Suhr Minimix II - complete schematic

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bluesfendermanblues
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Re: Poor Design

Post by bluesfendermanblues »

bluesfendermanblues wrote:
GatesofDawn67 wrote:I cannot believe they put the relay in the summing node of the op amp. Any noise that couples in here will see the total open loop gain of the op amp. The input resistor should go between the relay and the op amp.

The 49.8k's are probably the recommended load for the xformers. They could be wired as shunts and the summer could use 2k input and feedback resistor for lower hiss and less noise pick up.
Do you own a minimix II or have you tried one? If so, what hiss and what noise, are you refering to, the MMII is completely noiseless. Dont try to reinvent the wheel ;-) The relays are there in order for you to switch off parallel operation if you use eg a compressor Or eq in the loop.

@angelodp, I have build a clone on a peice of veroboard for my second rack, using the simplified schematic I posted - without xformers and relays - using a simple +/-15v supply. And it is aldo completely noiseless and transperant. :?
The relay's in the signal way are there in order to facilitate, muting the direct path (or muting the effects path) - see picture
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GatesofDawn67
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If it sounds good, great. It can be improved.

Post by GatesofDawn67 »

Do you own a minimix II or have you tried one? If so, what hiss and what noise, are you refering to, the MMII is completely noiseless. Dont try to reinvent the wheel The relays are there in order for you to switch off parallel operation if you use eg a compressor Or eq in the loop.
I agree that the proof in the pudding and If it ain't broke, don't fix it. If you like the box that's great. However, I am saying that there are many things they could done without costing more that would made it less susceptible to noise pick-up and generation.

Using it the way you do, those issues may never be a problem for you. Have you tried it in a noisy environment, like under stage lights?

It is not good engineering practice to place anything but the summing resistors in the summing node of an op amp. I have designed many audio products over the past 25 years and I have seen more than one engineer make the mistake of of stringing out a summing node and having it pick up power supply hum, radio stations, etc.

They can still have the relay, but placing it before the summing resistors is a more robust design.

What is completely ironic is they have an unused op amp that could have summed R2 and R3 before sending their signal to the relay. The output of an op amp is low-impedance which makes it immune to noise pick up.

If Suhr used a ground plane and put the resistors and relay as close to the op amp as possible, then it may be good enough.

If you follow this box with enough gain you may hear the hiss of the 49.8k resistors. 4.98k resistors will have 10 dB less hiss than the 49.8k.
bluesfendermanblues
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Re: Suhr Minimix II - complete schematic

Post by bluesfendermanblues »

Guys,

Here's a couple of pics of my DIY clone of the Minimix II.
Like I said, its works exactly like the original that I have in my other rack.

I know its not a beauty 8), but it works.
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markusw
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Suhr Minimix II - complete schematic

Post by markusw »

Hey Claus,

thanks a lot for posting the complete schematics! :D

Best regards,

Markus
bluesfendermanblues
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Re: Suhr Minimix II - complete schematic

Post by bluesfendermanblues »

markusw wrote:Hey Claus,

thanks a lot for posting the complete schematics! :D

Best regards,

Markus
Thanks, have you build one yourself?
Diva or not? - Respect for Mr. D's work....)
Bob Walker
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Re: Poor Design

Post by Bob Walker »

GatesofDawn67 wrote:I cannot believe they put the relay in the summing node of the op amp. Any noise that couples in here will see the total open loop gain of the op amp. The input resistor should go between the relay and the op amp.

The 49.8k's are probably the recommended load for the xformers. They could be wired as shunts and the summer could use 2k input and feedback resistor for lower hiss and less noise pick up.
Nonsense. Historically, recording and broadcast consoles ran summing junctions (a.k.a. ACNs) the entire length of the console. Implementation dependent...
It is cheaper to switch both resistors with a form SPDT relay than a DPDT relay.
The MM2 has exposed summing node of a few inches. The enclosure is shielded as well. You have as much chance of RF getting into a resistor lead as a relay.

The input impedance of the transformer is 10K. The 49.9K resistors (not 49.8K!) were chosen to not load the transformer (reflected back to the primary). If 2K resistors were used as input resistors, they would effectively load the transformer secondary, since they are feeding a virtual ground.

Amp and effects noise swamps out any noise created by this circuit.
Bob Walker
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Re: Suhr Minimix II - complete schematic

Post by Bob Walker »

bluesfendermanblues wrote:Yes, the xformers are just for isolation purposes.

The reason the use 3 is that you can use a stereo jack to connect two effect units - one on tip, one on ring - and eac of the two returns 'get' a xformer.

IF you, however, flick the little switch you can alter the operation to balanced mode instead.

However, using transformers both send an return are IMO way overkill or over engineering. You can avoid ground loops simply by using xformer on the send OR using gound lift on either the send or return jack.

No! Ground lifting is NOT acceptable for pro musicians, especially when safety is a concern. Transformer isolation is the preferred method.
zombuswoof
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Re: Suhr Minimix II - complete schematic

Post by zombuswoof »

Sorry to bump an old thread but I was looking for technical info for this unit and stumbled on this thread via Google. I've been a lurker and a non- contributing member here for a while. With that said, I'm shocked there weren't any comments about the state of that pcb. It's filthy, covered in flux, and there's stray solder balls knocking about. Is it just me or does anyone else feel a compulsion to scrub that board down and clean it up? :?
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Structo
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Re: Suhr Minimix II - complete schematic

Post by Structo »

Please tell us how you really feel. :D
Tom

Don't let that smoke out!
vibratoking
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Re: Suhr Minimix II - complete schematic

Post by vibratoking »

zombuswoof wrote:Sorry to bump an old thread but I was looking for technical info for this unit and stumbled on this thread via Google. I've been a lurker and a non- contributing member here for a while. With that said, I'm shocked there weren't any comments about the state of that pcb. It's filthy, covered in flux, and there's stray solder balls knocking about. Is it just me or does anyone else feel a compulsion to scrub that board down and clean it up? :?
1st post? What PCB are you talking about? There are 2 in this thread. It would have been useful to specify exactly which one has you shocked. If you have lurked here a long time and paid attention, you would not be making this post, IMO. :roll:
bruce egnater
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Re: Suhr Minimix II - complete schematic

Post by bruce egnater »

I would assume the messed up board was the result of the hacking to figure out the circuit? Suhr's work is usually impeccable.
bluesfendermanblues
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Re: Suhr Minimix II - complete schematic

Post by bluesfendermanblues »

bruce egnater wrote:I would assume the messed up board was the result of the hacking to figure out the circuit? Suhr's work is usually impeccable.
You're spot on!

I had to use a little brute force in order to dissemble the Original Suhr Minimix II. If the original Suhr board, has any soldering stains or the like, It solely stem from my unsoldering and resoldering of the components. I also own an original Suhr Minimix, which also has very high build quality.

As I said initially in the beginning of this post:
bluesfendermanblues wrote: the US price is only USD 250, so its not worth your while to make a DIY version. The right components (e.g. 1% resistors), line transformers, omron relays, switches, DC|DC converters, jacks and hammond box....you cannot possible beat the price in US. So buy a real genuine version.

This schemo is only posted in order to show that the Suhr Minimix II is basically a buffer amp and a summing amp - no mumbo jumbo, no phase shifts, just a plain and simple quality product that delivers the goods.
Diva or not? - Respect for Mr. D's work....)
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