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I'm handy with a soldering iron but haven't taken the time to completely understand electronics, so here's a question that may be naive. I've got some schematics for a cascode tube mic preamp that I'm considering trying out. If possible I'd also like to make a transistor version. Is it possible to directly substitute transistors for the tubes and keep all of the other parts of the schematic in tact? I know the DC amount will have to dramaitcally change, but what about the rest? If possible, does anyone have a list of BJT and JFET transistors that can be interchanged with the different tube types? I'm always hearing about people swapping the tubes out of mics with transistors to give the mic a different sound and was wondering if it really is that simple.
Hi Blairl,
Welcome to TechTalk!
...And Nope, it's not as simple as that, sorry.
If you want a solid-state design, there's plenty to chose from.
But why would you want a transistorised tube design? People who change tubes in microphones to transistors do so because certain tubes (VF14, AC701K) are no longer available. It's certainly not because they believe that it sounds the same..
Best regards,
Jakob E.
Greetings blairl!
Yes & No. It really depends on the circuit. I'm sure you can design a pre where it's possible to swap. Audio Note did it with their M7 preamp (hifi stuff) where they did a tube and a MOSFET version with the SAME schematic ('cept the heater voltage).
Looking at my own stuff, I don't see such a big difference between the schematics. It's high voltage plate/collector-coupled stuff with the same kinda output buffers. The tubes run at 300-350V the transistor stuff 40-90V.
You can't directly substitute the glas with the sand, but it's close.
It would only work with simple stuff though. Symmetrical operation is impossible with tubes, since there's no PNP/NPN pairs.
You can make a cascodecoupled pre with tubes or transistors, but not for both without sacrificing *something*. I mean, it'll never be optimized for either curcuit. Sorta like Millenias 'wanna do it all' stuff, which imo, is a compromise.
I've never heard anyone putting a transistor into a tube mic for better sound? It's like Jakob sayz, to make up for a missing VF14 or whatever. Many people (Scott Dorsey & InnerTube) have put a tube into a transistor mic though. The InnerTube U87 is quite a killer.
Could be a very kool DIY thing. Anyone up for butchering an U87?
Shalimar
".. interesting on the first hearing, boring
on the second and increasingly annoying thereafter.. " Graham Hinton SSL engineer, on surround sound
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