Paraphase inverter question

[catalin gramada]

150_UL_6V6s (4).pdf.pdf

[Dave H]

I found that if the cathode resistor was shared and unbypassed, horrid blips of parasitic oscillation were generated when it was overdriven.

It was originally designed for hi-fi. You're not supposed to overdrive it

My guess is that in a perfect world with perfectly matched outputs which are unloaded the bypass cap isn't needed but in the real word with equal feed on/feedback resistors and 150k loads (Vox) it's better to have the capacitor.

[vintagekiki]

Paraphase inverter question

The best way to satisfy your curiosity is to do everything you described, perform DC measurements, and attach the circuit to the signal source and oscilloscope. Its implies that you share your experience with us.

http://www.valvewizard.co.uk/paraphase.html

http://www.r-type.org/articles/art-123f.htm

http://www.vias.org/crowhurstba/crowhurst_basic_audio_vol2_062.html

http://www.vias.org/crowhurstba/crowhurst_basic_audio_vol2_063.html

EDIT 190902

It work do the same, only you have two unnecessary capacitors more, whose value can affect to (low) frequency.
From ratio R4 vs R5 will depend on the symmetrical excitation of the outputs.

[Helmholtz]

Also the balancing resistors contribute to the effective PI load.

[Gingertube]

The Paraphase is great in simple /minimalist circuits - easy to add a 1 knob tone control
See the GA40 for example of this
https://music-electronics-forum.com/...ad.php?t=49627

Cheers,
Ian

[catalin gramada]

The Paraphase is great in simple /minimalist circuits - easy to add a 1 knob tone control
See the GA40 for example of this
https://music-electronics-forum.com/...ad.php?t=49627

Cheers,
Ian

Yes, mine project is fixed bias and imply some nfb amount over it. It works pretty well. Thanks for material.

[Dave H]

The Paraphase is great in simple /minimalist circuits - easy to add a 1 knob tone control
See the GA40 for example of this
https://music-electronics-forum.com/...ad.php?t=49627

That's a Paraphase which is a little different from the Floating Paraphase in the OP. One difference is the Paraphase doesn't have negative feedback and therefore has equal output impedances meaning it won't be unbalanced by being loaded.

I wonder why the Cathodyne and LTP became more popular in guitar amps when the Paraphase has more gain and output voltage than either of them? Is it something to do with overdrive performance?

[Tony Bones]

I wonder why the Cathodyne and LTP became more popular in guitar amps when the Paraphase has more gain and output voltage than either of them? Is it something to do with overdrive performance?

My guess is that it has to do with elegance. To an engineer, the paraphase looks (on paper) like a bit of a kluge compared to the cathodyne and LTP, both of which look like they would work well independent of tube characteristics.

In practice I like the paraphase, especially in hi-fi amps.

[pdf64]

Perhaps the paraphase’s greater output signal swing is more of a drawback than benefit for most applications? As it may worsen bias shift / blocking distortion when overdriven.

[catalin gramada]

Hello,
I have a hard time to do this stage completely quiet.It still have a tiny hum. I tried almost everything : different ways of grounding, doubling filter caps...and did not help at all,still have a tiny amount of noise. The only thing it helps to reduce to none is to raise the negative feedback amount. The noise is pretty consistent, meant no dependant by what is happen in front (first stage of paraphase input is shorted to ground) and is related between paraphase inverter and power stage. Any ideas, please ? Thanks

[catalin gramada]

This is the output




and these are floating paraphase outputs, (yellow inverted, blue non inverted)




paraphase input is shunted to the ground.

The noise sound more like 100hz ripple, but doubling filter caps value have no effect, and the ground is clean. Have no ideea how to fix it.

[catalin gramada]

...and think I get it...

This is the ripple of bias circuit



and with filter cap doubled (100uF added in parallel)




I have to check it one more time, as with the same bias circuit and LTP inverter the amp was absolutely quiet. I wonder what did the paraphase to be noisy? That meant the ripple was injected in to the loop and did not cancelled in common mode but amplified instead...have sense.. ?

And I still hear it in the speaker even with 200uF...

[Helmholtz]

This is the ripple of bias circuit

O.K., this makes sense as the fundamental frequency is 50Hz.
With perfect power amp symmetry bias ripple cancels. So there must be asymmetry. Can you post a drawing of the complete power amp?
Can you see the ripple at the power tube grids? Any difference between both sides?

[catalin gramada]

Thanks Helm, the last picture shows the ripple at power tube grids. There are two traces cause I splited the bias rail in two sections to can do individual adjustments. I,ll draw a sketch in a moment. Thanks

[catalin gramada]