Yes, slagle AVC which have an impeadance of 300 ohm
The Slagle AVC has an inductance of 20H. Which can be modified with the gap up to 170H. It will depend on the load that the AVC has (input impedance of your amp).
I have driven the AVC with the 4P1L a 4K7 input impedance and at low volume levels didn’t sound great. This was due to the above. You want to keep source to load impedance ratio at least 1:10 and if you want to use the AVC at high attenuation positions (e.g. Low listening levels) then you will have to re-stack the AVC laminations to increase the inductance.
I suggest you reach out to Dave Slagle or put the question out on his forum.
I haven’t measures the output impedance of the 01a preamp amp afraid. It’s 1/gm but gm of the BF862 at such lower VDS levels isn’t the value published on the data sheet. I suspect is somewhere between 50-100 ohms maximum.
Ale
As hustlers always say in fiction – “I await my trunk’s arrival from America”…
Should be 10 nice little UV globes arriving soon with my 20 of 01As. I wonder if they sound any different from their successors. Cool pointy top.
I’m doing a shootout for the cathode resistor – it’s really worth optimising this design.
I’ve managed to solder some BF862s with my caveman technique – magnifying glass held in the vice on my workbench. I really should look at better equipment!
You’re leading the way with your experiments on the filament resistor Andy.
We will should do a proper shootout of 01a and compare the CX201a to the UV201a to see what differences.
By testing them so far on the bench I found them to be a bit more microphonic and less linear when pushed to the limits in comparison. However the final proof will be on its sound. They are even older valves, so am sure they have their own fingerprint to discover!
Soldering the BF862 is tricky and poor soldering can lead to disappointing results. That´s why I use the microscope and special flux and solder for SMD. I learned the lesson the hard way when building the discrete DAC boards for the Starlight. With the equipment I have now can get excellent results in very short time frame. In this way I can offer to other DIY-ers the additional BF862 and protection zener (both SMD devices) soldered in the board for a small additional cost. If you don’t know how to/ or want to solder SMD then is a no brainer option.
Hi!
Ale, do you have a SSHV2 regulator in this built?
Hi, no need for any HT regulator when using a gyrator load
Thanks Ale, can output of this preamp drive a low impeadence (300 Ohm) AVC?
do you really mean 300ohm load?
Yes, slagle AVC which have an impeadance of 300 ohm
The Slagle AVC has an inductance of 20H. Which can be modified with the gap up to 170H. It will depend on the load that the AVC has (input impedance of your amp).
I have driven the AVC with the 4P1L a 4K7 input impedance and at low volume levels didn’t sound great. This was due to the above. You want to keep source to load impedance ratio at least 1:10 and if you want to use the AVC at high attenuation positions (e.g. Low listening levels) then you will have to re-stack the AVC laminations to increase the inductance.
I suggest you reach out to Dave Slagle or put the question out on his forum.
I haven’t measures the output impedance of the 01a preamp amp afraid. It’s 1/gm but gm of the BF862 at such lower VDS levels isn’t the value published on the data sheet. I suspect is somewhere between 50-100 ohms maximum.
Ale
As hustlers always say in fiction – “I await my trunk’s arrival from America”…
Should be 10 nice little UV globes arriving soon with my 20 of 01As. I wonder if they sound any different from their successors. Cool pointy top.
I’m doing a shootout for the cathode resistor – it’s really worth optimising this design.
I’ve managed to solder some BF862s with my caveman technique – magnifying glass held in the vice on my workbench. I really should look at better equipment!
Andy
You’re leading the way with your experiments on the filament resistor Andy.
We will should do a proper shootout of 01a and compare the CX201a to the UV201a to see what differences.
By testing them so far on the bench I found them to be a bit more microphonic and less linear when pushed to the limits in comparison. However the final proof will be on its sound. They are even older valves, so am sure they have their own fingerprint to discover!
Soldering the BF862 is tricky and poor soldering can lead to disappointing results. That´s why I use the microscope and special flux and solder for SMD. I learned the lesson the hard way when building the discrete DAC boards for the Starlight. With the equipment I have now can get excellent results in very short time frame. In this way I can offer to other DIY-ers the additional BF862 and protection zener (both SMD devices) soldered in the board for a small additional cost. If you don’t know how to/ or want to solder SMD then is a no brainer option.
Cheers
Ale