WE 16a Horns!

16a horn
hi-fi speaker cables 🙂

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.

Gyrator PCB prototype

 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

Goodbye 814SE Amp, it’s been a fantastic journey

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.

Filament bias and winter heating system
814SE Amp
814 output valve
814SE Amp and Lenco Turntable
+HT supply
6D22S rectifiers
HT power supplies

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 🙂

Gyrator bias discussion

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.

PSR analysis 01a CCS and res divider

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):

LND150 extract from datasheet

  1. It’s true the LND150 varies a lot with temperature (see attached), however if it’s operated at low current (e.g.<500μA) the variation is small. In a cascoded pair for this circuit the drift in the output voltage is small. Simulated in Spice I get about 6.35mV/°C. The resistor divider will be better of course but you need a smaller values to reduce impact of dR/dT. This creates another problem which is the reduced PSR. With a compromise divider to balance idle current and PSR you can get 5 times less variation with temperature in the circuit under discussion – see below (e.g. 1.4mV/°C)
  2. For a smaller value of resistor divider the PSR is impacted and significantly lower than the CCS. If you don’t have a well filtered supply, the PSR benefits of the gyrator will be reduced due to this. For example, I did some quick comparisons by simulating my 01a preamp. I used a 235KΩ/220KΩ and a 23K5Ω/22KΩ divider options with a typical film decoupling cap of 4.7μF.

PSR analysis divider and CCS

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

01a preamp out CCS vs resistor divider

 

 

 

 

 
The voltage variance is really small with temperature and this circuit in particular isn’t affected by such small drift in my view

Flexible HT supply

The return of the Jedi

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

 

 

 

 

DHT day

DHT in excess

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:

  1. 4P1L SE LL1682: a great sounding amp overall which sounded as well as it measured. A must amplifier to listen to!
  2. 4P1L PSE (O’Netics OTs). This one particularly revealed an issue with the 4P1L driver configuration as it was running out of steam at about 2W before distortion creeped in. I think Andy will look into fixing this shortly. It also showed a slight dip above 10kHz up until 20kHz which may be attributed to the O’Netics.
  3. 4P1L PSE which I nicknamed the “Daemon” as it nearly screwed up my measurement gear due to some nasty grounding issues. We decided to give up on testing the response of this amp after this.

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:

  1. 4P1L Siberian Gen 3
  2. Andy’s 26 preamp, filament bias, LL1692 step down transformer and Rod Coleman regulators.
  3. Tony’s 30sp with Rod Coleman regulators and depletion FET CCS loads
  4. 01a preamp Gen2 

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:

Andy’s HT supplies
4P1L Gen3 preamp, 01a Gen2 preamp, Tony’s 30sp preamp and Andy’s 26 preamp
Andy’s 4P1L SE Amp
What a mess on the floor!
First tests on the 01a, 4P1L preamps into Andy’s 4P1L SE Amp
wiring 01a, Slagle’s AVC and 4P1L Preamp into Andy’s 4P1L SE
Andy’s 4P1L PSE
Andy’s 4P1L PSE a.k.a “The daemon”

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. 30sp

All 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)

 

 

6GE5 Pentode Model

A quick trace of a NOS Tung-Sol 6GE5 measuring around 113%:6ge5 test

Derived the Spice models using Dekker’s ExtractModel tool. The uTracer has a limit of 200mA so it’s not possible to trace the extended set of curves for this valve. However, this is not a limitation to produce a good model.

Here is the triode matching:

6ge5 triode
6ge5 triode

I run a set of curves at various screen voltages from 100V up to 200V at 25V steps to generate the pentode model The saturation effect is visible on higher currents above 140mA as you can see below:

6ge5 Vs=100V
6ge5 Vs=100V
6ge5 screen current at Vs=100V
6ge5 screen current at Vs=100V
6GE5 Vs=200V
6GE5 Vs=200V

Below is the triode model, you can dow Continue reading “6GE5 Pentode Model”