Using the Gyrator PCB board:
JFET Buffer
Fall 2016
End of summer is here, and for some the beginning of the building season. Well, not for me am afraid. My parental duties and work are keeping me very busy these days. I don’t have the free time I used to have before (I guess I’m not the only one on this so won’t rant on it). Today, building DIY audio gear is a matter of a well planned and negotiated free-time that worths more than gold to me. Well, that’s the way it goes. Anyhow, I picked up my daughter from nursery yesterday and on the way back I was faced with this beautiful landscape. I guess nature give us some gifts from time to time, you just happen to be on the right place at the right time:
Standing on the middle of the street with the pram was a bit dangerous so had to park my daughter on the side whilst I managed to take this picture. Time ago, I’d have taken probably a long time to take this snapshot, but now it was as quick as a bank robbery. Just take the phone out and shoot – you can’t take your time when you have a crying toddler on the pram!
A tail of buffers
I think I have spent far too much time designing, building and testing preamplifier, perhaps more than amplifiers lately. I don’t know why. I guess I fell in love with the preamps and their contribution to sound overall. Who knows, who cares.
SMD soldering for gyrator PCB
I have a new microscope for SMD soldering. If you want your gyrator PCB with a presoldered BF862, now it’s possible!
Running
A common theme of our age, run. We keep running, but not physically only. Our minds are constantly interrupted, like an CPU IO interrupt. Well, sort of. You get the gist. We run from home to work, from there to here, from here to nowhere. The reality is though, we are always on the move. Do we really like that? Hey, probably no, but that’s the way things work these days.
I have a hectic life myself, no doubt. As so probably you. Either way, the most precious moments in life – at least in the XXI century – is to unwind, stop and enjoy a bit of the slow movement. Slowly put the needle on that record, slowly sit down on your comfy sofa and slowly pour that single malt.
The rest is your imagination that I will so much struggle to put into words
Ale
Playing
UV4 PTFE sockets
Looking to build a new 01a Gen2 preamp shortly. This time will be for the rare UV-201a valves. They need a special socket UV4 rather than the usual UX4. See width difference of both filament pins. In the UV4 all pins have same size as below:
Weather they have brass or bakelite bases, the new UV4 sockets produced by Luciano Bandozzi (Jakeband) are of supreme quality. I highly recommend them:
I already reviewed these and you can see more info here. I hope to post some pictures of the new preamp shortly
SiC MOSFET Follower Driver
How many more times
Led Zeppelin wrote a fantastic song on their first album: how many more times. You may not be a rock fan, but hey: what a great song. How many more times do I want to get back to this “slew rate” theme? I don’t know, as much as I have to. Plenty of comments out there of bad designs with wimpy drivers attempting to take the 300B/2A3 or even 45 valves to full tilt with disappointing results. Either way, they always blame the valves.
I came back to revisit the driving of capacitive loads effectively as I’m working on a new 4P1L PSE amplifier. Slowly, but getting there. Previously I looked at adding a buffer to the 01a preamp as a result of slew rate limitations found in Tony’s implementation of this preamp.
The circuit design
Building gyrator boards
I’ve been on some business travel so haven’t had much time to work on stuff, however I did get a set of gyrator boards for a friend and a customer:
- BF862 configured for 4P1L preamp
- 2SK170 configured for 01a preamp
4P1L preamp with BF862 gyrator
Many have asked me about this preamp with gyrator load. Here is the latest implementation which I preferred most in terms of sound. The mu resistor is 470Ω which is a nice compromise between BF862 transconductance and distortion. I adjusted it on test. I use a 100nF for C1 so R6 is 10MΩ. R4 can be either 300KΩ, 330KΩ or even 390KΩ. Difference would be only on the voltage range for the CCS. I found running it at 25mA to be perfectly fine, some BF862 can even do J310. I prefer this SMD compared to the J310. It performs much better even at high frequency:
Tony’s 01a Preamp
I went to see my friend Tony today and helped him to fix his 01a preamp implementation. Time ago Tony used a prototype version of my gyrator PCB to build the Gen2 preamp with the addition of an output follower to address the slew rate limitations he had on his system due to the larger capacitive load.
Luckily we found the fault easily and it was a bad solder in one of the smoothing HT chokes. Once fault was rectified, we proceeded to take some measurements of this preamp.
