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Broskie's Unbalancer
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Author:  SoundMods [ March 21st, 2023, 6:17 pm ]
Post subject:  Re: Broskie's Unbalancer
Stuart Polansky wrote:
SoundMods wrote:
Stuart Polansky wrote:
I'll read up on those Tom. The Unbalancer doesn't use any signal transformers. I'll post the schematic later. The Izzy Wizzy phono stage has a differential output stage. The plates are connected just like a push pull amp to an interstage transformer. It's been highly praised. We'll see how it sounds, whether the elimination of coupling caps, but the addition of a transformer is better or worse.

Stuart

How about a plain and simple differential input connected through XLRs?


That works fine if I wanted balanced out. I may someday.

You can go from a differential input and do a summing network to singled-ended for the output. Or -- still balanced you can just tie the non-inverted output to the RCA center pin and the inverted out to the ground return. You're working from scratch you can do just about anything. Your power amp(s) could be modified to have a differential input before the phase inverter stage.
Author:  Stuart Polansky [ March 21st, 2023, 6:26 pm ]
Post subject:  Re: Broskie's Unbalancer
David McGown wrote:
Stuart,

Since you are committed to PP amps, the natural thing is to keep everything balanced (differential) to the power amp. No more phase splitter. It makes no sense to convert back to single ended out of the preamp and then split phase again at the amp. I know the OddWatt amps do the phase splitting in the output stage, so it would require a little rework to convert the SRPP driver into a differential, but hey, it is only resistors and perhaps another signal capacitor. But that is a system wide change and upsets everything including interconnects (right after you upgraded to RCA Audio Envy!). You should really look at Allen Wright's designs for a fully differential preamp/amplifier. Some really interesting and good stuff there.

All you are doing is executing in vacuum tubes what the Topping does with an opamp when it converts from balanced to SE after the DAC. The most basic circuit is a summing amplifier executed with a single opamp. Maybe the tube circuit will sound better, but maybe not. It is cheap to put something together with what Tom is suggesting. A pair of transformers is another solution that is easy to try without upsetting everything. Jensen and Cinemag makes some. I think I may even have a pair of Cinemag transformers that may work, I will have to dig around.

I have been toying with balanced in explorations of powerful versions of First Watt amplifiers (converting a stereo 25W Class A to a 100W monoblock), but have backed off because I realize that (1), I prefer tubes, and (2), a 30W tube amplifier does almost everything I need or want for the music I listen to.

David

Site keeps logging me off and erasing my reply! Dammit
Author:  HAL [ March 22nd, 2023, 8:57 am ]
Post subject:  Re: Broskie's Unbalancer
Stuart,
Looking forward to your listening impressions with the unbalancer running with the E70V.

Rich
Author:  Stuart Polansky [ March 22nd, 2023, 12:06 pm ]
Post subject:  Re: Broskie's Unbalancer
[/quote]
That works fine if I wanted balanced out. I may someday.[/quote]
You can go from a differential input and do a summing network to singled-ended for the output. Or -- still balanced you can just tie the non-inverted output to the RCA center pin and the inverted out to the ground return. You're working from scratch you can do just about anything. Your power amp(s) could be modified to have a differential input before the phase inverter stage.
[/quote]

No, the amps I'm using right now cannot be modified in that way. The output stage IS the phase inverter.

I am not rebuilding all components in my system. For new builds, maybe all balanced. You never know unless you try.

Attachments:
Oddblock.PNG
Oddblock.PNG [ 268.59 KiB | Viewed 15903 times ]
Author:  Stuart Polansky [ March 22nd, 2023, 12:10 pm ]
Post subject:  Re: Broskie's Unbalancer
HAL wrote:
Stuart,
Looking forward to your listening impressions with the unbalancer running with the E70V.

Rich


Me too Rich!

At least two other friends are building balanced input line stages, one of which will have very high quality input transformers.

We'll have a shoot-out and certainly compare the results to both the RCA outputs and XLR-RCA cable interconnection.

Stay tuned!

Stuart

Attachments:
Circuit.PNG
Circuit.PNG [ 45.3 KiB | Viewed 15903 times ]
Author:  SoundMods [ March 22nd, 2023, 10:27 pm ]
Post subject:  Re: Broskie's Unbalancer
"No, the amps I'm using right now cannot be modified in that way. The output stage IS the phase inverter."

I get it. I am surprised the cascode front-end has enough oomph to drive the output stage. Yet we all heard them during the get together.

BTW -- a tube that betters any 6SL7 is the 6SU7. The 6SU7 is a premium mil-spec version with matched halves.
Author:  Roscoe Primrose [ March 23rd, 2023, 12:29 am ]
Post subject:  Re: Broskie's Unbalancer
That's not a cascode...

Roscoe
Author:  SoundMods [ March 23rd, 2023, 10:54 am ]
Post subject:  Re: Broskie's Unbalancer
Roscoe Primrose wrote:
That's not a cascode...

Roscoe

SRPP -- Cascode.......Potato -- Pota'toe

Kissing cousins.
Author:  David McGown [ March 23rd, 2023, 11:36 am ]
Post subject:  Re: Broskie's Unbalancer
SoundMods wrote:
SRPP -- Cascode.......Potato -- Pota'toe

Kissing cousins.


Hardly. Completely different functionally. Cascode = Pentode w/high gain, upper section needs a plate load to work, high impedance output. SRPP = PP amplifier at 1/2Mu gain, no plate load on upper section, low impedance output.

David
Author:  Stuart Polansky [ May 4th, 2023, 8:14 am ]
Post subject:  Re: Broskie's Unbalancer
Finished the preamp yesterday, electronically. Still need to label the controls and tube sockets; install a mesh bottom cover.

Gain of 7 single ended, 14 balanced. Started with RCA 6CG7s at the input, JJ ECC99s for the followers. 0A2 & 0B2 gas tubes, 6DN4 damper diodes, cascoded DN2540 current source for the B+, simple bipolar 2N4444 (I think) current sinks in the input tails. Miflex coupling and output caps for the high output. Walt's electronic components 5uF (paralleled for 10uF) for the low output which goes to a miniDSP (5K input impedance). Used the eBay $25 stepped attenuators for gain. 100k stereo units, one per channel. Signal wiring is either Cardas of solid silver within Teflon sleeves. Relay switching of inputs. Unbalanced inputs feed signal and "ground" to the input grids.

Initially tried it out with the same homemade XLR--RCA cables I was using, made with Neglex cable. Then switched to a pair of World's Best Cables using Neutrik connectors and also Neglex cable.

With life's challenges and my own laziness getting in the way, it took two months to complete. It was worth the wait.

The improvement is substantial, most notably space between instruments, amazing to hear really. I think I may have my final line stage!

Can't wait to get a pair of AE O'nestian interconnects and try out some different input 6CG7s (I have some nice Sylvanias). But right now, I just can't stop listening.

Hope to have a meet in July, because May and June schedules are packed with car events.

Stuart
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