Whistle Rock Audio ML12 preamp BUILD/HELP thread!

[Bobby Baird]

Cards built. Now to build op-amps. Case arrives next week.

 

[Bobby Baird]

First one.

 

[TwentyTrees]

Hey, great job! Picked up a bunch of these PCBs a few years ago intending to do something similar but never got round to it, you've inspired me to bump it up the build queue.

Nice to know that all 8 definitely fit in a Frank case.

 

[Bobby Baird]

Hey, great job! Picked up a bunch of these PCBs a few years ago intending to do something similar but never got round to it, you've inspired me to bump it up the build queue.

Nice to know that all 8 definitely fit in a Frank case.

For each case I used 42 m3 6mm Harwin R30-3000602 standoffs for the cards to give output transformer clearance. Cards 1 & 8. The outside edge standoffs rest on the side rails of Frank's NRG case, so I went with 6 m3 Harwin R30-3000502 5mm standoffs there. Also the screws on the sides of the case come into contact with the cards causing a potential short. Those have to cut short with a dremel, as well as above the channel 1 attenuator. I opted for the Hairball 1/8" shaft 600 ohm t-pad there. If using attenuator capaciotr C6 has to be short enough to fit the pot above it on the panel. Tight tolerances in those areas with this configuration. Cards are further secured to Frank's rail system from above the boards with 24 m3 Harwin R30-1002802 28mm standoffs. The remaining standoffs are secured with m3 nuts. As an option you could use 34mm standoffs to reach the top panel of the NRG case to secure the boards. I went with terminal blocks as molex connectors are in short supply when I was putting together the bom. Although, with this configuration of the cards stacked right next to each other wiring will be a challenge with the terminals blocks. Back of the case is connected to power suppy using a Aviator 5 pin cb style connector. One could opt for a 5 pin xlr as well. Here are the panel designs for an NRG case from Frank. You can use as you see fit. Rename extention fpd.

 

[TwentyTrees]

Thanks for taking the time to share that, both the info and the templates - it's incredibly helpful to be able to follow in someone else's footsteps on something like this.

If I understand right, the cards are suspended from the mounting rails but also have standoffs on the bottom to maintain distance from the bottom of the case, is that right? Neat idea, good way to maximise the space in there.

 

[Bobby Baird]

Yes you are correct. Card are supported by standoffs from the bottom and held in place by top rail from above standoffs.

 

[Bobby Baird]

I set up this board to be a 8ch line level to mic level attenuator board for my new rack unit. It will have 4 12 position terminal strips for wiring to analog tascam pinout for in's and out's. The circuit is a balanced u-pad. I'll get a few made if anybody wants one. The circuit presents a 10k load to line level device and a 178ohm load to preamp input transformer providing 35dB attenuation.

 

[Ricardus]

I set up this board to be a 8ch line level to mic level attenuator board for my new rack unit. It will have 4 12 position terminal strips for wiring to analog tascam pinout for in's and out's. The circuit is a balanced u-pad. I'll get a few made if anybody wants one. The circuit presents a 10k load to line level device and a 178ohm load to preamp input transformer providing 35dB attenuation.

I'd be intererested in a couple.

 

[Bobby Baird]

Here's the schematic and the project box the board is sized for. Steel Project Box 4 1/2" x 3-3/4" x 1 5/8" Punched for 2 DB25 Connector | eBay
Resistors 1% https://www.mouser.com/ProductDetail/Vishay-Dale/RN60D1780FB14?qs=gY232B2Eg6xG1OPNv63FAA==
0.1% https://www.mouser.com/ProductDetail/Vishay-Dale/RN60C5001BB14?qs=cGPY83Tj7TGvXTs8WhN9zg==
Wire direct to board are use 4 12 position TE Connectivity or similar 2.54mm spacing https://www.mouser.com/ProductDetail/TE-Connectivity/1-282834-2?qs=A%2Bip%2BNCYi6MYASy3N4v9Sw==

 

[Bobby Baird]

I'd be intererested in a couple.

It will be a couple week turn around at that point if you want to pay postage + what ever the cost per board may be probably a couple bucks I'll mail you a couple. Good way to fatten up digital samples and synth through your new preamps.

 

[Ricardus]

It will be a couple week turn around at that point if you want to pay postage + what ever the cost per board may be probably a couple bucks I'll mail you a couple. Good way to fatten up digital samples and synth through your new preamps.

Just give me an idea about how much it will be. Where are you shipping from?

 

[Bobby Baird]

$5.00 per board ENIG Surface Finish. $10.00 shipping priority flat rate envelope. From Austin, Texas. The whole project should cost around $50.00 to make one 8 channel box. Not including the d25 breakout cables. Just ordered 5 be here in 8 to 10 days.

 

[Bobby Baird]

Line Pad boards showed up. They look nice. Also been wiring up the 3128. Getting close. Everything is coming together. Hopefully get my neighbor Ramy Antoun that owns the A&F Drum company to run some custom drums mic'd up to them.

 

[TillM]

@Bobby Baird that's some really nice work !!!
Congrats !
I use my ML12 since 5 years without any issues. This Preamp rocks !

 

[Ricardus]

Line Pad boards showed up. They look nice. Also been wiring up the 3128. Getting close. Everything is coming together. Hopefully get my neighbor Ramy Antoun that owns the A&F Drum company to run some custom drums mic'd up to them.

I know I'm getting old and my memory sucks, but those blue PCBs look familiar!

 

[Bobby Baird]

I know I'm getting old and my memory sucks, but those blue PCBs look familiar!

 

[Bobby Baird]

Since this project's power supply gerbers were lost. I have been working on resurrecting the board to go with the open source preamp and di boards. Only difference is the bridge rectifier was obsolete, so I chose a KBP202G package to replace it since it has the same spec as the original part. Thoughts?

 

[Brian Roth]

I vaguely recall this project from many years ago but all the docs on post #1 are gone. Rather than dig through 13 pages in this thread in hope of finding newer docs, is there a location to find that info? Thanks.

Bri

 

[Bobby Baird]

All the docs on post #1 are gone.

Here's what I have.

 

[Brian Roth]

Thanks!

Bri