MLA

So, what base voltage would you recommend, and how to set this up on the SRX Plus board? (or maybe the input tubes are well within cathode-filament voltage limits already)?

So, how to think about volume pot values in front of these? 10K?

No problem! and I'm always happy to fund the quality improvement work at USPS that this surely finances

Looking good!

Definitely no problem then. Thanks for the measurements!!!

Have the transconductance amp up and running at 25V currently. Brilliant sound, really like it! In addition to being good for planars, also does wonders for my older AKGs. While waiting for a few more resistors to arrive so I can set the GRLV at 30V (simply didn't have any useful combo at hand), is it possible to estimate the current draw at 30V? Thinking of running a balanced version off a single GRLV.

A monster indeed. Magnificent!!!

Running my CFA2 at +/- 24V rails currently, but thinking about testing something a bit higher, given that the Transconductance Amp seems to benefit from slightly higher rails. Is this thinking about it backwards? and if not, what is the highest voltage possible in stock configuration (given adequate heatsinking)?

Payment sent. Thanks!

Paid. Thanks!

Well, adding the files to Kevin's server definitely makes most sense, so that I would suggest as plan A, with the other proposal as plan B.

Well, I can install KiCAD and export something suitable for ordering PCBs and then pass on to mwl168 if that is the question?, or is there something else I can do to help? Would really like to try your PSU :), so just let me know how I can support...

Interested in 2 amp boards! As for PSU, I would prefer JimL's version or none, as I already a few suitable PSU boards from the KGST and Carbon builds laying around waiting to be used.

Great, thanks!!!

Sounds exactly like what I need! If powering this from GRLV, what components other than the opamps need higher voltage rating to stay intact at 30V?

I built the CFA2 a while back and am very happy with it, its great for the HE-500 I have, and works really well with the loaner planars I've managed to test it with (PM2, LCD-X). Guess I have to build this one as well and compare Any major differences to be expected in performance?

Definitely 2mm. Spent some time swapping tubed of different age and make into alternate positions to find a low inital offset to start adjusting from, and 1,6 mm flexes a bit too much for mental comfort... Also, as the dn2540 show quite a bit of variability, make sure you order a couple of extra values for the current source/sink set resistors. I had to go about 20% lower than specified on the board to get the currents right.

Indeed, my mistake. I think maybe the original publication intent was october? and then it was pushed back (grasping at straws to excuse my bad memory here :)). As for a GB, mwl168 and I had a quick chat on this and given that it may work out for him to take the lead and the very good quality of the boards from PCBnet, I think that would be option A. If the cards fall differently for some reason, I can be plan B (no, not a literal quote from the spouse). As for payment, a common way of doing this that has been successful in the past is to have people commit and then paypal their order's worth to the GB lead, who then places the order and ship things out, so each participant fronts his/her own cost.

As for previous issues of Audio Express, I believe the two issues prior to the current one are always available for download if you make a digital subscription, so October and November will be downloadable for a few weeks more (i.e. before the January issue comes out).

And I'm interested in 2-3 boards as well; have some beautiful 6SN7 GTB awaiting use.

Well, point to point is cool but board is simpler, at least in my experience. I would recommend the SRX-plus edition, it's a fantastic amp built with relatively few components, so limited things can go wrong, and figuring out how to trim all the current sources to balance everything out is a great learning experience (or at least was for me :)). Since there's only like 13 components per channel for the amp and a similar amount for the PSU, making a BOM is not so complex, and Mouser is your friend in this :). However, If you'd prefer a listing, JimL has a complete component list in his articles on the SRX-plus in Audio Express, the Oct and Nov issues, along with a lot of advice on how to grasp and trim the circuit. Very good read! As for boards, last time I checked making a board run of the SRX plus from Dr Gilmore's gerber files the cost was around 70-80 USD from one the cheaper PCB firms for a run of 5. If more people are interested and if you'd like help on this, I could make a small run for 5-10 boards and ship out, no problem!

Done

True true, the original circuit really is a very clever design within the design goals and constraints of the day. Your analysis has been a most interesting read. However, it's not for everyone to undertake that next logical update based on new technology so still: much kudos to your work on this!

Haven't had that much time to spend with it yet. Would say though that it reminds me of a beer commercial that ran a few years back "[insert brand here] - worth waiting for..." You did a great job designing this! (and many thanks to Kevin Gilmore for drawing up the board!)

I have 4 spare amp boards (consequences of a a minimum order of 5 and a successful first build attempt :)). Anybody need one, send me a PM and I'll be happy to ship it your way for cost of postage. Note: at least in my build, I had to lower source and sink resistors 20% to get to the intended currents so make sure you measure your dn2540s. Update: all boards spoken for!