ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Anyone built tube preamps from schematics?

:

9/25/2004 4:00 AM
VEK	Anyone built tube preamps from schematics? Just wondering if anyone has had any luck building tube preamps from schematics, clones? I'm talking stand alone preamps (CAE, Soldano?) Thx VEK

9/26/2004 2:03 AM
Dan	I am in the process of designing and building a tube preamp. In a floor pedal style. I have built the Hotbox but, I am not impressed. I am buiding my own. I am trying to produce a Hybrid Marshall/Fender Tweed sound. It has 3 gain stages. Anyway, I build them from a schematic I have drawn. I am trying a very different style of point to point layout.

9/28/2004 1:01 AM
Jon Fleig	VEK, I built a dual fender blackface preamp into a 1U rack box for my bass player. Essentially a clone of an Alembic F-2B. Utter simplicity compared to the CAE/Soldano sort of thing, but a good project if you're a less experienced builder like me. Pics and description at: http://www.frontiernet.net/~jff/af2b/Dual_Channel_Blackface-style_Preamp_for_Bass_Guitar.html -Jon

10/7/2004 4:27 PM
Brutus	Jon, how did the alembic clone sound? Was it worth building in your opinion? Sounds like an interesting piece to do. Brutus

10/13/2004 2:34 AM

Brutus,

The Alembic clone is in my bandmate's bass rig - a Crown PB 2 power amp into SWR Goliath and Triad cabinets. He bridges the inputs and feeds the each channel output to a channel of the Crown. Each channel has a treble-middle-bass tone stack EQ'd for the cabinet - even the bright switches are useful.

It's clean, deep, sparkly, and smooth.

A great $150 tube project, and I learned alot while doing it.

-Jon

10/14/2004 5:32 PM
steve	Jon, I'm curious about the PT you used. I looked at your web page, but got confused about how the PT is configuered. What voltage are the secondaries? How do you derive the filament voltages? TIA, Steve

10/22/2004 1:20 PM

Steve,

Sorry it's taken me a while to reply - I'm in Japan on business.

The PT I used is a Stancor LB-1220 dual-primary, dual-secondary flatpack. It has 4 windings:
2 identical primary windings designed to be
connected to the AC line, and 2 secondary windings designed to supply 10 VAC output.

I use it in a non-standard way.
I feed 120 VAC line voltage into 1 primary winding
I use the other primary winding as a high voltage OUTPUT. Both primary windings have the same number of turns, but only about 107 V comes out this winding due to core losses. I feed this 107 VAC into the full wave voltage doubler circuit that is shown on the web page. When rectified and filtered, this provides about 250 VDC @ 3 mA for the plates of the 12AX7's.

There are two identical secondary windings, each producing 10VAC. I connect the secondaries in parallel, rectify with 4 diodes connected as a full wave bridge, and filter with a 3500 uF 35V capacitor. This provides about 12 VDC @ 300 mA for the filaments.

Here is the data sheet for the Stancor "low-boy" transformer series. The second page has a very clear wiring diagram for standard use.

http://www.stancor.com/pdfs/pg27_28.pdf

Ask if you need more advice.
-Jon

Page 1 of 2