Help Troubleshooting volume loss PLEASE

[Khron]

Part of that is probably the 6V filament supply maybe?

To be honest i have no real idea if these last tests were made with or without the tube installed.

 

[sonolink]

To be honest i have no real idea if these last tests were made with or without the tube installed.

Sorry, I didn't mention it since I thought it had to be installed. All the tests were done with the tube installed. Should I repeat them without it?

Cheers
Sono

 

[sonolink]

Hi again,

I decided to empty the board completely and repopulate it with new components from the same batch I bought except C1 (10uF/250v) for which I used a different one. I decided this because the cap I was using was bought on Amazon because it was really small, but since we are troubleshooting and the big one comes from Mouser, just to rule out everything dodgy...
I have also left out the 7806 regulator bit that feeds the heaters for now.

After repopulating the board I switched it on and got 260VDC, slowly dropping down. I left it on for more than 10 min and it stabilises around 250VDC.

After that I tried the same thing now with the Amazon cap. The result after 10 minutes is it stabilises around 255VDC!! It oscillates a bit but just a few millivolts.

So next I suppose I should add back the heaters system. I'll do that and report back.
Cheers
Sono

 

[sonolink]

Hi guys!
So, I added the regulators with the caps and measured and got HV=250VDC stable. It takes about a few minutes to stabilise. When switched on it goes up to 260 then drops down slowly until 250-255 and STAYS THERE!!
I checked the heaters and 6v were present and stable as a rock.

So after that I added the preamp circuit WITHOUT the distortion diodes (C11, R17, R18 and D3, D4, D5 and D6) and without the tube. Measured again and alles gut!

So I finally added the tube to the board and measured voltages again.
HV=220VDC
Tube: pins 1 and 6=110vdc, pins 3 and 8=1.5vdc, pins 4 and 5=6vdc
There is 0vdc across all pots pins.
All the measurements were taken using the One Spot PSU.

So what's left to do now is to add the distortion diodes circuit and if that's ok I'm baffled at what the hell was going on before...after that I'll add the balanced output and the cabsim and report back.

Thanks again for your time and help
Cheers
Sono

 

[sonolink]

Hi again,

I'm happy to report that I added the distortion diodes and everything is cool
After that I added input and output jacks, put it in its box and plugged it into my amp to see what it would sound like. It sounds awesome, either in front of the amp or in its FX loop return.
BTW there's no more hiss and no scratchy pot. So I'm very happy but I still wonder what was the problem. Obviously something I did wrong. Since I still have the old board I'll check later if all the components are the right ones, etc.

Next step is to add the balanced output and report back
Cheers
Sono

 

[sonolink]

Hi guys,
Got some news

I added the balanced output to the preamp and everything is fine BUT there's hiss and some hum. When plugging it into the amp it is less noticeable (although maybe that's subjective since I'm using headphones when plugged into the soundcard, so everything is like more "obvious").

Anyway, there is hiss and some hum, so first I checked that the hum wasn't my guitar single coils and it's not since it happens without the guitar too, and when I touch the pedal's grounded parts like jacks or the footswitch it goes away.

This does NOT happen when in bypass. In bypass it's dead silent. I tried connecting the pedal to the soundcard through the unbalanced output jack (to bypass the balanced output and the behaviour is exactly the same).

I recorded some audio for you. First you'll hear the pedal bypassed without the guitar plugged in. It's DEAD silent. After that, you'll hear switching the effect on, with considerable hiss and light hum "behind it". You'll also hear me touching the footswitch (hum goes away).
After that I plug the guitar in bypass mode and play some chords, and repeat the same with the effect on. All the pots are at 12 o'clock.
After that you'll hear me moving the Gain pot (no more scratching!!!)
And at the very end you'll hear the diode distortion switch moving. It makes a light "clic".
I tried all this with a reliable new tube and it's the same.

View attachment GTR02.mp3

Any ideas/suggestions please?
Cheers
Sono

 

[Khron]

This does NOT happen when in bypass. In bypass it's dead silent.

When the tube stages are bypassed, or the cabsim, or both?

 

[sonolink]

When the tube stages are bypassed, or the cabsim, or both?

When the tube stage is bypassed. Cabsim is not yet installed, only balanced out. When tube stage bypassed signal is clean either at unbalanced out and at the balanced output

 

[Khron]

Well, even that first triode has "quite some" gain to begin with.

https://www.ampbooks.com/mobile/amplifier-calculators/output-impedance/calculator/

100k plate resistor and 1.5k cathode resistor (bypassed) has a gain of (up to) 61x or so / 35dB. That'll be amplifying everything (including hum) by a relative lot.

Then again, if the hum goes away "when I touch the pedal's grounded parts like jacks or the footswitch it goes away", that points to some ground loop / earthing issue.

Is this going into an instrument input, or a line input, on your Ultralite? Is the power supply of that earthed (3-pin mains) or not? And does that connect to a laptop, or a desktop?

 

[sonolink]

Well, even that first triode has "quite some" gain to begin with.

https://www.ampbooks.com/mobile/amplifier-calculators/output-impedance/calculator/

100k plate resistor and 1.5k cathode resistor (bypassed) has a gain of (up to) 61x or so / 35dB. That'll be amplifying everything (including hum) by a relative lot.

My God, that's huge!! Probably the hiss has to do with that then. Maybe I should look for a way to tame that output a bit? Is that happening because the preamp wants to output into a high impedance input?

Is this going into an instrument input, or a line input, on your Ultralite? Is the power supply of that earthed (3-pin mains) or not? And does that connect to a laptop, or a desktop?

It's going into the jack input of IN1 on the Ultralite. Being a combo input I think it works as an instrument input when using jack connector.
The ultralite is connected only through usb to my macbook on battery (PSU not connected)

Thanks for your help
Cheers
Sono

 

[Khron]

Maybe I should look for a way to tame that output a bit?

The tonestack & "gain" are already doing that, at least to some extent.

It's going into the jack input of IN1 on the Ultralite. Being a combo input I think it works as an instrument input when using jack connector.

Exactly. When's the last time you've seen or heard of a balanced instrument input? And especially if you're using the balanced-out, why would you NOT want to go into a line input?

The ultralite is connected only through usb to my macbook on battery (PSU not connected)

Ultralite can't be USB-bus-powered, so i assume that's powered with its own not-earthed PSU? And do you still get hum without touching the enclosure, if you connect the macbook's psu?

 

[sonolink]

Exactly. When's the last time you've seen or heard of a balanced instrument input? And especially if you're using the balanced-out, why would you NOT want to go into a line input?

Sorry, I don't quite follow you. I assumed that the combo inputs on the Ultralite are mic input if using the XLR connector and line input if using the jack connector. I'm using a TRS jack cable between the balanced out of the pedal and the soundcard input.. Should I try a different input, like IN3 that is TRS only then?

Ultralite can't be USB-bus-powered, so i assume that's powered with its own not-earthed PSU? And do you still get hum without touching the enclosure, if you connect the macbook's psu?

Ultralite can be USB powered, at least my old firewire one can (it's the mk3).
If I connect the Macbook PSU nothing seems to change. I've noticed that if I touch the macbook hum disappears.

Since the pedal is clean when the tube stage is bypassed, I think probably it's a gain/impedance thing and that the noise floor raises and lets us listen to the hiss and hum (not sure if that makes any sense actually...)

Shall I add the cabsim circuit or it makes better sense to fix the noise first (or it doesn't matter?)

Cheers
Sono

 

[Khron]

I assumed that the combo inputs on the Ultralite are mic input if using the XLR connector and line input if using the jack connector.

Sure, that's why it (ONLY) says "Mic/Instr" right under it, right?

Ultralite can be USB powered, at least my old firewire one can (it's the mk3).

It can be powered via Firewire, but not via USB. Pretty sure about that. Manual says:
"Connect the UltraLite-mk3 to the computer here via either FireWire or USB2, using either the standard 1394 FireWire A or USB cable provided with your UltraLite-mk3. There’s not much difference, except that FireWire offers bus-powered operation (without the DC power supply)."

USB can only provide (from a computer) up to 500mA / 2.5W; Firewire can provide up to 1.5A @ 12-30V. Bit of a difference there, i think you'll admit.

If I connect the Macbook PSU nothing seems to change. I've noticed that if I touch the macbook hum disappears.

Well, that doesn't help much then - i guess the last few generations only had two-pin (double-insulated) power supplies

I think probably it's a gain/impedance thing and that the noise floor raises and lets us listen to the hiss and hum

Well, sadly, in the real world it's difficult (or rather impossible) to ONLY amplify the intended signal, but not the noise...

 

[sonolink]

Sure, that's why it (ONLY) says "Mic/Instr" right under it, right?

Sorry, I still don't follow you. What am I doing wrong?

It can be powered via Firewire, but not via USB.

Sorry, I meant FW. Well I meant that I'm not using any PSU. It's only connected to the laptop.

Well, that doesn't help much then - i guess the last few generations only had two-pin (double-insulated) power supplies

I don't know if it's a language barrier or something else, but I'm sorry, again I don't follow you. I don't understand what you mean.

Well, sadly, in the real world it's difficult (or rather impossible) to ONLY amplify the intended signal, but not the noise...

Do you mean that I'll have to live with that? That's just the way it is?

 

[Khron]

Sorry, I still don't follow you. What am I doing wrong?

As you can read under the XLR-combo connectors, those are for mics and instrument inputs. That could work, if you connect the "direct out" unbalanced into one of those. The "DI out" you'll want to connect to one of the line inputs on the back.

I don't know if it's a language barrier or something else, but I'm sorry, again I don't follow you. I don't understand what you mean.

https://en.wikipedia.org/wiki/Appliance_classes#Class_II (double insulated)
versus
https://en.wikipedia.org/wiki/Appliance_classes#Class_I (earthed)

When you touch the metal enclosure, you're conducting the leakage current (which causes the hum) to earth, that's why it goes quiet. The laptop's power supply not being earthed doesn't help.

Do you mean that I'll have to live with that? That's just the way it is?

I wonder if the hum still presents, if you hooked up the Ultralite to a desktop or another laptop with an earthed power brick.

 

[sonolink]

As you can read under the XLR-combo connectors, those are for mics and instrument inputs. That could work, if you connect the "direct out" unbalanced into one of those. The "DI out" you'll want to connect to one of the line inputs on the back.

I think I got all this wrong from the start.
I thought that the correct input for an unbalanced output (like a preamp or a guitar pedal) would be a line level input, a HighZ (instrument) input or a mic input through a DI box.

My idea behind adding the balanced output to the pedal was to have like a DI inside the pedal, to be able to connect directly to a mic input with a mic cable and avoid having to use an external DI for that.

What would you advise to achieve that?

https://en.wikipedia.org/wiki/Appliance_classes#Class_II (double insulated)
versus
https://en.wikipedia.org/wiki/Appliance_classes#Class_I (earthed)

When you touch the metal enclosure, you're conducting the leakage current (which causes the hum) to earth, that's why it goes quiet. The laptop's power supply not being earthed doesn't help.

I see what you mean now. Thanks for the links

I wonder if the hum still presents, if you hooked up the Ultralite to a desktop or another laptop with an earthed power brick.

I'm gigging now but tomorrow I can try plugging it into a Behringer XR18 mixer I have and report back since I don't have a desktop

Thanks a lot for your patience and help
Cheers
Sono

 

[sonolink]

Hi again,

This morning I hooked the pedal to my Behringer XR-18 using a mic cable into CH1........it sounds simply awesome!! There's no noise whatsoever and the sound is in it's range (I mean not too weak nor too strong and the pots are totally usable). No hum. Just pure Fender sound

You were right Khron, the unearthed laptop/Ultralite was the source of the hum problem.
So I'm going to add the cabsim now

One little question: to my taste, the Bass pot doesn't really add much bass when turning it to the right. It subtracts bass when turning it to the left though. How could I make it work so that it adds more bass when cranking it up? Is it the pot value (B25K), C8 (47nF), or none of those?

Thanks a lot for all your help!!
Cheers
Sono

 

[Khron]

One little question: to my taste, the Bass pot doesn't really add much bass when turning it to the right. It subtracts bass when turning it to the left though. How could I make it work so that it adds more bass when cranking it up? Is it the pot value (B25K), C8 (47nF), or none of those?

https://robrobinette.com/How_The_TMB_Tone_Stack_Works.htm

https://www.duncanamps.com/tsc/ (Windows only though)

 

[sonolink]

https://robrobinette.com/How_The_TMB_Tone_Stack_Works.htm

https://www.duncanamps.com/tsc/ (Windows only though)

Very interesting reading. Thanks a lot for the links
I think I'll try lowering the Mids pot to 10k, the tone slope resistor to 56k and the Mids cap from 47 to 22nF to increase a bit bass response (especially to use it with a bass). I have to be careful not to loose the "Fender Shimmer"...

I'm quite amazed at how good this thing sounds already, WITHOUT the cabsim!!

Also, I tried it with different tubes: JJ ECC83S, Russian 6N2P, ElectroHarmonix 12ax7 and Telefunken ECC82. They all sound great, although the russian is a bit hissy after a while playing.
I've read that it could be because it needs more plate current?
The others are beautifully silent and sound absolutely fenomenal.

Thanks a lot for your time and help
Cheers
Sono

 

[MidnightArrakis]

I assumed that the combo inputs on the Ultralite are mic input if using the XLR connector and line input if using the jack connector.

[I assumed that the combo inputs on the Ultralite are mic input if using the XLR connector and line input if using the jack connector] -- The NEUTRIK "Combo" connectors are designed to accept "balanced" (or, "stereo") signals from either an XLR-style connector or a 1/4-inch (6.35mm) TRS-style connector.

The actual signal-level -- type -- being fed into the the "Combo" connector can either be at "mic-level" or at "line-level", but.....>> NOT BOTH EITHER "MIC-LEVEL" OR "LINE-LEVEL" << depending upon which mating connector type that is used to insert into this "Combo" connector. In other words, despite which connector type is used as the inserted connector, the signal-level must both be either "mic-level" or "line-level" and the input circuitry of the piece of equipment containing the "Combo" connectors must also be designed to accept the appropriate incoming signal.

>> EXCEPTION: -- There are "Switching-Combo" connectors which could be used within specialized circuit designs whereas the 1/4"-connector could be used as a "line-level" input and the XLR-connector could be used as a "mic-level" input. Although such a use would be possibly considered to be "rare", it is nonetheless.....a possibility to accomplish!!!






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