Author: Ale Moglia

"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)

814 SE Amp: upgrading the gyrator loads

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The upgrade made to the 814 SE was quite simple, I replaced the gyrator carbon 4M7 for a Holco one and the mu resistor for a Mills 820R MRA05 5W. The capacitor was finally reduced from the outrageous 1uF Mundorf Mcap EVO Oil Gold to an 220nF 450Vdc Mundorf Mcap EVO Silver Oil.

The main change was the capacitor and proved to have no loss impact on the bass. I have recently made the OT change so cannot comment on the overall impact in the sound of these changes. I can say at this stage that I cannot notice any big change. It sounds as good as before!

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I’d have expected a noticeable change by reducing the size of the cap, but in this case I didn’t.

Custom Transformer Supplier in Europe

Custom transformer supplier

Custom OT

Given I had several emails asking about the output transformers I used in the recent upgrade of the 814 SE Amp, I asked Mr. Vincenzo to kindly provide an email address so you can reach directly to him. You can send your request via the form below which protects his email address from internet SPAM :).

Alternatively, if you don’t want to use the form below you can browse his website (in italian only sorry).

 

 

814 SE Amplifier: Custom Output Transformers

 Improving the 814 SE Amplifier

photo 3After more than a year listening to this fantastic amplifier, it was time to do the first significant improvement to it despite I resisted to modify it after so much work and effort put into the design and build. The evident upgrade was the output transformer. When frequency response was measured, it was evident to see that the HF response was lower than expected. This is the result of the transformer and its configuration in this circuit. The LL9202 is a better OT for higher impedances and in this circuit, it is used in the 6KΩ /8Ω mode.

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01a Preamp Gen2: Build (Part 2)

Spent this afternoon building a compact modular base for the UX-4 sockets, a custom tag strip and the filament bias resistor array. Given the very low power dissipation on the filament resistors they can be placed below the valve socket board to minimise space. The actual size of resistors is a killer, but I have a stock of these lovely wire-wound ones:

Also the gyrator boards were mounted on top of the output teflon capacitors, again to minimise space. The trimpots to set the anode voltage are located at the top for handy adjustment if necessary:

01a Preamp Gen2

The return of the 01a stage

SX201a in actionI remember my first 01a pre-amplifier to be one of the best sounding ones I ever had. The uniqueness of its tone, detail and clarity was astonishing. Perhaps it is due to the warm tone it provides and I guess this is the reason why Thomas Mayer branded his design as the “sound processor”.  I fell in love with the sound of a CX-301a and the joy of listening to this stage was so great that I found a fantastic excuse now to re-build this stage. My Starlight Discrete DAC has a very low output due to the step down transformer it has. I can only get 500mV as maximum output level. Not enough to drive my system to full level.  This was a perfect argument for me to look at building a simple amplifier stage that could add the sonority of the 01a in my system.

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HY1269 curves

HY1269 I’m a big fan of the thoriated-tungsten filaments and I value them not just because they do look very cool, but fundamentally due to how they sound in a single-ended stage. I hope to build a nice push-pull amp with these type of valves soon.

I found a pair of HY1269 valves recently. This valve is not well-known amongst the used ones out there but they do have some interesting characteristics as a directly heated tetrode that would be interesting to consider it for a plate-to-grid (Schade) feedback configuration.  With its 30W of anode dissipation capability, it’s a good candidate for an output stage. However, it’s quite likely that you will have to drive it in A2 to get the most out of this valve. Like designs using 811a and similar transmitting valves, the HY1269 can be operated in class A2 even with no signal on the grid.

As per my “Robustiano” design using the 6P21S, it would be nice to see extracting 6W or more out of this  transmitting valve. I’m sure that the thoriated-tungsten touch will provide a lovely sound if properly implemented.

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Starlight Discrete DAC Festival – London 2014

Jon’s ESL 6C4C drivers
Oh, are you taking a picture?
Bipolar discrete DAC ready
Final adjustments to the bipolar DAC guinea pig!
It never goes as planned
One hand is never enough
Jonathan’s Ti48 + DAC

A lot was already said about this fantastic day at Jon’s. The Starlight CD + Discrete DAC festival didn’t go as planned but we had a wonderful time. I had the chance to bring my own Starlight and sounded nice in Jon’s system despite the ground loop issue. Not clear what it was, despite it played well at low AVC levels but not when volume was increased. Perhaps was the load? Anyway, lots of tests from differential DACs to cathode follower outputs and Tom’s bipolar version.

I have to admit that the transformer coupled DAC sounded very transparent and detailed. The valve output gave a warmer tone and even harmonic contribution. The 6N1P implemented as cathode follower was very well received.

Tom’s bipolar DAC implementation is very promising. Clearly the tiny DC bias saturated the AVC and bass wasn’t good. Once we added the coupling PIO it came back to life with a subtle sound I enjoyed very much. Some challenges aside with the ESL resonances which I hope Jon can sort out soon.

Food and hospitality were superb in another unusual warm September day.

Most of all, a great day with fantastic company.

Thank you all

Ale