Boosting signal generator or op amp outputs to >+30 dBu

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mediatechnology
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Re: Signal generator output ranges

Post by mediatechnology »

Yup, AFAIK Deane Jensen (RIP) came up with the concept of sticking an inductor in between the input devices.
This is another one of the urban "Group DIY Myths" like the "Cohen" Mic Preamp topology.

Dick Burwen in the ADI Model 121 used emitter inductors in 1966.

Image
Dick Burwen's ADI121 Op Amp with emitter inductors circa 1966. Image Courtesy of Jung, Op Amp Applications, Figure 8-11.
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JR.
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Re: Signal generator output ranges

Post by JR. »

I stand corrected,,, :oops: So Sam and Deane were both standing on the shoulders of a different giant.

Sometimes it's useful to know what is worth copying,

BTW is this the same Burwen who sold a commercial single ended noise reduction back in the early '70s?

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mediatechnology
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Re: Signal generator output ranges

Post by mediatechnology »

I think so. The same Dick Burwen.

I had also thought Jensen had "invented" the emitter inductor. When I saw Jung's cite I thought "wow," things are not what they appeared to have been.

But if you look back even further you may find some inductors in the emitters of Bell Labs' transistors.
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JR.
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Re: Signal generator output ranges

Post by JR. »

That's logical for them to show up in discrete designs especially around RF. The Jensen opamp was my first exposure to inductor degeneration of a LTP. In reading the journals there was discussion about reducing the transconductance with resistors, or using JFETs, but i guess most of the design effort was related to making ICs so inductors were not a go to component. I was not familiar with the Burwen cite... So thank you and WJ.

Jack Sondermeyer who I worked with at Peavey was an application engineer for RCA back around then... I could ask him about early transistor design but I don't know if he is still alive... He had a stroke over ten years ago, and didn't do email or phone calls after that.

Reg Williamson the big dog tube amp guy talked about slew rate and NF stability criteria in connection with his design for WWII radar receivers.

My dad's WE notes are all tube stuff from 30s. Lots of inductors but mostly greek to me. I would expect tubes to be lower transconductance (like fets) so not in need of input stage LTP degeneration. Not that a circuit designer back then would ever throw that many active parts into making a single gain stage.


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juniorhifikit
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Re: Signal generator output ranges

Post by juniorhifikit »

mediatechnology wrote:Scott: Your re-posted sch looks fine though you'll probably want to add a Cc and Cfb around the 5534


That's one of those things I'm always too lazy to draw in when scratching on a napkin, as I think of it as a given. But thanks for reminding me.
One additional thing you can do is bypass the 5534 differentially with a single C rather than C3/C4.
That way the Qs don't have to slew current to charge them.


I've never done that - hmmmm... What math does one use to determine how much C when doing it differentially? I did read some of the "balanced output" thread where it was mentioned.
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mediatechnology
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Re: Signal generator output ranges

Post by mediatechnology »

That's one of those things I'm always too lazy to draw in when scratching on a napkin, as I think of it as a given. But thanks for reminding me.
Yeah me too. None of my circuits ever show power connected or bypass.

I would just start with a 100 nF from Vcc to Vee. In the input-capacitorless preamp I also use electrolytics. Since there's a constant 30V (or so) across the capacitor when connected differentially there's not a lot of current that needs to be slewed. The cap itself is bootstrapped at both ends.
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Re: Signal generator output ranges

Post by mediatechnology »

The 140V P-P LTC6090 is interesting: http://www.linear.com/docs/42316
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Re: Signal generator output ranges

Post by JR. »

That's pretty remarkable, I knew that CMOS opamps were getting better at normal voltages but that kicks as_.

Only 60dB of open loop gain at 10kHz but should be respectable for modest inverting gain of 2x or 3x.

Might be worth checking out for KISS high voltage driver.

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Re: Signal generator output ranges

Post by juniorhifikit »

mediatechnology wrote:The 140V P-P LTC6090 is interesting: http://www.linear.com/docs/42316
Wow, and under $6. Too bad it's not stocked at Digikey
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Re: Signal generator output ranges

Post by mediatechnology »

I built the 5534/BD139/BD140 circuit.
With +/-31V supplies (the max on that particular PSU) I was able to get ~ +24 dBu unloaded.
I set the dividers to provide 30V across the 5534.
The total Vce Sat is large so the circuit requires high power supply voltage for the peak actual output delivered.

Raising the supply voltage of the 5532 to 40V I can get 40V P-P (+25 dBu and change) with +/-31V supplies.
The bias resistor values were 4K7/10K.

I suspect that with +/-36V rails MCI was able to get maybe a +26 to +27 dBu clip point.
I recall that this circuit was primarily used in the 500-series EQ to replace the discontinued HV Harris "2002."
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