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op-amp based, high-gain, high rail voltage, preamp
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Old 18th November 2017, 11:35 PM   #11
CharlieLaub is offline CharlieLaub  United States
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op-amp based, high-gain, high rail voltage, preamp
Hi Mark,

Thanks for the advice on the modeling approach. I will download LTSPICE and give that a try. For some reason I imagined a higher value for the GBP of the OPA132 - it's actually LESS than the LTC6090. Thanks for bringing that to my attention.

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Originally Posted by mchambin View Post
Why don't you go first at 20dB with just the LTC6090 to see what you get.
Then, if a best thd is your concern you can go at gain 3 with the LTC6090 and you will have plenty of op amps you can use in front of it.
Is 20+dB in one stage not a bit too much?
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Last edited by CharlieLaub; 18th November 2017 at 11:39 PM.
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Old 18th November 2017, 11:45 PM   #12
xrk971 is online now xrk971  United States
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op-amp based, high-gain, high rail voltage, preamp
Quote:
Originally Posted by CharlieLaub View Post
I have been following the thread on you lender preamp project with interest. In the meantime I am thinking about other options I could do and that lie within my "comfort zone". A 2-stage op-amp preamp is something I can build up using PCBs and parts that I already have lying around - I just need to buy the op-amps.

I came on the 2-op-amp gain stage approach via the the bootstrapped approach, where I found myself asking why I would need to bootstrap if I could just find an op-amp that could handle higher rail voltages. This led me to the LT6090. Anyway, because of some of the pitfalls of bootstrapping if I do not use the 2-stage approach I will just try your circuit once it has had a little more proving time.
I agree that if you can use a HV opamp, go for it. Btw, the MoFo is dead quiet with the Aksa Lender preamp. I can connect headphones and use as a headphone amp and the sound is gorgeous. Here is 2vpp into 8ohmms dummy load and headphone is connected in parallel with dummy load.

Build This MoFo!-aksa-lender-pre-mofo-2vpp-8ohms-fft-png
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Old 19th November 2017, 01:30 AM   #13
indianajo is offline indianajo  United States
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Cool. I have 5532 & 2n5401/5551 in the stock bins. High voltage op amps are not typically stocked at my goto supply, & I've been monkeying around with LM1875 (which is not stable under gain 10) and LM49810 (which has pins too close together to solder without a purpose made board) I have DIP project boards that solder very nicely.
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Old 19th November 2017, 01:46 AM   #14
xrk971 is online now xrk971  United States
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Give it try. I was blown away by how easy it was and why I did not know about it sooner.
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Old 19th November 2017, 05:02 AM   #15
CharlieLaub is offline CharlieLaub  United States
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op-amp based, high-gain, high rail voltage, preamp
Careful there... the 5532 is 2 channels. But the rail voltage tracking can and will vary from channel to channel, along with the output signal, so you cannot use a single 5532 for a bootstrapped 2-channel gain stage.
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Old 19th November 2017, 07:14 AM   #16
xrk971 is online now xrk971  United States
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Who needs opamps anyways when 6 transistors can swing 70vpp into 10kohms with this kind of profile? (100v single supply rail, 20dB gain)

Click the image to open in full size.

More here (change out inputs for MMBT5401, change a few resistance values, make Vcc 100v):
http://www.diyaudio.com/forums/solid...ml#post5248794
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Last edited by xrk971; 19th November 2017 at 07:18 AM.
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Old 19th November 2017, 09:13 AM   #17
BesPav is offline BesPav  Russian Federation
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Quote:
Originally Posted by CharlieLaub View Post
The idea I have in mind is to have a 2-stage op-amp gain circuit

Do you need help with arrangement like this:
IMG_6534.JPG
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Old 19th November 2017, 09:21 AM   #18
xrk971 is online now xrk971  United States
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op-amp based, high-gain, high rail voltage, preamp
Quote:
Originally Posted by BesPav View Post
Do you need help with arrangement like this:
Attachment 646635
It's very hard to see due to poor photo quality and screen raster bit/fringe interference. Please use CTRL + Print Screen to capture your screen to a bitmap. Then save in "Paint" or other graphic program and upload as JPG or PNG file.

Within your sim program, there is usually a screen bitmap capture function. I know LTSpice has it and so does TINA.

Thanks,
X
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Old 19th November 2017, 09:38 AM   #19
BesPav is offline BesPav  Russian Federation
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Quote:
Originally Posted by xrk971 View Post
It's very hard to see

Excuse me for my laziness.
Common Emitter OPS?

Most of the info in graphs for easy of understanding, entirely nominals will be different, so there are only main idea.
First opamp doesn’t have local feedback.
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Old 19th November 2017, 02:44 PM   #20
BesPav is offline BesPav  Russian Federation
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Let's start from something like this.
Attached Images
File Type: png LME49710+LTC6090.png (125.9 KB, 162 views)
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