Samuel Groner
Well-known member
Note that C5 and C9 do not make much sense as connected now. Should go between output and inverting input of the first opamp.
Samuel
Samuel
Dual Opamp MicPre
- Thread starter CJ
- Start date
Help Support GroupDIY Audio Forum:
CJ
Well-known member
I thought it would be easier to just wire a small cap across
the pot, rather tha add a wire to stretch it to a resistor. I think
it will funtion about the same.
I went looking for some 100 K pots, and much to my chargrin, all
I had were the screwdriver type.
So I took a spin over to Andy's Garage for Ohmites.
Well, it was night so I got out an LED flashligh to go a huntin, and
what do I see hidden back in the cobwebs and daddy long legs?
A Fairchild 670 pwr trans and filter, new in the frikin box! Packaging
from 1950 included! The stuff that pops out of this guys place......jeez!
Of course he didn't know he had it. I had asked him a million times already. :grin:
God Almighty! Christmas in April!!!
http://vacuumbrain.com/The_Lab/TA/The_Hole!/ctc_pwr.jpg
Anyway, I scored the pots and bought the iron and an HP AC meter.
He thru in this box, perfect for this project.
I think I will wire the cool meter up as a batery indicator.
Got the board stuffed, should have this thing crankin tonight!
http://vacuumbrain.com/The_Lab/TA/The_Hole!/micpre.jpg
He threw this in, too.
I do not know what it does, I bet PRR probably knows.
There is an Ouncer 2 heidden in there that I have to give back to Andy after I strip this guy.
http://vacuumbrain.com/The_Lab/TA/The_Hole!/simplex.jpg
http://vacuumbrain.com/The_Lab/TA/The_Hole!/ouncer.jpg
the pot, rather tha add a wire to stretch it to a resistor. I think
it will funtion about the same.
I went looking for some 100 K pots, and much to my chargrin, all
I had were the screwdriver type.
So I took a spin over to Andy's Garage for Ohmites.
Well, it was night so I got out an LED flashligh to go a huntin, and
what do I see hidden back in the cobwebs and daddy long legs?
A Fairchild 670 pwr trans and filter, new in the frikin box! Packaging
from 1950 included! The stuff that pops out of this guys place......jeez!
Of course he didn't know he had it. I had asked him a million times already. :grin:
God Almighty! Christmas in April!!!
http://vacuumbrain.com/The_Lab/TA/The_Hole!/ctc_pwr.jpg
Anyway, I scored the pots and bought the iron and an HP AC meter.
He thru in this box, perfect for this project.
I think I will wire the cool meter up as a batery indicator.
Got the board stuffed, should have this thing crankin tonight!
http://vacuumbrain.com/The_Lab/TA/The_Hole!/micpre.jpg
He threw this in, too.
I do not know what it does, I bet PRR probably knows.
There is an Ouncer 2 heidden in there that I have to give back to Andy after I strip this guy.
http://vacuumbrain.com/The_Lab/TA/The_Hole!/simplex.jpg
http://vacuumbrain.com/The_Lab/TA/The_Hole!/ouncer.jpg
beckertronix
Member
Hey, I have one of those too. It's part of a theatre sound system. Simplex had some connection to Altec and Western Electric. I think it was made by Altec and branded Simplex. Almost all of the info I have on this stuff is from Japanese audiophile websites.
I hadn't even noticed the tranny in that switch panel; I'll have to go dig mine out.
-tim
I hadn't even noticed the tranny in that switch panel; I'll have to go dig mine out.
-tim
CJ
Well-known member
:guinness: :guinness: :guinness: :guinness:
:thumb:
:sam:
:thumb:
:sam:
CJ
Well-known member
Plugged it in and it worked from the git go.
Thank you, becuase I do not have time for the voltmeter.
Idylwood's Webster input got put to use. Thanks!
Plenty of gain, around 150 to 200 voltage wise.
No oscillation.
Have to go home for fidelity test.
BAck view with the board mounted...
DIY means anything goes for laberls:
Ran out of red...
Thanks to everyone for the circuits and help!
It's ready for the hole!
cj
Thank you, becuase I do not have time for the voltmeter.
Idylwood's Webster input got put to use. Thanks!
Plenty of gain, around 150 to 200 voltage wise.
No oscillation.
Have to go home for fidelity test.
BAck view with the board mounted...
DIY means anything goes for laberls:
Ran out of red...
Thanks to everyone for the circuits and help!
It's ready for the hole!
cj
CJ
Well-known member
Tried it out with the Piezo and it works great, even on a metal barbell that's going down the hole.
Tons of gain, you can hear the light stroke of a safety pin scratching the metal surface.
Capacitance un affected by the metal.
Use it on your National!
I was thinking of crawling down the hole with a nakita cordless to D and T some mounting bracket holes for the piezo, that ladder is really gonna be shakin, so I want good contack thoughout the festivities.
Figured a small C clamp would be a lot better than workin down there, just clamp and run.
Taking duct tape for the cabling.
Lots of hum on the non transformer piezo input side due to unbalanced guitar type signal.
I wonder if I changed that first stage to differential input on the piezo channel would help?
I do not have time to try that now.
One good thing, there won't be any hum at the hole!
Battery powered and hum free enviroment should make it pretty quiet.
Some clown camer in here and started talkin bout batteries being noisy, remember that?
I didn't wanna say anything, but batteries have capacitance that shunts any noise that it generates.
Battery power noisy? Come on!
Yhis 4134 is really quiet and clean. Clipping is no fun of course, and with a +/- 9 supply, you won't have a ton of room.
I clipped it with a telecaster bredge pickup at about 1/4 gain setting.
Is there any way to put a slight plus bias on those coupling lytics?
I read that if lytics are reversed biased, they can generate noises and pops for hours after the event, until the effects go away.
I don'yt think that will be a problem with 63 volt caps on an 18 supply.
Food for thought.
OK, moding this Shure 57 with a new transformer.
Can't wait.
Tons of gain, you can hear the light stroke of a safety pin scratching the metal surface.
Capacitance un affected by the metal.
Use it on your National!
I was thinking of crawling down the hole with a nakita cordless to D and T some mounting bracket holes for the piezo, that ladder is really gonna be shakin, so I want good contack thoughout the festivities.
Figured a small C clamp would be a lot better than workin down there, just clamp and run.
Taking duct tape for the cabling.
Lots of hum on the non transformer piezo input side due to unbalanced guitar type signal.
I wonder if I changed that first stage to differential input on the piezo channel would help?
I do not have time to try that now.
One good thing, there won't be any hum at the hole!
Battery powered and hum free enviroment should make it pretty quiet.
Some clown camer in here and started talkin bout batteries being noisy, remember that?
I didn't wanna say anything, but batteries have capacitance that shunts any noise that it generates.
Battery power noisy? Come on!
Yhis 4134 is really quiet and clean. Clipping is no fun of course, and with a +/- 9 supply, you won't have a ton of room.
I clipped it with a telecaster bredge pickup at about 1/4 gain setting.
Is there any way to put a slight plus bias on those coupling lytics?
I read that if lytics are reversed biased, they can generate noises and pops for hours after the event, until the effects go away.
I don'yt think that will be a problem with 63 volt caps on an 18 supply.
Food for thought.
OK, moding this Shure 57 with a new transformer.
Can't wait.
rafafredd
Well-known member
Hey CJ, it´s a hell of a nice looking box. Let us hear the hole! :razz:
Interesting, what tranny are you going to use?
I tried the "no tranny at all" mod but i think it kinda sucked, you loose that
"brilliance" of the stock sm57.
BTW, i cut a banjo-track yesterday with a stock sm57, sounded great.
CJ
Well-known member
Kit, Pmroz sent me a bag of goodies and this was one of them in thar.
Flatter than granny's ass.
Can't wiat to hear it in a few minutse.
Never taker the diaphragm cover off the 57.
You will never get that stainless snap ring back on.
So this is the new look for the modded 57.
Note that you do not have to remove the cover to swap out the xfm r.
I am jazzed! After just a few phone calls, I managed to locate some used shot puts for the hole. And they were a few blocks away at play i again sports.
The guy was giving me weird looks, loading up onb shotputs, barbells, golfballs, steroids,...!
Pleas, no jokes about cajones.
I know these ain't gonna bust up on the way down.
BNo sir, you are in for a great tape recording when these bounce off the steel ladder at 200 MPH!
Just a warning, if doing a battery supply, plus and minus with two batts, just putting a sw on the top B+ is not goo enough.
The chip will drain that lower rail batt unless a double sw is used.
I do not know if it is good for the chip to run with bottom supply only.
My circuit draws 20 ma with just the bottome batt.
16 with both batts.
Flatter than granny's ass.
Can't wiat to hear it in a few minutse.
Never taker the diaphragm cover off the 57.
You will never get that stainless snap ring back on.
So this is the new look for the modded 57.
Note that you do not have to remove the cover to swap out the xfm r.
I am jazzed! After just a few phone calls, I managed to locate some used shot puts for the hole. And they were a few blocks away at play i again sports.
The guy was giving me weird looks, loading up onb shotputs, barbells, golfballs, steroids,...!
Pleas, no jokes about cajones.
I know these ain't gonna bust up on the way down.
BNo sir, you are in for a great tape recording when these bounce off the steel ladder at 200 MPH!
Just a warning, if doing a battery supply, plus and minus with two batts, just putting a sw on the top B+ is not goo enough.
The chip will drain that lower rail batt unless a double sw is used.
I do not know if it is good for the chip to run with bottom supply only.
My circuit draws 20 ma with just the bottome batt.
16 with both batts.
bcarso
Well-known member
[quote author="CJ"]Lots of hum on the non transformer piezo input side due to unbalanced guitar type signal.
I wonder if I changed that first stage to differential input on the piezo channel would help?
.....Some clown camer in here and started talkin bout batteries being noisy, remember that?
I didn't wanna say anything, but batteries have capacitance that shunts any noise that it generates.
Battery power noisy? Come on!.....
Is there any way to put a slight plus bias on those coupling lytics?
I read that if lytics are reversed biased, they can generate noises and pops for hours after the event, until the effects go away.
Food for thought.
[/quote]
(1) If the piezo is truly floating and the cable is really 100% effective for electric fields you shouldn't have hum. A diff input would be pointless unless you are trying to reject conducted errors, or had no choice but to run unshielded. Make sure the pickup itself is adequately shielded too.
(2) Batteries are not completely quiet, self-capacitance notwithstanding---they couldn't be, given the electrochemical processes at their heart*. The noise is mostly at low frequencies. I posted a link in the middle of a regulator discussion thread to something showing actual battery noise measurements a while back. What of course they are superb for is isolation. Given that your amps have good PS rejection they should be wholly adequate.
(3) 'Lytics get into trouble anywhere you want to look depending on how susceptible the circuit is. Most leakage current under normal bias is circa tens of nanoamps for values in the low single to two-digit microfarad range. The CYA spec of manufacturers is much much worse, so much so that in many apps they would be unusable. And there is noise in that leakage current too. I recommend bipolar if you're not sure what the bias is going to be.
When the application is uncritical and the reversal of bias not sustained, I've put 50V 'lytics in circuits that occasionally see 2-3V reverse. Once, when I missed a silkscreen reversal in a bypass for a uC and associated stuff on a little board in a satellite powered speaker, the part which may have been a 10V or 16V one was subjected to continuous reverse 5V
Nervously testing some units, I found that the current never got horribly large initially, and then over time the 'lytic reformed and worked fine! I forget how many we had shipped at that point (maybe of order 10k), but the relief was palpable.
*Standard cells are pretty damn good, but you can't draw any current from them. Even then NIST had banks of them to average for the standard voltage reference. I think now they have tied the volt to frequency using jospehson junction paraphernalia.
I wonder if I changed that first stage to differential input on the piezo channel would help?
.....Some clown camer in here and started talkin bout batteries being noisy, remember that?
I didn't wanna say anything, but batteries have capacitance that shunts any noise that it generates.
Battery power noisy? Come on!.....
Is there any way to put a slight plus bias on those coupling lytics?
I read that if lytics are reversed biased, they can generate noises and pops for hours after the event, until the effects go away.
Food for thought.
[/quote]
(1) If the piezo is truly floating and the cable is really 100% effective for electric fields you shouldn't have hum. A diff input would be pointless unless you are trying to reject conducted errors, or had no choice but to run unshielded. Make sure the pickup itself is adequately shielded too.
(2) Batteries are not completely quiet, self-capacitance notwithstanding---they couldn't be, given the electrochemical processes at their heart*. The noise is mostly at low frequencies. I posted a link in the middle of a regulator discussion thread to something showing actual battery noise measurements a while back. What of course they are superb for is isolation. Given that your amps have good PS rejection they should be wholly adequate.
(3) 'Lytics get into trouble anywhere you want to look depending on how susceptible the circuit is. Most leakage current under normal bias is circa tens of nanoamps for values in the low single to two-digit microfarad range. The CYA spec of manufacturers is much much worse, so much so that in many apps they would be unusable. And there is noise in that leakage current too. I recommend bipolar if you're not sure what the bias is going to be.
When the application is uncritical and the reversal of bias not sustained, I've put 50V 'lytics in circuits that occasionally see 2-3V reverse. Once, when I missed a silkscreen reversal in a bypass for a uC and associated stuff on a little board in a satellite powered speaker, the part which may have been a 10V or 16V one was subjected to continuous reverse
5V Nervously testing some units, I found that the current never got horribly large initially, and then over time the 'lytic reformed and worked fine! I forget how many we had shipped at that point (maybe of order 10k), but the relief was palpable.
*Standard cells are pretty damn good, but you can't draw any current from them. Even then NIST had banks of them to average for the standard voltage reference. I think now they have tied the volt to frequency using jospehson junction paraphernalia.
pmroz
Well-known member
.
CJ,
great, you found something handy in that box.
Might need to protect the cable-to-piezo... i mean mechanically isolate the cable from the ladder, else you get vibrating-cable-tapping-on-ladder junk. And duct-taping cable to ladder will probably add mud to the actual piezo signal.
Maybe you're using a different thing/cable, but with all the piezo pickups here (Dean-Markley, Zeta, Fishman, telephone plunger-mic)... the smallest little cable-tap makes big output. Rubbing just the cable with a finger creates a surprisingly loud signal. On upright bass with 2ft of cable this used to be a hassle, and sticking cable to body only made it worse. If you have a dozen feet or more of cable, and want to mic ladder vibrations, could get ugly.
How about foam pipe-wrap around the cable... the black stuff, yunno?Comes in 4ft sections, 4x4ft pack is $3-4. You could also wrap the body of the 57 for a little shotput shock protection.
Peace, Paul
CJ,
great, you found something handy in that box.
Might need to protect the cable-to-piezo... i mean mechanically isolate the cable from the ladder, else you get vibrating-cable-tapping-on-ladder junk. And duct-taping cable to ladder will probably add mud to the actual piezo signal.
Maybe you're using a different thing/cable, but with all the piezo pickups here (Dean-Markley, Zeta, Fishman, telephone plunger-mic)... the smallest little cable-tap makes big output. Rubbing just the cable with a finger creates a surprisingly loud signal. On upright bass with 2ft of cable this used to be a hassle, and sticking cable to body only made it worse. If you have a dozen feet or more of cable, and want to mic ladder vibrations, could get ugly.
How about foam pipe-wrap around the cable... the black stuff, yunno?Comes in 4ft sections, 4x4ft pack is $3-4. You could also wrap the body of the 57 for a little shotput shock protection.
Peace, Paul
CJ
Well-known member
Great!
Just in time becuase I am leaving tonight.
Yes, I was going to use every foot of the 12 foot cable that came in the D Marrkeley box.
Thanks Brad! I kind of suspected the diff amp would not help much. Shielding the piezo is a good idea, thats where most of it seems to be coming from.
Do they shield these when they mount them to the inside of your guitar? If so, how?
These piezo's certainly leave much to be desired as far as guitar micing. Not only does it pick up string vibration, it picks up everything else as well, suck as rubbing or tapping the top of the guitar, no wonder the pros still ues soundhole mics as well. But for this app, it's perfect.
I tried out the SM 57 mod, the new transformer, and so far I like the stock model better. Maybe the xfmr I used was not perfect for that job. I am thinging maybe a moving coil trans stuck in there would be better.
Just in time becuase I am leaving tonight.
Yes, I was going to use every foot of the 12 foot cable that came in the D Marrkeley box.
Thanks Brad! I kind of suspected the diff amp would not help much. Shielding the piezo is a good idea, thats where most of it seems to be coming from.
Do they shield these when they mount them to the inside of your guitar? If so, how?
These piezo's certainly leave much to be desired as far as guitar micing. Not only does it pick up string vibration, it picks up everything else as well, suck as rubbing or tapping the top of the guitar, no wonder the pros still ues soundhole mics as well. But for this app, it's perfect.
I tried out the SM 57 mod, the new transformer, and so far I like the stock model better. Maybe the xfmr I used was not perfect for that job. I am thinging maybe a moving coil trans stuck in there would be better.
bcarso
Well-known member
[quote author="CJ"]...Shielding the piezo is a good idea, thats where most of it seems to be coming from.
Do they shield these when they mount them to the inside of your guitar? If so, how?
These piezo's certainly leave much to be desired as far as guitar micing. Not only does it pick up string vibration, it picks up everything else as well, suck as rubbing or tapping the top of the guitar, no wonder the pros still ues soundhole mics as well. But for this app, it's perfect.
I tried out the SM 57 mod, the new transformer, and so far I like the stock model better. Maybe the xfmr I used was not perfect for that job. I am thinging maybe a moving coil trans stuck in there would be better.[/quote]
Do use foil-shield cable if you can manage it. Single-braid is only about 94% effective, and spiral-wrap worse. The foil shield does have the drawback of being stiffer though.
For really demanding apps when the cable has to be flexible and have low triboelectric noise there are some double-braid types with graphite between the insulation of the central conductor and the shield. Better still is to put the preamp frontend with the pickup.
Do they shield these when they mount them to the inside of your guitar? If so, how?
These piezo's certainly leave much to be desired as far as guitar micing. Not only does it pick up string vibration, it picks up everything else as well, suck as rubbing or tapping the top of the guitar, no wonder the pros still ues soundhole mics as well. But for this app, it's perfect.
I tried out the SM 57 mod, the new transformer, and so far I like the stock model better. Maybe the xfmr I used was not perfect for that job. I am thinging maybe a moving coil trans stuck in there would be better.[/quote]
Do use foil-shield cable if you can manage it. Single-braid is only about 94% effective, and spiral-wrap worse. The foil shield does have the drawback of being stiffer though.
For really demanding apps when the cable has to be flexible and have low triboelectric noise there are some double-braid types with graphite between the insulation of the central conductor and the shield. Better still is to put the preamp frontend with the pickup.
ioaudio
Well-known member
[quote author="bcarso"]
Do use foil-shield cable if you can manage it. Single-braid is only about 94% effective, and spiral-wrap worse. The foil shield does have the drawback of being stiffer though.[/quote]
i did wonder about this before. i used some computer networking cable with a foil-shield between a tube mic and the psu and it seemed perfectly quiet. i never replaced it, though i´m know it´s not been made for 180 volt...
Do use foil-shield cable if you can manage it. Single-braid is only about 94% effective, and spiral-wrap worse. The foil shield does have the drawback of being stiffer though.[/quote]
i did wonder about this before. i used some computer networking cable with a foil-shield between a tube mic and the psu and it seemed perfectly quiet. i never replaced it, though i´m know it´s not been made for 180 volt...
Walrus
Well-known member
[quote author="CJ"]
Never taker the diaphragm cover off the 57.
You will never get that stainless snap ring back on.
So this is the new look for the modded 57.
Note that you do not have to remove the cover to swap out the xfm r.
[/quote]
Putting the tape round the 57 like that makes it into an near omnidirectional mic as it blocks sound from reaching the rear of the diaphragm.
Not that it matters down the hole!! :thumb:
Never taker the diaphragm cover off the 57.
You will never get that stainless snap ring back on.
So this is the new look for the modded 57.
Note that you do not have to remove the cover to swap out the xfm r.
[/quote]
Putting the tape round the 57 like that makes it into an near omnidirectional mic as it blocks sound from reaching the rear of the diaphragm.
Not that it matters down the hole!! :thumb:
CJ
Well-known member
Thanks and interesting point!
Now that you told us about the snap ring...maybe I ccan do it right.
Have to try a 150 ohm xfmr while I'm at it.
Now that you told us about the snap ring...maybe I ccan do it right.
Have to try a 150 ohm xfmr while I'm at it.
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