DIY All-Tube Phono Preamp Project
Part 5, Circuit Board–Chassis Integration
The Finish Line
By Steve Graham
This is it. We wrap it all up here. I hope I’ve enticed a few people to give this project a try. Yes, there have been many long attachments detailing the build procedure, but it’s the pictures that take up a lot of space. If you tackle this project, just take it step by step. Scrolling down to the attachment links below will get you to the finish line.
Commonly available parts have been chosen. If you wish to colour outside the lines, parts and layout wise, the results may surpass those I’ve achieved, or they may not. Both the prototype and the unit our patron Adrian commissioned were off and running well, straight out of the gate.
Though my measurement capabilities are crude at best, I was able, with the help of a Hagerman inverse RIAA filter, to measure the RIAA correction of the phono amp. I can’t give a real definitive answer, but I’m confident the RIAA correction is flat with +/- 0.25 dB from 20 Hz to 20,000 Hz.
While I had the equipment set up I also checked the RIAA response of the Shindo Aurièges. The Shindo sounded a bit ripe in the bottom end, and measurements confirmed this. Relative to 1,000Hz, the Shindo was down by a fraction of a dB at 20,000 HZ, but up by 1.5 to 2 dB at 20Hz. Both channels measured the same, so I don’t think the rise was related to component aging.
I couldn’t help but do a bit of tube rolling on Adrian’s preamp before I shipped it off to him. The kit was supplied with JJ E88CC (6DJ8 equivalent) and JJ ECC81 (12AT7 equivalent) tubes. I decided to try my favourite inexpensive tubes of these types from the 6DJ8 shootout and 12AT7 shootout, that I did for WoS.
NOS Tesla ECC88 and Tung-Sol reissue 12AT7W tubes replaced the JJs. Compared to the stock tubes included in the kit, there wasn’t a big difference in sonics, at least in the short listening I gave them. The JJ set might have been slightly more detailed in the upper mids and highs but by no means were they shrill at all. They also might have been a bit tighter in the bass, but the Tung-Sol/Tesla set seem to dig a little deeper at that end of the spectrum.
One factor that was no doubt limiting performance was the step-up transformer used. The K&K Premium SUT wasn’t available, so I had to make do the DIY Cheapo from the same review. Doubtless the K&K would have revealed more differences than the Cheapo.
In one performance aspect, the Tung-Sol/Tesla combination outshone the stock JJ’s. The noise level was lower than the JJ’s. There was less hiss audible with the Tung-Sol/Tesla pair installed. Not that there was a lot with the JJ’s – I had to put my ear to the tweeter to hear it, but it was noticeably louder than the other set of tubes. The Tung-Sol/Tesla combo hadn’t been selected for low noise, just tubes I’d pulled at random from some of my other gear. Even a pair of NOS Tesla E88CC’s that I got for ten bucks a pop were quiet. If I’d had the K&K SUT (and had time permitted), trying my fave current production Genalex reissue E88CC might have been enlightening.
A big thanks to our patron Adrian, without whom this project would not have been possible.
Link to: Attachment Board – Chassis Integration Part 4.2, PDF (updated 3/05/2019)
And Editor’s thanks to Steve for this Herculean effort to document and guide us through a very cool project. Hope to hear some feedback soon from our patron, Adrian.
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