Yamaha M512 Mods
« on: March 29, 2021, 02:03:59 PM »
Here goes another Yamaha mixer thread...

I got a pretty clean Yamaha M512 from a local shop, and I thought I'd consider using it as a vibey preamp option. 12-channels of cheap-ish input transformers sounded like a fun deal to me especially for drums. I had an old RAMSA mixer years ago that I used for a similar thing, but the size was a little ridiculous. This is a lot more compact and could easily be put away when not in use.

So here's what I'm thinking:
-Add balanced outputs
-Swap Preamp TA7322P opamps (IC1, IC2)
-Recap
-Tweak EQ frequencies

Balanced Outputs
I think I've got two main options here. Either way, I would be diverting the pre-fader FB send to a switching TRS jack. The question is, to transform or not to transform? I can either do some psuedo impedance balancing using a resistor and capacitor as described by Jensen (https://www.jhbrandt.net/wp-content/uploads/2014/11/Interconnection_of_Balanced_and-Unbalanced-Equipment.pdf), or I could add in some OEP A262A2E transformers. One is obviously way cheaper than the other, but I did find a good deal on a dozen OEP transformers.

Opamp Swap
The TA7322P is a real pain. For starters, it's a single opamp in a 9-pin SIP package that runs on a +-25VDC supply.

Problem #1 - SIP Package
There are some solutions/adapters that will fit the SIP pinout and adapt to something like a OPA604 or similar. The most common solutions are fairly pricey (~$4 per adapter x 2 x 12 = $$$).

Problem #2 - Supply Voltage
Most modern opamps won't tolerate more that +-18VDC. I was thinking I could throw in a pair of 7.5V zener diodes to each opamp to lower it down closer to 18V.
 
Problem #3 - Inventory
I have about 20 LME49720 dual opamps laying around, and I'm thinking that sounds cheaper than 24 new single opamps. However, I would need to figure out an adapter solutions that could potentially utilize both channels of the LME49720.

Recap
I only count about half a dozen electrolytic caps touching the the signal path between the input and fader. Any reason to replace any others?

EQ Frequencies
Without getting to use this in a session yet, I have no idea what to expect from the EQs, but the word on the web is that they could use some love. (https://groupdiy.com/index.php?topic=51214.0)

Anyone have any thoughts or see any red flags?


Re: Yamaha M512 Mods
« Reply #1 on: April 06, 2021, 11:02:59 AM »
I've got some parts in, so I'm prepping to install the TRS jacks along with the OEP output transformers. I got them for $6 each, so I think it's probably worth the mounting headache verses the RC impedance balancing.

I've got to work out if there's an easy way to still use the switching jacks along with the transformer. I don't really care to preserve the FB output, but maybe it's a good thing to attempt.
« Last Edit: April 06, 2021, 12:36:52 PM by collinTHEbrewer »

Re: Yamaha M512 Mods
« Reply #2 on: April 06, 2021, 02:30:28 PM »
Does this make sense for connecting the output transformer? If I grab the signal directly from the opamp output while maintaining the existing connections, am I causing any issues?

dogears

Re: Yamaha M512 Mods
« Reply #3 on: April 06, 2021, 03:30:48 PM »
I made a version of our M2 discrete op amp in that SIP footprint / pinout for a client. If you want to try some out let me know.


 

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