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
User avatar
karatestu
Posts: 1291
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 » Tue Aug 28, 2018 9:20 am

Been messing about with my nva style amps again :guiness;

I use some 25-0-25 EI transformers on the front ends of my mid tweeter amps. Got em from Les W and very nice they are too.

I was only using one of the secondary windings and they have two. Decided to parallel them up and use the whole of the transformer so set about the wiring changes. I then realised that previously I had wired them up wrong :shock: I had used the winding start and centre tap from one secondary and the winding start from the second winding.

WTF. It was a total fluke that it worked so well and did not go bang. What a numpty :oops: :roll: , well at least I have the guts to own up to it here.


I have them wired up correctly now and secondary windings in parallel. Sounds better or maybe I am just expecting it to sound better. Living for the city playing now . Waiting for the bus to drive through my room.
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1291
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 Aug 29, 2018 3:38 pm

Put transformers back to single secondary as with the two centre tapped secondary windings in parallel I was getting a small amount of hum through the speaker. On switch on the hum was in both channels but stopped on one after a short while but the other one continued to hum. Very strange.

I need to think some more over why that happened cos I like to know these things. Anyway decided to try my 200va single secondary toroids again and see what I think.
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1291
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 Aug 29, 2018 4:54 pm

More thinking about how to fully utilise the two centre tapped windings on the EI transformers. I am going to try this - the lower picture.

Image

Dotted line shows how the 0V connection is made. Seems to me a better idea than just paralleling the secondary windings up. I cant find anything on the net about paralleling two centre tapped windings into the same rectifier bridge .

There is something I like about the EI transformers on the front ends and want to use them if possible even though they are only 100VA 25-0-25 (x2). There is nothing wrong with the sound from the 200va toroids but I have a slight preference for the EI even though they are smaller.
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1291
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 03, 2018 7:46 pm

Currently using MBR20200CT Schottky diodes for rectification and 10,000uf (x3) caps on the output stages of my amps. This has replaced soft recovery diodes and 2,200uf (x3) with very low value inductors in between ie CLCLC. Front ends still using 6,800uf (x3) with same inductors between the caps and the nva based amps now have exactly the same psu as my Avondale mono blocs (on bass duties) but without the regulators.


The process is slow but I need to evaluate every change for a while before I am sure of the changes that happen. No inductors in psu for output stage, next stage is to remove them from the front end psu's and then evaluate that. The end goal being keeping it simple if that is what sounds best to me. But I need to go through this slow process of change to really know what is happening.

Currently listening to Bob Marley :dance: I find it to be good music for assessing these things.
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1291
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 05, 2018 3:16 pm

Preparing for my new to me TIS for the nva based power amps. Fitting some phono sockets as the old cables had din on one end and 6mm spades on the other. Well this is diy you know. Slowly inching forward to the end (years away I hope :grin: ).

Snipped some unused 0V wires out of the system today - from unused active preamp boards and old power amp boards. They were still connected to 0V as in my haste I did as little work as poss to make changes. New thicker mains lead on the nva based amps as well.


I already knew that the psu without inductors between the caps for the output stages was going to be better cos i remember the improvement when i did it to the Avondale amps.
Naim, Linn & Harbeth fanboy

User avatar
karatestu
Posts: 1291
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 » Thu Sep 06, 2018 5:26 pm

Swapped din sockets etc for phono and put new to me TIS cable in.

Greeted with hum. WTF. Stops when I touch the faraday outer sleeve on the TIS or the plug body with my finger. Does not happen with the Avondale amp. I even reinstated the signal earth connection to safety earth in my cd player but still hums.

Stumped
Naim, Linn & Harbeth fanboy

User avatar
Dr Bunsen Honeydew
Posts: 29242
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 » Thu Sep 06, 2018 6:15 pm

It is a shotgunned cable so will be more open to hum but not that much. If touching the outer of the plug and the cage causes hum then you have an earth problem too many or too little. Sometimes shotgun cables are not good, for example never use for TT arm leads. So if they don't work there and you can't work out the problem you have to use them elsewhere in the system. It is not the cable as I have been using them for years, they were my work system / dem cables.
Image

User avatar
karatestu
Posts: 1291
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 » Thu Sep 06, 2018 7:00 pm

Thanks Doc. I didnt mean the cable was at fault.

The hum goes away when i touch the cable not the other way around.
Naim, Linn & Harbeth fanboy

User avatar
Dr Bunsen Honeydew
Posts: 29242
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 » Thu Sep 06, 2018 7:30 pm

Then its an earth problem, you are earthing the noise.
Image

User avatar
karatestu
Posts: 1291
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 » Thu Sep 06, 2018 8:11 pm

Thanks, I thought as much. I need to have a play around with things. Only things that have changed are sockets and cable. It was absolutely fine before.
Naim, Linn & Harbeth fanboy

Post Reply