Volume loss on custom built switcher (looper)... help?

[boroman]

Guys, I made my own looper/switcher that has only 3x 3PDT (loop) switches. One engages TUNER (and mutes the signal), middle one is just for the Fuzz, and third one controls rest of the effects. Simple.
High quality wires, switches, cabling.

[Photo below]

My signal goes through: BASS -> ZVEX SUPER HARD ON -> SWITCHER etc... -> AMP (yes, Zvex buffer is wired before everything)
Everything works. Switching, tuner bypass, etc.
However, even with everything switched off (or Zvex on, or zvex off) I get few decibels down from the signal comparing to straighforward connection BASS>AMP
It's not hi-end loss due to impedance cabling etc. Just volume down.

If 3PDT switches weren't wired right, there should be some problems like: ground loops, buzzing, no signal... but WEAKER signal? How's that possible?
I know that's hard to diagnose, but maybe some tips.. I just dont know where to do now. PS: It's PITA to disassemble everything, but I tripe checked my soldering and connections...

[Helmholtz]

Schematic?

[tedmich]

Zvex circuit is a pretty odd one (5 MOhm input, BS107P transistor) and they say it does strange stuff with some guitars...how's it sound without that one?

[Mick Bailey]

Measure the end-to-end resistance of each loops' hot and ground respectively, and the resistance from hot to ground. Volume loss means either some unwanted resistance to ground, or series high resistance somewhere. Also, be sure you don't have a cable with a conductive screening layer that's touching a signal connection. This can give the symptoms described - sometimes as low as 10K Ohm to ground.

[Mark Hammer]

Take a look at this, and ponder whether it addresses the difficulties you're experiencing with your selector unit.

[boroman]

Zvex circuit is a pretty odd one (5 MOhm input, BS107P transistor) and they say it does strange stuff with some guitars...how's it sound without that one?

I mean, loss of volume is with zvex on and zvef off (hard bypass), so it's not zvex
I've tried to bypass zvex completely from the circuit and I still have few dBs lost.
BUT I dont have any loss in volume when I did the test not plugging the guitar but audio interface and 1k sinus through it and back. It's identical volume... Only when bass is plugged (no matter what bass, no matter which cable).

Mick Bailey I'll try to measure it now - I quite dont get the idea, but I will search and try to undestand.
Helmholtz It's a pretty strightforward switcher, pictrures below. I have checked wiring twice today, everything seems allright
Mark Hammer Thank you, I'll watch this. But signal from soundcard goes without volume loss. I have highest quality 3PDT "silent" switches I could find.

[boroman]

Not really sure how to measure those impedances across... I connected bass to the switcher

Bass + cable = 10.5kOhm
Bass + cable + SWITCHER = 9.8kOhm (measured at the output jack of switcher, everthing switched off)

Also, I measured ground-to-ground from input jack to output jack and it's like 0.8-0.9 Ohm (also input ground to other ground in the circuit at 3PDTs etc. shows the same values)

[Mark Hammer]

Fifty-some years ago, my bedroom "sound system" consisted of plugging the output of the crystal cartridge in my turntable into my guitar amp. One day, I was trying to connect them, but the turntable and amp were on different sides of my bedroom and I couldn't reach both cables at the same time. My dad happened to pop into my room to ask me something. I was holding on to a cable plugged into the amp, so I asked my dad if he could hand me the connecting cable from the turntable. He cooperated, but did one of those accidental errors, where he extended the wrong hand, holding on to the turntable wires with his right hand and sticking out his left hand to my free hand. To our mutual surprise,the turntable (which was playing a record at that point) was louder than it normally was through the amp when the cables were physically connected. My kid sister came in the room and we got her to hold my free hand and my dad's free hand, and it got even louder.

I have absolutely no explanation for it, but it happened, and surprised the dickens out of us. I don't know what sort of contact I was making with the hot lead of the cable to the amp, nor what sort of contact my dad was making with the hot lead of the (mono) turntable cable, though I'm pretty confident it wasn't particularly specific.

Sometimes stuff happens.

[Helmholtz]

BUT I dont have any loss in volume when I did the test not plugging the guitar but audio interface and 1k sinus through it and back. It's identical volume... Only when bass is plugged (no matter what bass, no matter which cable).

That test seems to confirm an impedance loading effect .

The very low output impedance of the audio interface won't notice a say 50k load.
But surely your bass would and even the Z-Vex might.

Maybe one of the switch contacts is bad, making contact when it shouldn't.

(You can't measure impedance with a DMM.)

[Mick Bailey]

Take the instrument and effects out of the equation: Plug a patch lead in each loop to bridge both FX loops send/return. Now plug a lead into the input, and a lead into the output. The unit should behave like it isn't there, so measure the input resistance tip to tip, and sleeve to sleeve respectively. Both readings should be close to zero, which shows continuity (if you first short your meter probes that will give you the lead/probe resistance - subtract this from any subsequent reading you get). Now measure the input tip to sleeve - it should read open circuit. You could also measure the output tip to sleeve. Try this with the loops activated or deactivated. All readings should stay the same.

[boroman]

Okay. I have surrended in testeing, but removed two shielded cables (that went to Zvex and back) and wired it classic way.
All OK now, so thanks again for addressing the issue somehwere on the "shield". It deafinitely was that.

But I have next question.
Example:

I am plugged into the switcher, but nothing is connected through all of the loops. Just input cable from guitar and output cable to amp. Question is - now when I hit one of those 3 switchers that engage loops, it should be completely silent, right? nothing connected so no signal coming back to the loop. But I hear very very small amount of signal in the amps' speakers. So something is passing the signal just a bit. Are those 3PDT switches that are not perfect? And I should live with that, end of story?

[Mick Bailey]

In theory, it should be silent, but in practice you may have some capacitive coupling within the wiring or the body of the switches that passes a tiny amount of signal. This doesn't affect the operation of your switcher.

What do you mean when you said you wired the Zvex the "classic way"?

[boroman]

In theory, it should be silent, but in practice you may have some capacitive coupling within the wiring or the body of the switches that passes a tiny amount of signal. This doesn't affect the operation of your switcher.

What do you mean when you said you wired the Zvex the "classic way"?

Thanks, I may live with that...
By "classic" way, I meant now it's like bass > zvex > switcher (via patch cables)
Previous was bass > switcher input -> that was wired with shielded cable to zvex in, the same went out of vewx out (hardwired to switch input pin), > switcher