While I consider this my best work to date, the documentation trail has become hopelessly scattered and I don't have a write-up on my web page yet, so for the moment let me try to regroup in this blog post and make some sort of gateway/portal to the project.
The followup to the Sapphire 3 started out as a generic musing on stacked diamond buffers and current mirror amplification, coalesced for a bit as the ill-fated Project Unity before becoming part of the Sapphire line initially as a temporary measure as something I could drop in my existing chassis for testing. The first iteration kept the open loop buffer of previous Sapphire iterations, but now I'm running the 4.1m boards closed loop I realize I've ended up at just the classic, dictionary definition current feedback amplifier. Sigh. So much for originality. It sounds great though, so I'm not as upset about it as I might have been.
Posted 22nd April 2017 at 04:30 AM bygooglyone Updated 22nd April 2017 at 04:40 AM bygooglyone
After a few months of playing with loudspeaker drivers and software fixes to code that I wished I had never written in the first place, the lure of the BJT loomed large again...
There I was, sitting at my desk, and pondering where these dark feelings were coming from and how to scratch that evil itch, and my eyes came to rest upon that most ludicrous of things - the amplifier of 100 transistors.
About a year ago, or so it seems to me sitting here, I built this homage to the BC549, or as the engineer in me says, "Laughably stupid thing, which probably shouldn't work. Who would be dumb enough to try and find out?".
It needed a case. It needed a power supply. It deserved each of the above that would allow it to work, and ideally take an equally "left field" approach. it should never have been built, but it had. It should have been put in the back of a very dark, locked cupboard, but it had not.
Posted 21st April 2017 at 01:05 AM byrjm (RJM Audio Blog)
Updated 21st April 2017 at 04:44 AM byrjm(revised to 2.0g (capacitors C9 and C10 misslabelled))
In hindsight the original CrystalFET suffered from overreach. To obtain the 55 dB midband gain required for an MC phono stage lots of other things I might have wanted to build into the design like degenerative feedback were discarded.
Degenerative feedback as it applies to JFET amplifiers is the practice of leaving the source resistor partially or completely unbypassed. It reduces the voltage gain, but linearizes the dynamic operation of the amplifier - coercing the gain to the ratio of the source and drain resistors rather than leaving it defined by the JFET transconductance. The circuit gain can then be fixed by the designer without worrying so much about matching devices.
The CrystalFET circuit is a traditional two stage passive photo preamplifier design, the only novelty here is the addition of a second JFET configured as a source follower to each amplifier stage. To obtain above 50 dB gain no degenerative feedback could be used, and the JFETs had to be not...
DCSTB Board $20
DCSTB Board $25
Transistor Kits for the DCG-3 and the DCSTB are available. Full kits are also available.
DCG-3 Transistor Kit $ 40 - includes matched transistors where needed.
DCG-3 Full Kit (includes transistor kit) $75
DCSTB Kits Note that DCSTB kits only cover half the board. Additionally, if you wish to run at a higher bias and...
Posted 11th April 2017 at 10:38 PM bywmeyer Updated 14th April 2017 at 10:59 AM bywmeyer(forgot the caps value though members would look up supplied part #)
Would anyone be interested in purchasing Hafler 9505 PS capacitors? I am looking into acquiring brand new caps not NOS. I'm not sure what I will be charging but if I was to make a guess I would say about $100.00 each. The 9505 uses 4 of these. You can also use these in other projects as well. The small size makes it perfect for a low profile amplifier. These are very hard to find. Here is the part number, DCMX203U100CJ2B Please let me know if this works for anyone out in the diy world, Please chime in. The caps are 20,000uF 100vdc 3.635"tall x 2.5" dia with lead spacing of 1.13".
These are a direct drop in for the Hafler 9505 TransNova amplifier or this number also. i am waiting for a reply. 3186FD203T100BPA1