freestompboxes.org

Hi all!

I just got this unit in as the owner needed to know if it could run on a 'normal' voltage instead of the 15V 400mA centre positive power adapter.

The unit has a single 12AX7 tube

'The Eden Glowplug Bass Tube Warmer Pedal makes achieving an authentic tube tone a breeze. Leveraging tone circuitry designed particularly to improve and complement your bass sound, the Glowplug gives depth and warmth to your sound, unleashing the natural harmonics of your strings. From mild tone warming to a fuller tube roundness, the Glowplug is capable of providing an extensive selection of tune sound to various types of players. It will warm up your bass tone and add some charm and tube character.'

I traced the unit; as you can spot the power supply is regulated to 12V on two individual power supply paths; the part that is not regulated is only used for switching. It works fine on a 12 - 18V power supply. For the owner of this unit I swapped the traces on the print so it could be run with a centre-negative power supply, which is more common in the guitar-pedal world
For pics, check my Instagram

Thanks! Great work!

Hi Bernard

This unit needs to be feed with more than 9Vdc in order to keep operating the 12AX7 heater properly.
Also, the output of the voltage multiplier (at the upper right corner of your drawing) will be decreased noticeably.

Cheers,
Jose

The proper filament voltage is achieved by inserting a 1N4001 diode as shown in the schematic detail.
With the modification, an 18VDC plug-in power supply is necessary.
A power supply with 15VDC is anyway a bit low.
It can happen that the minimum allowed voltage drop across the voltage regulator is undercut by mains voltage fluctuations, also without diode.

I wonder how good a 12AX7 sounds on 45 volts

That's a lot of opamps.