Building a DIY amp with NVA amplifier boards

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r3xj0hn570n
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Re: Building a DIY amp with NVA amplifier boards

Unread post by r3xj0hn570n »

karatestu wrote: Mon Feb 06, 2023 6:43 am For the input and output stages I now have a curved tinned wire going over the top of the board and connecting thd two caps. I do worry this is not optimal and that the bus bar between them should be as short as possible. You mostly see psu caps very close together with a short link between. Do you have any thoughts on that Rex ?
The current loop area from the +ve rail, cap, earth bar, cap, -ve rail, through the output transistors back to the +ve rail represents inductance.
Probably something to minimise.

karatestu wrote: Mon Feb 06, 2023 6:43 am You mention bleeders (discharge resistor to ground) in each group :grin: - do you recommend this just for safety reasons ? What resistance and wattage do you suggest ? I believe that the value shouldn't be too low as it wastes power during normal use but obviously the higher the resistance the longed it takes to discharge the caps. By the way, I always discharge them with a 60w lamp before messing about with them. With the speakers connected (4 ohm load) I always find they have all discharged apart from the output stage positive rail overnight.

Thanks, Stu
It's reasonable to expect something that's been off for a while to have discharged. In DIY equipment, it's up to you to define 'a while', but if your banks become separated (as in a fault), it's been off 'a while', you touch something and it connects again and 'BANG', the charged caps discharge into the dead short representing the discharged caps and all of sudden you have hearing issues. It's not fun.

Even a 1/4w resistor dissipating 0.01w is fine, but recalc according to your definition of 'a while'.
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karatestu (Tue Feb 07, 2023 7:05 am)

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

r3xj0hn570n wrote: Mon Feb 06, 2023 10:27 pm
karatestu wrote: Mon Feb 06, 2023 6:43 am For the input and output stages I now have a curved tinned wire going over the top of the board and connecting thd two caps. I do worry this is not optimal and that the bus bar between them should be as short as possible. You mostly see psu caps very close together with a short link between. Do you have any thoughts on that Rex ?
The current loop area from the +ve rail, cap, earth bar, cap, -ve rail, through the output transistors back to the +ve rail represents inductance.
Probably something to minimise.

karatestu wrote: Mon Feb 06, 2023 6:43 am You mention bleeders (discharge resistor to ground) in each group :grin: - do you recommend this just for safety reasons ? What resistance and wattage do you suggest ? I believe that the value shouldn't be too low as it wastes power during normal use but obviously the higher the resistance the longed it takes to discharge the caps. By the way, I always discharge them with a 60w lamp before messing about with them. With the speakers connected (4 ohm load) I always find they have all discharged apart from the output stage positive rail overnight.

Thanks, Stu
It's reasonable to expect something that's been off for a while to have discharged. In DIY equipment, it's up to you to define 'a while', but if your banks become separated (as in a fault), it's been off 'a while', you touch something and it connects again and 'BANG', the charged caps discharge into the dead short representing the discharged caps and all of sudden you have hearing issues. It's not fun.

Even a 1/4w resistor dissipating 0.01w is fine, but recalc according to your definition of 'a while'.
All good stuff Rex, thanks.

Having the main part of the psu remote is starting to become a real pain in the arse. Connections being the main one. I have 24 wires (16 DC and 8 0V) to pass between the two boxes. Single circular connectors big enough for thaf many contacts are real expensive and probably don't take the gauge of wire I like to use (fat).

I do have some Neutrik speakon 4 contact connectors that I have used for DC before. To keep things heat and orderly :grin: I would need eight of them with three contacts used in each. Good job the boxes will have big back plates.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by TroutFisher »

karatestu wrote: Tue Feb 07, 2023 7:22 am Having the main part of the psu remote is starting to become a real pain in the arse. Connections being the main one. I have 24 wires (16 DC and 8 0V) to pass between the two boxes. Single circular connectors big enough for thaf many contacts are real expensive and probably don't take the gauge of wire I like to use (fat).
Here you go.

https://www.ebay.co.uk/itm/224927449842 ... R_rrrrbFYQ
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karatestu (Tue Feb 07, 2023 12:35 pm)

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

TroutFisher wrote: Tue Feb 07, 2023 11:32 am
karatestu wrote: Tue Feb 07, 2023 7:22 am Having the main part of the psu remote is starting to become a real pain in the arse. Connections being the main one. I have 24 wires (16 DC and 8 0V) to pass between the two boxes. Single circular connectors big enough for thaf many contacts are real expensive and probably don't take the gauge of wire I like to use (fat).
Here you go.

https://www.ebay.co.uk/itm/224927449842 ... R_rrrrbFYQ
Thanks. Looks just the job .
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

A page on the screening of audio cabling and noise. Thus is from a manufacturer although a usually foo free and modestly priced one. J don't have thd knowledge to argue with it.

https://www.bluejeanscable.com/arti ... n.htm

I need to buy some coax it would seem.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Geoff.R.G »

karatestu wrote: Thu Feb 09, 2023 6:34 am A page on the screening of audio cabling and noise. Thus is from a manufacturer although a usually foo free and modestly priced one. J don't have thd knowledge to argue with it.

https://www.bluejeanscable.com/arti ... n.htm

I need to buy some coax it would seem.
Stu, that very short article doesn't cover everything by any means. To start with a co-axial cable is a capacitor which has advantages and disadvantages for audio signals. A common way to think of a screened cable is a series of inductors with capacitors connecting the junctions to earth. You need to select your cable with care if it isn't going to have a negative effect on the overall sound.
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karatestu (Thu Feb 09, 2023 6:15 pm)

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Geoff.R.G wrote: Thu Feb 09, 2023 10:14 am
karatestu wrote: Thu Feb 09, 2023 6:34 am A page on the screening of audio cabling and noise. Thus is from a manufacturer although a usually foo free and modestly priced one. J don't have thd knowledge to argue with it.

https://www.bluejeanscable.com/arti ... n.htm

I need to buy some coax it would seem.
Stu, that very short article doesn't cover everything by any means. To start with a co-axial cable is a capacitor which has advantages and disadvantages for audio signals. A common way to think of a screened cable is a series of inductors with capacitors connecting the junctions to earth. You need to select your cable with care if it isn't going to have a negative effect on the overall sound.
Thanks for the advice Geoff. Really don't know the best way forward. I am getting some noise pick up with my haphazard wiring. Maybe as a next step I should tidy it up and route the signal next to the signal 0V bus bar and see where that gets me. If that doesn't solve it then I will try twisting. Coax will be a last resort - would have to find the lowest capacitance available.

I think part of the problem may be the passive line level filter I created at the input of the power amp boards. I just tagged the coupling caps on the sgnal input post. Touching them with my finger makes strange noises. Nick Gorham said he wraps his coupling caps in foil and connects to 0V as they are very efficient ariels.

Stu
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