HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

Having bought blind an A60 and P90 on eBay I have now eventually finished the project. I made a bespoke acrylic case for the amp board using an identical heatsink as per current NVA a60/70/80's . Same upside down format but with 4 x 4700uf DNM 4 terminal caps in separate amp case which splits into 2 halves to allow access. The 2 x 500va transformers are in separate acrylic PSU unit with 2 x DNM slit foil 10000uf caps per rail.

The caps on the boards were all replaced with original NOS ( except for 50v Vishays ) and NOS original 10 A Darlingtons. So it is like a new amp and still needs a lot of running in. Sound wise very happy with it lots of solid bass nice sweet top end ( the DMN's I am sure help here ) and wide engaging soundstage. I am very pleased with it and did not expect it to be as good. Might build a second PSU with single 500va transformer to power input stages and switch existing PSU to powering only output ie 3 x 500va in total.
The P90 was upgraded using stepped attenuators ( Many thanks Clive ) fitted with Charcroft Z foil output resistors ( for £30 this was a seriously VFM no brainer upgrade ). It was already all silver wired so despite the aluminium case it is a Mk 2 1/2 in my book !
I invested time and money in this project as I believe pre 2000 ‘old’ NVA boards have a slightly fuller sweeter and more dynamic edge than the current boards but at the expense of a marginal in loss in detail.

But time to move onto the next project and build one of Colin Wonfor’s wonderful SECA amps.

VERY nice !!!!!

Magnifico

Fantastic

Congratulations. A true labour of love.

Richard tested the DNM slit-foil capacitors (they were all the rage at the time), but he didn't use them due to price. Whether he (or others) thought they sounded any better, I don't know, but you may well find some thoughts in the archive.

As part of our listening tests, Tomasz built an S150 with a set of NOS old boards to compare against the current boards. We didn't get less 'sweetness' in that like for like comparison, but different combinations of components may well produce different results.

We listened to the Charcroft resistors when we were upgrading stepped attenuators but preferred the Audio Note resistors, regardless of price. nilsatisnisioptimum - the Charcrofts were the 'more expensive' resistors fitted to my own P90SA that you heard when you came to my place.

One thing we likely would have done differently is to have a layout that places the output devices towards the centre of the heatsink, for optimum heat dispersion. You might want to monitor the running temperature as you are using a large transformer.

Many thanks for sharing. You've certainly given that old A60 a serious upgrade and a new lease of life

Many thanks for everybody's kind comments and to Paul for taking the time to comment comprehensively.

It was a very steep learning curve this project especially as I had to rebuild the right hand channel which I stupidly blew up along with my A30 when trying to bi-amp a set of Royds. I could have replaced the ITT caps with Mundorfs etc but costs then rise and you may not end up liking the resulting sound characteristics so I stuck with original NOS.
Richard did like slit foil caps as they removed the need for bypass filters but as you say the cost was uneconomic. Interested to read of your comparative tests which i did with my A30 ultimately preferring the A60 ( using the same PSU's for both). The differences I noted are marginal not night and day and again subjective.
I do recall stupidly saying to Richard many years ago I preferred the older boards which met with as you would expect a lot of gruff comments. He did however begrudgingly concede that one reason for redesigning the boards ( apart from reduced size and cheaper build ) was to extract more detail/clarity at the slight expense of other features.

P90 resistor wise again very subjective and I thought the Charcrofts would complement the A60 board better. I know Richard was a big fan of Shinkoh resistors which I think the Audio Note ones are based on.

Good point about the heatsink and it does get hot especially when fully encased. I need to ventilate it better and will not add another 500va transformer until I can get it running cooler. Problem with the stereo boards is the transistors all face the same way whereas with the newer mono boards you can put them back to back as it where with only 2 transistors per side of the sink. The case was a bit of a nightmare to build and next time I will go simple and practical.

As you were talking about resistors: Last year in November I ordered a stepped attenuator blue switch (the ones Richard used) at hificollective , 10K, 0,5W Takman Metal Film Shunt with Charcroft Z-Foils, found it not to be a bit disappointing and then ordered two 10K 2W Audio Note Tantalum non-magnetic resistors and replaced the Z-foils with them. So if anybody here likes to have all that, I'm open to offers or exchange against NVA speaker cables (not LS2) with at least 3 meters length.
I'll send the bills with them (there should be still warranty). All together without shipping costs was about 160 GBP. After this expensive trying I went back to the standard pot after about three weeks and for my ears it still sounds best. Uninsured shipping would be 5 Euros, insured one 14 Euros.

Where did you get leds and what resistor did you use.

Hi Daniel,

I don't know if you ask 29mile or me. For me: the resistors of the attenuator are 0,5W Takman Metal Film, the load resistors two 10K 2W Audio Note Tantalum non-magnetic resistors added at the moment. I could solder in the Z-foils as load resistors if you like before shipping. There were no extra leds needed. If your question was towards 29mile forget this answer.

Daniel Quinn wrote: ↑Thu Sep 17, 2020 6:01 pm Where did you get leds and what resistor did you use.

RS components 2mm round as per NVA I think here

https://uk.rs-online.com/web/p/leds/7870055/

Used 2k resistor but still a little bright.