Under consideration, but not straightforward, and it has implications for the layout of the amp (phono stage fitted or not) as we would want it to be retrofittable.SteveTheShadow wrote: ↑Sun Jan 02, 2022 11:41 pm This integrated DIYNVA amp concept seems to be extremely successful. If Paul and Tomasz are resurrecting the idea of an integrated, then good on them. Offering the future NVA integrated with an upgrade of a built-in moving magnet only phono stage, at a price premium, whilst keeping MC capability and multiple regulators exclusively with the separate phonos, could be something to think about. Integrating the MM phono board into my own setup seems to have produced no problems, only benefits. In a commercial product however, it might be out of the question.
Another DIY SS Amplifier with NVA Boards
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Re: Another DIY SS Amplifier with NVA Boards
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Re: Another DIY SS Amplifier with NVA Boards
Is taking the power + & - from the amp board supply a ‘common’ method in integrated amps- I wonder if there is any effect on the power delivery, current or voltage to the input stage of the amp boards. Is there sufficient in reserve with the capacitors used?
Great looking amp and build
Great looking amp and build
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- SteveTheShadow (Mon Jan 03, 2022 4:22 pm)
Analogue Source -
Denon DP47f; AT-VM95SH- RigB 9
GL-59; ARB uni pivot; AT- Signet mc
Nva phono mm/mc
Doug Self balanced Pre amp
Akai 4000DS mk2 R2R
Digital Sources- Argon Pi4 v2; IfI iUSB 3.0, Ifi Neo idsd Dac;
Tidal / Radio Paradise
Amplification Nva 300va mono blocks
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Denon DP47f; AT-VM95SH- RigB 9
GL-59; ARB uni pivot; AT- Signet mc
Nva phono mm/mc
Doug Self balanced Pre amp
Akai 4000DS mk2 R2R
Digital Sources- Argon Pi4 v2; IfI iUSB 3.0, Ifi Neo idsd Dac;
Tidal / Radio Paradise
Amplification Nva 300va mono blocks
Speakers Lii Audio F-15 in Open Baffle; Ls6
Weiduka AC8.8- for digital sources
Mini BMU for analog sources
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Re: Another DIY SS Amplifier with NVA Boards
We would consider doing it in an amp fitted with separate input and output transformers, taking the power for the phono from the input transformer.Latteman wrote: ↑Mon Jan 03, 2022 2:51 pm Is taking the power + & - from the amp board supply a ‘common’ method in integrated amps- I wonder if there is any effect on the power delivery, current or voltage to the input stage of the amp boards. Is there sufficient in reserve with the capacitors used?
Great looking amp and build
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Re: Another DIY SS Amplifier with NVA Boards
Just to add to Paul’s comment. In the days when integrated amps had phono stages, there was no problem with powering them from the single power transformer. My old Naim NAIT 2 would be a good example, or any A&R amp such as the A60 I once had: any standard amp for that matter. Phono boards don’t tend to draw much current, and they would have been decoupled from the other stages by the use of RC filters.Latteman wrote: ↑Mon Jan 03, 2022 2:51 pm Is taking the power + & - from the amp board supply a ‘common’ method in integrated amps- I wonder if there is any effect on the power delivery, current or voltage to the input stage of the amp boards. Is there sufficient in reserve with the capacitors used?
Great looking amp and build
Mine is of course decoupled by a regulator, as would be any phono stage built into an NVA integrated amp.
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Re: Another DIY SS Amplifier with NVA Boards
An alternative to simply attenuating the input is increasing the feedback ratio of the amp. This has other advantages too.SteveTheShadow wrote: ↑Fri Dec 31, 2021 8:24 pm
I also took the opportunity to attenuate the input with a potential divider ahead of the volume control. With this, the 2V output of the CD player and streamer drops to 800mV and with my high efficiency speakers, I can now get the volume above eight o’clock without blowing out the windows.
The NVA circuit normally has about 30dB of gain. You can drop 3dB out of this by dropping the series 18k resistor to 10k. It's this one.
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Re: Another DIY SS Amplifier with NVA Boards
Thanks. I’ll have a look at that option and thanks for pointing me to the location of said resistor. I’m a bit concerned that increasing the feedback levels might introduce instability, though I don’t know an awful lot about transistor circuitry. With that in mind, I could of course be worrying unnecessarily.r3xj0hn570n wrote: ↑Fri Jan 07, 2022 11:02 pm
An alternative to simply attenuating the input is increasing the feedback ratio of the amp. This has other advantages too.
The NVA circuit normally has about 30dB of gain. You can drop 3dB out of this by dropping the series 18k resistor to 10k. It's this one.
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Somebody’s stepping on my plastic sandals. Joe Jackson (1979)
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Re: Another DIY SS Amplifier with NVA Boards
How about we let Rex try it out first and then he can report back on any fireworksSteveTheShadow wrote: ↑Sat Jan 08, 2022 9:35 amThanks. I’ll have a look at that option and thanks for pointing me to the location of said resistor. I’m a bit concerned that increasing the feedback levels might introduce instability, though I don’t know an awful lot about transistor circuitry. With that in mind, I could of course be worrying unnecessarily.r3xj0hn570n wrote: ↑Fri Jan 07, 2022 11:02 pm
An alternative to simply attenuating the input is increasing the feedback ratio of the amp. This has other advantages too.
The NVA circuit normally has about 30dB of gain. You can drop 3dB out of this by dropping the series 18k resistor to 10k. It's this one.
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Re: Another DIY SS Amplifier with NVA Boards
Fair enough. Next time i have my test amp apart i'll try it. Hmm , could just jumper a 22k on top...
There are other circuit mods i won't be reversing, but they don't affect the circuit stability.
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Re: Another DIY SS Amplifier with NVA Boards
OK, here is a rebuilt original curcuit AP20, -10dBFS 1kHz sine out the sound card.
As an addendum, here is the output with the differential input emitter resistors (120R) jumpered (and FB back to 18k)
Here it is with the 18k feedback resistor jumpered with a 22k.
Less output as predicted. Nothing untoward showing on my scope.As an addendum, here is the output with the differential input emitter resistors (120R) jumpered (and FB back to 18k)
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Re: Another DIY SS Amplifier with NVA Boards
Thanks for that Rex, that is very helpful.r3xj0hn570n wrote: ↑Thu Jan 13, 2022 4:53 am OK, here is a rebuilt original curcuit AP20, -10dBFS 1kHz sine out the sound card.
AP20-original-at--10dBFS.jpg
Here it is with the 18k feedback resistor jumpered with a 22k.
AP20-10krfb-at--10dBFS.jpg
Less output as predicted. Nothing untoward showing on my scope.
As an addendum, here is the output with the differential input emitter resistors (120R) jumpered (and FB back to 18k)
AP20-diff-bypass-at--10dBFS.jpg
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