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op-amp based, high-gain, high rail voltage, preamp
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Old 19th November 2017, 03:55 PM   #21
CharlieLaub is offline CharlieLaub  United States
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I was thinking of trying a single stage with the LTC6090 on an SOIC-->DIP adapter, using PCBs from this project of mine:
4-channel gain stage with power supply

If I could find a dual amp in a DIP-8 package that could handle at least +/- 22V rails I would try that, too.
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Last edited by CharlieLaub; 19th November 2017 at 03:57 PM.
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Old 19th November 2017, 03:57 PM   #22
Mark Johnson is offline Mark Johnson  United States
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op-amp based, high-gain, high rail voltage, preamp
Have some fun: apply the bandwidth-risetime equivalency principle (link to Wikipedia)

op-amp based, high-gain, high rail voltage, preamp-wikipedia_eq-png

to the LTSPICE plots in post #21. Risetime from the transient analysis plot, and bandwidth from the AC analysis plot. This circuit's closed loop gain, in decibels, is
  • Av,cl = 20 * log10(R3/(R1+R2)) = +30.6 dB

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Old 19th November 2017, 04:04 PM   #23
DPH is offline DPH  United States
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Quote:
Originally Posted by CharlieLaub View Post
I was thinking of trying a single stage with the LTC6090 on an SOIC-->DIP adapter, using PCBs from this project of mine:
4-channel gain stage with power supply

If I could find a dual amp in a DIP-8 package that could handle at least +/- 22V rails I would try that, too.
LME49860? It's just a LME49720 binned for 44 V between the rails vs 36 V. Heck you could just try a few DIP 49720's and see if they pass muster. (the 860 and 720 are literally the same silicon)
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Old 19th November 2017, 04:41 PM   #24
xrk971 is online now xrk971  United States
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op-amp based, high-gain, high rail voltage, preamp
Much easier to read, thanks. LME49710 is nice driver - you will need dual PSU now at two different rails.

Here is 90vpp design I just came up with. Still 5 transistors and now 0.0076% THD for 90vpp into 10k.

AKSA's Lender Preamp with 40Vpp Output-aksa-lender-preamp-hv-v2-1-90vpp-10kohms-fft-jpg
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Old 19th November 2017, 04:49 PM   #25
DPH is offline DPH  United States
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And a bit slower but still looks like it'd be more than functional in this application: ADA4522 (55V rail-to-rail) or ADA4700. But I'd be greedy and try to build a composite (admitting that their low bandwidth complicates the matter). Looking up, basically BesPav hits that one fairly well.

Or, heck, given the 20 dB gain gives you some phase margin budget, a bootstrapped front end opamp and a discrete PP class A output buffer on the back end (or grab something from Jim William's compendium of good ideas).
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Last edited by DPH; 19th November 2017 at 04:51 PM.
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Old 19th November 2017, 04:54 PM   #26
CharlieLaub is offline CharlieLaub  United States
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If I can live with 44V Vs,max there is the OPA275 in a PDIP-8 package:
OP275 Datasheet and Product Info | Analog Devices

Ah, yea, the LME49860 on +/-22V looks like a winner and has a higher GBP. I would need to put it on an SOIC to PDIP adapter.

The ADA4522-2 is a bit GBP limited, like the OPA275, but can operate at +/-27.5V giving a little more headroom. Since none of these are rail-to-rail, you have to keep in mind where it will clip WRT the rail voltage.

Since my gain stage board has 4-channels I can run the gain through two stages and still accommodate two separate channels. All of the ICs must operate from the same supplies, however, so no 2-stage high/low Vs arrangement is possible.
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Last edited by CharlieLaub; 19th November 2017 at 04:58 PM.
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Old 19th November 2017, 05:13 PM   #27
00940 is offline 00940  Belgium
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opa275 : about 41.6vp-p on 44v
opa604: 42vp-p on 48v (the dual pdip version is still around but expensive)
lme49860: 42vp-p on 44v

The lme has clearly better specs though. The opa604 has the advantage of being a jfet input one, which can come in handy.
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Old 19th November 2017, 06:24 PM   #28
BesPav is offline BesPav  Russian Federation
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Quote:
Originally Posted by Mark Johnson View Post
Have some fun: apply the bandwidth-risetime equivalency principle

Complicated correction, SR mostly defined by LTC6090’s output stage.

Quote:
Originally Posted by xrk971 View Post
Much easier to read, thanks. LME49710 is nice driver - you will need dual PSU now at two different rails.

You’re welcome!
No, just 2x zener+cap+resistors for +-15 Volts from +-70 V rails.

Quote:
Originally Posted by 00940 View Post
The opa604 has the advantage of being a jfet input one, which can come in handy.

Jfet input with a such low-resistance source (2 kOhm at inverting input) aren’t advantage. Just simulate noise.
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Old 25th November 2017, 08:44 AM   #29
mchambin is offline mchambin  France
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For a 44V op amp.
Let us not forget the old good NE5534.
Pretty good audio performances.
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Old 25th November 2017, 03:10 PM   #30
Mark Johnson is offline Mark Johnson  United States
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op-amp based, high-gain, high rail voltage, preamp
Quote:
Have some fun: apply the bandwidth-risetime equivalency principle to the LTSPICE plots in post [#20]. Risetime from the transient analysis plot, and bandwidth from the AC analysis plot.
Bandwidth at the closed loop gain is 250 kHz by eyeball (red intersection)

10% - 90% risetime is 2 usec by eyeball (white abscissa).

BW * RT product is 0.5, pretty close to theoretical prediction (0.34)

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