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Old 4th December 2003, 12:46 PM   #501
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Quote:
Originally posted by Cheong
I am concerned with the switch on thump for my 1969 version. It is used to drive my horn speakers with 96dB sensitivity. The switch on thump causes the woofer to jump out at an alarming amplitude. Any good ways to reduce this or even eliminate the switch on thump?

I do not have any switch on thump, it depends on the way, sequence of how I turn the system on.

1/ switch pre-amp on first, use mute and/or select other line source with no input/output.
2/ switch JLHs on
3/ place CD in DVD player
4/ select CD line source and turn mute off
5/ play CD

No thump noise at all

Chris

PS : actually my pre-amp is on 7/24
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Old 4th December 2003, 01:44 PM   #502
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I made my 1969 version too, and have no turn-on-thump. Did you change any values from the original schematic (input bias cap, feedback cap? etc)..

gr,
Thijs
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Old 4th December 2003, 02:05 PM   #503
Cheong is offline Cheong  Singapore
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"I made my 1969 version too, and have no turn-on-thump. Did you change any values from the original schematic (input bias cap, feedback cap? etc).."

I use the 2N3055, Input Capacitor change from 0.5uF to 0.22uF, a single power supply for both channels: L-R-L (10000uF-0.5ohm-10000uF) with a 300VA transformer, output capacitor from 2500uF to 3300uF, a 2k ohm resistor shorting the output to ground.


Any advise is much appreciated.
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Old 4th December 2003, 09:48 PM   #504
eLarson is offline eLarson  United States
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Quote:
Originally posted by millwood

they are what I have. In that particular design, about 30ma goes through the collector. so a medium power bjt will work but I happen to have none of them thus the 15030.
Fair enough answer. I'm definitely intrigued by the concept and am interested to hear how it ends up.

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Old 4th December 2003, 11:23 PM   #505
Cheong is offline Cheong  Singapore
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"Originally posted by Chris Ma
I do not have any switch on thump, it depends on the way, sequence of how I turn the system on.

1/ switch pre-amp on first, use mute and/or select other line source with no input/output.
2/ switch JLHs on
3/ place CD in DVD player
4/ select CD line source and turn mute off
5/ play CD

No thump noise at all "

I have a passive attenuator (5k ohm) built in the amplifier and even with all auxillary equipment off and the passive attenuator wiper at ground, I still experience the thump when the amplifier is switched on. Any ideas why?
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Old 5th December 2003, 07:15 AM   #506
mikelm is offline mikelm  England
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Quote:
Originally posted by Cheong
with all auxillary equipment off and the passive attenuator wiper at ground, I still experience the thump when the amplifier is switched on. Any ideas why?

If you have built the original 1969 version, when you turn on the amp you have to charge up the o/p capacitor. It seems normal to me that this will give a turn on thump.

I would be interested to hear if anyone understands how anyone with the 1969 version could avoid this.

My way around this is to use two amps per channel in balanced working mode. If the two amps are identical the switch on thump will be totally absent.

mike
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Old 5th December 2003, 07:47 AM   #507
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Quote:
Originally posted by mikelm



If you have built the original 1969 version, when you turn on the amp you have to charge up the o/p capacitor. It seems normal to me that this will give a turn on thump.

I would be interested to hear if anyone understands how anyone with the 1969 version could avoid this.

My way around this is to use two amps per channel in balanced working mode. If the two amps are identical the switch on thump will be totally absent.

mike
Mike,

I agree with your diagnose. Another way to avoid it would be to go to bipolar supplies, with a servo to null the output DC and get rid of the output cap. But, come to think of it, that may still cause a thump from asymetrically rising voltages and current in the amp. Maybe he should just put in a delayed speaker relay?

Jan Didden
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Old 5th December 2003, 12:35 PM   #508
Cheong is offline Cheong  Singapore
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Maybe he should just put in a delayed speaker relay? Jan Didden
It will work provided that the output capacitor is first charged up with another 8 ohm resistor. There will be no thump when the output contacts is change from the resistor to the speaker using relay.
But... we are concerned that the relays may degrade the sound as the smaller sizes relays typically have small contacts.
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Old 5th December 2003, 10:03 PM   #509
mikelm is offline mikelm  England
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Quote:
Originally posted by Cheong
I am concerned with the switch on thump for my 1969 version. It is used to drive my horn speakers with 96dB sensitivity. The switch on thump causes the woofer to jump out at an alarming amplitude. Any good ways to reduce this or even eliminate the switch on thump?
what impedence are your speakers ?

these high sensitivity speakers are often 12 ohms.

if this is the case, or even if they are 8 ohms, you could try a relay that leaves a 4ohms resistor across the o/p until about 3 seconds after turn on.

I would imagine that with the limited current capability of the amp this resistive shunt would reduce the power going to the speaker at turn on.

what do others think of this idea ?

do you think that it would help ?
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Old 6th December 2003, 02:06 AM   #510
Cheong is offline Cheong  Singapore
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Quote:
what impedence are your speakers ? mikelm
The speakers are LOTH-X AMAZE rated at nominal of 8 ohms at 96dB/Watt.
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