Toft ATB Master Module upgrade - Help Please?!?

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morls
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Post by morls » Tue Jan 13, 2015 3:37 am

Now that the master module has been upgraded, now would be a good time to think about the master fader. Would something like this be a worthwhile replacement for the stock Bourns:

P&G Stereo 104mm 1K Log 3000 Series Fader

I think the Bourns is a 10K, while the P&G is 1K. Would this be a problem?

Cheers

Stephen

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Post by The Scum » Tue Jan 13, 2015 11:22 am

Again, without a schematic, anything proposed is purely a guess.

It depends on what it's loading and what's loading it.

Some consoles place the master fader right after the insert return, with no buffer amp. That means the fader serves as the load for anything external that gets patched in. 1K is just low enough that I'd be reluctant to load things with it.

Sometimes master faders have a load or feed resistors on the wiper, before the next amplifier stage. You might need to scale that resistor to match.

Is the preceeding stage capacitively coupled to the fader? The cap value was probably calculated with the 10K load, and might need to grow by 10X to compensate for the lower load.

The wiper is often capacitively coupled into the next stage, as well. In general, the cap will be big enough that a smaller fader shouldn't effect it.
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Post by Drone » Tue Jan 13, 2015 12:06 pm

It appears P&G did make a 10K, why not replace like with like?

http://www.audiomaintenance.com/acatalo ... _info.html
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Post by morls » Tue Jan 13, 2015 1:27 pm

Thanks for the replies...
Some consoles place the master fader right after the insert return, with no buffer amp. That means the fader serves as the load for anything external that gets patched in. 1K is just low enough that I'd be reluctant to load things with it.
The fader is after the insert return. The signal path is:

insert return → buffer amp → master fader → capacitor → opamp → capacitor → master out

The buffer amp pre-fader is an LME49720NA. Quoting from the data sheet:
To ensure that the most challenging loads are driven without compromise, the LME49720 has a high slew rate of ?20V/μs and an output current capability of ?26mA. Further, dynamic range is maximized by an output stage that drives 2kΩ loads to within 1V of either power supply voltage and to within 1.4V when driving 600Ω loads.
I'd have to confirm the value of the cap immediately following the fader. The opamp is an LM6172IN, followed by a 220uf cap before the master out.

Am I right to think the 49720 would drive a 1K fader?

What are the advantages (if any) of a 1K fader vs a 10K fader?

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Post by The Scum » Tue Jan 13, 2015 2:09 pm

Am I right to think the 49720 would drive a 1K fader?
The datasheet seems to be indicating that it's happier driving loads above 2K, and that you'll reduce headroom a bit...1K is between their stated points of 2K and 600 Ohms, so interpolate...1K means maybe it probably craps out at ~1.2V shy of the rails.
What are the advantages (if any) of a 1K fader vs a 10K fader?
Maybe you prefer the feel of a P&G fader. It might be a higher-grade component, and there's possibly less self-noise..but comparing carbon to conductive plastic might also be apples-to-oranges, noise wise.

There's less advantage if the rest of the circuit has to change to accomodate, especially if you have to gain large electrolytics.

But it's only a 50-quid experiment, right?
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Post by morls » Tue Jan 13, 2015 3:32 pm

I don't want to lose headroom. Maybe 5K is a happy medium?

http://ralaudio.com/pdf/tkd/cpa9000s-e.pdf

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Post by The Scum » Tue Jan 13, 2015 4:03 pm

When Audio Maintenance have the 10K P&G in stock, why swap values at all?
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Post by Drone » Tue Jan 13, 2015 4:28 pm

A propos of nothing, this reminded me of the Dan Garcia interview in issue #71 where he talks about comparing P&G faders to the API faders with the lamps in them, maybe you should check them out :D
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morls
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Post by morls » Tue Jan 13, 2015 4:28 pm

good point. If there are no sonic advantages to lower resistance then I think I'll stick to 10K.

Cheers

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Success!

Post by morls » Sat Jan 24, 2015 1:05 pm

Just wanted to update my progress. After getting the power supply repaired - and replacing some of the IC's that were also damaged - I've finished the mods, and couldn't be happier. I want to thank all who replied for all their help, it really is great.

I especially want to thank Jim Williams for posting his mods. It's such a generous thing to do, and the difference it has made to the sound is fantastic.

Having something go wrong has proved a blessing in disguise. It forced me to do a lot of work towards really understanding how the module works, and I'm very happy to have been able to get it up and running. Although some mistakes are inevitable, I'm learning a lot.

Stephen

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Post by I'm Painting Again » Wed Feb 25, 2015 4:12 pm

oh the drama and excitement..thanks for sharing this..glad to hear it worked out

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Re: Success!

Post by qmp » Mon Jun 18, 2018 12:03 pm

morls wrote:
Sat Jan 24, 2015 1:05 pm
Just wanted to update my progress. After getting the power supply repaired - and replacing some of the IC's that were also damaged - I've finished the mods, and couldn't be happier. I want to thank all who replied for all their help, it really is great.
Did you end up replacing the fader? My toft has some failing faders and I want to replace them. did the P&G fit? or what did you end up using?
Thanks much for any info!

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Re: Success!

Post by A.David.MacKinnon » Mon Jun 18, 2018 6:07 pm

qmp wrote:
Mon Jun 18, 2018 12:03 pm
morls wrote:
Sat Jan 24, 2015 1:05 pm
Just wanted to update my progress. After getting the power supply repaired - and replacing some of the IC's that were also damaged - I've finished the mods, and couldn't be happier. I want to thank all who replied for all their help, it really is great.
Did you end up replacing the fader? My toft has some failing faders and I want to replace them. did the P&G fit? or what did you end up using?
Thanks much for any info!
The OP has 14 posts on their account and they’re all in this thread. The last one was in 2015. Chances are they’re long gone.
You should stick around though (and welcome to the board). Someone may have an answer (or not). Either way it’s a good spot and you’ll learn something. I have.

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Re: Toft ATB Master Module upgrade - Help Please?!?

Post by ShinyBox » Tue Jun 19, 2018 8:51 am

I asked a friend, the original faders were alps.

If the P&G faders are the right throw length, they should be able to fit. The fader should connect to the main board via a header, so you will likely need to figure out what wires go where, but it should at least be doable.

ju

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Re: Toft ATB Master Module upgrade - Help Please?!?

Post by alexdingley » Sat Jun 30, 2018 5:49 am

I had some great chats with Kevin at PMI, and though their policy is not o release a schematic “to individuals”, I think the spirit of that policy is “don’t give out schematics to anyone who you don’t have an NDA with.” If you off to sign an NDA (non disclose agreement), they might be totally okay with handing you a schematic.

Incidentally, Jim is 100% dead on about the fragility of those PCBs... I replaced the original pots on my master fader, and on both the CR pot and the Phones pot, I scorched the through-traces. Caused a nasty ground issue.

Would love to have someone more capable than myself go over my master board and clean up my mess (also would love those upgrades) in the meantime, I’m not summing through my Toft... it’s now a 16 channel pre and EQ bank.

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