top of page

This is the EDISON 1 (60 watt Mono block Audio Amp). It was designed to turn a stereo mix from your PC, MAC computer or laptop into a mono mixdown and reproduce old school sounds that are rich. The power transformers run backwards and eliminate extra tubes and expense and produce clean audio you won't expect from the audio input.


Stereo to mono mix down accomplished in the T1 audio transform, not the input patch cord. Some sound cards or Pro-Audio Pre amps may require this feature and a mix down in the patch cord into the T1 audio transformer may short or burn out your pre amp.

DO NOT PUT THE VARIAC INSIDE THE CASE OR LOUD NOISE WILL OCCUR. The Variac is pictured inside this chassis in an attempt to fit everything inside. The amount of shielding required dictated moving the Variac outboard. See the last picture for final configuration.

The inside of this solid Oak cabinet is lined with 0.010 aluminum sheets to make it safe in the event of fire. May pass UL certification at that point.

NOTE: We provide free tech support as my schedule allows to help you build this amp. 

This Oak case is aluminum lined inside to prevent fire.

This mono Block Amp was dedicated to the world famous Thomas Edison that invented audio reproduction technology, including the vacuum tube that lead the way to these circuits that changed the audio world as we know it today. 

Variac controls the high voltage plate power supply allowing slow power up and max. use of power supply filter caps of the min. size. 

Variac is housed inside steel case from Hammond and connected to the high voltage plate transformer via a 4 pin XLR cable. Input into the T1 audio transformer is via a TRS jack in the front as shown. 

Octagon mirror (from Joann's Fabric store) helps deflect heat energy from the tubes away from the high powered filter caps. The Variac is connected to the amp via a 4 pin XLR cable. Small AC filament transformer (from Radio Shack) powers all 4 tubes and the high voltage plate transformer is controlled via the Variac and it's filament winding is not used. 

Lower transformer and DC choke and wire wound pot are the grid power supply (B+ and B+2) for the V1, V2 tubes. This is full filtered and DC choked for clean input.

Upper wire wound pots are for VR1 - VR4 adjustments.

Case is aluminum lined for electrical safety, LF and RF suppression and fire suppression.

Micro switch on right hand marked "Input common OFF / ON" is SW1 for audio input floating / non floating ground.

LED lights indicate when AC filament power is available from separate AC filament transformer (Radio Shack unit). Steel case is a Hammond Manufacturing unit. 

4 Pin XLR jack is used on the Variac steel case and the back of the Mono Block amp to connect the high voltage plate transformer via a XLR cable. 

This is the power supply schematic. First published 4/2/2018. Use at your own risk.

This drawing released to PUBLIC DOMAIN

NOTE: RY1 is for a different configuration; not used here.

CA1 is a 5 conductor wire and may be found at Home Depot or online wire store.

LF1 is a AC line filter with C-13 cord needed to connect to wall outlet. Allied Electronics: Allied Stock#: 70133281

T4 bias transformer (F3-56)

Power supply for this circuit is coming with the publication of the build manual. In the meanwhile you must design and build your own at your own risk

T1 audio input transfomer hookup to J1

T1 audio input transformer installed inside aluminum case to keep input clean from LF and RF interference. Preferred to have steel instead. 

T2 audio transformer

T2 plate transformer from Hammond (270HX)

Clean Class A Vacuum Tube Audio Amp.

SW1 switch is for floating or non floating ground on audio input. If you are connecting a PC or MAC computer you want the SW1 switch to be in the grounded to chassis ground. If you are hooking up Pro-Audio to the input, put SW1 in the floating ground position which is "OPEN". In order for this Balanced patch cord to not become an antenna for noise, only one end of the cable can be grounded. Since most computer sound cards outputs are NOT grounded to chassis and earth, the SW1 must allow the tube amp side audio transformer side to ground out the patch cord. Pro Audio equipment on the other hand may very well have a grounded output jack so you must leave SW1 open to allow only one end of the patch cord to be grounded.

NOTE: We run two JBL book shelf speakers in series for a better sounding output. This makes it a 16 ohm load instead of the 8 ohm load the audio output transformer was designed to handle. NOTE: Power tests done with a "KiIlawatt" meter show the filament power supply draws 29.3 watts at .96 power factor (PF). The high voltage power supply "B+1" , "B+2", and "B+" draw 76.7 watts at .88 PF. Total power consumption of all power supplies is 106 watts at .88 PF. NOTE: B+1 high voltage input voltage is 500 VDC.

Final System Configuration

The final system setup includes a Ion Record player that connects into the One Little Bear Audio switch (it accepts XLR and TRS cable for balanced and unbalanced input). From there it goes into a DBX 231S 31 channel EQ before being sent into the Mono amp where it changes the stereo input back to old school mono. Inorder to keep the signal stereo, you must make 2 of these Mono Block amps. My opinion is that this setup sounds better than any stereo system I have ever owned. 

One Little Bear Audio Switch

The unit shown has been updated with the MC3. Its available on amazon at: 

MC3 is a 3-IN-3-OUT (XLR*2 RCA*1) passive audio splitter / audio switch

2 stereo XLR + 1 stereeo RCA inputs and 2 stereo XLR + 1 stereo RCA outputs

Function 1: switch among different sound sources or amplifiers and compare their sound performance

Function 2: convert signal from balanced XLR to unbalanced RCA or from RCA to XLR

Pure passive device without any impacts on sound quality. Mini size suits very well for desktop and home use.

BlueTooth Receiver

This KlarkTeknik DW 20BR brings this audio setup into the state of the art concerning playing music from your cell phone/TV/ laptop in a wireless fashion. 

Pro Audio Outputs

Use unbalanced or balanced outputs depending on your equipment needs. We bought this unit at for around 80$ US. Money well spent.


Must have an EQ to adjust the sound inputs to the amp and speaker. This 31 channel EQ is a sweet addition to this setup. Search the internet for DBX store for this or other DBX eqs. The last peice of audio equipment in our setup is a CD/DVD player with built in volume control on the remote control. 

bottom of page