Author: Ale Moglia

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

СГ2С Russian voltage regulator test

Here is a quick test of a russian СГ2С (SG2S) 75V voltage valve regulator:

The CCS is a classic cascoded DN2540 MOSFET. A russian PIO capacitor is bypassing the regulator and the input impedance is the Pete Millet’s interface impedance. HT is a well regulated variable power supply.

When near maximum bias current is achieved (circa 30mA), the noise floor is surprisingly low: -85.5dB / 53uV.

Need to capture input of power supply at the CCS input 🙂

Edit: after measuring the power supply noise level and finding that is near -90dB, came up to the conclusion that the above noise level is the VR noise. Quite good for a simple (but effective) voltage regulator. Gary Pimms used this configuration many times on his designs…

Update

Upon request from Vyacheslav, here is the noise analysis for different current points:

As you can see it’s very linear. There is a 4dB difference between 5mA and 40mA.

Also tested ripple attenuation using a poor-regulated HT power supply. Here are the interesting results:

  • 62dB @50Hz
  • 80dB @100Hz

 

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Salas HT shunt regulator SSHV2

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It took me probably half an hour to build this brilliant shunt regulator. I waited for a long time until picked up this board and stuffed all components. I will use it in my next generation of DHT preamps.

Output ripple is below 5mV, can’t even measure it given the noise in my workbench. The test gig included my variable power supply (600V) feeding the shunt regulator which was set for 40mA. output load is three 3K3 power resistor clads (50W each).

I adjusted the regulator to provide about 160V, so current is about 16mA. Interesting to seer the harmonic profile to have a higher peak at 200Hz compared to the 100Hz harmonic….

From VU to LULU, Lou Reed @ Royal Festival Hall

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Had the chance tonight of going to a Lou Reed gig here in London. It’s probably the fourth or fifth time I managed to see him performing live, a real privilege. This man continues to reinvent himself, the greatest challenge every artist has…

Why not say that also enjoyed the classics like:

Heroin, waiting for my man, white light, and street hassle!

Without attempting to sound like a critic, a great pleasure to see him (again).

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Digital source (MPD)

Playing digital music on my 45SE

When moved to the UK 6 years ago faced the challenge that I couldn’t move my personal CD collection. So ripped as many as I could on mp3 / m4a / AIFF with the best quality I could. Didn’t take a hi-fi approach on those days as didn’t have the time nor the knowledge. Just wanted to get my huge CD collection with me and had just a few days to address it. Currently I have a collection of about 100GB of digital music. Can’t fit in an iPod or not very interested in using an iPod for playing a part of it. Problem is that my computer is not in the same room where my 45 SE is 🙁

Looking at how to address this problem, Rob (DHTRob) suggested using voyage linux + mpd as a music server. I was considering a Raspberry Pi, but long lead times at the moment pushed me to look at alternatives.

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So here is the first quick build for this digital music station. A tiny Linux server with WLAN and mpd running on it. My collection is all stored now on an SSD 128GB usb disk. The voyage Linux server is powered by a shunt 18V regulator.

What comes next is the USB DAC, which is on its way 🙂

 

26 DHT preamp with LL2745 OPT

Today I managed to finally test the Lundahl LL2745/8mA specially designed by Lundahl for Thomas Mayer for a 26/01a preamp / line stage.

The circuit tested is here.

Initially did some tests with fixed bias, normal DC heater supply from my workbench and HT from a passive capacitor multiplier also available in my workbench. Circuit breadboarded has long cables and we shouldn’t expect good 50/100Hz noise levels as have many transformers and things around 🙂

Test 1: fixed bias

  1. Vgk=-6,8V
  2. Ia=6mA, Va= 119V
  3. THD=0.033% @ Vo=1.4Vrms

;

Test 2: fixed bias with Rod Coleman regulator

  1. Vgk=-6,8V
  2. Ia=6.5mA, Va= 119V
  3. THD=0.031% @ Vo=1.4Vrms
  4. Vf=1.4V (minor starvation)

Test 3: Filament bias with Rod Coleman regulator

  1. Vgk=-6,3V
  2. Ia=6.5mA, Va= 119V
  3. THD=0.031% @ Vo=1.4Vrms
  4. Rfilament=5Ω, Vf=1.4V (minor starvation)

As we shown earlier in other tests, filament starvation reduces THD slightly as expected. The OPT performs really well. Probably will look at starving a bit more filaments whilst doing a listening test

Will now proceed to rebuild the 26 DHT preamp with LL1660 with this circuit 🙂

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126C OPT

After testing 4P1L with the 126C OPT, Paul Leclercq suggested a different operating point to see if distortion above 8Vrms on the OPT version was due to grid current. So firstly did a quick test with the CCS and found that -15V and 170V was a good operating point for 15mA. The 4P1L performs brilliantly with CCS and THD is only 0.05% when driven to 10Vrms.

 

 

Unfortunately distortion with 126C grows exponentially above 9Vrms. OPT is tested floating and not sure if is the Pete Millett interface a limitation with it.

EDIT

Andy Evans suggested that secondary green should be negative so phase is 180. Aparently there is a thread meantioning the distortion introduced by the way I was using the OPT.

Anyway, problem sorted! Look at now how nicely the 126C can perform at 10Vrms: