Hi gentlemen, I've been asked by a friend if I can build him a mic preamp and I'm looking for some projects/schematics but can't really find anything that suits the requirements [not that they are high at all].
It must have:
-a decent freq response [the flatter the better]
- +48v phantom power for condenser mics
-not so expensive building costs
and that's pretty much it. it doesn't even have to have tubes in it necessarily.
I made a lot of search both on google and here but only found expensive kits or stuff without +48v,,,
Anyone can point me in the right direction please?
[btw, altho I built a few tube guitar amps, I'm a complete newbie at mic preamps]
It must have:
-a decent freq response [the flatter the better]
- +48v phantom power for condenser mics
-not so expensive building costs
and that's pretty much it. it doesn't even have to have tubes in it necessarily.
I made a lot of search both on google and here but only found expensive kits or stuff without +48v,,,
Anyone can point me in the right direction please?
[btw, altho I built a few tube guitar amps, I'm a complete newbie at mic preamps]
Have you looked at the Jensen Transformer website?
WELCOME TO JENSEN TRANSFORMERS, INC.
They kinda-sorta wrote the book on mic preamps. Lots of examples and spec circuits...
Bill
WELCOME TO JENSEN TRANSFORMERS, INC.
They kinda-sorta wrote the book on mic preamps. Lots of examples and spec circuits...
Bill
I've heard that the Hamptone, Gyraf G9 are also good kits.
If you want a Op-amp based preamp, here is another good build - the AS083 on the page:
JENSEN TRANSFORMERS, INC. - APPLICATION SCHEMATICS
Here is one I am considering building from the Jenson Transformers site. It's 3 circuits on the site that I merged together. I started a thread last week on this:
http://www.diyaudio.com/forums/tube...de-tube-mic-preamp-12ax7-12au7-schematic.html
I may rework the circuit to accept a 12AT7 or 6922 in first stage.
If you want a Op-amp based preamp, here is another good build - the AS083 on the page:
JENSEN TRANSFORMERS, INC. - APPLICATION SCHEMATICS
Here is one I am considering building from the Jenson Transformers site. It's 3 circuits on the site that I merged together. I started a thread last week on this:
http://www.diyaudio.com/forums/tube...de-tube-mic-preamp-12ax7-12au7-schematic.html
I may rework the circuit to accept a 12AT7 or 6922 in first stage.
Attachments
It doesn't really take that much to make a good-sounding tube mic preamp.
I can't scan but I can mail. If you pm me an address I'll look for the drawings I made for mine -- but it's just a 12ax7 and a 6sn7; you could probably figure it out just as well. I did have access to a pretty nice regulated power supply, so I might be considered to have cheated a little.
B
I can't scan but I can mail. If you pm me an address I'll look for the drawings I made for mine -- but it's just a 12ax7 and a 6sn7; you could probably figure it out just as well. I did have access to a pretty nice regulated power supply, so I might be considered to have cheated a little.
B
Jensen schematics look good but transformers bring up the price. This guy wants to start cheap and then, possibly, step up gradually.
88Man, that AS083 seems a bit complicated because of layout issues [as stated in the pdf]. Your project seems quite interesting shame the output transformer is listed at $137! [btw, search facility doesn't like 3 or less letter words so your thread didn't come up when I searched for 'mic preamp' - shame]
Bamalama, I pm'd you my email address but re-reading your message I guess you meant my physical home address, didn't you?
I have seen also this Bizzar Green Pre: Green Mic Pre and
DIY Factory - green mic-pre
Any opinions about it? I'm not a "if it doesn't cost a thousand bucks then it'll sound sh**" guy,,,
88Man, that AS083 seems a bit complicated because of layout issues [as stated in the pdf]. Your project seems quite interesting shame the output transformer is listed at $137! [btw, search facility doesn't like 3 or less letter words so your thread didn't come up when I searched for 'mic preamp' - shame]
Bamalama, I pm'd you my email address but re-reading your message I guess you meant my physical home address, didn't you?
I have seen also this Bizzar Green Pre: Green Mic Pre and
DIY Factory - green mic-pre
Any opinions about it? I'm not a "if it doesn't cost a thousand bucks then it'll sound sh**" guy,,,
Hey, B, I just emailed you a couple amateurish drawings.
You have to go for the Jensen. For the hours you're going to spend putting all this together, building a power supply, getting the tubes...the input transformer is almost the least of it.
Tell your friend that you're going to give him something real. And of course, have fun doing it...!
B
You have to go for the Jensen. For the hours you're going to spend putting all this together, building a power supply, getting the tubes...the input transformer is almost the least of it.
Tell your friend that you're going to give him something real. And of course, have fun doing it...!
B
In the end I ended up with the Green Pre by Peter Cornell. My friend is pretty skint so we opted for something cheap and effective. He's pretty interested in a tube preamp too tho so in the future I think I'll have the chance to build the amp in the schems kindly provided by Bamalama [thanx again pal!].
Anyhow, on the 48v, the Green pre uses this PSU. What preamp you gonna use? Opamp based I imagine, given the spec of your tranny.
Anyhow, on the 48v, the Green pre uses this PSU. What preamp you gonna use? Opamp based I imagine, given the spec of your tranny.
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Thanks for your reply,
Im planning on building this design I drew up http://www.diyaudio.com/forums/tubes-valves/171647-microphone-preamp-design.html
The transformer is a Danbury preamp transformer, 250v 0.1A, 6.3V 1.5A and the third winding is 15v 1A.
Thanks for the PSU circuit, obviously I wouldnt need a lot of it because I dont need the -15v to 15v supply, but some helpful things there, thank you.
Im planning on building this design I drew up http://www.diyaudio.com/forums/tubes-valves/171647-microphone-preamp-design.html
The transformer is a Danbury preamp transformer, 250v 0.1A, 6.3V 1.5A and the third winding is 15v 1A.
Thanks for the PSU circuit, obviously I wouldnt need a lot of it because I dont need the -15v to 15v supply, but some helpful things there, thank you.
I really don't know what's the current consumption of 48v mics, reading on wikipedia it says somthing along 1 or 2mA per microphone. I don't know the current consumption of the EF86 but if it's something around the 12AX7 currents, I guess you can just implement a voltage divider off of the B+ supply, not?
Phantom power is fed through two 6.8K resistors effectively in parallel (3400 ohms equivalent) If the mic were to short out the phantom power to ground it can only draw 14mA. Since the mic needs some voltage to operate, the practical maximum is something like 12mA.
If you use 16mA for sizing the voltage dropping or power supply circuit it will be fine.
Michael
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I mean when I design PS for a micpre I consider 16 mA per input minimum, because if some singer wearing some high hill shoes crashes a cable the PS would survive, the show still going on... It is just a little bit more than 48V shorted to ground through 3.4K resistance.
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