Building a DIY amp with NVA amplifier boards

A place for DIY project discussions.
Forum rules
1. No ad-hominem
2. No spamming or shilling
Lurcher300b
Posts: 640
Joined: Tue Jun 14, 2016 1:58 pm
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by Lurcher300b » Mon Sep 10, 2018 3:52 pm

Dr Bunsen Honeydew wrote:
Mon Sep 10, 2018 2:14 pm
They are not Avondale amps, that may be the problem. You need to do it the NVA way. KISS.
There may be some cunning power supply hum cancellation that is being broken by using separate supplies.

User avatar
karatestu
Posts: 1358
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Mon Sep 10, 2018 5:14 pm

Lurcher300b wrote:
Mon Sep 10, 2018 3:52 pm
Dr Bunsen Honeydew wrote:
Mon Sep 10, 2018 2:14 pm
They are not Avondale amps, that may be the problem. You need to do it the NVA way. KISS.
There may be some cunning power supply hum cancellation that is being broken by using separate supplies.
I have no idea what that means :(

I thought I had it sorted for a while with the other channel which I had left alone (twin supplies left as they were), just disconnected from mains, passive pre and speaker.

I wired it back in and it was dead silent for a little while and i could not here crackling in the speaker when stroking the faraday cage on the TIS with a screwdriver. But shortly afterwards i heard the hum increasing again (ear against mid driver) and the crackling strated again when stroking the faraday shield on the cable.


Bonkers. It is like a charge building up on the shield over time ?
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1358
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Wed Sep 12, 2018 1:25 pm

A bit of progress made here.

Firstly I went for a bog standard bridge rectifier and a pair of caps for each psu. Wired centre tap at the end of 2" stubs coming off the 0V wire linking the caps. I soldered the speaker return wire to the end of the 0V stub on the output stage side (next to the centre tap wire). The input and output stage psu 0V was connected by a very short link right at the caps.


With TIS connected to passive pre and nothing else turned on (there is still a path from psu & signal 0V to mains safety earth through the CDP) then the hum was just as bad as before. :angry-screaming: :angry-screaming: :angry-screaming:

Just about to throw it all in the bin when i decided to cut the very short (less than an inch) 0V link between the psu's and run a wire from the input stage psu 0V to the 0V connection on the NVA amp board. So in effect the two psu's 0V are now starred at the nva amp board. The result is a massive reduction in hum volume. With my ear touching the mid driver i can only just hear it.


Dont know if this is as good as i can get it or if i can eliminate the TINY amount still left. I put my diy avondale amps on the speaker to compare and there is a similar miniscule hum with them as well.


Seems that introducing a larger resistance between the two psu's 0V has (a 12" long, thinner wire - with crocodile clips of course) worked wonders . Or it could be the fact that the two psu's are not sharing an 0V return from board to psu's ? Waffling now.
Naim, Linn & Harbeth fanboy

SteveTheShadow
Posts: 1026
Joined: Thu Sep 12, 2013 5:24 pm
Location: S Yorks
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by SteveTheShadow » Wed Sep 12, 2018 1:31 pm

Like I said, remove the direct link between the PSUs :mrgreen:
Glad it's working now.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Large sealed cabs, with Fane 12-250-TC 12" full range drivers.

User avatar
karatestu
Posts: 1358
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Wed Sep 12, 2018 1:51 pm

SteveTheShadow wrote:
Wed Sep 12, 2018 1:31 pm
Like I said, remove the direct link between the PSUs :mrgreen:
Glad it's working now.
Hi Steve,

Aye, I just read again what you posted the other day, Should have listened to you . As I had them before with a short link between the caps , there was never a loop because that was the only connection between the two psu 0V's. They have to be connected somewhere before they exit the monobloc power amp. It has had me puzzled somewhat. Then the Doc said he linked his but I was unsure of exactly where.

The two psu's are still linked but at the amp board 0V connection. From there to the phono socket and off to the passive pre. I still have the speaker 0V return soldered to a Tee off 0V link between the caps of the output stage psu.

The insertion of a TIS interconnect was what brought this to my attention. If there was any hum before with a screened interconnect that used screen for 0V then I never heard it. As soon as the TIS went in - swarm of bees.

I will never completely understand this diy hobby. Learning as I go though.
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1358
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Wed Sep 12, 2018 2:34 pm

Having my first proper listen to these TIS between passive pre and nva based power amps. Hum escapade put this on hold :roll: Avondale amps on bass are still using chord company speaker cables (not twisted) as interconnects. :naughty:

What i am hearing with the TIS is definitely different to what i had before (Naim snaic with one core used as signal and shield used for 0V). Capacitance will definitely be lower with the TIS.
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1358
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Wed Sep 12, 2018 4:56 pm

Going to try my potential divider (10K in series and 604R to ground) right on the end of the nva amp boards and see what happens. That will eliminate a load of soldered connections, plugs & sockets and 75cm TIS.

I don't know if there will be any change. Can only use the nva amps though so comparisons will have to be done with just my small semi omni speakers not the big ass bass mutha.

That got me on to thinking of having all the amp psu remote and then put all the nva amp boards together with potential divider central to them. Short wires to amp boards and 0V.

Like a two box 6 channel integrated. What could possibly go wrong :guiness;
Naim, Linn & Harbeth fanboy

User avatar
Dr Bunsen Honeydew
Posts: 29541
Joined: Wed Jul 11, 2012 7:26 pm
Location: Muppet Labs
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by Dr Bunsen Honeydew » Wed Sep 12, 2018 6:19 pm

Well it's a bloody miracle nothing has blown up yet.

User avatar
karatestu
Posts: 1358
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Wed Sep 12, 2018 7:30 pm

Dr Bunsen Honeydew wrote:
Wed Sep 12, 2018 6:19 pm
Well it's a bloody miracle nothing has blown up yet.
Ha ha :lol: . Only thing i ever blew was a super regulator where i connected the raw psu to the output. Must have been lucky. Jinxed myself now :roll:
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1358
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Great Britain

Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Sat Sep 15, 2018 11:30 am

More fannying about with these amps.

One channel is now completely silent (no it hasn't blown up) and the other has a TINY hum . The only difference between the two is wiring layout so all I need to do is replicate the wiring from the silent one in the other. :grin:

Just goes to show that wiring up does make a difference. Funny thing is the one I thought would be the quietest actually isn't :roll: Disconnecting signal 0V to mains safety earth in my cdp has no effect on hum now, it stays almost inaudible on that one channel. So I have left system 0V floating.
Naim, Linn & Harbeth fanboy

Post Reply