DIY Mic Preamp

[Infernal Death]

Ok don't know if that's the right section but since there are randomly some questions about recording gear i think this could be interesting for some of you guys. I builded some gear and my newest one was just completed. I took some pics but they are crappy because i don't own a dedicated digital camera so i had to use the camera from a cell phone.
Here are the pics:









Some technical info. It's a two channel all-tube mic preamp, only tubes, caps and resistors in the signal path [img]images/icons/smile.gif[/img] The only semiconductors are in the power section. For each channel you have a input and output section gain control. The input is switchable between line, mic and mic with 48V phantom power (line input is the same as mic input, just with a -20db pad). You can flip the phase with a switch and it has a build-in low cut.
Oh and a d.i. input for instruments. For testing I plugged in my bass and it sounds very very cool.
Anyway if there are some questions i am happy to answer them [img]images/icons/smile.gif[/img] .

Flo

[Cleveland Metal]

Re: DIY Mic Preamp

Hey, nice job there! Toroidal transformer even? Very cool!.

[Infernal Death]

Re: DIY Mic Preamp

Thanks for the kind words.
The torodial transformers are used because of easy mounting, big power output (the tubes,which are JJ ECC82 run on 250V DC ) and because they are quieter in such an environment.
Mic preamps like this one are quite sensitive and if you use a normal power transformer it can be that you get some hum on your audio signal chain.
Those small metal boxes on the last two pics are the audio transformers and they are very sensitive to power transformers, especially the input audio transformers. That's why the main board is mounted more to the left and the torodial transformers are mounted in the right corner to get the most space between all the transformers.

Flo

[Infernal Death]

Re: DIY Mic Preamp

Thanks again for all the nice words.
No it wasn't a kit. I bought all the components and etched the boards myself, stuffed them and mounted them in the case (which had to be drilled and painted). Was quite some work [img]images/icons/smile.gif[/img]
Axtogrind you can find schematics, infos and pcb layouts here:
http://www.gyraf.dk/gy_pd/gyraf_diy.html
This Mic Preamp is the G9. There are also some other very cool projects. I already builded the SSL Mixbus compressor and the 1176LN compressor. The Calrec EQ is nearly complete and so is the Pultec tube EQ. Just need some parts and they are ready to go (i hope [img]images/icons/grin.gif[/img] )

Flo

[Cleveland Metal]

Re: DIY Mic Preamp

You fabricated all that? Damn, now I am impressed. You should be proud, it's very nice.

Bravo! [img]graemlins/notworthy.gif[/img]

[Lev]

Re: DIY Mic Preamp

thats incredible that you built all that stuff yourself. How long did it take to build each one?

[Infernal Death]

Re: DIY Mic Preamp

Well the biggest credits go to the guy from gyraf.dk because the info he provided is very mandatory for my own success in building this stuff [img]images/icons/grin.gif[/img]

As for how long it took. Well it really depends. It always took several weeks but mostly because i needed to save up some money to buy missing parts. I think real build time should be around 20 hours maybe. Don't know for sure since i never watched how long it took me. Of course it also depends very much if the gear works when first fired up or if somethings wrong. I got quite some problems with the 1176LN compressor. First there was a missing ground connected on one of the caps near the voltage regulator which causes the regulator to blow up. After i found out and cleared this error i got severe distortion. Using an oszilloscope (a must for error finding) it took me some time to find out that a trimmer potentiometer wasn't connected on one pin.
Well at the end it worked out and i have learned quite a bit while testing and error search [img]images/icons/grin.gif[/img]
It's a very cool compressor and a absolute classic in the recording industry for the use of rock music.

Flo

[Shotgun]

Re: DIY Mic Preamp

Originally posted by Infernal Death:
Axtogrind you can find schematics, infos and pcb layouts here:
http://www.gyraf.dk/gy_pd/gyraf_diy.html

<font size="2" face="Verdana, Helvetica, sans-serif">SWEET. Thank you! I enjoy building someone else's hard work, but my stuff never comes out as pretty as yours. I try, but it never does. [img]graemlins/toast.gif[/img]


Can't wait for clips!
Keith

[Cleveland Metal]

Re: DIY Mic Preamp

Yep, my CAE3+se preamp has a toroidal just for those purposes. It "was" one of the reasons I wanted it.

Now, the big push is to swap it for a regular transformer of higher quality than the toroidal they used... Consensus from the designer and other owners is the regular transformer gives the CAE a more amplike sound... Bah... I liked the toroidal!!

You fabricated all that or it was a kit?

[Lev]

Re: DIY Mic Preamp

wow thats awesome.. you should post some clips of it [img]images/icons/smile.gif[/img]

[Shotgun]

Re: DIY Mic Preamp

WOW! Great work!

I'm always looking for projects like that, where did you get the schematic? Nice boards, too!

I've been jonesing for a new board to etch, but haven't found the right project.

Keith

[Budman68]

Re: DIY Mic Preamp

Very nice job! Very neat and orderly. NicE! [img]graemlins/toast.gif[/img]


Dave->

[sevser]

Re: DIY Mic Preamp

Very cool Flo.

[Infernal Death]

Re: DIY Mic Preamp

Well here is a short clip of the mic preamp in action.

http://mitglied.lycos.de/InfernalDeath/TestG9-02.mp3

I really don't think you can judge the micpreamp well from the clip but oh well you guys asked for it [img]images/icons/grin.gif[/img] The unit itself is really high quality but as always hard to judge from any clip (and my playing isn't helping either [img]images/icons/grin.gif[/img] )
It's a drum track (Cubase midi track linked to VSTi Battery) and 2 guitar tracks panned to the right and left. Nothing eq'ed just played straight to disk.

Flo

[Shotgun]

Re: DIY Mic Preamp

OMG! I LOVE YOUR CLIP!

too cool, man!

Keith