I've got a project a brew'n in my head. I've got a good ole Shure SM-57, but I've dumped my dumpy Rad Shack mixer board so I don't have anything that I can use as a pre for recording. I was thinking of buying a cheap ART mic pre then I started thinking (uh oh).
I've got a bunch of lo-z transformers I've pulled from a Bogen PA amp. I don't know what the exact ration is, but I'd guess about 1:4? I've also got a beefy 15vdc wall wart and miscellaneous 12vdc wall warts. I've also got a salvaged transformer that could probably spit out about 45vac if I ignore the center tap.
I could copy the mic pre from the Bogen MX60a, but it only uses half a 12ax7 from what I can tell. So I'm thinking going my own way and using perhaps a small pentode of some sort or both sides of a 12at7.
The Emu sound card I'd like to feed has a 10k ohm input on it, so I'm guessing that should be tube friendly.
I'd like to use some of my neglected tubes: 6AU6's, 6KT8's , 6GH8's, 6AN5's, 6AN8's.
Any suggestions?
I've got a bunch of lo-z transformers I've pulled from a Bogen PA amp. I don't know what the exact ration is, but I'd guess about 1:4? I've also got a beefy 15vdc wall wart and miscellaneous 12vdc wall warts. I've also got a salvaged transformer that could probably spit out about 45vac if I ignore the center tap.
I could copy the mic pre from the Bogen MX60a, but it only uses half a 12ax7 from what I can tell. So I'm thinking going my own way and using perhaps a small pentode of some sort or both sides of a 12at7.
The Emu sound card I'd like to feed has a 10k ohm input on it, so I'm guessing that should be tube friendly.
I'd like to use some of my neglected tubes: 6AU6's, 6KT8's , 6GH8's, 6AN5's, 6AN8's.
Any suggestions?
I'm thinking either a 6KT8 or a 6GH8 may be the way to go even if I can only use one side of the tubes. I don't see why I couldn't use the pentode side in triode operation.
It appears the Bogen TM-200 mic transformer has an input of 200ohms. I need to figure out what the output is.
I figure a target voltage of about 80v would do. If I go over 100v then the electrolytics I've got laying around can't be used in the power supply.
Time to fire up Tube Cad.
It appears the Bogen TM-200 mic transformer has an input of 200ohms. I need to figure out what the output is.
I figure a target voltage of about 80v would do. If I go over 100v then the electrolytics I've got laying around can't be used in the power supply.
Time to fire up Tube Cad.
Hi,
All of those tubes you mentioned can be rather microphonic, depending on brand.
The 6GH8 is a nice tube, but save it for a mu-stage follower for a line driver. Maybe on the backend of your mic pre 🙂
The 6AN8 and 6AU6 would be my choice of those for the frontend, especially if trioded.
Though I have not worked yet with the 6KT8.
Cheers!
All of those tubes you mentioned can be rather microphonic, depending on brand.
The 6GH8 is a nice tube, but save it for a mu-stage follower for a line driver. Maybe on the backend of your mic pre 🙂
The 6AN8 and 6AU6 would be my choice of those for the frontend, especially if trioded.
Though I have not worked yet with the 6KT8.
Cheers!
I thought this link has an interesting idea. Figure 4 especially.
http://www7.taosnet.com/f10/mustage.html
I'm thinking the 6KT8 would be ideal where the triode side could provide a good bit of gain. Microphonics may be a problem though, but I guess I'll have to just try it and see.
I won't need a extra gain stage will I? I'm hoping to get away with a single 6KT8 if possible.
http://www7.taosnet.com/f10/mustage.html
I'm thinking the 6KT8 would be ideal where the triode side could provide a good bit of gain. Microphonics may be a problem though, but I guess I'll have to just try it and see.
I won't need a extra gain stage will I? I'm hoping to get away with a single 6KT8 if possible.
I was just playing with Duncan Amps psu tool. A voltage doubler circuit with the 40vct transformer using the 2200uF 100v caps may squeeze about 90vdc out. I'll have to find something for the heaters.
I think Geek has the right idea. 6AU6 frontend followed by a 6GH8 mu-stage. I've got a mess of 6AU6's and seven 6GH8's about. I suspect things will be sub optimal at the low voltages though.
I think Geek has the right idea. 6AU6 frontend followed by a 6GH8 mu-stage. I've got a mess of 6AU6's and seven 6GH8's about. I suspect things will be sub optimal at the low voltages though.
whitelabrat said:
Transformer in the picture looks like it is capable of plenty of current -- why not build a voltage doubler?
Absolutely. The PT was pulled from a yucky power amp, so I'm guessing it's good for at least 1A at 40v. I just realized that it probably won't fit into the chassis I have sitting there.
I do have an unhappy Realistic MPA-95 (100W mono). It could be a donor for a chassis, XLR sockets, and Power Transformer. I'll check it out tonite.
I'm liking the Realistic as an iron donor. The PS appears to generate about 65vac, which should be good for about 140vdc from a voltage doubler circuit. That should be fairly optimal for the tubes involved. I'll just need to use higher voltage rated caps on the smoothing end of things.
You could 'stack' your capacitors in series (parallel a 220k? resistor on each cap) and make a 200V 1100uf cap.
Or,do you have any old PC power supplies around,or other likely switch-mode supplies? They usually have at least one HV (200-400V) rated cap inside. 😉
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