Tag: gyrator PCB

EF86 – 300B XLS SE Amplifier build

Here is a very nice build from Dan Kercher on his contraption of the 300B amplifier with auto bias. The driver is an EF86 with SiC diode biasing, the topology is a hybrid mu-follower and a source follower drives the output stage. Filaments are DC with Rod Coleman’s board:

Dan Kercher’s EF86 – 300B XLS SE Amplifier build

More details can be found below:

Hi Ale, 

I wanted to thank you for all of your PCBs.  I just finished a project that uses your Gyrators, SiC bias boards, and SiC Source Followers.  I'm so happy with the results.  Details posted on Audio Asylum.  

https://www.audioasylum.com/forums/tubediy/messages/27/276814.html


Cheers, 

Dan 

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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300B/845 Amp: Driver Options

For more than 6 months I’ve been playing with a lot of satisfaction my 300B amplifier with the 47 driver. Since then, I’ve made 2 modifications:

  1. Major one was the introduction of my Open-Baffle (OB) speakers. These are the “Liionidas” based on the LiiAudio C-15 and W-15 drivers. I need to do a proper write-up of these, but have to admit their sound has taken my system to another level. They are simply superb. Detail and dynamics are beyond expectations. Nothing less to be expected from the designer (Leon Huijgen) :
Initial test of the Liionidas OB speakers
  1. Second modification was minor, I removed the Zobel network from the input LL7903 to minimise loading to the source. Also, after several tests I found that the impact in the HF resonant peak is minor as the source has some resistance (below 100Ω) which is beneficial. So the 300B amplifier looks like this now:

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300B SE Amp: 47 Driver

Going DHT end to end

As previously mentioned, I played around with the 46 driver.  I love it sound and is a great valve. However, there were 2 reasons that pushed me to switch to the 47. Firstly, I wanted an extra tad of gain. Secondly, I have a nice stash of RCA 247 globe which measure extremely well. I’ve been reserving it for a 47 PP amp with local feedback (a la Pimm) and hopefully will get to in the future. Anyhow, the 47 in triode mode has a mu of about 8 which in combination with the SUT, gives me good gain to drive my 300B. After tweaking on the bench the stage for optimal swing and distortion performance, I ended up with the following circuit:

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300B SE Amp: 46 Driver (Part II)

The 300B amplifier journey continues as planned. A bit lower than expected, however small steps being made. Recently I mentioned about the 46 driver.

I made some progress on the LL7903 step-up transformer which is wired on 1:8.

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3 versions of the gyrator board

Three hybrid mu-follower (aka gyrator) board generations

From left to right: 1) Standard Rev08 PCB with full flexibility of FET and TH components. 2) Rev 1.0s board with SMD except Rmu, protection drain resistor and LED as well as space for any nice big PIO capacitor. 3) the smallest version of all, all SMD except Rmu, film cap and standard TO-220 top FET and multiturn trimmer.

Very happy with the results in the board development. It does take more time and precision (you will need a microscope) to work with the MELF resistors and the SMD components in general. However, it’s worth the trouble if you’re looking to reduce the footprint.

The return of the Mule (RE084)

It’s been a while since I experimented with preamps again. I settled as a permanent setup with my 01a/ER801a which I love. However, I wanted to continue with my experiments so I built a new Mule, let’s call it “Mule 2” for now. It’s based out of multiple PCBs which simplifies the construction process and reduces build time:

 

The Mule is back!

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Mini Hybrid Mu-follower board test

 I had a  go first at a mini-gyrator board using SMD. Blimey, it’s hard work to get all these crammed into such a small footprint.
I did a quick test with a D3a and worked fine at 100V/10mA (low voltage of course). It was +35dB flat up until a couple of Mhz. Even the over-current LED works!
Footprint is as small as you can get: 45mm x 25mm 🙂
More to report later!

6e6p-dr Headphone Amp – part 3

6e6p-dr HP amp in action – cap coupled output

I’ve been running with this HP amplifier for a few weeks now and I have to say I’m delighted with it. I matched a pair of 6e6p-dr on my eTracer and after fiddling with the operating point a bit, I settled for Ia=25mA and Va=180V. Anode voltage will depend on the valve as said before, the Russian valve parameters tend to be all over the place. Anyhow, expect anode voltage to be around 170 to 185V. The beauty of the gyrator PCB is that you can adjust the anode voltage with the trimpot.

Continue reading “6e6p-dr Headphone Amp – part 3”