KT88 Williamson Balanced input?

[thommy]

I'm building a pair of williamsons but my whole system is balanced apart from this circuit. First thought was that I could just bypass the phase splitter with the balanced lines but of course that misses the input stage. I have very little knowledge of tube amps, built an EL34 single ended some years ago by following the schematic and it works fine but i dont know why.

Have a kit and circuit for the williamsons but purchased it a while ago and the seller (Bluebell Audio) is no longer around to consult. I can do the hack of tieing cold to ground on the input stage but since I'm building the things point to point it seems i could easily.build the circuit ij a different way, usibg the phase splitter as a second input tube instead as they are both 6SN7s.

Ideally I want a mentor, someone senior who will get some joy out of passing along the knowledge of traditional tube amp construction but any information that might point me in the right direction would be welcome.

 

[GWM]

Well I think you have 2 choices, build it as it
is and supply with a single ended input. Redesigning a Williamson to be balanced
is a major job only for the experienced who
has some measuring kit,
The alternative is to build an existing balanced design, I would suggest Alan Wrights PP-2C you can use the KT88’s
output transformer and probably power
transformer.
I would go over to DIY audio and ask this
question, plenty of people on there that will
help.

 

[PigletsDad]

Simple solution: use an input transformer, to go from balanced in to the unbalanced Williamson circuit. Sowter 4600 would do, I think, about £43.

See https://www.sowter.co.uk/acatalog/E_A_Sowter_Ltd_ISOLATOR_BALANCERS_2.html

 

[thommy]

Simple solution: use an input transformer, to go from balanced in to the unbalanced Williamson circuit. Sowter 4600 would do, I think, about £43.

See https://www.sowter.co.uk/acatalog/E_A_Sowter_Ltd_ISOLATOR_BALANCERS_2.html

Thankyou this is a great solution that can be reversed later on if my needs change.

 

[thommy]

Well I think you have 2 choices, build it as it
is and supply with a single ended input. Redesigning a Williamson to be balanced
is a major job only for the experienced who
has some measuring kit,
The alternative is to build an existing balanced design, I would suggest Alan Wrights PP-2C you can use the KT88’s
output transformer and probably power
transformer.
I would go over to DIY audio and ask this
question, plenty of people on there that will
help.

I spend a lot of time on DiyA, so will look at the PP-2C too, thanks!

 

[GWM]

You can do what PD suggests but it just adds an additional loss in the signal path for no benefit,I assume your source has both single ended and balanced out if not
you can still connect the balanced out to
the Williamson by using the + and earth to
the single end input.I’ve done this before
works fine.

 

[thommy]

You can do what PD suggests but it just adds an additional loss in the signal path for no benefit,I assume your source has both single ended and balanced out if not
you can still connect the balanced out to
the Williamson by using the + and earth to
the single end input.I’ve done this before
works fine.

Yeah thats what I initially suggested but for some reason asumed it wasn't the 'right' way to do it. Have fed a CD signal to my balanced hypex amps by just tying ground and cold together. Apart from the loss of gain I dont know what the disadvantages are, and headroom is not an issue.

Whole system is DIY so I can make it do whatever I want but it would be most convenient and least disruptive to put an XLR socket on these tube amps.

 

[GWM]

There are many DAC’s that wire their RCA outlets this way, I used to use an audiolab DAC and the designer confirmed this was
how it was wired.

 

[GWM]

One thing to be careful of though is don’t
run both single ended and balanced together, just one or the other.