All about electronic valves and hi-fi
Here are some picture of my slow progress on this flexible power supply. I started with the layout of the parts before any marks were made on the top plates:
Once I was happy with the layout, I submitted myself to the mercy of the most dreadful job on earth which is metalwork!
Merry Christmas to all!
When I was still a teenager and learning saxophone I came across this wonderful version of “Get thy bearings” by King Crimson. The power of the electrified alto sax blew me out my mind. Ian McDonald clearly found a way to drive the saxophone there and bring a new sound to the 1969’s progressive rock. Surely he didn’t experience any of this slew rate thing 🙂
In my previous post, I explored the slew rate challenge of the 01a preamp:
You may probably already asked yourself: what is this “slew rate” business? Has this guy lost his mind? Probably I have, but not due to this interesting phenomenon. The second question that should have probably popped in your brain is: why? Well, writing about this stuff came up by sheer coincidence.
We tested my friend Tony’s 01a preamp which has an older gyrator board I made for him about 3 or 4 years ago. The preamp (as well as his system) sounds extremely good in my opinion and the 01a has brought a new clarity which is what you’d expect as a result of the introduction of a DHT stage. We decided to run some frequency response tests since Tony has made some interesting mods to his Push-Pull amp. We encountered an unexpected challenge as I didn’t have the right XLR connectors for my testing gear so we run the FR tests on the power amp with the 01a.
The 01a preamp measured as expected with a flat response up until 40kHz before the sound card rolloff kicked in – I’m aware of this and this is the limited bandwidth of my current portable measurement gear. The distortion was also really low (H2 predominantly ) with less than 0.02% for 2 Vrms output signal. This test was done with Pete Millett’s interface which has an input impedance of 100kΩ: Continue reading “Slew Rate in Preamps”
If my wife thinks I’m insane, she should have come to Peter’s place to see this marvellous Western Electric 16a horn replica made by this man. A beautiful horn indeed. The sound is quite particular and has very attractive sound image which is closer to a mono than stereo and you need to get used to it. It’s worth listening to. Peter has an three-way active crossover. The horns are driven by a 6B4G amp. We listened to several tracks and enjoyed listening to it during the brief session before a fantastic Curry we had last night.
First sets of PCB arrived today. Thanks to Tom Browne for the great PCB work, and it worked first time round. The PCB can accommodate different FETs like 2SK170, BF862 and J310 to suit most of the requirements
If you’re interested in the final PCB let me know, production run shortly due to large number of request for this circuit for DHT preamps and drivers
Ale
After 2 years of listening pleasure, it’s time to retire the 814SE monster amp. With its breadboard nature and high voltages around, this is not safe to have around with my daughter now being 8 months old. Sad to see this amp go and I hope to listen to it some time in the future.
What is was really painful for my back was to lift this ton of iron up to the attic. It’s so heavy and not keen to move it for some time. This amp has been a fantastic learning experience for me, as well as a huge challenge. High voltages, A2 operation, DC-coupling and the mix of sand with plenty of iron here in a 100% DHT amp was the right mix to give me several headaches along the build and testing stages. However, it’s a beauty to listen to, in particular thanks to the 46 and 814 valves which are unique in my view for this circuit and also the optimal tuning of the operating points and the iron used.
Enough for now, however I’m still working on my safer 4P1L PSE amp, so watch this space 🙂
A very interesting point was raised on the 4P1L DIYAudio thread around the gyrator circuit using CCS and whether a simple resistor divider was better than the CCS due to the LND150 temperature drift.
I’ve tried both options and I’d say I prefer the CCS despite the variation with temperature for the following reasons (which people may well disagree):
The PSR of the CCS is above 100dB whilst the PSR of the resistor divider goes from 56dB (235KΩ/220KΩ divider) down to 37dB (23K5Ω/22KΩ divider).
In practice, I implemented two different circuits as I had a shunt regulator before when I had a resistor divider and now I don’t have any shunt regulator but I use the CCS version.
Looking at the output PSR as the gyrator provides additional rejection to noise. The resistor divider PSR is about 73dB and CCS is 30dB better anyway
The voltage variance is really small with temperature and this circuit in particular isn’t affected by such small drift in my view
Time has come when breadboarding and HT is not longer an option. With a baby around, I was forced to remove most of the valve equipment. However, the return of the Jedi is closer than you expect. With very little time, albeit at continuous pace when I get a free 30min here or there every weekend, I keep very focused on my objective. The 814 SE monster amp is close to retirement (probably before Christmas) and although I have a fantastic LME amp already working, I need to get the valves back on the scene providing I can prove I’ve complied with “heath and safety” – as my wife well put it.
Well, I had a nice attempt of a wooden frame made out of pine wood. Yes, I’m really bad at woodworking but I’m getting better. The top plates are 4mm thick. I have added a nice set of 2 100mA meters at the front of the frame. A 300VA custom-wounded multi-tap HT transformer from JMS which gives me full flexibility from 100 to 500V in 25V steps. The supply is choke input (LL1638) and filtered with a set of nice 50uF oil caps and 20H chokes. Damper valves used with some nice SiC to form a hybrid rectifier.
Top plates are protected with paper before drilling!
This looks to be quite neat in my view!
The idea is to use this supply for my new 4P1L PSE, 300B and DHT Schade experiments with 6P21S/47 and 1624 valves. A lot planned and so little time for this unfortunately.
Cheers, Ale
We met yesterday at Andy Evan’s with our friend Tony for an interesting set of tests. Firstly we looked at measuring Andy’s 4P1L SE and PSE amplifiers:
Andy’s speakers are Mark Audio Alpair 10s full range in some standing 23L cabinets. They do sound great with a solid bass and detailed treble. Perhaps a bit higher on the treble, but they are worth every penny.
We set the listening session to rotate the amps as well as the preamplifiers:
In my opinion, I think we can draw a conclusion to the 4P1L-4P1L-4P1L configuration. Perhaps it’s the H3 harmonic profile, but it doesn’t sound good – a bit harsh on the treble. The challenge in my view was that one 4P1L stage driver wasn’t sufficient to bring out to life in full Andy’s system. It forced the DAC to swing higher output levels and didn’t sound as good as with the preamps.
Don’t get me wrong here, all the preamps sounded great, however there were subtle differences which showed that 01a was superior in this setup. The 26 was also outstanding as expected, however the 30sp was slightly thin. The three agreed on the evaluation carried out and we concluded that 01a-4P1L-4P1L was a wining formula!
The 01a brought a level of clarity that it was superior. The piano, bass, snare drums, brass and voices we listen to in detail across various test tracks sounded with a level of detail and delicacy which was unique. This was a surprise to all, as we were expecting a system with 2 stages to be the superior combination. I wish the 4P1L could have a gain of 20! 🙂
Here are some few pictures of the messy DHTs spread around:
Thanks Andy for hosting a great day.
Here are Andy’s impressions posted in DIYAudio of our great experience testing the preamps and the 4P1L SE and PSE amplifiers:
“I had a very interesting day today with Ale Moglia and a friend of ours, Tony. We auditioned 4 line stages. Amp was a PSE 4P1L, with 4P1L input (plate choke and FT-3 coupling cap). Speakers were Mark Audio Alpair 10s. Full range, 23 litre infinite baffles. We placed them in this rank order:
1. Ale’s 01A
2. 26 into LL1692A stepdown
3. Ale’s 4P1L
4. 30spAll DHTs and all sounded good – quite alike in having that DHT sound. I think they were all filament bias. Ale’s 4P1L line stage might have suffered from going into two more stages of 4P1L so may be better into a different amp. In that sense it may not be a definitive test, so the jury is out on that. We have known from past experiments that 3 4P1L stages in a row just don’t sound that good.
The 26 preamp was predictably nice, sweet and detailed. Audibly better than 30sp. Just a bit better in this context than Ale’s 4P1L but not far away.
The star without any doubt was Ale’s 01A preamp. It was just stunning. Quite magical. So if it’s a question of building a line stage, this to my ears supersedes the 4P1L. I never expected this – I’ve built 01A preamps in the past, but this is a very clever circuit. you can find it here:
01a Preamp (Gen2) | Bartola Valves
I do urge you to look seriously at this design. It’s a bit special. It was the only one of the 4 we auditioned that actually sounded better in the system than without it. There is enough gain with just the 2 4P1L stages in the amplifier, which I usually drive straight out of a ES9023 DAC. But adding this stage was a better sound. I never expect 3 stages to sound better than 2, but this did.”
(Andy Evans)
This is an audio blog, however I can’t avoid posting this. I’m proud for the Pumas team, a great honour beating Ireland 43-20 and moving into semifinals
