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[BUILD] Stroh Stereo Output Mixer
MUFF WIGGLER Forum Index -> Fractional Rack Modules  
Author [BUILD] Stroh Stereo Output Mixer

synthcube

build thread for the new stroh stereo output mixer

panel+pcb bundles are available here: http://synthcube.com/cart/index.php?route=product/product&product_id=6 93




synthcube

placeholder post for BOM, schematic, build guide and other documentation


J3RK

Update:

Build docs are now contained in the ZIP file in this thread:

https://www.muffwiggler.com/forum/viewtopic.php?t=150552

This is due to Comcast killing off personal web space. I've also given the docs to Synthcube and Thonk just in case. If at some point I get more time on my hands again, I'll set up some hosting, and put these up properly again. I just wanted to make sure they were available again in the meantime.


Blake Smith

Maybe this is a silly question. I'm putting together an order for parts on some different projects. I was wanting to include these new frac stroh modular circuits, and not having seen the pcbs yet I'm wondering what the appropriate lead spacings would be for the caps.


J3RK

2.5mm I typically use the blue TDK MLCC type. They're cheap, reliable, and the C0G/NP0 ones work in a lot of different applications.

I apologize for being scarce around here. That's about to change, and I'll be back up to full speed again with things. Just a very taxing couple of months.

I'll pop back and see if more questions pop up. Also, if anyone has more urgent questions, PM me. I'll see it in my email, and can respond a bit faster.

w00t


Blake Smith

Thanks for the info. I have a couple more questions:

There are a few components on the pcb drawings that don't show up on the BOMs, the FB's and BP1 - 10. I assume these are ferrite beads and bypass caps? Would 100nf mlcc types be appropriate for the bypass caps? They seem to be typical choices for that application.

Thanks,

Blake.


fracmonkey

I see 3 pots on each section of the mixer schematic but only 2 seem to have a spot on the front panel.

RV101 is a level pot and RV102 is a pan pot but what is RV1? It is basically also a level pot but is it really a trimmer to adjust maximum gain of the channel?

The PCB photo shows the same 3 hole pattern as the other pots so I'm not sure a trim pot would fit here.


Blake Smith

fracmonkey wrote:
I see 3 pots on each section of the mixer schematic but only 2 seem to have a spot on the front panel.

RV101 is a level pot and RV102 is a pan pot but what is RV1? It is basically also a level pot but is it really a trimmer to adjust maximum gain of the channel?

The PCB photo shows the same 3 hole pattern as the other pots so I'm not sure a trim pot would fit here.


Check out the end of this thread, there are a couple of photos of the build of this module. The RV1, etc, pots are multi-turn trimmers

https://www.muffwiggler.com/forum/viewtopic.php?t=7514&postdays=0&post order=asc&start=75


fracmonkey

I see---did not expect 20T trimmers.

What kind of earphones are you using? All mine are 32 ohm units and it seems unlikely that an op amp would drive them. The opa 2604 is advertised to drive 600 ohm loads but 32 ohms is pretty low.

I did some BBing with a TL074 and did get useable results as long as the volume was reasonable. The op amp would swing at least a volt or two at the 32 ohms.


slow_riot

OP275 can drive +/-40mA and would be worth considering.

For a future project the LT1010 buffer would be perfect for a heavyweight headphone output.


fracmonkey

Of course, there are a load of stereo headphone amp ICs out there. For example the TI TPA6111A2. About a buck. Most of them are SOIC these days....but I've soldered a few in my toaster oven!


J3RK

Sorry for the long delay! Things are getting back on track at home now, so I'll be much faster to respond now.

The OPA2604 will be fine for lower impedance as well. I've tested with my AKG 240MKIIs (lower (60R if I remember correctly)) and my wife's MKIs which are higher (closer to 600R I think.) It also works quite well for line levels.

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