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Old 2nd July 2012, 12:39 PM   #581
PHEONIX is offline PHEONIX  Australia
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Hello Edmond

>>Why should they fail as they are already protected by an over-current limiter?

Of coarse you are right , but my personal preference is for flame proof parts in these locations in the event of catastrophic failure.

Are you going to use relay speaker protection on the output.

Regards
Arthur
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Old 2nd July 2012, 01:23 PM   #582
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>Are you going to use relay speaker protection on the output.
Yes, by means of a relay or low Rdson MOSFETs. Don't know yet which of the two.

Cheers,
E.
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Old 2nd July 2012, 01:36 PM   #583
PHEONIX is offline PHEONIX  Australia
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Quote:
Originally Posted by Edmond Stuart View Post
>Are you going to use relay speaker protection on the output.
Yes, by means of a relay or low Rdson MOSFETs. Don't know yet which of the two.

Cheers,
E.
Do you have data on the THD performance of the low Rdson Mosfets at highish power >100watts. I assume you are using it in series with output of the amp or am I wrong.

Regards
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Old 2nd July 2012, 01:36 PM   #584
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Edmond Stuart View Post
>Are you going to use relay speaker protection on the output.
Yes, by means of a relay or low Rdson MOSFETs. Don't know yet which of the two.

Cheers,
E.
Why not use electronic fuse and loudspeaker protection as in JLH 80W MOSFET amp, I used something similar(regulator not stabilizer) and it works very good.
dado
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Old 3rd July 2012, 12:00 PM   #585
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Hi Damir,

Do you have a link to the schematic, please?

Cheers,
E.
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Old 3rd July 2012, 01:25 PM   #586
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Edmond Stuart View Post
Hi Damir,

Do you have a link to the schematic, please?

Cheers,
E.
Edmond some schematics are here: http://www.tcaas.btinternet.co.uk/ETI5-89a.gif
and here:A Paul Kemble web page - JLH mosfet amplifiers.

and you can look how I did somthing similar for my TT amp:ThermalTrak+TMC amp
Damir
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Old 3rd July 2012, 02:43 PM   #587
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Thanks Damir.
I will have a look at it later on, because at the moment I'm finishing the adaption* of the schematic to the PCB version (a lot of work). Besides, LS protection will be put on a separate PCB and will be one of the next steps.

* That also means the incorporation of a DC servo, making the amp even more complex. As a matter of fact, I'm doing it with huge aversion: adding (read: wasting) needlessly a dozen extra components, simply because some gurus say that any electrolytic cap (no matter what type or brand) in the NFB loop is bad.

Cheers,
E.
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Old 3rd July 2012, 03:16 PM   #588
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Edmond Stuart View Post
Thanks Damir.
I will have a look at it later on, because at the moment I'm finishing the adaption* of the schematic to the PCB version (a lot of work). Besides, LS protection will be put on a separate PCB and will be one of the next steps.

* That also means the incorporation of a DC servo, making the amp even more complex. As a matter of fact, I'm doing it with huge aversion: adding (read: wasting) needlessly a dozen extra components, simply because some gurus say that any electrolytic cap (no matter what type or brand) in the NFB loop is bad.

Cheers,
E.
JLH used quite high values for the feedback resistors in his 80W MOSFET amp to allow use of film type cap, in particular case polycarbonate type.
What about JFET in LTP, is it possible to avoid cap all together? Some famous amps are without cap in the feedback and no DC servo eider.
all the best in your PCB design.
Damir
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Old 3rd July 2012, 04:06 PM   #589
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Default keep it simple, but not simpler

Hi Damir,
>Some famous amps are without cap in the feedback and no DC servo eider.
So, if I do it this way, I'm 'in good company'. In addition, I can add a trim pot, just as you did in your TT-amp.

>all the best in your PCB design.
Thank you! As already said, it will be not an easy job: a 4 layer PCB with 300+ components! (almost as complex as a motherboard)

Cheers,
E.
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Old 3rd July 2012, 07:44 PM   #590
Steven is offline Steven  Netherlands
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Quote:
Originally Posted by Edmond Stuart View Post
...That also means the incorporation of a DC servo, making the amp even more complex. As a matter of fact, I'm doing it with huge aversion: adding (read: wasting) needlessly a dozen extra components, simply because some gurus say that any electrolytic cap (no matter what type or brand) in the NFB loop is bad.
Hi Edmond,

You could keep the elcap in the servo, but still isolate the servo almost completely from the amplifier, just using thermal coupling between servo an amplifier. Tandberg did that with some of their amplifiers in the past. Example: Tandberg 3000A, shown here. Q102 is the servo LTP driving two resistors R111 and R110, thermally coupled to the diodes CR101...104 of the input bias current sources.
I assume most audiophiles will not argue a servo with no electrical connections to sensitive input circuits. Also, the loading of the amplifier output with an RC filter to drive the servo will not harm any half decent amplifier.
Furthermore it is an open loop amplifier (i.e. no global feedback) with Hawksford EC for the power stage with MOSFETs.
Tandberg_3000A_Rev2_Page_6.jpg
Cheers, Steven
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