Good Buchla reverb?

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Dreadwvlf
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Good Buchla reverb?

Post by Dreadwvlf » Fri Jun 11, 2021 1:22 am

Anyone out there building any Buchla reverbs? Maybe the 275? I am thinking it would be nice to have one in the case and I don’t see one anywhere. Have the issues with the 275 clone been resolved?

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Re: Good Buchla reverb?

Post by jimfowler » Fri Jun 11, 2021 3:48 am

275, 289, 2H9

What issues do you speak of?

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Re: Good Buchla reverb?

Post by Dreadwvlf » Fri Jun 11, 2021 3:57 am

jimfowler wrote:
Fri Jun 11, 2021 3:48 am
275, 289, 2H9

What issues do you speak of?
Hey Jim! Well I read mainly about some grounding stuff in the 275? That’s the one I was mainly looking into. Weren’t there issues with them though?

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Re: Good Buchla reverb?

Post by jimfowler » Fri Jun 11, 2021 7:20 am

Use quality shielded cable to/from tanks and omit the breakout board. Also there’s a resistor change to increase the reverb signal. I’ll try and find the post...

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momo
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Re: Good Buchla reverb?

Post by momo » Fri Jun 11, 2021 9:59 am

I think the issues might be not so much technical but that the module may sound like an approximation of what it ought to sound like (per the bottom of page 1 of the MEMS thread). I think the MEMS folk touch on it in the recent SoU podcast, along with other remarks across other r clones.

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Siren
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Re: Good Buchla reverb?

Post by Siren » Fri Jun 11, 2021 10:11 am

Approximation or not, I have two of them and they sound gorgeous. As Jim said, use quality cable to get good results - I noticed a world of difference just switching from the modern era tinijax to the older type thick Switchcraft. Quality shielded rca’s goes without saying.
They both suffer from a weird problem though, where the left channel is stronger than the right one. Since both of mine are the same I’m thinking it is some sort of design issue rather than coincidence, but I may be wrong.
The breakout box is unfortunately unusable…hum deluxe.

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Re: Good Buchla reverb?

Post by levelhead3 » Fri Jun 11, 2021 1:41 pm

Dreadwvlf wrote:
Fri Jun 11, 2021 3:57 am
Well I read mainly about some grounding stuff in the 275? That’s the one I was mainly looking into. Weren’t there issues with them though?
I apologize - it may have been my concern you're referring to, voiced on multiple threads. For both PCB versions the ground on the 'to reverb tank' jack is tied to NGND whereas the ground on the 'from reverb tank' is tied to QGND. I've never heard a clear explanation as to why this was the case, and have always been concerned that feeding NGND to QGND through the tanks (and subsequent make-up gain amplifier) is responsible for adding noise to the module, especially with things like LED's.

Of course, there is also a jumper on both PCB which simply ties QGND to NGND directly. Which seems to defeat the whole purpose of having separate grounds, and I've never heard an actual functional explanation for this jumper either.

As has been mentioned by the MEMS folks recently, the 275r circuit bears little resemblance to the actual 275 circuit - some folks have indicated it might be closer to the one found in the 208.

But with the exception of the breakout panel, which is really completely useless on both PCB versions, the 275r does work just fine and sounds awesome. In certain environments it can be susceptible to system noise, but that's never stopped me from using or enjoying mine.

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Re: Good Buchla reverb?

Post by Peake » Fri Jun 11, 2021 1:52 pm

Jim Fowler found replacement RCA jacks for the 275r main PCB so you can plug quality RCA cables directly to the module. Thanks Jim!

The 275r sounds great, the vintage 190 dual reverb sounds great, and betting the MEMS 275 will be awesome!
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Re: Good Buchla reverb?

Post by Dreadwvlf » Fri Jun 11, 2021 5:18 pm

Any of you fine gents taking a commission to build a 275 for a guy any time soon? :)

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Re: Good Buchla reverb?

Post by tarandfeathers » Sat Jun 12, 2021 3:01 am

levelhead3 wrote:
Fri Jun 11, 2021 1:41 pm
Dreadwvlf wrote:
Fri Jun 11, 2021 3:57 am
Well I read mainly about some grounding stuff in the 275? That’s the one I was mainly looking into. Weren’t there issues with them though?
I apologize - it may have been my concern you're referring to, voiced on multiple threads. For both PCB versions the ground on the 'to reverb tank' jack is tied to NGND whereas the ground on the 'from reverb tank' is tied to QGND. I've never heard a clear explanation as to why this was the case, and have always been concerned that feeding NGND to QGND through the tanks (and subsequent make-up gain amplifier) is responsible for adding noise to the module, especially with things like LED's.
The send to the reverb tank in this design is a power amp dumping current into a motor, just about the "noisiest" signal you can think of and way worse than an LED passing a couple of mA. It definitely should not be returned to quiet 0V. The 0V path to the tank should be isolated from the chassis, and the tank should have an isolated input/grounded output.

I think Roman included the jumpers as an option for people who did not have a power supply with dedicated separate 0V rails, but even in that case I'd keep them separate back to the bus board/distribution.
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Re: Good Buchla reverb?

Post by shoegazer86 » Sat Jun 12, 2021 3:42 am

momo wrote:
Fri Jun 11, 2021 9:59 am
I think the issues might be not so much technical but that the module may sound like an approximation of what it ought to sound like (per the bottom of page 1 of the MEMS thread). I think the MEMS folk touch on it in the recent SoU podcast, along with other remarks across other r clones.
We also just found out that the 292B(r) is comprised of four Frankensteined 208 gates. Even the 13.5V supply is there, which is how Don did the local/remote feature on the 208. It does not serve any purpose on the 292B(r).
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levelhead3
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Re: Good Buchla reverb?

Post by levelhead3 » Sat Jun 12, 2021 6:43 am

tarandfeathers wrote:
Sat Jun 12, 2021 3:01 am
levelhead3 wrote:
Fri Jun 11, 2021 1:41 pm
Dreadwvlf wrote:
Fri Jun 11, 2021 3:57 am
Well I read mainly about some grounding stuff in the 275? That’s the one I was mainly looking into. Weren’t there issues with them though?
I apologize - it may have been my concern you're referring to, voiced on multiple threads. For both PCB versions the ground on the 'to reverb tank' jack is tied to NGND whereas the ground on the 'from reverb tank' is tied to QGND. I've never heard a clear explanation as to why this was the case, and have always been concerned that feeding NGND to QGND through the tanks (and subsequent make-up gain amplifier) is responsible for adding noise to the module, especially with things like LED's.
The send to the reverb tank in this design is a power amp dumping current into a motor, just about the "noisiest" signal you can think of and way worse than an LED passing a couple of mA. It definitely should not be returned to quiet 0V. The 0V path to the tank should be isolated from the chassis, and the tank should have an isolated input/grounded output.

I think Roman included the jumpers as an option for people who did not have a power supply with dedicated separate 0V rails, but even in that case I'd keep them separate back to the bus board/distribution.
Very interesting - the most commonly specified tank for the 275r (at least that I've read and encountered) is the 1BC2A1B, which is Input Grounded/Output Grounded - and so makes a direct connection between NGND and QGND.

I wonder if much of the noise issues could be addressed simply by switching to a 1BC2C1B,which is Input Insulated/Output Grounded as you've suggested. Damn, could it really be that simple? :doh:

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Re: Good Buchla reverb?

Post by tarandfeathers » Sat Jun 12, 2021 11:18 am

Quite possibly - it's still necessary to isolate the RCA jacks from the boat, which should be connected to Q. I've never built a 275r but I did note that the tanks are not listed in the BOM which seems like a bit of an oversight, so I presume folks were just guessing.

Things like this were one of the reasons I felt it was essential to include schematics when I publish my own projects. DIY without documentation provides neither the opportunity for the builder to learn from the work of the designer, nor for the designer to learn from the knowledge and experiences of people who build their projects, which is fine if all you want to do is shift a few units and make a buck, but is not exactly enriching for either party.
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Peake
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Re: Good Buchla reverb?

Post by Peake » Sat Jun 12, 2021 11:59 am

Is it possible to modify the tanks people already have to isolate the grounds?
This is not the place I'd imagined it to be.

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Re: Good Buchla reverb?

Post by papz » Sat Jun 12, 2021 12:54 pm

On Accutronics / Belton ones, the ground connection is a tab connected to the RCA socket and screwed to the metal case, you can unscrew it and pull out the RCA socket to cut the tab neatly.
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Re: Good Buchla reverb?

Post by shoegazer86 » Sat Jun 12, 2021 4:35 pm

On the original 275 - the reverb tank chosen was pulled from the tank enclosure and suspended in a bud box style enclosure.

Image
Image

It's interesting to note that the 275 was not really intended to come with the spring tank units, they were optional. This was likely due to many studios having their own dedicated reverb units, like some sort of AKG unit or a plate reverb so they could use the 275 as a FX Send/Return.

They take up SO much room in a case. Here is the back of U of I's case, they're on the bottom left, taped together.

Image

Anyway, Don's design is wildly different, namely with copious use of vactrols. The 275 will be the next focus for beta builds, as the board traces we have are confirmed to the schematics. Now it's just a matter of time until we get some samples.
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Re: Good Buchla reverb?

Post by jimfowler » Sat Jun 12, 2021 6:28 pm

Any chance you’d be willing to share said schematics so those of us interested can stare, study and wonder?

- Jim

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Re: Good Buchla reverb?

Post by momo » Sat Jun 12, 2021 7:07 pm

@shoegazer86 thanks for the knowledge and pics!

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Re: Good Buchla reverb?

Post by Happyanimal » Sat Jun 12, 2021 7:09 pm

Dreadwvlf wrote:
Fri Jun 11, 2021 1:22 am
Anyone out there building any Buchla reverbs? Maybe the 275? I am thinking it would be nice to have one in the case and I don’t see one anywhere. Have the issues with the 275 clone been resolved?
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Re: Good Buchla reverb?

Post by shoegazer86 » Sun Jun 13, 2021 7:22 am

jimfowler wrote:
Sat Jun 12, 2021 6:28 pm
Any chance you’d be willing to share said schematics so those of us interested can stare, study and wonder?

- Jim
Sure, but give us some time to get the beta build done with Dave, he is going to make sure there aren't any corrections that should be made. He will probably post it on his site after we are done.
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