Parallel Looper Issues

[Spacecommandant]

I've been working on a parallel mixer with optional tails switch. I modified the switch wiring from Induction's tails mod from the All-Star Digital Reverb, and incorporated the circuit grounding of the sends/bypass from Slacker's looper.
This version is currently working, although after plugging in power there is an initial large pop sound when either the On/Off switch or Tails switch is engaged. After waiting about 20 or 30 seconds after clicking either of these switches the first time, the switches no longer pop. I'm wondering if anyone has any ideas for eliminating this popping sound. Would it be worth trying JFET bypasses?
There is also a soft hiss in the background when engaged; what I'd describe as white noise. It's not super loud but it is noticeable at loud volumes. I'd like to reduce it as much as possible.
I'm also wondering if the 330k/47k resistors in the feedback loop of U2 are too large... those could likely be reduced, keeping the 7:1 ratio?
Any other insights and feedback for improvements would be greatly appreciated... thanks!

[madbean]

First check for any DC readings @ R16/17 and R6/R8 (alternate the switch state so you can check both when they are not in a ground state. If there's no DC reading from step 1, maybe put 1M resistors b/w lugs 1&2 (brown wire, ground wire) and lugs 3&2 (orange wire, ground) to see if that reduces the pop.

I'm not sure about you noise issue. I would audio probe U2A and U2B  pins 3 and 5 and compare noise against their respective output pins 1 and 7.

You also probably don't need R5, R22 nor R30.

[Spacecommandant]

Thanks so much. I'll give it a try!

[madbean]

A few other things I noticed:

You should really reconsider re-balancing the entirety of resistor values you've drawn here. Most of them can be reduced greatly (even eliminated) without compromising the signal integrity. The advantage of doing that is lower resistance values can reduce noise. If I have time, I'll re-work your schem with my suggestions tomorrow. I think your idea is great, it just needs a little finesse. I haven't quite gone through all the switching yet.

[jimilee]

Does anyone have an original Klein bottle schematic?


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[Spacecommandant]

A few other things I noticed:

You should really reconsider re-balancing the entirety of resistor values you've drawn here. Most of them can be reduced greatly (even eliminated) without compromising the signal integrity. The advantage of doing that is lower resistance values can reduce noise. If I have time, I'll re-work your schem with my suggestions tomorrow. I think your idea is great, it just needs a little finesse. I haven't quite gone through all the switching yet.

Thanks, Brian. Grateful for any advice.

[Spacecommandant]

First check for any DC readings @ R16/17 and R6/R8 (alternate the switch state so you can check both when they are not in a ground state. If there's no DC reading from step 1, maybe put 1M resistors b/w lugs 1&2 (brown wire, ground wire) and lugs 3&2 (orange wire, ground) to see if that reduces the pop.

I'm not sure about you noise issue. I would audio probe U2A and U2B  pins 3 and 5 and compare noise against their respective output pins 1 and 7.

You also probably don't need R5, R22 nor R30.

I'm not 100% sure I did this correctly but here's what I found: I set the multimeter to DC Voltage 200m and attached the black lead to ground.
I'm going to call the junction between R16 & R17 'A' and the junction between R7 & R8 'B.'
With the effect On, 'A' measured 0 and 'B' measured 04.4
With the effect Off, 'A' measured 04.4 and 'B' measured 0

[Aentons]

I'd bet that hiss you hear is partly from the gain set so high on the return opamps. You might need a quieter opamp if you are going to set the gain high and then have the volume after. The high value resistor noise will compound it. You could move the pot to the feedback loop (R20 and R28) to control the volume

[Spacecommandant]

I'd bet that hiss you hear is partly from the gain set so high on the return opamps. You might need a quieter opamp if you are going to set the gain high and then have the volume after. The high value resistor noise will compound it. You could move the pot to the feedback loop (R20 and R28) to control the volume

You're probably right. I'd like to be able to turn the volume completely down, though. Is there a way to configure the resistors for that?
I had a thought a few minutes ago about this. If I were to change R20 & R28 to 100k and R21 & R29 to 15k, I'd still maintain the 7:1 ratio and this would bring them down to a lower value.
If I made the 100k feedback resistor one gang in a dual gang pot and made the 100k volume the other gang in the dual gang pot, then as I turned the volume down I'd also reduce the op amp gain. I'm not sure if it would work as I'm imagining. I guess I'd have to try it out to see how it responds.

[Aentons]

It's a non inverting stage so it won't go below unity, but if you convert it to inverting it will go below. You could then take out one of the two inverting stages after it.

I'd just wait to see what Brian comes up with. I'm relatively new at this stuff, he's a real pro

[Aentons]

Does anyone have an original Klein bottle schematic?

Peter sells the download of it on the VFE site so I'm not sure he wants us passing it out. I'll tell you.. it's a real nightmare, especially all the mixing stuff

[Spacecommandant]

It's a non inverting stage so it won't go below unity, but if you convert it to inverting it will go below. You could then take out one of the two inverting stages after it.

I'd just wait to see what Brian comes up with. I'm relatively new at this stuff, he's a real pro

Great idea, thanks.

[jimilee]

Does anyone have an original Klein bottle schematic?

Peter sells the download of it on the VFE site so I'm not sure he wants us passing it out. I'll tell you.. it's a real nightmare, especially all the mixing stuff

My thought process is, it does what he is looking for, so he could at least see the schematic of the implementation.


Sent from my iPhone using Tapatalk

[Spacecommandant]

Does anyone have an original Klein bottle schematic?

Peter sells the download of it on the VFE site so I'm not sure he wants us passing it out. I'll tell you.. it's a real nightmare, especially all the mixing stuff

My thought process is, it does what he is looking for, so he could at least see the schematic of the implementation.


Sent from my iPhone using Tapatalk

I might check it out and try to make sense of it... thanks.

[Spacecommandant]

Here is a schematic of the Tails/Bypass designed by Slacker that I tried to incorporate. I changed R5 from 1k to 47k since it wouldn't work properly with 1k in an earlier version of my circuit.