More on the INA217 etc....

  • Thread starter Thread starter OneRoomStudios
  • Start date Start date
also something really interesting. i dont know how good this is but noisevault.com ( i had not been there in a while) seems to be moving towards haveing impulse models for different vintage and newer mic pre's etc. i guess for use in the free SIR software.
before it was basically reverb impulses as far as i knew.
anyone know more about this ?
 
Bob's Mods said:
TubePres, BlueTubes, Art Tube MP, MP105, etc, etc, just do not cut it. They lack dynamics, may be noisey and are subject to smearing and phase distortions that make creating a mix with them very tough.
Click to expand...

On the plus side, the ARTs are really easy to mod. Change the power supply diodes & caps, change the opamps, and change the tube, and you've got a killer tube DI for guitar. Plus it gets your fingers wet in this sort of thing.

As for components I'm totally with you. I just bought an A&H mixer and it uses JRC opamps. Sigh . . . I only have to change about 60 of them . . .
 
i dont know if this will help you hilarious , but i hope it does.
when ive seen people do this in the past, and ive done it myself.
its best to try one input channel and hear for major differences before doing the whole mixer. sometimes you can hear a vast difference , but sometimes it might be slight. would hate to see you do whole thing for nothing.
you might try the summing amps as well. i guess its smt based or are the op
amps socketed. kudos to you if its smt. i dont have the eyesight for that.
you might try contacting the following and find out what drop in replacements they have for the jrc. are they 45xx series op amps ?
some will send you free samples to try if you are nice to them.
try....analog devices, harris, maxim semiconductor, texas instruments,
and linear technology.
all the best.
 
I simplified the schematic by cutting out the DC offset circuit, and not switching the phantom off, obviating the need for non-polar caps which are harder to get and more expensive.

I'm trying to learn Freehand 10, so I drew up this layout. It may have mistakes - point them out if you find any. The parts may not fit correctly (depending on which individual ones are used) when it is scaled down to fit the IC (8 pin DIP), but I'd have to print it out and fit parts to it individually, which I won't have time to do for at least several days.
 

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manning1 said:
i dont know if this will help you hilarious , but i hope it does.
when ive seen people do this in the past, and ive done it myself.
its best to try one input channel and hear for major differences before doing the whole mixer. sometimes you can hear a vast difference , but sometimes it might be slight. would hate to see you do whole thing for nothing.
you might try the summing amps as well. i guess its smt based or are the op
amps socketed. kudos to you if its smt. i dont have the eyesight for that.
Click to expand...

Hehe, no it's not surface mount. In fact that's why I bought the board, it's a vertical mount panel for each channel, thus it's really easy to mod. The opamps are JRC 072s, I'm swapping in OPA2134s which I am familiar with, plus a few cap upgrades. I'm gonna do two channels plus summing amps, and see how that goes. I'll let you know.

OneRoom re: ART mods, it used to be on this site, but I can't find it now:

http://www.blacklionaudio.com/black_lion.htm

Unfortunately I can't find the file, I just have a hard copy.

But basically, it's an opamp swap, upgrade of caps & diodes, removal of a few caps, and some rewiring around the opamp.

I did the opamp swap, in my case to OPA2134 and without the rewiring required in the black lion mod. Also, I swapped the tubes for vintage units--I bought about 11 old tubes off eBay cheap and tried 'em until I got two good ones (I have the Dual MP). Those two improvements alone were huge.

I have the parts for the cap swaps, but haven't installed yet. I'm opting not to remove the caps recommended in the black lion mod, just upgrading to higher quality parts (Nichicon UPW) with bypass caps in a couple of places.

I also have a few 12AU7s laying around that I've been meaning to try.
 
crazydoc said:
It may have mistakes..
Click to expand...
Oops - I already noticed that the layout is the mirror image of what it should be - the IC's pinouts are ok if you mount it on the trace side of the board, but not on the opposite side as is customary. That's easy to fix, if you don't mind all the alphanumerics reversed.

Back to the drawing board.
 
Other than that it looks pretty good as far as I can tell, thanks Doc. Shouldn't R7 be a volume pot though? Unless the preamp has a fixed gain...I could be wrong.
 
OneRoomStudios said:
Shouldn't R7 be a volume pot though?
Click to expand...
Yes it is. I didn't mean it to be a fixed resistor - just wire the wiper and one side of the pot together and run a wire to one side of the R7 trace, and a wire from the other side of the pot to the other R7 trace.
 
Manning, I'm not familar with the type of resistor you are refering too. At least it's not ringing a bell. You should not have to resort to that extreme anyway. Using such resistors I doubt will result in an audible performance boost.
As far as I know there are no bi-polar dc wall warts. You have to construct your own bi-polar supply using an AC wall wart going into a full wave bridge rectifier. From there you tap off the neg side of the rectifier and add a negative regulator to generate a negative dc value.
 
bobsmods. i did see some bipolar supplies being sold on the net once but lost
the url i seem to remember. i know how they are put together but they are
a pain to do. particularly as friends bug me to do a quickie mic pre.
but i often dont have the time or the inclination to build the supply.
now i just tell friends buy a yamaha mg mixer. lifes simpler that way. its fine doing a bipolar supply to drive 8 mic pre's in a diy rack, but a pig to do for just one. i dont know if you'll find this interesting bobsmods but both linear
technology and maxim if i remember and maybe burr sell chips that are charge pumps and convert for example an incoming +ve to a -ve.
results in less parts. just an idea.
 
I know this is an old thread, but I plan to build a portable pre-amp using the TI INA217 schematic. Using two 9v batteries (for a +9, -9 bi-polar power supply) will there be a DC offset problem if I omit the part of the circuit here? Also, along the same lines, can this circuit be modified to bias the chip for a single +12v supply? If so how?

crazydoc said:
I don't understand. If we're still talkng about the 1NA217, pin 6 is the output. It goes to the next stage of your signal chain, which you could consider as going through a load to ground.
Just cut out the circled crap and ground pin 5.



Actually, I got a nice stretched diaphragm. The problem is that the sensor phototransistors are way too noisy, so I'm trying to work it out using photodiodes, but due to recent adverse events in my life I haven't been able to spend time on it. Maybe soon.
Click to expand...
 
TaperChuck said:
I know this is an old thread, but I plan to build a portable pre-amp using the TI INA217 schematic. Using two 9v batteries (for a +9, -9 bi-polar power supply) will there be a DC offset problem if I omit the part of the circuit here?
Click to expand...

There shouldn't be. TI puts the DC offset control on the chip for extreme fine-tuning, but the chips come with a pretty tight spec to start with. Anyway, there will not be a DC offset in the output signal because that would run through a DC blocking cap. However, DC offset in the chip would cause slight loss of headroom and distortion.
 
This looks very easy to make, with point to point wiring on a perf board, following crazydocs layout. I'd just build two of these circuits for stereo. What are the best capacitors to use for the DC bypassing? I think I'll delete the diodes and the DC blocking capacitors, since I already have a phantom power supply that has the DC blocking caps in it already.
 
You won"t get very high output useing 2 9v Batteries for a +-9v supply and you won"t have a Lot of headroom and the Batteries will run out pretty fast.....

Also for the DC Offset you can use Pretty much any fet input opamp so you would be better off useing a TL071 as they are much cheaper ,That is if you are going to use the DC Offset option......

I would suggest that you maybe look into a Low power opamp for a Portable preamp or even a Discrete preamp......I have a design for a Discrete Un-Ballanced input Preamp that uses cheap and easy to get transistors and will run off of a couple 9V batteries and will last for a very long time useing batteries....

If you want it let me know and I"ll post it for you....


Cheers
 
I've built this preamp, and I built the bipolar supply too. Easiest way is to build a 30v supply and divide it using a TLE2426 that costs the same(ish) as a the LM317HV regulators I'm using.

The virtual ground reference will perfectly divide your supply giving you +/- 15v. I used a 48v transformer too so that I had plenty of headroom for the 30v regulator, and so that I could make a 48v phantom supply in the same box (well, 44v, but close enough).

The 48v transformer I got from South Island Components for $14, which will be very helpful if you happen to live in the South Island of New Zealand, but completely useless otherwise.

And it all works perfectly and sounds great (to me at least, but I'm probably not the best judge of such matters).
 
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