[BUILD] Stroh Stereo Output Mixer

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[BUILD] Stroh Stereo Output Mixer

Post by synthcube » Fri Jul 31, 2015 8:55 am

build thread for the new stroh stereo output mixer

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Post by synthcube » Fri Jul 31, 2015 8:56 am

placeholder post for BOM, schematic, build guide and other documentation
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Post by J3RK » Thu Aug 20, 2015 8:13 pm

Update:

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

https://www.muffwiggler.com/forum/viewt ... p?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.
Last edited by J3RK on Tue Dec 01, 2015 3:19 pm, edited 1 time in total.
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Post by Blake Smith » Thu Sep 03, 2015 1:59 pm

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.

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Post by J3RK » Fri Sep 04, 2015 4:45 pm

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.

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Post by Blake Smith » Fri Sep 04, 2015 10:08 pm

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.
Last edited by Blake Smith on Tue Sep 08, 2015 1:28 am, edited 1 time in total.

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Post by fracmonkey » Sat Sep 05, 2015 1:07 pm

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.

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Post by Blake Smith » Tue Sep 08, 2015 1:40 am

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/viewt ... c&start=75

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Post by fracmonkey » Tue Sep 08, 2015 8:25 am

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.

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Post by slow_riot » Wed Sep 09, 2015 2:30 pm

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

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

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Post by fracmonkey » Wed Sep 09, 2015 3:37 pm

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!

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Post by J3RK » Tue Sep 29, 2015 11:08 am

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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Post by syncretism » Fri Nov 29, 2019 12:26 pm

Necrohhhhhh!

How deep is this module? I understand that Frac isn't really known for shallow builds, but I've only got BugBrand frames here, and I suspect that Tom Bugs has bigger fish to fry than designing a new UTL2B with feature parity right now.
Last edited by syncretism on Fri Nov 29, 2019 2:57 pm, edited 1 time in total.

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Post by soup » Fri Nov 29, 2019 2:23 pm

It depends how you build it. The one I built will not fit in a bug frame as the deepest part of the module, the frac power header/plug, is down the center of the module where the bug power distro is. If you used a 5 pin mta-100 power header in the euro footprint instead this wouldn't be a problem.

also...

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Re:

Post by aethyr » Tue May 19, 2020 9:42 am

how does it sound? i am considering one of these and would love your input. thank you!
soup wrote:
Fri Nov 29, 2019 2:23 pm
It depends how you build it. The one I built will not fit in a bug frame as the deepest part of the module, the frac power header/plug, is down the center of the module where the bug power distro is. If you used a 5 pin mta-100 power header in the euro footprint instead this wouldn't be a problem.

also...

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Re: [BUILD] Stroh Stereo Output Mixer

Post by soup » Tue May 19, 2020 10:48 am

It sounds fine I guess, or rather it doesn't really have a sound. I like it and find it very useful, to the point I was considering building a second one recently but the opa2604, the chip that's driving the headphones, is no longer available. There are a couple alternatives mentioned in this thread but I haven't tried them.

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Re: [BUILD] Stroh Stereo Output Mixer

Post by synthcube » Tue May 19, 2020 11:06 am

if it helps we have a fairly good supply of the OPA2604 here
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Re: [BUILD] Stroh Stereo Output Mixer

Post by J3RK » Mon Aug 10, 2020 11:21 am

Another good op amp for this that I use is the LME49720.
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Re: [BUILD] Stroh Stereo Output Mixer

Post by Brian2020 » Fri Nov 20, 2020 12:46 pm

synthcube wrote:
Tue May 19, 2020 11:06 am
if it helps we have a fairly good supply of the OPA2604 here
Do you still have an available supply of the OPA2604? I have gathered all the components for this build with the exception of the two output op-amps.

@Dr J3RK - I’ll check out the op-amp you suggested.

This might be a stupid question but would the CA3080 be suitable for this application? Are there any other recommended options that are readily available (preferably from Mouser) that I should check out? My headphones are Senheiser HD 280 PRO, 64 ohm if that makes any difference.

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Re: [BUILD] Stroh Stereo Output Mixer

Post by Brian2020 » Tue Dec 29, 2020 2:06 am

Thank you SynthCube for helping me out with the OPA2604s for this build (also got a couple extras for future projects).
I’m wondering if any others have built this module and modded it to accept more inputs. I would really like for it to have at least one AUX input which would go to both the left and right outputs. Doable or better to just build it how it was intended?

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Re:

Post by syncretism » Wed Jan 20, 2021 8:15 am

soup wrote:
Fri Nov 29, 2019 2:23 pm
It depends how you build it. The one I built will not fit in a bug frame as the deepest part of the module, the frac power header/plug, is down the center of the module where the bug power distro is. If you used a 5 pin mta-100 power header in the euro footprint instead this wouldn't be a problem.

also...

Image
Image

You know, I just twigged this; I thought the second image was an artifact of the camera angle or something, I guess. So, did you end up installing it perpendicular, using something like the CLee bracket, but for 3u? Or are you just working with the board's wider footprint?

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Re: [BUILD] Stroh Stereo Output Mixer

Post by soup » Wed Jan 20, 2021 10:08 am

The pcb is 3 inches wide, the same width as the 2 frac panel. It's simply attached with 2 m3 standoffs. My crappy camera lens is fucking with your perspective.

But I probably should point out that because of the size of the pcb it won't fit in the far right or far left spot of a bugbrand frame.
Last edited by soup on Wed Jan 20, 2021 4:35 pm, edited 1 time in total.

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Re: [BUILD] Stroh Stereo Output Mixer

Post by syncretism » Wed Jan 20, 2021 2:57 pm

soup wrote:
Wed Jan 20, 2021 10:08 am
The pcb is 3 inches wide, the same width as the 2 frac panel. It's simply attached with 2 m3 standoffs. My crappy camera lens is fucking with your perspective.

But I probably should point out that because of the size of the pcb it won't fit in the far right or far left spot of a bugbrand frame.

Ah, right, thanks. This is a problem familiar to me with several of my 4u modules in LW format. Craig Lee's bracket's been a great solution, though it rules out "superslim" boats.

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Re: [BUILD] Stroh Stereo Output Mixer

Post by soup » Wed Jan 20, 2021 4:45 pm

Actually scratch that, at 4" it will just fit between the flanges. I must have been confusing it with something else. It can be tricky fitting some diy things in a bugbrame frame but I have some deeper cases so I forget which ones.

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Re: [BUILD] Stroh Stereo Output Mixer

Post by syncretism » Wed Jan 20, 2021 9:03 pm

Well, thanks again for the detailed responses over time. You're a class act, soup.

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