Symmetric Reichert 300B push-pull

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Thermionic Idler
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#76 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

Right then, I think we have some completed models.

First up, the original schematic

Image

PSUD model for the output stage power supply, based on off-the-shelf Hammond models. 378X for the transformer, 193H for the choke.

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PSUD model for the input stage power supply, based on off-the-shelf Hammond models. 375X for the transformer, 193B for the choke.

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And the Spice model for the circuit, with the missing cap values worked out and the modified driver stage. I've gone back to using motor-run caps for the large values as they are half the price of the Mundorf Tubecaps, so the 80uF / 20uF values are restored.

Image

The predicted voltages are more or less where they should be, the output stage PSU is reading about 460V rather than 500, amd the input stage is slightly high on the driver stage (520V) but about where it should be on the 12SN7 stage.

Now to bring it all together in a KiCad schematic and build up a bill of materials, and figure out where everything is going to fit.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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izzy wizzy
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#77 Re: Symmetric Reichert 300B push-pull

Post by izzy wizzy »

I noticed you're using the LL1684. The data I've seen for it recommends only using a low Z source to drive it and the data sheet shows specs for 150R drive Z which seems very low. Plus the load on it seems quite low hence the 10k termination and low value Zobel. This could make the amp quite hard to drive. The LL1676 is an easier tx to use and has fantastic specs. Was it your intention to cater for low Z drive only?
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Thermionic Idler
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#78 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

izzy wizzy wrote: Wed Aug 12, 2020 9:08 pm I noticed you're using the LL1684. The data I've seen for it recommends only using a low Z source to drive it and the data sheet shows specs for 150R drive Z which seems very low. Plus the load on it seems quite low hence the 10k termination and low value Zobel. This could make the amp quite hard to drive. The LL1676 is an easier tx to use and has fantastic specs. Was it your intention to cater for low Z drive only?
Yep that was intentional - my preamp has very low Z balanced outputs - 66 ohms. Less phase shift with the lower impedance transformer.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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Thermionic Idler
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#79 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

I was trying to think of a more catchy name for this project, given that a number of changes have been made to the original circuit and 'Symmetric Reichert' is a bit of a mouthful.

Given the entirely differential nature of the design, I'm going to call it the Newton 300B, after Newton's third law. Once the full schematic is finalised (I think it's pretty much there now anyway), I'll probably start a new thread to cover the chassis design and build process.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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Paul Barker
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#80 Re: Symmetric Reichert 300B push-pull

Post by Paul Barker »

I think that’s a nice name except the 3rd law of motion existed in everything so it’s not unique to balanced push pull. A good name for ignoring the universality of physics... sorry.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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Thermionic Idler
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#81 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

I'm trying to work out if I need any grid stoppers in this thing. The original design does not specify any.

All the stages are relatively low gain, the highest mu stage is the 12SN7 and those are usually well behaved. The mu of stage 2 is less than 10 and I've rarely seen a 300B schematic with a stopper on its grid (with the exception of Tubecad where you see 1k resistors IIRC).

My thinking is to leave them out unless needed.

What do we think? As always, I'm very grateful for any feedback and advice on the subject.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
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jack
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#82 Re: Symmetric Reichert 300B push-pull

Post by jack »

Very nice. What model libraries are you using for the valves and xfrmrs?
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Thermionic Idler
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#83 Re: Symmetric Reichert 300B push-pull

Post by Thermionic Idler »

jack wrote: Sat Sep 12, 2020 8:23 pm Very nice. What model libraries are you using for the valves and xfrmrs?
I'm using the Ayumi library for the valves. The transformers were generated from a spreadsheet that someone put out there a while back (Transformer Models Rev4.xls), you put in the parameters and it generates the model for you.
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
Linestage: Bruno Putzeys Balanced Pre + Hans Polak relay mod, LCDuino control
Power amps: 300B PP 'Symmetric Reichert'
Speakers: FF225WK Big Mets
catzwisker2
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#84 Re: Symmetric Reichert 300B push-pull

Post by catzwisker2 »

Neal, Re your Sowter U082 transformer, have you used it yet ?
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