Author: Ale Moglia

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

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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801a preamp revisited (part I)

It’s been a long since I last posted here some project stuff. I’ve been busy with work and family. On my spare time, spent mostly listening to music, developing some synthesiser modules and playing music as well!

I missed ETF this year, sad to say. Work commitments made it impossible to  travel to France. Hope that’s not the case next year as am keen to get back. I’ve seen some pictures and feedback and seems it was a blast despite the COVID restrictions.

On my exchange with Rod Coleman regarding this post, I asked him to send me a pair of his latest DHT filament regulator (version 9) to test them on my 801a preamp with a cathode bias resistor (degenerated or un-bypassed):

Continue reading “801a preamp revisited (part I)”

DHT Supply PCB

I took me a couple of years but eventually found the time to build the BOM and a simple documentation guide for the DHT LT supply PCB. I’ve been using this PCB for a long time on most of my DHT preamps and in my current 300B SE Amplifier.

It’s a 16 x 8 cm board which can be stacked for a stereo DHT stage. Enough flexible is provided for all sort of filtering combinations (either choke to cap input supplies).

Some may say is a killer, but I add a common-mode choke to suppress HF noise from mains. I design my supplies with a no-compromise thinking and best possible components (e.g. including split-bobbin main transformers), chokes and capacitors to deliver the lowest noise possible to the filament supply.

This board doesn’t replace the filament regulator (e.g. Rod Coleman regulator), it’s just the raw supply circuit needed before them.

I will sell the remainder of my stock of these lovely ENIG finished PCBs. You can order them here.

DHTs and cathode bias degeneration

A few years back I went down the path of exploring different DHT in pre-amp stages for sonic improvements on detail and dynamics. I explored all sorts of different DHTs as have posted in the blog and many more I never got around to write up about.

Continue reading “DHTs and cathode bias degeneration”

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 

FT-3 Coupling Cap PCB

As several DIYers out there, I’m a big fan of the Russian teflon FT-3 capacitors in my preamps. I normally use the 220nF/600V ones as have plenty of them in stock. These are superb in my view, however mounting them is a royal pain in the back. I used turrets for some time, but I ended up building a simple PCB which has a cutout to fit the FT3, solder it firmly on big copper pads and then solder the connections from the PCB. Also added a bias resistor (either for charging/discharging the cap or for fixed bias) which is connected to a GND terminal. This GND terminal could be used for the negative fixed bias if required. The PCB can be stacked very easily as has 4 M3 hex standoffs:

Populated PCB (Without resistor) and empty PCB
lateral view with the FT-3 cap soldered on PCB

 

LL1943 / LL1933 SUT PCB V02 – Balanced option

After a long time, decided to update the PCB of the LL1943 SUT to provide extra flexibility on the grounding connection. This is in essence to ensure no ground loops and noise when either using balanced or un-balanced cabling from the cartridge into the PCB:

LL1943: note the additional jumpers added

The additional jumpers are in line with the recommendations from the Datasheet. Here is the diagram:

For a fixed connection (like in most of the cases once preamp has been tuned/optimised) you can replace the jumpers by solid core wire jumpers soldered to the pad for best connection and performance.

This PCB is also for the LL1933. Basically is the same SUT but with 1+1:8+8 instead of 1+1:16+16 windings.

I made a small batch (I won’t need more than 2 or 4! myself) so the remaining will go on first-come-first-serve basis.

845/813 SE Amp: And the iron is here

I’ve received several emails from people asking me why I’ve gone quite lately. Nothing to be alarmed, I’m just simply buried on the daily grind like many out there are on these Pandemic times. My work-life balance has changed dramatically. This left me with very little time on my hands to work on audio stuff. I won’t complain as many others are actually struggling to survive, that is tough.

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801a preamp build

I wanted to share a nice review provided by Lionel Borcelot on his journey in building the VT-25/10Y/801a preamp as shared previously. I think this is a good example on what to expect and how to adapt/reuse existing components at hand to get the most out of this design.  Bravo Lionel, excellent job.

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