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JamJar: an HPA-1-inspired power amp
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Old 15th January 2020, 12:53 AM   #791
Mark Johnson is offline Mark Johnson  United States
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JamJar: an HPA-1-inspired power amp
None of the suggestions between #772 and #788 made you happy before

... but ...

maybe you are thinking, perhaps I ought try them all again using the new analysis procedure?

My engineering tech used to say "even a BLIND pig finds an acorn, from time to time" and perhaps he meant, a random shot in the dark occasionally hits something worthwhile, if you make enough attempts.
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Old 15th January 2020, 01:03 AM   #792
JeffYoung is offline JeffYoung  Ireland
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JamJar: an HPA-1-inspired power amp
He he... oddly it was a couple of those suggestions backwards (increasing the VAS degeneration slightly to 15R and decreasing the gate stopper to 47R) that helped.

Compensation is indeed a mystery to me, but I've got lots of patience with SPICE.
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Old 16th January 2020, 12:33 AM   #793
JeffYoung is offline JeffYoung  Ireland
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JamJar: an HPA-1-inspired power amp
Armed with my new tools I've massaged the compensation on all three front ends. Margins are up across the board, as are slew rates, and frequency response in the CFA case.

The Hitachi front end is really starting to strut its stuff driving laterals:
-3dB FR DC to 250KHz
160 V/usec slew rate
0.008% 20kTHD @ 100 watts

Remember when it was called BuzzBomb? It now has 70 phase margin and 15dB gain margin.

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Old 16th January 2020, 06:50 AM   #794
jam is offline jam  United States
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Old 17th January 2020, 06:54 PM   #795
jam is offline jam  United States
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Jeff,

How good is the Hitachi front end driving a single pair of laterals with no drivers? Just curious,

Thanks.

Jam
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Old 17th January 2020, 09:19 PM   #796
JeffYoung is offline JeffYoung  Ireland
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JamJar: an HPA-1-inspired power amp
You'd need another current limiting strategy; even with 30V rails the flying catch diodes either clip too aggressively or don't keep the FETs from smoking with a short.

Ignoring that, I set the rails at 36V, dropped the drivers, flying catch diodes, and source resistors, reduced the currents in both differentials and set the bias at 110mA for 50W class A/B. It seems to perform admirably:

JamJar: an HPA-1-inspired power amp-jamjarjr-pdf
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File Type: pdf JamJarJr.pdf (142.6 KB, 293 views)
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Old 17th January 2020, 09:51 PM   #797
jam is offline jam  United States
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Thanks Jeff.

Just thinking about a pre-amp/ low powered amp, topology to use.

When will you be ordering boards to build the first unit?

Please let me know if there is anything I can help you with.

Jam

Last edited by jam; 17th January 2020 at 09:56 PM.
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Old 17th January 2020, 10:26 PM   #798
JeffYoung is offline JeffYoung  Ireland
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JamJar: an HPA-1-inspired power amp
I made a change yesterday to better-correct some square-wave overshoot, so they're "settling" again. (I like to have them make it through a week or so with no changes before I declare them "done".)

After that the plan is to order a pair of the KISS boards first to test the regulators since they're shared between all the front-end boards.
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Old 18th January 2020, 11:32 AM   #799
JeffYoung is offline JeffYoung  Ireland
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JamJar: an HPA-1-inspired power amp
While I let things settle, I've got a couple of questions about another topology. This is Greg Ball's SKA GB150:

Click the image to open in full size.

Question 1:

What's the purpose of the bootstrap from the VAS output back to the LTP leg?

Question 2:

Why the bypass caps (C10, C11) in the LTP CCSs?
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Old 18th January 2020, 12:59 PM   #800
Markw4 is offline Markw4  United States
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Jeff,
None of the embedded images you post are visible to some people in this thread. We only see that content when you attach a downloadable file we can use instead.
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