Two Rock JM Preamp

[cgmason1986]

I really want to build something like this Peace Hill FX standalone preamp for recording (image attached), I just want a sanity check on the schematic. From what I can tell this looks to be based on the Amplified Nation Wonderland layout - which I found the schematic for from M Fowler (marked up and attached). Am I missing anything in this schematic, or something extra that I don't need? I'm going to power it with one of these: https://frogpedals.com/index.php/produc ... er-supply/

Amplified Nation original thread:
https://ampgarage.com/forum/viewtopic.php?f=4&t=29774

Amplified Nation layout:
https://ampgarage.com/forum/download/fi ... &mode=view

[cgmason1986]

I went ahead and tried to build the preamp. The [first noticeable] issue I'm having is that the tube is not heating up. I'm getting 6V at the heaters, is there something else that I should check? I tried with a different tube as well. This is my first time trying to building something with a tube so I'm a little lost for troubleshooting. See pics attached, also including a pic of my layout if that helps.

Thanks-
Curtis

[markusw]

I went ahead and tried to build the preamp. The [first noticeable] issue I'm having is that the tube is not heating up. I'm getting 6V at the heaters, is there something else that I should check? I tried with a different tube as well. This is my first time trying to building something with a tube so I'm a little lost for troubleshooting. See pics attached, also including a pic of my layout if that helps.

Thanks-
Curtis

Looking at the layout heater pins 4/5 are missing a connection to GND.
Regards,
Markus

[Bombacaototal]

You seem to be using a skyliner-ish tonestack, Mayer uses classic. This is actually dumble stack, really different from Mayer Sig in amp, as you are missing gain stage which really changes things

[cgmason1986]

Looking at the layout heater pins 4/5 are missing a connection to GND.
Regards,
Markus

Thanks Markus - I'm 100% sure I've wired these heaters wrong. Right now I've actually got 6VDC connected to Pin 4, then jumper pin and pin 5, then wire from pin 5 to pin 9. To complete this circuit do I need a wire from 9 to ground? Or should I run 6V to pin 9 and then ground 4 and 5, does it matter? Also am I correct that since this a 6VDC supply I don't need to twist the wires since that just cancels AC hum?

[cgmason1986]

You seem to be using a skyliner-ish tonestack, Mayer uses classic. This is actually dumble stack, really different from Mayer Sig in amp, as you are missing gain stage which really changes things

Interesting - I was just using the Ceriatone/Amplified nation layouts for their JM sig clones. I'll have to do some more research on adding the gain stage. There's plenty of room in the enclosure to add more. Thanks!

[Bombacaototal]

You seem to be using a skyliner-ish tonestack, Mayer uses classic. This is actually dumble stack, really different from Mayer Sig in amp, as you are missing gain stage which really changes things

Interesting - I was just using the Ceriatone/Amplified nation layouts for their JM sig clones. I'll have to do some more research on adding the gain stage. There's plenty of room in the enclosure to add more. Thanks!

No worries, and bear in mind you will need to do adjustments to simulate the signal that is usually lost through the reverb circuit, as just adding the gain stage will sound different

[Guy77]

Yes that extra gain stage and simulating the signal changes with the reverb circuit is what really makes the JM Sig sound.
If your after that sound than you will need to add those changes. I have tried and without those changes its always different.

It would also be great to have a JM clone handy so that you can compare sounds and tweak as required.
But if your happy with the sound you have that is fine too!

Cheers

Guy

[markusw]

Looking at the layout heater pins 4/5 are missing a connection to GND.
Regards,
Markus

Thanks Markus - I'm 100% sure I've wired these heaters wrong. Right now I've actually got 6VDC connected to Pin 4, then jumper pin and pin 5, then wire from pin 5 to pin 9. To complete this circuit do I need a wire from 9 to ground? Or should I run 6V to pin 9 and then ground 4 and 5, does it matter? Also am I correct that since this a 6VDC supply I don't need to twist the wires since that just cancels AC hum?

Only connect pin 4 and 5. Then pins 4/5 to 6V and pin 9 to GND, or the other way round, doesn't matter.
This way the two heaters are in parallel.
If you also connect 5 to 9 you will short the heaters and therefore also the heater supply to gnd.
No need to twist the wires when using reasonable clean DC.

[cgmason1986]

Only connect pin 4 and 5. Then pins 4/5 to 6V and pin 9 to GND, or the other way round, doesn't matter.
This way the two heaters are in parallel.
If you also connect 5 to 9 you will short the heaters and therefore also the heater supply to gnd.
No need to twist the wires when using reasonable clean DC.

Gave that a shot - Somehow threw off all my voltages? Not getting any 6V - even right at the 6V pad connection on the power supply (reading 0.2V), pin 1 and 6 only reading about 70V and not responsive to the power supply trimmer. Switched it back to the wrong wiring and all the voltages are back to normal. Tried with 4/5 to 6V and 9 to ground and also 9 to 6V and 4/5 to ground.

[markusw]

Gave that a shot - Somehow threw off all my voltages? Not getting any 6V - even right at the 6V pad connection on the power supply (reading 0.2V), pin 1 and 6 only reading about 70V and not responsive to the power supply trimmer. Switched it back to the wrong wiring and all the voltages are back to normal. Tried with 4/5 to 6V and 9 to ground and also 9 to 6V and 4/5 to ground.

Did you remove the wire from pins 4/5 to pin 9?
Sounds like if you have a short from 6V supply to GND.

Edit:
This is how the heaters should be wired.

[cgmason1986]

Did you remove the wire from pins 4/5 to pin 9?
Sounds like if you have a short from 6V supply to GND.

Edit:
This is how the heaters should be wired.

Yea removed the 4/5 to 9 connection. Now it's just pin 9 to 6V, 4/5 jumper together to ground.

[markusw]

Yea removed the 4/5 to 9 connection. Now it's just pin 9 to 6V, 4/5 jumper together to ground.

How are the voltages if you remove the tube?
How many mA can you power supply provide?
Edit: Can you post the schematics of the heater power supply?

[cgmason1986]

How are the voltages if you remove the tube?
How many mA can you power supply provide?
Edit: Can you post the schematics of the heater power supply?

Removing the tube all the voltages look right. The power supply says 20mA

"This power supply PCB can supply 150VDC to 250VDC at approximately 20 milliamps. This is enough high voltage power to run 2 or 3 12AX7 or equivalent tube pre-amplifiers. It also can supply regulated 6 volts DC to power 2-3 tube heaters. "

Schematic is here on page 2:
https://frogpedals.com/wp-content/uploa ... on-1.1.pdf

*EDIT* no idea what happened - didn't change anything but now it seems to be working?? Maybe there was a short somewhere? We'll see after I button it all up. Thank you so much for all your help on this, and sorry for sending you on a wild goose chase.

[markusw]

Removing the tube all the voltages look right. The power supply says 20mA

"This power supply PCB can supply 150VDC to 250VDC at approximately 20 milliamps. This is enough high voltage power to run 2 or 3 12AX7 or equivalent tube pre-amplifiers. It also can supply regulated 6 volts DC to power 2-3 tube heaters. "

Schematic is here on page 2:
https://frogpedals.com/wp-content/uploa ... on-1.1.pdf

Does the heater voltage also dop to 0.2V with another tube?
Can you measure resistance from pin 9 to GND with and without tube, both power supply off?
Are you 100% sure that you did not mix up any pins on the tube socket? Sorry for asking.