All about Tubes, Tube Circuits, Tube Gear

Wednesday, June 13, 2012

Ju-Jutsu: The Ultimate Monoblock (Pt 2)

Here is the circuit for the WWII version of my amp, one of the first I built.
You can see why it is the cleanest of sounds:

Only two stages. Less than most preamps!

Two transformers.

3 caps.

It is an elegant solution to sonic purity.

Here are some notes:

I used Jensen transformers for the input;
any good output transformer will do.

It requires two heater supplies, one for the upper tubes, one for the lower.
Either float the upper or DC offset it from the powersupply at around 300 volts.

It requires two power supplies, 400-500 for the 1st stage, 700-800 for the 2nd.
The PSRR is so good, you only need simple, modest PS circuits.
You can run the 1st stage off a resistor/cap leg from the main B+.

The top tube was a 5998 in the power section (V3 A, V3 B).
You can also try a couple of 6L6s or 6V6s, in triode-mode.
The bottoms were a 1625s. 807s are equivalents (triode mode with the usual precautions)
6SN7s or 12AX7s will do in the first stage.

 At one point, the man who reviewed the amps was still in shock,
so he set up a series of A/B tests, and drove me and the amps all over Ontario.

At one particular location, a fellow had spent several thousand in parts,
for an elaborate SE amp,he had designed using very expensive transformers, silver wire etc., and some $10,000 pair of speakers.

He played me his rig for about an hour.
I had to admit it was beautiful, rich and warm, quite an accomplishment.
I said nothing, and neither did the reviewer.
We set up my monoblocks quietly, then spent the next 3 hours listening to everything he could throw at them.
It really sounded like Diana Krall et al, were in the room, saxes, accoustic basses and all.

He said the monoblocks were incredible.
I felt kind of sad that my amps had defeated his greatest efforts and expense.
We parted friends.

In a similar A/B shootout with Bryston's best and purest solid-state offerings,
we blew their amps out of the water.

It was a thrilling experience, never to be repeated.
I felt dishonest in a way, because I knew a key point of my innovation was based on the work of others.

Here's a pic of the pair that went on the A/B challenge:

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