Whilst listening to the master of Django
Author: Ale Moglia
"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)
ER801a Driver Stage
Received the ER801a today back from Thomas. They were working fine, it was a faulty UX-4 socket pin of my tracer which annoyingly made the grid to appear faulty and open at certain voltage level. I need to replace it.
Either way, they are now in my system and I can only say how much I was surprised with the sound of these. They take the detail and timbre of the VT-25 to a next level. Amazing result, happy to have these as part of my driver stage. The preamp is the 201a feeding the ER801a into the 4P1L PSE.
Highly recommended valves, worth the price indeed.
Morgan Jones’ visit
I had the pleasure of Morgan Jones visiting me today. We’d discussed for some time a meeting and I was looking for the right time. August looked to be it as I was taking some days off work before the arrival of our next child.
Morgan had planned to ride in his bike into London. What could have gone wrong? Well, after more than two months of hot weather and no rain, we had a classical British rainy day. He arrived completely drenched in his leather bike gear.
Oh well, it all went uphill after that. We listen to Tom Waits on the new setup after the DHT shootout held yesterday.
DHT Audio Shootout @ London
Here’s the summary of the shootout day we had yesterday at my place with Tony Rees and Andy Evans
Test Music
For testing the pre-amps Andy suggested the following 2 tracks:
- Ravel Feria (Cleveland/Boulez)
- Janacek The Cunning Little Vixen Act 3 Scene 7 “A vixen’s running through the woods” Prague Theatre/Gregor
Andy Evans
The Ravel is orchestrated for a large orchestra and percussion, and listening was particularly for the timbre of strings, brass and woodwind and the clarity of the percussion. The Janacek is for several different voices and chorus, and listening was for the tone and character of the voices and how well they were differentiated from each other. In both cases the overall clarity, life and crispness was considered.
Although I wasn’t familiarised enough with these 2 tracks myself, I found them to be an excellent choice and a reflection of Andy’s musical experience and knowledge as musician.
Continue reading “DHT Audio Shootout @ London”Crazy DHT shootout
We compared 10 different DHT preamplifiers today with Tony Rees and Andy Evans. Very insightful findings which I will report shortly
For now, a picture of the laboriously day we had!
Spud Push-Pull Amplifier
I devoted the majority of my audio life to single-ended DHT amplifiers. I don’t regret the path, however, I do not want a polarised perspective on amplifiers. I do like very much a good push-pull amp, though. Over time, I stumble across poor implementations or excessive use of gNFB. Local feedback (lFB) designs well implemented are music to my ears.
I played around with SPUD amps over the years, with happy results. One of them I loved over the breadboard is the 6e5p in push-pull. I will definitely build a definitive version of it. Here is the concept overall:
The input transformers is step up. It will need 1:4+4 ideally. My friend Dorin from DVB Transformers has a great device which I reviewed before and would be ideal for this amplifier. To simplify the power supplies, I used only one, which provides a bit of a strain into the source followers SF1 and SF2. If you have a good driver, you can omit them, I wouldn’t. They take care of the miller capacitance which is worsened by the step up transformer. It’s just a pair of PCBs, not big deal. RK1 is an arrangement with a pot to balance the bias. C1 is in ultrapath. I used an Oil 40uF one. T1 was a Lundahl 8K8:8Ω PP OPT.
The CCS provides a stable bias current into RBIAS1 which sets the bias voltage.
Here is the operating point I used:
The 6e5p is biased at about 40-43mA and 240V. It needs 5V bias so a cathode resistor of 58Ω should do. For 4W output in A1, you need 4Vrms, which only with a 1:2+2 step up should do. You can get about 5W in A2 or a tad more.
I loved the sound of the 6e5p as output stage (as much as I do as driver).
There are multiple variances to explore indeed
I have a pair of Toroidy PP OPTs with CFB, so would be interested in running them in tetrode instead.
ELROG ER801a Update
It’s been really hectic for me over the last months. You will notice that I’ve not posted anything on this blog. Moving house and running a house renovation project whilst doing your day job is tough. Despite all this, I managed to set up a temporary lab in my new place. Yes. The system is running and I have also a workshop (or kind of).
Hybrid Mu-follower Output Impedance
Where to start?
Well, I often get the question “what is the output impedance of the gyrator circuit?”. My response has always been “it gets close to 1/gfs as a good approximation”. Recently, I was asked the question again, but this time I decided to crack on the formulae, which is a daunting task for someone who has ditched calculus after obtaining Ms in Engineering degree more than 20 years ago.
For simplification let’s start with a simple hybrid mu-follower stage (a.k.a. Gyrator load) like the following:
The power of Music
6Э6П-ДР (6e6p-dr) preamp / driver
With a quick mod on one of my active preamps, I managed to implement very quickly the 6Э6П-ДР (6e6p-dr) driver in my system. Here is how the circuit looks like:
