Topic: Let's build a pre-amp!

[poorlyconditioned]

Nick Z's "V2 Killer" project will be finished soon. I believe I'm doing the field tests to it when it's done. I saw the prototype board to it. Basically, it has the IC's etc. of a  V2 without all the bells & wistles. 6v DC, 2 ch, xlr in-out, 48v phantom, clip LED's. Not sure what else he's planning to add, more ch's, ch pans, headphone/ AUX jacks, an ADC? I have the board pic, but I'd have to ask if I could post it first. If anyone is interested, let me know.

-K

Of course.  Please post any info.  Sounds great!

  Richard

[Krispy D]

Nick Z's "V2 Killer" project will be finished soon. I believe I'm doing the field tests to it when it's done. I saw the prototype board to it. Basically, it has the IC's etc. of a  V2 without all the bells & wistles. 6v DC, 2 ch, xlr in-out, 48v phantom, clip LED's. Not sure what else he's planning to add, more ch's, ch pans, headphone/ AUX jacks, an ADC? I have the board pic, but I'd have to ask if I could post it first. If anyone is interested, let me know.

-K

ding ding ding!

post away!

[tubehead]

Hey y'all this is my micpre that i've been working on, still in R+D tho at this point...in the pic the preamp PCB is stuffed and working, the smaller board is the AC power supply on a proto-board (in debug) and not in the picture are the metering circuit and phantom power supply which I have designs for on paper but no physical prototypes yet...I had planned it to be an AC powered studio device initially with a portable version to be developed later - the phantom supply is way easier to design using AC and a step-up transformer so I figured I'd go for that first...but due to time constraints both have been put on the back burner...on top of that I'm starting grad school in the fall so my free time is pretty skinny, but if there is enough interest I can pick up development again...the design is a one-gain stage minimalistic design using high quality parts - film caps, the same instrumentaion amplifier (burr brown INA103) as the V2, stepped gain settings etc. It sounds really clean and open, even with the bench supply I was using...bandwidth in the 100kHz+ range, balanced in, single ended output that can be used balanced because of a nifty impedance mirror circuit I found on shure's (or jensen's?) website...I had a batch of 10 boards made so i have 8 bare boards left...if you wanted to find a way to power the pre board and work out the phantom, metering and enclosure yourself I could be talked into getting rid of a few maybe...I'm planning on doing a solid brass plate enclosure so it'll be heavy-duty once I get the other circuits done and get to the box level design...I was thinking about using mini-XLRs but passed on the idea because everybody would have to get new cables made...although it was encouraging that somebody made a req for them Other than that, some of you migh know that i am also the 'engineering' half of custom connects, making the VX pocket lo-profile coax I/O, headphone cables, so I've been lurking on here for a while....old habits die hard, i've been lurking in newsgroups since the 80s feel free to drop me a line via email: nmz77@yahoo.com 

l8r...Nick


hmmm, no pic in the preview?! hopefully it will be attached to the post....

[RebelRebel]

heres the green mic pre..maybe itll give some ideas
http://www.diyfactory.com/projects/green/green.htm
http://1176neve.tripod.com/id10.html

and some schematics
http://www.gyraf.dk/schematics/schematics.html
http://www.one-electron.com/FC_ProAudio.html

[(((KB)))]

Hey y'all this is my micpre that i've been working on, still in R+D tho at this point...in the pic the preamp PCB is stuffed and working, the smaller board is the AC power supply on a proto-board (in debug) and not in the picture are the metering circuit and phantom power supply which I have designs for on paper but no physical prototypes yet...I had planned it to be an AC powered studio device initially with a portable version to be developed later - the phantom supply is way easier to design using AC and a step-up transformer so I figured I'd go for that first...but due to time constraints both have been put on the back burner...on top of that I'm starting grad school in the fall so my free time is pretty skinny, but if there is enough interest I can pick up development again...the design is a one-gain stage minimalistic design using high quality parts - film caps, the same instrumentaion amplifier (burr brown INA103) as the V2, stepped gain settings etc. It sounds really clean and open, even with the bench supply I was using...bandwidth in the 100kHz+ range, balanced in, single ended output that can be used balanced because of a nifty impedance mirror circuit I found on shure's (or jensen's?) website...I had a batch of 10 boards made so i have 8 bare boards left...if you wanted to find a way to power the pre board and work out the phantom, metering and enclosure yourself I could be talked into getting rid of a few maybe...I'm planning on doing a solid brass plate enclosure so it'll be heavy-duty once I get the other circuits done and get to the box level design...I was thinking about using mini-XLRs but passed on the idea because everybody would have to get new cables made...although it was encouraging that somebody made a req for them Other than that, some of you migh know that i am also the 'engineering' half of custom connects, making the VX pocket lo-profile coax I/O, headphone cables, so I've been lurking on here for a while....old habits die hard, i've been lurking in newsgroups since the 80s feel free to drop me a line via email: nmz77@yahoo.com 

l8r...Nick


hmmm, no pic in the preview?! hopefully it will be attached to the post....

The pic you sent me before is nicer!

-K

[VA_TAPER]

discrete powered dual-servo 990 based pre-amp...discrete powering for the rails and 48v via series miniature 12v or 6v sla's, jensen transformers in.  Modular design with jensen transofrmers and optional tape head compression circuit out, or direct to AKM a/d both as added cards to be swapped out of the feed from the 990's.

I've been working schematics on this for a while....still don't have it all done yet working from the deane jensen reference design + akm's proto board and a nakamichi record and play head ( probably to become an ampex in 1/4" 2-track head in the final design.)

peace, chris

[tubehead]

The 'green pre' project looks pretty nice, although the choice of a discrete BJT with the 5532 is an odd one, FETs would be way better to use, higher impedance and lower noise...that one has a balanced line driver on the output too, but I didn't think that was really necessary because most people use short (or super-short) cables to go from their pres to A/D or deck...the V2 has a nice line driver in it too but it's for doing a remote preamp setup, which is basically a niche application for permanent installations or venues etc.  I was also thinking about doing a swept gain setting, because doing the switched attenuator is kind of a bear to do, but it's a better solution...you can't use a standard pot to replace the attenuator because it requires a really goofy (nonlinear) curve to have a constant gain reduction per degree of rotation, so to do it you'd have to fix the gain of the amp and use a pot as a voltage divider after the gain stage - a bit noisier but also a bit easier to operate and trim in...still an option at this point tho.

the guy who posted the 990 comment, a 990-type discrete opamp would be really bad for a battery powered pre because of the power dissipation, those are usually class AB or (gasp) class A so they're burning off 75% of your battery power as heat - think AD-1000.  Transformers are nice to use, but they are what they are...expensive and fairly large but inherently DC blocking and bandwidth (noise!) limiting...one jensen transformer costs as much as 2 channels of my pre including board, parts and all...

[kennedy]

Hey y'all this is my micpre that i've been working on, still in R+D tho at this point...in the pic the preamp PCB is stuffed and working, the smaller board is the AC power supply on a proto-board (in debug) and not in the picture are the metering circuit and phantom power supply which I have designs for on paper but no physical prototypes yet...I had planned it to be an AC powered studio device initially with a portable version to be developed later - the phantom supply is way easier to design using AC and a step-up transformer so I figured I'd go for that first...but due to time constraints both have been put on the back burner...on top of that I'm starting grad school in the fall so my free time is pretty skinny, but if there is enough interest I can pick up development again...the design is a one-gain stage minimalistic design using high quality parts - film caps, the same instrumentaion amplifier (burr brown INA103) as the V2, stepped gain settings etc. It sounds really clean and open, even with the bench supply I was using...bandwidth in the 100kHz+ range, balanced in, single ended output that can be used balanced because of a nifty impedance mirror circuit I found on shure's (or jensen's?) website...I had a batch of 10 boards made so i have 8 bare boards left...if you wanted to find a way to power the pre board and work out the phantom, metering and enclosure yourself I could be talked into getting rid of a few maybe...I'm planning on doing a solid brass plate enclosure so it'll be heavy-duty once I get the other circuits done and get to the box level design...I was thinking about using mini-XLRs but passed on the idea because everybody would have to get new cables made...although it was encouraging that somebody made a req for them Other than that, some of you migh know that i am also the 'engineering' half of custom connects, making the VX pocket lo-profile coax I/O, headphone cables, so I've been lurking on here for a while....old habits die hard, i've been lurking in newsgroups since the 80s feel free to drop me a line via email: nmz77@yahoo.com 

l8r...Nick


hmmm, no pic in the preview?! hopefully it will be attached to the post....

what up nick? sounds like a great idea. welcome to the board 
hit me up if your still in need of an audio program 
peace, jk

[Nick's Picks]

this all sounds very good to me.
I'd like to see some custome designs start floating around.

I also had a defunct Ps2 that I thought about deconstructing in to something preamp flavored.  but I just ended up customizing it instead.

[muj]

TRANSFORMER  is important for me (re: PA taping), as it helps de-emphasize the room aspect in the recording, making a more focused recording. An A-B based pre-amp would be great, Transformer coupled input stage and ic based output or second gain stage, and dc powered external power supply.

[Church-Audio]

The transformer does what? de-emphasizes a room what does that mean?

TRANSFORMER  is important for me (re: PA taping), as it helps de-emphasize the room aspect in the recording, making a more focused recording. An A-B based pre-amp would be great, Transformer coupled input stage and ic based output or second gain stage, and dc powered external power supply.

[muj]

The transformer does what? de-emphasizes a room what does that mean?

TRANSFORMER  is important for me (re: PA taping), as it helps de-emphasize the room aspect in the recording, making a more focused recording. An A-B based pre-amp would be great, Transformer coupled input stage and ic based output or second gain stage, and dc powered external power supply.

the transformerless pre-amps i have used capture more room sound, the transformerbased helps to focus more on the p.a sound while decreasing  the room sound, i.e more focused recording.

hope that helped

[Chuck]

...this should be good... 

[Church-Audio]

Is that a joke? Your actually going to tell me that a transformer some how magically changes the acoustics of the room? WOW where can I get these magic transformers :_)

I think what you mean to say, I hope anyway is that because the ALL transformers are not linear that they tend to cut off low frequencies around 20to30hz and High frequencies around 18-20k (depending on the quality) And that your are hearing in fact "less of the room"

I think what you mean is that the transformers that you are using are CUTTING your extreme spectrum frequencies and thus giving you the perception of a lack of room in your recordings. Humm sounds like you need to spend more money on better transformers IMO I want my preamp to capture 100% of what is going on I will decide later on in post what to exclude. That way I don't have my gear deciding for me what I can and can not record.

Chris Church




 

The transformer does what? de-emphasizes a room what does that mean?

TRANSFORMER  is important for me (re: PA taping), as it helps de-emphasize the room aspect in the recording, making a more focused recording. An A-B based pre-amp would be great, Transformer coupled input stage and ic based output or second gain stage, and dc powered external power supply.

the transformerless pre-amps i have used capture more room sound, the transformerbased helps to focus more on the p.a sound while decreasing  the room sound, i.e more focused recording.

hope that helped

[muj]

well Chris..i am not going to spend time here debating the quality of the transformers, but i stand behind my findings