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Buchla 275r Breakout PCB/BOM issue, noise issue (solved)
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Author Buchla 275r Breakout PCB/BOM issue, noise issue (solved)
Peake
Roman's 275 sounds wonderful but the RCA jacks in the current BOM are for the earlier green PCBs, not the current black version. Created etch artwork from Apetechnology's green PCB scan for a home-etch breakout PCB. Also addressed noise and the use of shielded cable between the module and the breakout PCB. Original post and edits:

Working on a build and it appears a ribbon connector between the module and the breakout panel is implied but not detailed. The 6P closed headers appear to be the connector between them but...nothing more is mentioned and I don't see any discussion of it here or elsewhere. Thanks for any insight.

EDIT: The "From Reverb Tank" returns appear to use the PCB ground plane while the Send signal paths use a single, different ground off of pin 7 of the LM380s. I was wrong, this is not all common ground, DO NOT TIE THE "TO REVERB TANK" BREAKOUT GROUNDS TO THE CASE.

EDIT: See Page 2. Etched a new PCB for the RCAs on the BOM. Will run shielded RCA male cords off of the back to the female RCAs wired to the main module.
APETECHNOLOGY
there was a separate break out panel that it connects to. if needed, you connect via that cable.
i guess for external tanks.


spy seriously, i just don't get it
Peake
There are male 6-pin headers on the main and breakout PCB. My question is about the female 6-pin header parts which need wires or a ribbon soldered? on...looking at the description it says it is indeed an IDC type, MTA 100. I'll suppose eurack people know all about this? Never before encountered one. Considering several people have built this module without posting any questions on this topic I guess I'm a bit alone in this. I tend to solder point-to-point for reliability instead of using these sort of connectors.

https://www.mouser.com/ProductDetail/TE-Connectivity/3-640441-6?qs=%2f ha2pyFaduiy2XPHWv7QpOPqZkYDfRt%2fNbmy%2fxNHVbB5z%2fF%2f9WpkZA%3d%3d

http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchr trv&DocNm=114-1019&DocType=Specification+Or+Standard&DocLang=English&P artCntxt=3-640441-6
tIB
I have one with the backplate built by Roman - the backplate doesn't work and he didn't offer any support on fixing it. I can post pics if you like but really mines useless. Wonder if anyones back plates work?
tIB
From memory I think it was a header as opposed to point to point soldering - when using mine massive amounts of harsh digital sounding noise was present - no idea where the error is, and I've just ran from right angled cables direct to the connectors on the main PCB.
jimfowler
I'm in the middle of building one myself and have no intentions of using the breakout panel. Shielded wire from pcb2 directly to tanks.
Peake
The customer for whom I'm building this and I are wondering if the RCAs on the breakout PCB are grounded to the breakout panel and thus the case. If not, will consider hardwiring shielded cable instead of unshielded.

I'll take it when you disconnect the breakout panel from the module the noise goes away? Or when directly connecting the reverb RCA cords to the module while the 275 is mounted in the same place there's no or less noise?
tIB
From memory with the breakout panel I get angry digital noise (and no reverb signal), without I get reverb and a standard spring revert type signal-noise whine. I'd be interested to know how quiet you can get yours - mine is OK but noisier than I'd like (which TBH is no noise at all!).

Oh, and right angled rca jacks attach to the module in a powered boat, which is how mine connect.
tIB
As for grounding I wondered that too - be interested to know whether it is a design issue rather than my module...

I massively overpaid on mine - it was a 'one off not going to be released for DIY' type bulls hit thing. Cheap at (over) twice the price, and it didn't work as described. I'd be delighted to be even more annoyed by the thing... (which in fairness is a cool module, I'm just not used to losing a thousand dollars in a module purchase... live and learn)
Peake
It makes complete sense that the wiring from the breakout panel to the module should be individually shielded as are the RCA cords connecting to the module or panel. With the module still in the case it should be easy to see if connecting the RCA cords directly to the 275 PCB with the breakout disconnected eliminates/reduces the noise experienced when the breakout cable is in place. tIB you are indicating that yes, skipping the breakout and connecting the RCA cords directly to the PCB RCAs solves the problem.

Edit: No, the standoffs on the breakout panel are NOT connected to ground on the breakout PCB, so unless the RCA jacks are in solid contact with the breakout panel they will not be grounded to the case in that manner. Haven't received the jacks yet, can't verify.

If that's not enough I'm thinking about shielding the module with Mu metal:

https://www.pmlindia.com/products/mumetal-foil

Pardon me, I'm thinking out loud more than interacting. Thank you for the replies. Hoping we can all gain ground on this issue.
tIB
Think out loud all you like - I'll keep an eye out for when you fix the issue!

Interested if shielding would reduce what's left of the high pitched hum in mine - I'd love to get rid of that...
Peake
Someone found the 208r reverb was noisy until they cut the PCB solder trace out from the final component in the signal path and soldered shielded wire directly to that component, it's documented on Dave Brown's page, he may be the one who found it, would be confirmed there if so. I believe there were several inches of trace involved, much more than I'm looking at on the 275.

This is only a concept. Do destructive mods to your PCB traces at your own responsibility.

I'm looking at a rev2 275r PCB set, flat black, and there are a couple inches of traces out from the initial and final components in the send and return signal paths which might be acting as antennae. It would be worth trying to cut those traces and cut the RCA cords and solder and ground there as required. The right side's To Reverb Tank signal path runs to the - side of the 330uF SMD cap.

The "From Reverb Tank" returns appear to use the PCB ground plane (Quiet Ground) while the Send signal paths use a single, different ground off of pin 7 of the LM380s. I was wrong, this is not all common ground, DO NOT TIE THE "TO REVERB TANK" BREAKOUT GROUNDS TO THE CASE.
tIB
I'm not sure this is helpful or not but I tried it minus the reverb tanks connected before and still had the same noise - I wondered whether the cables/tanks were responsible for the noise... they weren't.
Peake
Would you be willing to power down your system, remove the 275, disconnect the reverb tank cables and breakout cable, and with the module protected from shorts outside the case, power up and monitor it to see if the noise diminishes?
tIB
Yeah, though I've done that before - was the same. I did some investigating ages ago and ruled out placement and tank position. I could do it again though to double check of required...
Peake
I believe...so the module has some noise and whine. That's something I've also seen mentioned about the 208. Someone had a cap to diminish the reverb whine...I think the thread is here on MW.

Don't worry about checking again, thanks for being willing.

My customer and I have decided to hardwire RCA cables to the back of the breakout panel with male RCA ends which can be plugged onto the female RCA jacks on the module. Shielded, removable, no IDC/MTA header crimp tool etc. nonsense.
tIB
Let me know how it sounds noise wise - I'm game for recording mine if helpful.
Peake
That's cute; the PCB-mount RCA jacks arrived today and they're nowhere near compatible with the PCB. Entirely different, can't be made to work. Double-checked the BOM and I'd ordered the part from it.
tIB
Let me know if you need a photo of mine for reference...
Peake
I'm working on the black PCB version. Where did everyone find the correct PCB-mount RCA female jacks for it?
Peake
Thanks to everyone for the help. I have this build up and running using shielded RCA cables directly off of the module PCB to the tanks and am getting no buzz (no 200e modules here to fully test though). This is a great module.

-Are everyone's CV Mix outputs very quiet compared to EQ and Reverb only outs?
-Do you get a degree of cross-feed from one channel into the other's reverb send?
tIB
I don't recall any cross bleed on mine though I've read about it elsewhere - I'm away at the minute but will check all in return. Promising that yours is silent...
tIB
Any chance of a photo of where/how you connected the tanks please?
Peake
I've wired RCA female jack pairs directly to the PCB with strain relief tie-downs. I'm going to etch a replacement for the original breakout PCB using the RCA jacks shown in the BOM and wire a set of long RCA male cords to it so the breakout is easily disconnected.

tIB
Thanks - we're those rca cables soldered to the rca mount points on the board or somewhere else? I'm trying to work out how/why you got the noise down so I can hopefully do the same...
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