DIY Tube Phono Project Part 5: Circuit Board – Chassis Integration

The finished WOS - Tubecad Tetra Phono Project…..and friends

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.

 

Measurements:

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.

Tube Rolling:

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 1, PDF

Link to: Attachment Board – Chassis Integration   Part 2, PDF

Link to: Attachment Board – Chassis Integration   Part 3, PDF

Link to: Attachment Board – Chassis Integration   Part 4, PDF

 

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.

 

Related Articles

2 Comments on DIY Tube Phono Project Part 5: Circuit Board – Chassis Integration

  1. This is epic, thanks for sharing! 😀

    I was thinking on building myself a TU-8340VK amp but I may actually give this a try first. If I understood correctly this setup is for 120v? Would I be able to use the same transformers on 240v by wiring the input sections in series?

    You said the TU-8340VK COULD be your last tube amp. And it looks like you are happy with the results of this preamp… But after all the $$, and time you put into this project, could you say this may be the last phono pre amp someone could have?

  2. Steve Graham // 2018/12/07 at 2:15 pm // Reply

    Bruno,
    Yes, the transformers used in this project have dual primaries that can be connected in series for 240 volt operation. Could this be the last phono amp someone might want? Hard to say. What I will say is build the stock kit and if you like it consider upgrading the tubes and possibly the output and coupling capacitors for even better sound. An audiophile friend built a Tetra and it has displaced a Bottlehead phono stage in his equipment rack. I put Mundorf Supreme Silver Oils in the prototype (stolen from another project) but stayed with stock tubes. When I say stock tubes I didn’t get the complete kit for the prototype. I just bought the amplifier board and sourced the parts myself. I bought the PS-3 power supply kit complete. The prototype uses all 12AT7 / ECC81 tubes. In my case they are Tung-Sol reissue (Russian) my go-to, no nonsense, 12AT7. The stock kit that I built for our kind patron Adrian, uses 6DJ8 / E88CC input tubes and 12AT7 / ECC81 for output duty. As a first shot at upgrading the sound in this version I’d replace the stock JJs with NOS Teslas or finances permitting, Gold Lion reissue (Russian) E88CCs for the input tubes and Tung-Sol or Gold Lion for the 12AT7 output tubes.

    As to which to get first, the TU-8340VK or the Tetra Phono, there is the availability issue to consider. Elekit, it seems, doesn’t make unlimited runs of their kits. Once all are sold they don’t necessarily make a new batch. The Tubecad Tetra and PS-3 are in stock now but when a production run is sold off Mr. Broskie doesn’t necessarily order more boards right away. You could wait several months for them to become available again.

    I’ve actually listed my TU-8340VK for sale on a Canadian Audio site. It’s not that I dislike it but it wasn’t getting a lot of use and I want to finance other projects. As you are inquiring about 240 volt products (the TU-8340 can be configured for 240 volts) I’m guessing you might be in Europe. Shipping might be expensive on a heavy amp like the TU-8340.

    At any rate, thank you for your interest in Wall of Sound. I hope you build one of the amps discussed. Or hopefully both.

    Regards, Steve Graham

Leave a comment

Your email address will not be published.


*