Fun with Feedback

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andrew Ivimey
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#166 Re: Fun with Feedback

Post by andrew Ivimey »

I don't like the look of it, schematic wise, makes me wonder about the strange components, why for example 200pf - it ain't right all this feedback stuff - what's wrong with simple triode into simple triode with as few capacitance as possible ...and feedback - this lady's not for turning, no, no No! stamps foot.

Does it really sound that good ( yeah I know NVA is rubbish) ?

ducks and runs - so long suckers- Happy New Year. I'm in Lviv.
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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pre65
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#167 Re: Fun with Feedback

Post by pre65 »

andrew Ivimey wrote: Sun Jan 08, 2023 6:59 pm Happy New Year. I'm in Lviv.
Beware of drones. :shock:
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Nick
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#168 Re: Fun with Feedback

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I did just run the numbers and cant help thinking the 200pf may be a bit more than is needed, unless I am wrong that will start to reduce the gain from around 8kHz. But I guess you have scoped it all out.
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#169 Re: Fun with Feedback

Post by Cressy Snr »

Nick wrote: Sun Jan 08, 2023 7:22 pm I did just run the numbers and cant help thinking the 200pf may be a bit more than is needed, unless I am wrong that will start to reduce the gain from around 8kHz. But I guess you have scoped it all out.
Hi Nick,
Yes, there is scope (s’cuse the pun) for reducing the cap value, maybe down as far as 68p. I was being a little bit belt and braces until I could be sure that nothing untoward was going to occur with the pentode conversion. It scopes out quite well but I think there is still room for improvement to the corners of the 10KHz square wave and the rise/fall time. A bit of further tweaking of the compensation network might get it better.
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#170 Re: Fun with Feedback

Post by Cressy Snr »

andrew Ivimey wrote: Sun Jan 08, 2023 6:59 pm …it ain't right all this feedback stuff - what's wrong with simple triode into simple triode with as few capacitance as possible?
Everything? :mrgreen:
Does it really sound that good?
Yes.
Last edited by Cressy Snr on Sun Jan 08, 2023 9:53 pm, edited 1 time in total.
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#171 Re: Fun with Feedback

Post by Cressy Snr »

pre65 wrote: Sun Jan 08, 2023 5:16 pm From what Ant says you've got a good amp there Steve.

Would you agree with Ants appraisal ?
Yes I would. It is very good indeed. However, I’m not about to start getting all evangelical about pentodes. The only way for folks to decide whether or not they like these thermionic outcasts is to build something. Enter this realm and all that minimal or zero feedback stuff goes out the window. A whole set of wizarding skills are required. 🧙‍♂️ but I found it interesting and ultimately very rewarding.
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andrew Ivimey
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#172 Re: Fun with Feedback

Post by andrew Ivimey »

Who's a thermionic out cast here?

Most of us have been, are still up to our ears in it.
(A few may look back fondly remembering the joy)

But why set up an Aunt Sally just to shoot her down to an audience who knows a great deal about all this thermionic stuff. It's daft.

Audio Talk wouldn't exist if nobody knew what you were doing. We'd just think you were bonkers.

Apologies if I sound aggressive or rude Steve but...
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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#173 Re: Fun with Feedback

Post by Cressy Snr »

Power Pentodes were what I was referring to as the thermionic outcasts of the hi-fi world not people. Don’t understand your anger.
Anyway I can’t be arsed to argue anymore. I’ve built something I like, I put a huge amount of work into learning about the maths and engineering stuff required to achieve what I’ve achieved. The mistake was posting about the bloody thing. I really have no idea what I’m supposed to have done. I thought I was among friends here.

I’m afraid it’s over and out. I don’t need the aggravation.
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#174 Re: Fun with Feedback

Post by pre65 »

Cressy Snr wrote: Sun Jan 08, 2023 11:00 pm
I thought I was among friends here.
You are Steve, just remember that. :D

But being friends does not mean we automatically agree with everything you do, or say.
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#175 Re: Fun with Feedback

Post by Cressy Snr »

OK
But I still have no Idea what I’ve done wrong. Perhaps someone could explain the nature of my apparent faux pas.
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#176 Re: Fun with Feedback

Post by Nick »

I don't think you have done anything wrong Steve and I don't think Andrew is angry. I think though there is maybe a suggestion to make. I suspect you forget which forum this is (as Andrew said) you don't need to make everything a narrative
We can understand what you have done and why and find it interesting without having to make it into a story. Other places may need that but not here. It can get in the way of the interesting part. Just my take on it. Likewise you don't need to create conflict for the sake of the narrative. It just creates imaginary tribes and aggression where it's not needed.

Also, friends don't have to agree all the time. It can be fun to argue.
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#177 Re: Fun with Feedback

Post by IslandPink »

Nick wrote: Sun Jan 08, 2023 11:52 pm I don't think you have done anything wrong Steve and I don't think Andrew is angry.
That was exactly what i was thinking of posting as I read this just now !
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#178 Re: Fun with Feedback

Post by Cressy Snr »

OK point(s) taken. Thanks chaps. :)
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#179 Re: Fun with Feedback

Post by Cressy Snr »

Anyway, using the only polystyrene cap values I have in the parts box, I managed to work something else out for the step network on the input stage anode and the one in the feedback loop. So here is the diagram:
Heretikpentode 2.0.png
Heretikpentode 2.0.png (72.3 KiB) Viewed 4304 times
Works nice.
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#180 Re: Fun with Feedback

Post by Cressy Snr »

Was revelling in Pat Metheny’s “As Falls Wichita etc, then came a smell of burning, followed shortly after by smoking wreckage. My beautiful sounding creation! I’m devastated, no really. It was the most exquisite sounding thing and now it’s a pile of dead scrap. :(
No doubt I’ll get it going again following an investigation, but Karma can be a right bastard sometimes. :lol: :lol: :lol:
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