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The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
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Old 12th March 2019, 10:41 PM   #551
maxlorenz is offline maxlorenz  Chile
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Here, some pics about the present state of the SONY TA-5650, while I rest and plan the next move.
I recorded a video with my portable phone but it does not sound good...I will try to make something better...

Cheers,
M.

PS: I forgot I opened an exclusive thread for this but failed to update it...
Attached Images
File Type: jpg SONY TA5650 -CASCODO2 CFP SCHEMA.jpg (294.1 KB, 130 views)
File Type: jpg SONY TA5650 CFP input.jpg (933.9 KB, 125 views)
File Type: jpg SONY TA 5650 speakerBP.jpg (498.2 KB, 108 views)
File Type: jpg SONY TA 5650 HS.jpg (580.7 KB, 101 views)
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Old 13th March 2019, 08:56 PM   #552
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by maxlorenz View Post
Here, some pics about the present state of the SONY TA-5650, while I rest and plan the next move.
I recorded a video with my portable phone but it does not sound good...I will try to make something better...

Cheers,
M.

PS: I forgot I opened an exclusive thread for this but failed to update it...
Hi Max,

What you've done makes no sense.
When wanting to reduce the miller effect of the Vfet's, the drain should be kept at a fixed voltage, which is only the case when the external pots are connected to gnd.
In the current set up the drain moves with the same voltage swing as the output, only reducing the power consumption in the Vfet's a bit, but that is most likely not necessary.
So first try to let the thing work without the added BJT's in the output stage until you are happy with the sound.
At a later stage you can always extend your experiments.


Hans
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Old 14th March 2019, 10:42 AM   #553
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by Hans Polak View Post
Hi Max,

What you've done makes no sense.
When wanting to reduce the miller effect of the Vfet's, the drain should be kept at a fixed voltage, which is only the case when the external pots are connected to gnd.
In the current set up the drain moves with the same voltage swing as the output, only reducing the power consumption in the Vfet's a bit, but that is most likely not necessary.
So first try to let the thing work without the added BJT's in the output stage until you are happy with the sound.
At a later stage you can always extend your experiments.

Hans
Maybe, I've tried it both ways and now I am doing listening tests. It does not sound bad at all. When I'll upgrade to big power BJTs, I'll tie them to ground, as you recommended.
As I see it, now the BJTs are fed with signal from two pins.

In a perfect world, I would attach a switch to swap from one to the other option and try to discriminate if the "sensical" option outperforms the "wrong" one

We can explore options based on an hypothesis from the accepted model but sometimes we could find unexpected results...that makes experimentation fun. Or, we can be totally fulled by our own expectations.

Thanks!
M.
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Old 14th March 2019, 12:26 PM   #554
Symon is offline Symon  United Kingdom
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Hi Max,
I agree with Hans, I'm not sure where you are going with this circuit.
If Connect the 10K pots to ground and not to the outout as shown, then
the BJTs will cascode the VFets, but it will limit output to +/- 10volts.
I observe the cascode BJT's are only rated at 10W each and have a Vceo
of 30volts so youc can't increase the voltage very much, perhaps 14V as a
reasonable max voltage or the BJTs will self destruct near clipping.

As Shown the BJT's are operating within safe limits, apart from running in
parallel without current sharing emitter resistors isn't a reliable way to
double power handling.

Anyway, an interesting experiment, just watch the limitations of the
devices.

Regards,
Symon
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Old 15th March 2019, 10:17 AM   #555
maxlorenz is offline maxlorenz  Chile
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Guys, thanks for manifesting your concerns. I always learn from your advices.
I know about current sharing.
The listening tests are performed in the Tannoy Autograph clone system: Beyma coaxials are 98db/W/m for the woofers, plus the amplifying effect of the front and back loaded horns.
I am confident that the amp is working in the milliwatt region most of the time.

Check out my signature later. I will post a short video (recorded with my phone) of a TV video from the 70's I downloaded from youtube. That way they cannot block it.
I assume it is videotape transfered to digital: ADD.

Attached is the future plan for the Sony. I am exploring a "common-source Amnesis" project also, just for fun.

Chhers,
M.
Attached Images
File Type: jpg SONY TA5650 -CASCODO2 CFP SCHEMA.jpg (293.8 KB, 69 views)

Last edited by maxlorenz; 15th March 2019 at 10:21 AM.
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Old 15th March 2019, 11:02 AM   #556
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by maxlorenz View Post
Guys, thanks for manifesting your concerns. I always learn from your advices.
I know about current sharing.
The listening tests are performed in the Tannoy Autograph clone system: Beyma coaxials are 98db/W/m for the woofers, plus the amplifying effect of the front and back loaded horns.
I am confident that the amp is working in the milliwatt region most of the time.

Check out my signature later. I will post a short video (recorded with my phone) of a TV video from the 70's I downloaded from youtube. That way they cannot block it.
I assume it is videotape transfered to digital: ADD.

Attached is the future plan for the Sony. I am exploring a "common-source Amnesis" project also, just for fun.

Chhers,
M.
That looks much better.
The BJT's will draw quite some base current, so it may be wise to also put caps to gnd.
Isn't this a fantastic hobby ?
I'm anxious to hearing your listening experience.


Succes, Hans
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Old 15th March 2019, 02:33 PM   #557
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by Hans Polak View Post
That looks much better.
The BJT's will draw quite some base current, so it may be wise to also put caps to gnd.
Isn't this a fantastic hobby ?
I'm anxious to hearing your listening experience.


Succes, Hans
Thanks!

I updated my signature. Of course, the phone's mic does not make it justice.
I will post more short clips, but I have no patience to edit the circumstances.
This is the pre+power connected: big spades from speaker cables did not allow direct power amp connection from TVC. I have to get rid of those, as I prefer bare cable.

Amadeus Quartet playing Beethoven's (I think) 6th string Q live on TV.

Yeah, I will use the pot just to find optimal operation point and then maybe zener//cap to PS with a big 1K to 2K resistor to ground...and then swapping to output?
I have to see what is better, if cap to PS or cap to ground. Potential difference will be smaller from base to PS...
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Old 15th March 2019, 06:32 PM   #558
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by maxlorenz View Post
I have to see what is better, if cap to PS or cap to ground. Potential difference will be smaller from base to PS...
You’re right
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Old 16th March 2019, 02:41 PM   #559
Symon is offline Symon  United Kingdom
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Hi Max,
minor point, but the objective of the BJT's is to keep the voltage across the FETs
constant to reduce capacitive effects. So the BJT reference should be the power rail.
That way it eliminates power rail noise or sag from affecting the FET.

I think this makes life easier as you just need a 10Volt zener and capacitor from
each of the power rails to set the respective BJT base voltage.

Also the MJ15024/5 devices are rather slow FT 4Mhz and low gain 15 to 60 compared
to the 2SC5200 / 2SA1941 pair (FT 30Mhz and gain of 75 to 150). So you need to
pick bias current carefully depending on which you use.

Regards,
Symon
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Old 16th March 2019, 05:19 PM   #560
tvi is offline tvi  Australia
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Have you looked at the TA-N7 service manual?
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File Type: png tan7.png (15.1 KB, 36 views)
Attached Files
File Type: pdf TA-N7 new circuit operation.pdf (795.2 KB, 13 views)
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