How much !

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Dr Bunsen Honeydew
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Re: How much !

Unread post by Dr Bunsen Honeydew » Sun Jan 13, 2019 7:52 pm

With two transistors !! I trust no one to tell the truth in this industry it has become a industry disease to tell porkies. Not saying so in this case, just my go to as it happens so often. Where is Nick when we need him.

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Quarknosis
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Re: How much !

Unread post by Quarknosis » Sun Jan 13, 2019 8:35 pm

I have owned both a Sugden A21 and an early version of the A21a (the one with the orange power switch) from the 90's and I have to agree with DSJR about the original version. I enjoyed the A21a though, probably my favourite pre NVA amp.
NVA BMU - NVA Phono 1 - Systemdek IIX/Rega RB250/Denon DL160 & Philips CD 104 with NOS mod - TIS & SSP mkii - NVA AP70sa - Epos ES11.

Lurcher300b
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Re: How much !

Unread post by Lurcher300b » Sun Jan 13, 2019 10:07 pm

Dr Bunsen Honeydew wrote:
Sun Jan 13, 2019 7:52 pm
With two transistors !! I trust no one to tell the truth in this industry it has become a industry disease to tell porkies. Not saying so in this case, just my go to as it happens so often. Where is Nick when we need him.
Its a clever single ended design (so class A), the upper transistor is operating as a cunning opto coupled current source load for the lower transistor. It works because they are sodding big transistors with a big gm, so there is enough gain in the one stage + transformer.

Quads current dumping is a all together more complex solution that involves two amplifiers in one, a big one to do the heavy lifting and a small one to do the tinkly bits. Great idea, but never sure its been as successful as it sounds at first. Once you start to try and implement the idea its hard to stop the big amp from stomping all over the small one.

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Dr Bunsen Honeydew
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Re: How much !

Unread post by Dr Bunsen Honeydew » Sun Jan 13, 2019 10:34 pm

But surely they interfere with each as both are carrying signal, the beauty of real Class A is its simplicity. The extra circuitry in this must interfere.

Lurcher300b
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Re: How much !

Unread post by Lurcher300b » Mon Jan 14, 2019 12:10 am

Dr Bunsen Honeydew wrote:
Sun Jan 13, 2019 10:34 pm
But surely they interfere with each as both are carrying signal, the beauty of real Class A is its simplicity. The extra circuitry in this must interfere.
Well, no more or less than the output transformer in the anode load interferes with the output valve. That circuit is as real class A as any IMO. If you replace the current source with a 300k 75KW watt resistor and the voltage rail with a 500ma 150kv supply you have much the same thing with a simpler circuit. Though it will have some practical problems.

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Dr Bunsen Honeydew
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Re: How much !

Unread post by Dr Bunsen Honeydew » Mon Jan 14, 2019 12:31 am

OK noted

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