JamJar: an HPA-1-inspired power amp

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#262
I sketched up an idea, need to add some values. it looks like I used everything in my shed :rofl:
 

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#263
jam said:
...This effect is more apparent in orchestral climaxes, you can still detect it during low level passages.....while it does not sound bad it makes the music sound more polite for want of a better word to describe it's effects. There was also the issue of stability...
Click to expand...
Thanks, I think I got enough to examine further with measurement, hopefully I'd eventually find a way to null or alleviate the compression.
 
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#264
Itsmee said:
Ditto, been thinking about Jung's GLED431 + opamp, add a shunt output transistor, make R2 & R4 adjustable, temp stability wouldn't an issue, a thermistor is needed anyway.
Click to expand...

I’ve been thinking of trying it out on a lateral mosfet output stage, so no thermistor would be required.
The main reason is I can use any type of capacitor value at input without worrying about stability issues.
I know I probably shouldn’t worry so much about using electrolytic capacitors but my intention is zero feedback or 6dB at most on the output stage, so I’d prefer using Low value polypropylene caps and not have to worry about potential instability problems of using TLV431.
 
#265
I'm still following this thread with some interest. I have matched triplets of the lateral Mosfets used in the old Hafler amps (2SK134, 2SJ49). The latest six-pack schematic looks suitable for scaling back to three pair of output devices. I'm hoping that the lower rail voltage will help me stay within the thermal capacity of the Hafler heatsinks and chassis. Original power rails were +/– 63V for the P230, which will probably be the donor.


Edit:
Scratch the idea of using the Hafler heat sinks. They are too small to get reasonable power output.
 
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#266
Oooof. The laterals have considerably lower power dissipation than the verticals I'm using in Beefcake. So my dead-short survivability was nothing of the sort.

I've fixed it in the usual way. Don't say you didn't see this coming.... 😀

attachment.php


Note that now that we're up to 6 pairs matching is going to be much more difficult. As a consequence I've added source resistors. (Sigh.)

Cheers,
Jeff.
 
#267
TungstenAudio said:
.... The latest six-pack schematic looks suitable for scaling back to three pair of output devices.
Click to expand...

I think that design works well with two caveats:

1) requires a large stereo chassis
2) will require a new set of laterals if you accidentally short the output

(Note that because it has no source resistors if you electrically isolate each channel heatsink you can dispense of the mica under the laterals, lowering their die temp a non-trivial amount.)
 
#269
JeffYoung said:
Oooof. The laterals have considerably lower power dissipation than the verticals I'm using in Beefcake. So my dead-short survivability was nothing of the sort.

I've fixed it in the usual way. Don't say you didn't see this coming.... 😀

attachment.php


Note that now that we're up to 6 pairs matching is going to be much more difficult. As a consequence I've added source resistors. (Sigh.)

Cheers,
Jeff.
Click to expand...

You could buy double die lateral mosfets.

http://www.exicon.info/PDFs/ecw20n20-z.pdf

Don’t add source resistors until you’ve actually done your matching, you still may not need it, and only apply the bare minimum for your matched devices.
These are the benefits of diy - Designing a formula 1 car vs a Toyota Camry.
 
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#274
I still prefer feedback but I am in agreement that 6db can sound worse. We should allow the option to operate the final design to operate with a nd without feedback.

Non-feedback amplifiers do not perform as well with low impedance and reactive loads.

I believe John Lindsey Hood has a good article about distortion vs. the amount of feedback used.

Jam
 

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#276
I have stabilised the Hitachi topology, at least in SPICE.

Now here's the really interesting bit: it has the same distortion spec (0.0006%) at 1W as it does at 100W (and at 200W into 4ohms).

But it's still terrible at 10kHz (1.4% @1W). Even more oddly, it actually drops at 100W (0.9%). 😕
 

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#279
JeffYoung said:
I have stabilised the Hitachi topology, at least in SPICE.

Now here's the really interesting bit: it has the same distortion spec (0.0006%) at 1W as it does at 100W (and at 200W into 4ohms).

But it's still terrible at 10kHz (1.4% @1W). Even more oddly, it actually drops at 100W (0.9%). 😕
Click to expand...

I think it would be preferable to use P Channel Jfets at Input. Just cascode with bipolars if you want to go over 25V rails.

You should be able to get rid of C2 in feedback loop.
 
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