Tag: 01a

01a Preamp by Nash

 

It’s always satisfying to see someone else enjoying the end result of their build work. Here’s a great example of Nash building his take on the 01a low gain DHT pre-amp:

Hi Ale,

Its now over two months since I have been listening to your low gain version of the 01A preamp in concert with a Slagle AVC after it.

Over a span of a few years I have built several preamps and I can honestly say that this one is substantially better than any of the others. As a classical music fan I value attributes like clarity, timbre, body, weight and speed and your design delivers! I would like to use the analogy of a superb cake with icing- the cake is the 01A pre and the icing is the AVC. Thank you for a great design!

I have recently replaced RMu and the divider resistors with the TT Electronics PFC series SMD resistors mounted on a 1206 adapter. These are tantalum nitride resistors and they sound wonderful in this application. 

Further, I am getting interested in your 300B SE builds. Are you using a preamp before these? Please send me a link to your latest work in this area which you feel I should consider.

Regards,
Nash Bapasola  in NJ

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The low gain DHT pre-amp library

For more than 10 years I’ve been experimenting, designing and enjoying DHT pre-amps. Without over-dwelling on this subject, to me DHT preamps bring the unique sound transparency and detail we all seek for. They can make night or day difference in any system. And is not about gain, hence I’m focusing on sharing this blog entry.

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01a Low Gain DHT preamp (finished)

It was a half-hour job to mod my Mule preamp by swapping out the UX-120 and introducing the 01a (CX-301a in fact), add the resistor divider to deliver low gain on this preamp:

01a mule

I set the valves at 115V/4mA. The Source Followers are running at 15mA and the resistor divider is actually 100KΩ/33KΩ (Kiwame) which is what I had at hand. It worked like a charm.

The 01a is driving my Slagle AVC into the 300B amplifier. I can say I can hear now the subtlety of the thoriated-tungsten filaments of the 01a with the extra level of gain I was hoping for. The amp sounds very dynamic at high level and with the clarity of the 01a.

01a mule

This is indeed a clear winner. I will leave this preamp on my system for a while to confirm further impressions. For now, I just simply love it.

01a Low Gain DHT preamp

How many times I’ve been asked “how do I lower the gain of the DHT preamp?” many builders love the DHT sound and yet don’t really need that gain. Of course when you use a transformer load, step down is the obvious choice. And it works really well when you invest in a very good quality OPT.

However, when you use DHT with high rp, generally most of the low current ones, you face a tough challenge with regard to frequency response.

With the hybrid mu-follower topology (aka gyrator) we have the problem that the gain is fixed to nearly mu.

I’m in love with the DHT sound and in a preamp a 01a and the 801a/VT-25 DHT Preamp Update preamp cannot be beaten in my view. They all deliver a gain of 8 with a hybrid mu-follower topology.

This can be overcome in the following way: Continue reading “01a Low Gain DHT preamp”

DHT Folded Cascode Experiments

Here we are on holidays and surprisingly I struggle to find any free time in which I can sit down in front of a tablet and write this blog entry. This is actually quite good as it’s a sign of me being disconnected and looking after my daughters. Life is good.

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Tuning the system for ETF

This year I entered the shootout competition and will bring my DHT system to the European Triode Festival in France. It’s comprised of the ER801a stage plus the 01a (if extra gain is needed) and the 4P1L PSE output stage

I will have to swap out the amorphous OPT for the Monolith Magnetic ones as the speaker load is 5R.

It’s going to be interesting!

01a with filament SiC bias

I tried the below configuration and the results are very promising.  Sound is as good as previously implemented SiC cathode bias.

Now looking at the TH and frequency response:

The stage performs as expected. I built some prototype PCB for the SiC filament bias. One board per channel. If there is any interest, I will run a bigger batch

 

Sounds great, as always.

Cheers

Ale

 

ER801a Driver Stage

ER801a as Driver in my system

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.

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:

  1.  Ravel Feria (Cleveland/Boulez)
  2. Janacek The Cunning Little Vixen Act 3 Scene 7 “A vixen’s running through the woods” Prague Theatre/Gregor


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.

Andy Evans

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. 

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