Topic: DIY preamp

[AT853rxwh]

Well I got my sp-preamp and it seems a bit more detailed than the cheapo canakit.  Course when I didn't have the soundpro I thought it had lots o detail... DAMN THIS HOBBY!!!    

[jk labs]

Gentelmen

this DIY preamp sounds like an interesting undertaking.  

I think you'll manage to interface the transformer and the INA103 just fine.

Looking at the 018 schematic, my suggestion is to lift the grounded leg of the transformer and connect the "center" of the transformer to ground (ground the middle of the transformer "output-short" by using two resistors (50% of single res value) and two caps (200% of single cap value) for RN, CN and RL mounted symmetrically around ground.
Then there is no DC flowing in the secondary winding either.

Then the INA (which has bjt inputs) sees the same source impedance
and potential on both inputs. And voila - the resulting offset might just be
of academic interest. (And you can rip out the entire branch with R3, R5 C3 R6 etc).

Now you have a nice, truly balanced input signals for the INA.

I don't think the PSpice will yield that much.  The transformer is a known (spec sheet wise -not wrt to spice modeling).  The INA is well described.

The true unknowns are really the stray elements C and L, ground planes or lack of such, bypass caps .. None of which are easily captured for modeling. And the pulse/freq responce can be manipulated by the transformer's RN CN & RL load.  

But do a very carefull  _noise_ analysis.  The INA want's the lowest source
impedance. Can you provide that?  

I am not sure why you need all that gain. And I not sure why you don't just reproduce
the original circuit using the AD797.

But heck,  I am all for experimenting! And I will suggest you build the circuit first with cheapo xformers  from Radio Shack just to get going.

JK

 

 

 

[Thomas]

hey jk
welcome to the forum, i have drooled over your products for a long time.  thanks for the advice, i am a beginner to all of this, and have just started to get into my major classes where we really start to do design.  i have been thinking of building the one in the schematic lately since this is my first shot at building.  Should i just buy a transformer from radioshack that is a 4:1 ratio?  i think i read that the jensen one is like 600:150?? im not sure though.   could i just replace the cheap transformers for the jensens when i was satisfied with the rest of the circuit?  One thing that has me sort of apprehensive about this is the $ of the jensen parts, if i could try it with no risk of damaging expensive parts, i would have no worries.  thanks again for the advice & +t.

[jk labs]

Hi Thomas!

Thanks!  Great forum this taperssection with lots of useful information on a slew of topics.  

Yes, I think that making a "beta" of this mic-pre using a cheapo transformer is the proper way of testing your
ideas. It will bring out the weaknesses in the current
design, allow you to refine the circuitry and establish if it's worth to build the real thing.

All this without much investment on your part.  The winding ratio of the cheap transformer is not important.  It's role is just to present a balanced signal to the INA. (Some issues of noise etc exist but that's very much of secondary interest right now).

One more thing, the INA163 uses current feedback so you might be forced to reconsider my advice of just balancing the input impedances and ignore the DC offset....  

Regards and best
Jon

[Thomas]

After taking this project to one of my professors and asking him for advice, it has become abundantly clear that i need one more class under my belt to do this design competently.  I took digital electronics this summer, (p-n junction, transistors, logic families, fabrication, and implementation), and am currently enrolled in the second part of that class analog electronics (amplifiers,???)  so after this semester i would like to design from scratch using the same basic layout of the jensen designs.  i also would like to try my hand at deisgning my own chips because we have a chip fab here on campus, and my DigElec professor is in charge of it    Maybe a preamp on a chip kind of like the DPA thin film amplifiers that enable the small size of their mics.

[Elana]

i also have been looking into making a preamp of my own.  do you have any schematics in particular that you were thinking about?  you may want to consider throwing the INA103/163 behind that transformer for the main part of the gain stage.  or if you prefer, you could replicate the inside of the INA103 as i did for the gain stage here.  





hopefully this circuit will work as a clapper to turn on and off a light.

Alright, that whole page scares me, especially the "J-K Flipflop" you wrote on the top.  Those things are pure evil.  One more reason why I'm CS and not CompE or EE.  Props for attempting a DIY preamp though.

[BobW]

i also have been looking into making a preamp of my own.  do you have any schematics in particular that you were thinking about?  you may want to consider throwing the INA103/163 behind that transformer for the main part of the gain stage.  or if you prefer, you could replicate the inside of the INA103 as i did for the gain stage here. 
hopefully this circuit will work as a clapper to turn on and off a light.

Alright, that whole page scares me, especially the "J-K Flipflop" you wrote on the top.  Those things are pure evil.  One more reason why I'm CS and not CompE or EE.  Props for attempting a DIY preamp though.

I thought it was a Schmitt Trigger.............I suck at solid state !

[Thomas]

Alright, that whole page scares me, especially the "J-K Flipflop" you wrote on the top.  Those things are pure evil.  One more reason why I'm CS and not CompE or EE.  Props for attempting a DIY preamp though.

that whole page gets me moist (pardon my french).  the exact reason why im EE not CS.  well im not actually EE im WE but with a specialization in hardware,  which is great because i don't have to take any power classes   

power=

[kuba]

And how about this one: http://sound.westhost.com/project66.htm  ..15V isn't ideal, though.