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P3A Special Edition question
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Old 17th August 2018, 02:29 AM   #31
Ian Finch is offline Ian Finch  Australia
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I found P3A dicey to tinker with too. For curiosity, I also reverted to earlier versions like P3 to hear what Rod Elliott meant by his descriptions.

To clarify earlier comments, I referred to mods that reduce the existing sound effects, as Ivan stated for his objective. I suggest that this is not a good starting point because in principle, it would mean taking a complex whole and working backward to some, as yet undefined operating condition. I think perhaps this would rely more on good luck and lots of iterations rather than design intent to lead the way.

The blameless concept design is an obvious starting point but there are others mentioned that are easier to tinker with whilst already producing useful sound effects. I don't say there is only one way - several inspired design ideas are posted here every week so there are plenty - maybe too many ideas already, to choose from..
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Old 17th August 2018, 03:24 AM   #32
Ian Finch is offline Ian Finch  Australia
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Quote:
Originally Posted by Bigun View Post
Ian, I tinkered with it to arrive at my TGM8 and would say it was worthwhile.
I couldn't argue with that and more power to you for the upcoming TGM11-20 series However, you have considerable engineering skills and used analysis tools effectively in designing your TGM series. Not many DIYs here are likely capable of tackling the critical design issues that arise.
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Old 17th August 2018, 03:28 AM   #33
de Ocampo is offline de Ocampo  Philippines
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I believe that the key factor here is the bootstrap circuit, I have done a totally different approach while experimenting with my own CFP design that uses a push pull VAS scheme. Bimo, Calvin & Valery helped me out in fine tuning the circuit, and in my observation the oscillation is very critical in the VAS stage, The output cannot tame it efficiently.
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Old 17th August 2018, 04:41 AM   #34
ivanlukic is offline ivanlukic  Serbia
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I too noticed that P3A is not very tolerant of upgrades when I changed the gain on my P3A built with TIP35C/36C. I raised the gain to 47 times (around 33dB) and noticed very big bandwidth limitation on square waves. In original form amp is tailored for basic specs, not for upgrades. Fortunately higher gain resulted just in lower bandwidth, which was noticable in listening tests, but not in instability.
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Old 21st August 2018, 03:28 PM   #35
jromxt is offline jromxt
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Default modified circuit

Hi,
Here's my modified circuit in ltp and vas.

thanks,
jromxt
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File Type: jpg ltp current mirror-zener voltage source.jpg (552.8 KB, 112 views)
File Type: jpg modified ccs loaded vas.jpg (308.2 KB, 111 views)
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Old 22nd August 2018, 02:19 AM   #36
Ian Finch is offline Ian Finch  Australia
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That's a bit more than modified - I'd say "re-designed".
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Old 22nd August 2018, 04:49 AM   #37
ivanlukic is offline ivanlukic  Serbia
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I like jromxt mods very much, especially CFP VAS. No doubt the mods will improve the amp to another level.
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Old 22nd August 2018, 09:38 AM   #38
jromxt is offline jromxt
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Hi,
That vas arrangement I got it from D. Self figure f., alternative buffering arrangement uses bootstrapping resistor.The ccs provides 6 ma to vas.I have observed that I need to change the feedback capacitor to 47uf/50 volts to make the treble sound transparent just like the sound of the original bootstrap vas. This is subjective observation.

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jromxt
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