs
« Reply #3 on: May 03, 2020, 01:56:25 AM »
> the impedance mismatch made it useless unless you plug into a hi-z input.

What are you using for this NOT-high input impedance?

Impedance at fader wiper varies from zero to 1.65k to 0.88k. 20k loads have hardly-any effect (bump the fader a half-mark). Yes, a 600r load makes a 12dB drop, but who does that?

Re: Modifying Tascam 488 with post-fader direct outs
« Reply #4 on: May 03, 2020, 12:40:51 PM »
> the impedance mismatch made it useless unless you plug into a hi-z input.

What are you using for this NOT-high input impedance?

Impedance at fader wiper varies from zero to 1.65k to 0.88k. 20k loads have hardly-any effect (bump the fader a half-mark). Yes, a 600r load makes a 12dB drop, but who does that?

Maybe I need to try the simple way again. Can you show me how you got the impedance at the fader? I’m trying to figure it out but am stumped.

ruffrecords

Re: Modifying Tascam 488 with post-fader direct outs
« Reply #5 on: May 03, 2020, 04:57:15 PM »
There is already quite a lot hanging off the wiper of that poor little fader. For starters there are the two AUX send 10K in parallel plus a 5k1 in series with the pair so that's about 10K overall. Then there is the pan pot circuit which in total looks like less than 5K. So the total load already on that pot wiper is about 3K3. With the fader full up that 3K3 is in parallel with the 10K of the fader making the total about 2K5. Add the 1K2 series resistor at the top of the fader  and the driving op amp needs to be able to work into a load of 3K7. Most op amps these days will drive a 2K load reasonably well so it should be ok. If you take an output direct from the fader wiper and feed it into a 10K bridging line input then worst case there is another 10K across the fader bringing the paralleled total down to 2K. The op amp now has to drive 2K+1K2 = 3K2 so it should still be OK.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


 

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