John Curl's Blowtorch preamplifier part II

[simon7000]

REF #91771 above,

BTW - I used an HP4194A Z analyzer way back then.

-RM

I used my AP and built a shaker table out of a JBL pro woofer. Used an accelerometer to verify shake, rattle and roll.

Stacked plate capacitors could be oriented so the microphonics were minimized. Electrolytics had minimal problems. The physically larger version of many capacitors of the same manufacturer and type also were better.

No real surprises.

Now for the microphone preamps used outside small rooms, a transformer input is my first choice. But the center tapped transformer does not work with Earthworks or other differential pair style phantom power microphones as the current draw is not balanced.

 

[simon7000]

Name dropping (and then deflecting) must be an high end audio modus operandi 😛.

Actually with the right reference name many of these folks will be glad to talk to you. But of course they expect a measure of respect.

 

[31697B]

Name dropping (and then deflecting) must be an high end audio modus operandi 😛.

That's a stretch, even for you, Waly

-RM

 

[31697B]

Actually with the right reference name many of these folks will be glad to talk to you. But of course they expect a measure of respect.

 

[31697B]

I used my AP and built a shaker table out of a JBL pro woofer. Used an accelerometer to verify shake, rattle and roll.

Stacked plate capacitors could be oriented so the microphonics were minimized. Electrolytics had minimal problems. The physically larger version of many capacitors of the same manufacturer and type also were better.

No real surprises.
.

Nice test idea... certainly useful for caps used n speaker crossovers and located inside the bass enclosure. What/how were you measuring while shaking them?

In very high Z circuits - such as C mic-preamps... a vibration of a cap whose movement is between ground plane and cap can cause noise similar to a capacitor with loose windings.


THx-RNMarsh

 

[Waly]

Actually with the right reference name many of these folks will be glad to talk to you. But of course they expect a measure of respect.

I'm sure they do have expectations. But sorry, I'll pass, I'm not interested in high end audio beyond the entertainment value of ruffling some voodoo feathers 😛.

 

[31697B]

I'm sure they do have expectations. But sorry, I'll pass, I'm not interested in high end audio beyond the entertainment value of ruffling some voodoo feathers 😛.

We've always known that about you, waly.

 

[scott wurcer]

Now for the microphone preamps used outside small rooms, a transformer input is my first choice. But the center tapped transformer does not work with Earthworks or other differential pair style phantom power microphones as the current draw is not balanced.

Picture? Do you mean the standard Schoeps circuit, I thought that was only a problem with hot plugging. Or...

Condition:

Early models of Earthworks microphones (see Models Affected) and Earthworks model M30 microphone will become unstable and oscillate with transformer-balanced microphone inputs such as Sound Devices MP-1, MP-2 and MixPre.
Result:

An audible, objectionable, high signal level oscillation at the preamplifier input makes these microphones unusable with transformer-balanced inputs.
Models Affected

Earthworks microphones with serial numbers below #3000 are susceptible to this oscillation problem.
Earthworks model M30 will exhibit this problem, regardless of serial number.
Earthworks microphones with serial numbers ending with the letter "A" and are above serial #3000 should not exhibit this problem.
Please contact Earthworks directly at (603) 654-6427 or at Earthworks High Definition Microphones if you have any questions about the compatibility of Earthworks microphones with transformer-balanced inputs. note: The USBPre works properly with all models of Earthworks microphones.
Additional Note:

Extreme instability (oscillation) may also occur with compatible Earthworks microphones if less than 48-volt phantom power is applied to the microphone. Always use 48-volt phantom power with Earthworks microphones. In addition, Earthworks microphones draw very high current, so expect poor battery runtime with portable audio equipment.

 

[Waly]

We've always known that about you, waly.

The Royal "we"? Then June 7, 1977 applies.

 

[simon7000]

Picture? Do you mean the standard Schoeps circuit, I thought that was only a problem with hot plugging. Or...

Simply put I had the transformer get hot. A phone call got the response that they knew that didn't work. So never went any farther, just avoided the issue. Thanks for the additional information.

RNM,

I used a 9V battery with a resistor to bias the capacitors and monitored the shaking with an accelerometer. First graphs are accelerometer, resistor and ceramic capacitor. Second is various capacitors. Somewhere I have the labels. But the final picture pretty much shows all the devices under test.

 

[31697B]

Simply put I had the transformer get hot. A phone call got the response that they knew that didn't work. So never went any farther, just avoided the issue. Thanks for the additional information.

RNM,

I used a 9V battery with a resistor to bias the capacitors and monitored the shaking with an accelerometer. First graphs are accelerometer, resistor and ceramic capacitor. Second is various capacitors. Somewhere I have the labels. But the final picture pretty much shows all the devices under test.

Nice.

😎🙂


-RNM

 

[31697B]

The Royal "we"? Then June 7, 1977 applies.

I can loan you my 40 cal Glock so you can put yourself out of your misery.

Or the Mossberg 410. Your choice. Bullet is free.


-RM

 

[Waly]

I can loan you my 40 cal Glock so you can put yourself out of your misery.

Or the Mossberg 410. Your choice. Bullet is free.

Wow, you are a true gentleman. I have to pass this generous offer, though, I'm afraid the rest is not silence.

P.S. FWIW, my mother was on that boat.

 

[gerhard]

But we must admit that he is well prepared for self criticism.
I know, ehm, knew someone who recognized just 6 weeks ago
that he filled a badly needed void. :-(

Gerhard

(methinks he was not right)

 

[gpapag]

Low technology talk.
Check where the outer foil of a cap is to be connected in low noise circuits.
Check by just touching the cap outer surface with a finger and use an oscilloscope to watch the interfering noise or listen to the hum with an amplifier. You don’t have to build any circuits (the guys are talking too much)

https://www.youtube.com/watch?v=BnR_DLd1PDI
https://www.youtube.com/watch?v=0BD5pxxwxe0

George

 

[Max Headroom]

Peter Ledermann talks about the setup, care & feeding of the phono cartridge.

Dan.

 

[scott wurcer]

Wow, you are a true gentleman. I have to pass this generous offer, though, I'm afraid the rest is not silence.

P.S. FWIW, my mother was on that boat.

Guns too, I never would have guessed. I guess it wasn't the Grateful Dead concert.

 

[EUVL]

Anyone can suggest a fully differential (input & output) opamp with JFET input ?


Thanks in advance,
Patrick

 

[Waly]

Guns too, I never would have guessed. I guess it wasn't the Grateful Dead concert.

No, not on the Thames 😀. I have framed a nice picture of mom with Paul Cook, taken during the ride.

 

[scott wurcer]

Anyone can suggest a fully differential (input & output) opamp with JFET input ?


Thanks in advance,
Patrick

Could you clarify? The standard differential A/D drivers use four resistors for feedback, it's inverting feedback so the FET's buy you nothing. I posted an idea a few weeks ago using a new THAT part to make a diff out in-amp with an external FET pair. Leadless package only, I'm not set up for that.

EDIT - It's the THAT 1580, built mine with an AD625 but this part is probably better for this.