Building a DIY amp with NVA amplifier boards

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Fri Sep 07, 2018 5:13 pm

Some progress here after work.

Started by changing the earthing arrangement in the nva based amps.

Went back to star earthing the 0V connection to the amp board and 0V connection psu on front end at the clean end of the output stage 0V . Speaker return to dirty end of 0V at rectifier end. Also put wires along side each other that were in the same current loops. Effect was bugger all. Still a moderately loud hum, no reduction at all.


Started messing about with the transformers whilst amp was switched on . I noticed the hum changing volume as I moved the little toroid around . Disconnected the psu's for the other adjacent mono bloc and tightly twisted the lead in and out wires on both the transformers still connected. This helped a lot and the hum reduced in volume considerably. Played around with position of both transformers and got them in a position where the hum is only just audible with my ear touching the mid driver.


Feel like I have got somewhere with this. I can still hear a noise through the speaker when I move a screwdriver along the faraday cage of the TIS cable. I am listening to one channel with all 3 drivers and the other with just the big 12" on the end of the Avondale amps. Sounds promising even though listening to the whole of the left channel and a third of the right.

Gonna play around and tidy up the arrangement in the pre amp next which looks like your usual diy work in progress (think spaghetti junction).

So does it still sound like I have an earthing problem or not ?
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Dr Bunsen Honeydew
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Dr Bunsen Honeydew » Fri Sep 07, 2018 5:36 pm

Feck nose, so much oddity I haven't a clue what is going on - enjoy yourself though.
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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Fri Sep 07, 2018 7:57 pm

Dr Bunsen Honeydew wrote:
Fri Sep 07, 2018 5:36 pm
Feck nose, so much oddity I haven't a clue what is going on - enjoy yourself though.
I haven't a clue whats going on either :lol: That is true to a certain extent and it is fun finding out. I do get a bit annoyed though when unexpected things happen and things aren't perfect first time.
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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Mon Sep 10, 2018 10:08 am

Done some more messing about with nva based amps.

Tried a few things and nothing worked - even a crocodile clip around TIS faraday cage to mains safety earth with system earth floating. No joy.


This morning I tried a cheapie phono cable between amp and pre and it still hummed. WTF. I only originally became aware of the hum when I introduced phono sockets and TIS between pre and power. So that didn't make sense to me.


Next step was to put the nva based amp back to single psu for the whole board. No hum with cheapie phono cable. Swapped cheapie for TIS and no hum. So somehow having separate psu's for front and back end was causing the problem. Well I never noticed it prior to getting the TIS.

Not sure exactly what the problem is

* interaction between transformers - doc does not have a problem
* earthing

Not sure how it could be earthing as I did same as Avondale amps - one 0V link between output stage cap bank and input stage cap bank (straight after the last pair of caps on each )

Any ideas anyone ? Starting to go slightly mad here.
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Dr Bunsen Honeydew
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Dr Bunsen Honeydew » Mon Sep 10, 2018 11:17 am

Learning process :mrgreen:

Can't see what you have done so cannot comment. Ignore it and do something else and then all of a sudden "ding".
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SteveTheShadow
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Re: Building a DIY amp with NVA amplifier boards

Unread post by SteveTheShadow » Mon Sep 10, 2018 12:22 pm

Is the 0V link between the output stage cap bank and the input stage cap bank the cause of the hum loop. In a dual PSU, aren't you going to cause a loop via the interconnect 0V, the 0V inter PSU link and the speaker cable 0V? Just thinking out loud. I'm compleely crap at earthing schemes, but it seems logical. I would have thought that with a dual PSU, you would be going for complete isolation between the stages. Connecting them together at the final cap end of each seems counter intuitive.
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
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Dr Bunsen Honeydew
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Dr Bunsen Honeydew » Mon Sep 10, 2018 12:33 pm

I connect them and no hum. I bet it will be something silly he has been staring at and hasn't seen. I do that sometimes, and as I say walk away, when you come back to it it is suddenly obvious.
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Lurcher300b
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Lurcher300b » Mon Sep 10, 2018 1:50 pm

I would have thought that with a dual PSU, you would be going for complete isolation between the stages. Connecting them together at the final cap end of each seems counter intuitive.
But with a stereo amp, they will always end up connected via the interconnects to the source component. There is never a perfect solution, just a good enough one.

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Mon Sep 10, 2018 2:05 pm

Thanks for your input Doc, Steve & Nick.

I copied exactly how Les at Avondale does his voyager amps which also has separate psu for input & output stages. The only difference being my Avondale amps have a regulator on the input stages.

In the Avondale & nva I have one psu on output transistors & driver transistors and the other on LTP and VAS. I cut the middle of the 3 wire links on the nva board power rails.

I am going to draw a picture out of how I did it and post it up here.
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Dr Bunsen Honeydew
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Dr Bunsen Honeydew » 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.
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