Rackmount pedals & noise experimentation

BaronWilhelm · October 30, 2016, 02:35:15 PM

I've been building my latest pedals in a rack format to keep them tidy. I have a "MIDI" relay daughter board I built which is included on each one. I've been working lately to reduce the noise floor on these as much as possible. I've started to use shielded wire on all the inputs until the first gain/amplification stage. My question is about the lack of a true enclosure like on a floor pedal. I'm not even sure if the noise would just be exactly the same in a box and it is just the nature of the circuits. I'd like to do some further experimenting with an oscilloscope and move the exact "pedal" in and out of a box to see the difference. Should I expect that to be true? Does anyone have any suggestions on how to reduce noise in this layout? Any info pertinent to my project would be awesome, I'm still learning and doing a lot by trial and error which is labor intensive. Any tips which would cut out some grunt work would be much appreciated.

BaronWilhelm · October 30, 2016, 02:36:08 PM

I forgot to post the pics...

PRR · October 30, 2016, 02:53:49 PM

Open frame chassis directly under a AC power source looks dubious to me. Surely you can put the big 60Hz *away* from your small audio?

BaronWilhelm · October 30, 2016, 02:57:09 PM

Quote from: PRR on October 30, 2016, 02:53:49 PM
Open frame chassis directly under a AC power source looks dubious to me. Surely you can put the big 60Hz *away* from your small audio?

Oh absolutely! The rack is otherwise empty. That is exactly the kind of tip I was looking for. Thank you so much for your reply

How much distance do you think would be sufficient? 3U? More?

PRR · October 30, 2016, 04:04:07 PM

> How much distance

May I propose "try it and see"?

Take the Furman out and set it as far away as posible. Find all other line-power boxes in the area and move them away. Now listen to your rack as you or a helper brings the line-power stuff in closer.

Maybe it can be adjacent. Maybe it must be 2 feet away. Depends some on how the Furman is shielded and a LOT on how your modules are (or are not) shielded.

In recording and big PA we'd put the power-strip below the (insensitive) power amps, and the low-level signals at the top of a 4'-6' rack.

Mark Hammer · October 31, 2016, 08:27:40 AM

Love the modular approach.

BaronWilhelm · October 31, 2016, 08:42:42 AM

Thanks Mark!

nefthy · November 04, 2016, 02:29:07 PM

I very much like your approach. Was thinking of doing something along this lines my self, although I think I will go more along the lines of the 500-series modules, with power, bypass and interconnects being on the rack side.

Where did you get the aluminium trays? Custom cutting and bending seems way to expensive in this part of the world (like $60 per module)

Concerning your original question, are the module shelves enclosed in metal casing? If not, this will probably help. Do you have audible noise issues?

ElectricDruid · November 04, 2016, 02:48:49 PM

If you're not in a stomp box format any more, you could try using a larger-headroom bipolar supply. +/-12V or +/-15V would be typical. Get your input signal level up to +/-5V or more and you'll see a big improvement in your S/N.

Also if you've got MIDI in there, you've got a microprocessor decoding MIDI and switching that relay. How well separated is the uP power from the audio power? There's a potential for noise there too.

Tom

BaronWilhelm · November 04, 2016, 03:17:34 PM

Thanks! I had a long look at the series 500 module design too, but settled on the Eurorack format in the end based mostly on cost. Here are the mounting brackets I used http://store.synthrotek.com/3U_Eurorack_Brackets

For the faceplates, I ordered a few of these blank panels http://syinsi.com/product/blank-panels/ to try in different sizes, then got a bunch cut at onlinemetals.com in 2mm 5052 aluminum 5.125" tall. I found the best sizes were 6hp for one knob column, 10hp for two.

The cabinet I designed and built myself with some 16U rails from eBay. The aluminum trays were inspired by this video https://www.youtube.com/watch?v=n-ugh8sbHw4 I bought a large piece of 24 gauge 5052 aluminum sheet and just cut it with metal shears, then bend and drill the bracket by hand.

My front panel has all the knobs/switches and a "soft" momentary switch to handle the bypass switching. In the rear I have connections for audio In/Out, power, and RJ11 jacks for daisy chaining my communication lines. I decided on putting the interconnects on the back and using the patch bay to save real-estate on the front panel, and to not clutter the face of it with cables everywhere. I think that was the right decision so far.

The daughterboard is a ATTiny85 which monitors the switch for the relay bypass and do communications. Upstream I have a single Arduino master unit with a MIDI interface to send events and other various USB commands. The pedal CPUs are inactive except when switching, so I don't think it's contributing much if any noise. The result is I can hookup my Helix and can assign my DIY pedals to footswitches.

As for the noise, I was not even sure if the noise I was experiencing was "normal" After a lot of investigating it turned out to primarily be from the cheap-o switching wall wart I was using to power the whole thing. I built myself a 400mA linear regulated supply and the noise dropped noticeably. I did some experiments with the effects in and out of enclosures and noticed no difference so I don't *think* that is an issue anymore.

QuoteIf you're not in a stomp box format any more, you could try using a larger-headroom bipolar supply. +/-12V or +/-15V would be typical. Get your input signal level up to +/-5V or more and you'll see a big improvement in your S/N.

Tom, thanks so much for your suggestion. I'm going to investigate that right now. Do you have any further detail or links that would be helpful? I'm going to have to do some more research to fully understand your comment, I'm still a bit of an electronics newb

ElectricDruid · November 05, 2016, 02:15:07 PM

Quote from: BaronWilhelm on November 04, 2016, 03:17:34 PM
QuoteIf you're not in a stomp box format any more, you could try using a larger-headroom bipolar supply. +/-12V or +/-15V would be typical. Get your input signal level up to +/-5V or more and you'll see a big improvement in your S/N.
Tom, thanks so much for your suggestion. I'm going to investigate that right now. Do you have any further detail or links that would be helpful? I'm going to have to do some more research to fully understand your comment, I'm still a bit of an electronics newb

Well, I don't know where to say to start! Pretty much all audio electronics *except* stomp boxes runs on bipolar supplies and having a bipolar supply often makes life a lot simpler. I do a lot of synthesiser electronics too, and you'd see quite a bit of overlap with guitar stuff on some of the synthesiser DIY sites - filters like wah pedals, VCAs for tremolo/envelope effects, etc etc - except on larger bipolar supplies.
Aha! That's the answer! You could have a look at Frequency Central! Not only is Rick another example of someone who spends time in both the synth and the pedal worlds, but he's done "cross-over" synth modules based on pedal designs.
You might like:

http://www.frequencycentral.co.uk/?page_id=1484
(Meth Amp, based on the Big Muff, with a ton of extras and voltage control)

http://www.frequencycentral.co.uk/?page_id=647
(Continuum phaser, based on Rick's earlier pedal designs)

Full disclosure - Rick and I have worked together on many projects. Frequency Central do versions of some of my Druid projects, and I've helped Rick with PCB designs and other bits and bobs.

Tom

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Rackmount pedals & noise experimentation