Building a DIY amp with NVA amplifier boards

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Alfi
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Alfi »

I'm really keen to see what's happening here guys and good luck with your projects!!

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Re: Building a DIY amp with NVA amplifier boards

Unread post by Chunk McDaniel »

Me too Alfi. I have really enjoyed Steve and Stu's adventures in speaker development so far. Now for some New Adventures in Hifi. Good name for an album that!

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Some progress made today - blame it on the weather :dance:

I had to decide what orientation any heat sink would take (horizontal or vertical) so I knew how to bend the output transistor legs and where. Decided on a horizontal plate like in my other creations. Not 3mm copper sheet this time but 6mm aluminium sheet. Other bits can be added to it later (vertical fins) or I could always go back to using 3mm copper sheet. I have a 60cm square sheet of copper left that I could use. Aluminum 6mm sheet is in plentiful supply here :grin:

Output transistor legs were bent, scraped with a Stanley knife blade to make them nice and shiny and then inserted in to the nva amplifier board. I held the transistor in a pair of pliers so the bend was not near the body - don't want to stress anything and let any moisture invade.

Image

I used blutack to hold them in position whilst i used a small aluminium plate to make sure the transistor backs were flat against the sheet and everything was at the right angle. We need flat surface contact between the transistors and the heat sink to get the heat away as fast as possible. I will be using sil pads, nylon bolts and a smidge of heat transfer paste (snot). The Loctite glue is good stuff but expensive and I want to be able to get the boards off easily.

The transistors were soldered in taking care that I had them the right way round. The solder joints were a joy to make :grin:

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I made sure the transistor legs were scraped and cleaned with isopropyl alcohol before soldering commenced. After soldering, cleaning the joints with alcohol on cotton wool buds produced nice shiny joints :grin:

I decided to insert the transistors from the under side of the board so the transistor legs could be bent at 90 deg to leave the body horizontal and easily bolted to a horizontal plate heat sink.

Image

This gives a little space between the board and the heat sink for better air flow and less chance of shorting. The weight of the board and any stress from the wiring will all be on the transistor legs so a supporting leg at the other end of the board is probably a good idea.

I have arranged the initial parts (won't be the final parts) on a 60cm square 20mm sheet of chipboard which will slide in my "rack". Aluminum heat sink sheet is 40 x 45cm x 6mm and is probably overkill. I intend to make it smaller so that only the amp boards sit on it and put it on small legs for better airflow.

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The 200VA 27.5-0-27.5 V transformers at the front , then an Avondale cap bank with 3x 2200uf caps and the amp board further towards the back. I have it orientated with the output transistors towards the caps so the small signal wiring and front end of the amp board are further away from the transformer . Transformer to amp board distance at the moment is 23cm edge to edge .Only thing with that is the 0V connection is further away from the smoothing caps and the positive and negative DC wiring may have to cross (unless I turn the cap bank upside down)...can't have everything.

I need to mount a small vertical panel at the back to temporarily fix the phono sockets and speaker outlets. Then I can do some wiring and the fun really begins. I have yet to make my own rectifier/cap bank so am going to use this Avondale one at first.

Oh happy days :grin: :guiness;
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Re: Building a DIY amp with NVA amplifier boards

Unread post by _D_S_J_R_ »

A little bit of truth, a little bit of foo.....

May I suggest you use the rubber bump-ons at the back of the board, one on each corner. These newer slightly taller feet should be fine and keep the board fairly level. A dab of Bison on the domed part of the feet (so you can remove them if necessary) will be just enough to anchor the feet and the rear of the board in place, and it's not as permanent as Superglue as you're not going to ship these boards all over ;)

The 'foo' part is that the feet are slightly flexible and may offer some vibration support - all very well raving about Black Ravioli feet, but if amps are so sensitive to isolation so you 'hear' the effects, it should be possible by subtraction to isolate the effect if it's really there I'd have thought...

What are you using for the audio connections to the RCA sockets?
Last edited by _D_S_J_R_ on Thu Mar 01, 2018 4:02 pm, edited 1 time in total.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Hemmo1969 »

Where would one find a fine silver based wire the likes used in a multi thread speaker cable..... been wanting to tinker with some makeshift cables??

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

_D_S_J_R_ wrote: Thu Mar 01, 2018 3:52 pm A little bit of truth, a little bit of foo.....

May I suggest you use the rubber bump-ons at the back of the board, one on each corner. These newer slightly taller feet should be fine and keep the board fairly level. A dab of Bison on the domed part of the feet (so you can remove them if necessary) will be just enough to anchor the feet and the rear of the board in place, and it's not as permanent as Superglue as you're not going to ship these boards all over ;)

The 'foo' part is that the feet are slightly flexible and may offer some vibration support - all very well raving about Black ravioli feet, but if amps are so sensitive to isolation so you 'hear' the effects, it should be possible by subtraction to isolate the effect if it's really there I'd have thought...

What are you using for the audio connections to the RCA sockets?
Thanks for your suggestions Dave :grin:

I decided I did not like the board being so close to the aluminium sheet so soldered the output transistors in so there is 7mm gap between the two. All those component legs poking through the underside of the board and solder joints just rang the alarm bells. The little rubber bump-ons are not tall enough to provide any support now. I have various things to try instead of them which are easily made to 7mm height - all made out of rubber or silicone.

Surely vibration will be getting in to the board any way through the output transistors ? This amp wont be going anywhere so I don't need to make it drop proof although I will be making sure it is completely safe.

Wire to the RCA sockets is something I have yet to decide on. I have some silver wire that I bought from hifi collective an age ago. What do you reckon ? It has a removable ptfe sleeve (clear). I could even use it without the sleeve if I think it is going to safe. Ordered some phono sockets and other stuff from rapid which should be here soon.

Stu
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Lurcher300b
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Lurcher300b »

Hemmo1969 wrote: Thu Mar 01, 2018 3:58 pm Where would one find a fine silver based wire the likes used in a multi thread speaker cable..... been wanting to tinker with some makeshift cables??
I have used these many times

https://www.wires.co.uk/acatalog/ag9999_bare.html

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

_D_S_J_R_ wrote: Thu Mar 01, 2018 3:52 pm
What are you using for the audio connections to the RCA sockets?
How about a small length of TIS ? :lol: And a small length of TSCS to the speaker outlets? :grin:

I have a bit of LS2 here that I had to cut off the cables in my second system that I could use

Silver wire from hifi collective is 2mm I think. Too thick ?

Stu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by _D_S_J_R_ »

For short audio connections if the amp is open to the elements, how about short off-cuts of SC?
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

_D_S_J_R_ wrote: Thu Mar 01, 2018 5:17 pm For short audio connections if the amp is open to the elements, how about short off-cuts of SC?
It will be open to the elements initially - no case. But eventually it will get built in to a wooden structure with no metal except heat sinks. Think of deep sideboard furniture with the sound system built inside it :dance:

I am not a box swapper (just a sideboard swopper :lol: ) so once I am done with experimenting that is it, In to the housing it goes. The finished thing will be my final system, hopefully. Only source components will be visible and all cabling will be done internally (except mains and speaker cables of course). It has taken a lot of thinking about to get the design where it is now. I had to think about getting transformers as far away from anything else as possible, making signal connections as short as possible, heat management and making sure that I can remove elements of it for repair etc.

I dont have any spare SC to chop up :o

Stu
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