Do you realize it's you that's paying for it?
Isolated stompbox power supplies sharing a board, share the ground plane? Or fully isolate?
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kato
Well-known member
I added a back channel of connectable ground points just in case it would help to use capacitors between the ground planes. But after reading this thread, I may just remove them; they're probably unnecessary and may just confuse people.
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It's called wisdom.my mind gets slower every day....
JR
kato
Well-known member
LOL. Definitely.
I'm pretty cynical, but not so cynical that I think they'd do this for pure marketing hype. ¯\_(ツ)_/¯ Well, maybe I am.
I'd like to think an engineer would step in and say, "This is entirely unnecessary. One single secondary will do the job." I'm not the type to pay for a Lexus when my Toyota will get me there.
Do you realize some of us actually are engineers?
moamps
Well-known member
The problem is not in the possible dirty voltage of the power supply, but in the current consumed by each pedals box and a certain resistance of the connecting cables. The power supply may have a perfect voltage, but the current it provides has an alternating nature (especially in the case of pedals that contain a bunch of digital ICs) and can induce a certain AC voltage on the cable resistance. This voltage is actually the ground (common) loop voltage that adds up to an audio circuit with a useful signal if these power supplies are not isolated from each other.
Audio, control and digital grounds/common lines and returns for the same reason are mostly separated in consoles. Also some manufacturers use balanced buses to reduce crosstalk between channels because audio ground/common reference is polluted by all return currents from channels.
I don't enjoy sharing embarrassing facts about Peavey but that episode of Undercover Boss was more embarrassing than anything I could share. In hindsight it is hard to imagine why they ever agreed to do that show. It is tired modern remake of the old "queen for a day" formula where some low level worker gets a free house /college education/whatever. That is the company buy-in (quid pro quo) for the presumably good publicity they are supposed to get when thankful employees gush their joy and happiness on network television.
There were multiple cringe worthy moments from that entire show, I knew many of the people involved from working there 15 years. WRT to the one female worker who was less than complementary to Hartley when asked it should be obvious why. Over the last several years she saw the vast majority of her co-workers laid off, and saw her own educational assistance, vacation, and other indirect pay cut backs. Rather than being thankful for the opportunity to work there she was probably wondering what would be cut back next.
I have known several wealthy/famous people who had a poor self awareness and misread how they are perceived by those around them. I had an OK personal relationship with Hartley but he had me escorted out of the building by security guards immediately when I gave him my 2 weeks notice.
I have slept fine ever since voting with my feet.JR
moamps
Well-known member
The first reply you got was from a fellow with a PhD title. Of course, not from MIT, so you should take his opinion with a grain of salt.
The customer is always right, even when horribly wrong, as long as they are willing to buy the SKU.
JR
JR
Bo Deadly
Well-known member
Ground plane > power cable > pedal > patch cable different pedal > power cable > ground plane. That makes a loop. What am I missing?
Matt Syson
Well-known member
The grounds should be isolated for each output because there will be a shield connection of the audio signals linking the pedals which are likely to be linkerd in various permutations, sometimes with unnecessarily long cables, maybe coiled up to try and tidy them. Other random power transformers or switchmode supplies 'just for this gig' or more frequently. If it is guitar signal it may be high impedance direct from the guitar (a stomp box in direct bypass for some songs perhaps) or dropping to a 'more robust' buffered impedance level when the box is active. To do a decent job it needs to be as 'idiot proof' as possible because you can guarantee that at some point it will get tested, possibly at a most embarrassing moment. Transformers with an interwinding screen between primary (mains) and the low voltage secondaries are a good (but more expensive) idea to reduce the posibility of mains borne HF 'rubbish' getting into the (ultimately) DC outputs. This brings it to common mode noise which should have some way of reduction. It takes considerable effort to make truly 'quiet' DC supplies. Power and signal grounding inside mixing desks has kept me busy for 40+ years and surprisingly those that perform with least unwanted noise follow basic principles put forward by the early inventors/scientists like Michael Faraday.
OK, that makes sense.
Tell me how it is a problem.
So how would the "ground" travel from pedal to pedal?
We're talking pedal boards here, audio connections are made with short TS cords.
So... The thing that having these floating power supplies solves is pretty straightforward: Imagine 2 pedals - One high gain analog and one digital. If you have a single 12vdc supply and have 2 linear regulators to have 2 outputs that share a ground, you end up having the digital pedal sending nasty digital currents back to the reference ground at the powersupply which is common to both pedals. These currents modulate the ground on the analog high gain pedal creating a nasty noisy mess. When you have floating 12vdc supplies with each having a 9vdc regulator to its output, the nasty ground currents each have seperate ground return paths to their respective supply, but have quiet reference grounds to each other via the audio cable between them. Dont think of grounds as grounds - think about them like resistors or better yet inductors.
THis is my first post by the way, so Hi!
kato
Well-known member
The first reply you got was from a fellow with a PhD title. Of course, not from MIT, so you should take his opinion with a grain of salt.
FWIW, I took it as gospel and sent my gerbers off to manufacturing. Thanks!
Bo Deadly
Well-known member
EMI induces currents in said loop. The signal line will not have the same currents and therefore there will be differences between the signal and 0V line voltages which equates to noise.
Instead of being coy, why not just explain how to "think it over"?
kato
Well-known member
Ha, sorry. Didn't mean to uncover any old wounds. I was always proud of my Peavey gear. My bass amp with that giant 18" Black Widow pumped out a primal low end that kicked the ass of any boutique 4x10 bass amp with aluminum cones.
I guess the show was theoretically a PR trainwreck but it didn't make me think any less of the company. It just reminded me that globalization has reduced American manufacturing to a husk of its former self and made me nostalgic for the days before every company had to relocate their jobs to stay competitive.
Glad to have your historical perspective.
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kato
Well-known member
Yeah, this is a good point. Thanks for joining the conversation. Welcome!
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