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Old 15th November 2003, 04:32 PM   #1
DomKo is offline DomKo  Canada
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Default JLH 10 Watt class A amplifier

Hi,

I am building the above 10W amp.

What is the input impedance of the circuit?

Is there somebodyelse using passive preamp for this 10W amp?

Regards
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Old 16th November 2003, 02:50 PM   #2
Geoff is offline Geoff  United Kingdom
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A little over 50k for the original 1969 single supply rail version and just under 47k for the later 1996 dual supply rail circuit.

The 1969 version can be easily modified for a 100k input impedance. Email me if you would like details.

A 10k pot at the input works fine provided it is fitted in the power amp enclosure or the interconnect between the pot and the amp is kept short (say <2m).
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Old 16th November 2003, 03:38 PM   #3
Geoff is offline Geoff  United Kingdom
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Default Correction

My last post should have read "A little over 45k for the original ....", not 50k.

Also, it should be noted that the input filter (R3/C2) on the 1996 version causes the input impedance to fall above 3kHz, reaching 20k at 20kHz.
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Old 18th November 2003, 06:32 AM   #4
DomKo is offline DomKo  Canada
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Default 100k input impedance modification

Hi Geoff,

Thank you for your advice.


I am building the Update Higher Power Aug 2003 Version 10W JLH.

Power Supply is CRC topology. 100,000uF, 2.5R and 10,000uF.
15V X2 160VA Dual Toroidal Transformer.

The voltage rail will be 15-18V depending on the 2.5R. The ripple is about 4mV. (Using PSU Designer to simulate the design).


I concern 45K / 100K Input impedance which will be better for the 'Passive Preamp'. ?

10K Pot is it suitable for the 'Passive Preamp' ?



Best regards,
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