transformer based phase splitter

[SemperFi]

SemperFi, on the XSM.

Which transformer are you using, 10K:10K?

Since they are line matching transformers, they are not designed to handle dc in the primary. Do you run the parafeed input?

10k:10k, 15k:10k, and 10k:600.
So not to mislead anybody, I use them PP-PP usually with 6922 in LTP config. I have used one SE-SE but only b/c one of the primary windings opened up after me manhandling it too hard. That was in a guitar amp and only 1mA.
Ive used them with trioded 6V6s to drive 6L6s in bass guitar amps.
I like them but probably b/c I dont know what Im missing since Ive never tried any high end ones. For the price they are hard to beat.

 

[pieter t]

As previously stated, Lynn Olson did work along these lines. Look here. Lynn too warns of the very difficult load this sort of circuitry presents to the driving electronics. Use a big, honking, MOSFET source follower running at about 30 mA. of drain current ahead of the phase splitting trafo.

You talked about Lynn Olsen using differential amps; he did not.
In his Amity, Aurora and Karna amps he uses a line level input phase splitter transformer.
He indicates that the output impedance of the stage driving the input transformer should be under 2k.

 

[Eli Duttman]

What is this, if not differential, AKA balanced?

 

[waltube]

I tested a good solution but not so simple to impelement using in input a Sowter 3575 trafo

In this case you can use the unbal Or bal configuration from the input by a switch.
The only thing is the feedback look from output that must be on two rows.
So one of the termninal must be up from ground; one solution is to connect a 100 ohm 3 w resistor for each output terminal to ground to have a reference.
I found a solution having a center tap on secondary of the OT to ground, with a ytrafo custom made.
It works fine


Walter

 

[martyh]

So, by having the input going to pin 1, p2 to ? . on the secondary the p3 to one tube and p4 to ? then p5 to the other tube. Or both outputs to 2 different sections of a dual triode. You don't happen to know of a schematic of an amp where this type of IT is used as an input splitter.

This is what I would try

Primary
Pin 1 in hot
Pin 2 ground

Secondary
Pin 6 upper triode grid
pin 8 lower triode grid
pin 7 ground or bias voltage

If it is noisy try lifting pin 7 and use 47K resistors from each grid to ground or bias voltage.

 

[ArcticBrew]

I have one of these. I bought it for experiments in learning.

This idea is outside my wheelhouse of experience but...mosfet source follower for input, transformer as phase splitter, 12AU7 or 6SN7 as drivers for output tubes.

I would appreciate constructive feedback on the idea.

Steve

 

[analog_sa]

mosfet source follower for input, transformer as phase splitter, 12AU7 or 6SN7 as drivers for output tubes.

What is the purpose of this? The topologies of the 1930-s have seldom been improved upon soundwise. No idea why you need those mosfets to drive the phasesplitter. If primary inductance is insufficient choose low Rp tubes, or just a decent transformer. 6SN7 is probably a reasonable driver for pentodes but i will never consider driving DHTs with it. And why waste all the wonderful opportunities a transformer offers when driving output tubes directly?

 

[ArcticBrew]

The transformer is a UTC-0-6 ouncer audio unit. No DC on the primary and max output level of 6mw.

It was stated earlier that if used at the input a low impedance source is best.

 

[directdriver]

If you worry about the UTC O-6's low impedance of the primary being hard to drive at the input, then just use it in reverse so you have 95K at the input and secondary becomes 15K. Use two matching 7.5K resistors tied to ground and, voila, you have yourself a very balanced phase splitter. Of course, you will lose some gain this way, about 2.5 times step down but that's not too bad. Just use higher gain tubes at the input stage.

You can study SY's circuit for example.

 

[ArcticBrew]

Thanks DirectDriver. I am not trying to build a finished amplifier. This is a learning exercise. I will probably try what you described also.

But, I am not interested in throwing away the gain and want to use low mu tubes as drivers.

When I suggested a source follower before the transformer it was in reference to Eli Duttman's post. Though I don't know if what I described is what he meant. Hence, my asking the question.

I have several preamps. Two of them use cathode followers for outputs. But, I am not taking these out of service. The others do not and would be the input for this experiment.

 

[directdriver]

But, I am not interested in throwing away the gain and want to use low mu tubes as drivers.

I was assuming you have a two stage driver, input tube and driver tube. Most people use a high gain tube at the input anyway. If don't want to lose gain, then a line level 1:1 ratio bridging transformer will work well for you and they're not that expensive, certainly cheaper than interstage transformers!

 

[ArcticBrew]

This is a junk box build. I have a sufficient amount of pieces and parts.

I want to use the UTC-0-6 transformer at the input.