start-up sequence of Aikido preamp / SS power amp - diyAudio
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Old 5th May 2007, 11:39 PM   #1
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Default start-up sequence of Aikido preamp / SS power amp

It seems that common dogma is that the preamp should be switched on before the power amp and that the power-amp is switched off before the preamp. This seems to be particularly the case for SS power amps.

Does anyone have experience of this with an Aikido preamp?

Using Bruce Anderson's homebrew tubed power amp, it certainly did not matter which switch-on / off sequence was used with my Aikido. I kept asking Bruce "Are you sure?" before switching on/off the Aikido with his amp fully switched-on. Anyway there were no nasty pops and thumps and his Lowthers remained intact. In fact it seemed that the music simply faded on then off.

However, I have a SS power amp. It is an AKSA 55N (homebuilt kit). I really do not want to kill it. Neither do I want to upset my speakers (Polk rt600's), if I killed my my wife would suspect a conspiracy to get new speakers.

I have been very paranoid about ensuring that the main amp is switched-on last and off first. My wife seems to have this down. Next week, my mother-in-law is arriving for a couple of weeks. We get along really well. So, I would like to be sure that she is unlikely to cause the death of SS amp and/or speakers, and a souring of relations.

Should I be truly hung-up on this problem? Has anyone killed SS equipment due to a mis-switched Aikido?

Thanks,
Charlie
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Old 6th May 2007, 06:28 PM   #2
GRD is offline GRD  United States
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Default One Idea

I built a tube preamp to use with a SS amp. As a safety precaution, I connected a shorting switch on the output of the preamp. So I short the preamp prior to shutting down. And unshort when everthing is on and it's time to listen. Not foolproof (if you forget) but one option to consider. I really don't want turn-on or turn-off transients hitting my SS amp.
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Old 7th May 2007, 10:03 AM   #3
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Aikido should suffer pretty little from turn on transients, especially if you use it like Broskie (one tube for input and one for output).

However, to keep you safe, you can use a relay that shorts the output with no power applied and unshorts it 20-30 seconds after power on.

Cheers
Andrea
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Old 7th May 2007, 10:58 AM   #4
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Charlie,

Any preamp should be turned on first and allowed to warm up a short time before switching on any power amplifier. This is true for SS equipment and even more true for tube based equipment. The Aikido needs to be on and stable before switching on a SS power amplifier. Granted the Aikido has a capacitor on the output which blocks DC from getting to the power amplifiers input and some SS power amplifiers have a cap on the input whose function is to block DC. It is also essential to allow the Aikido to warm up as to eliminate any "thump" that you can get by not allowing it to warm up first.

My SS amplifiers will thump if the tube preamp is not allowed to warm up enough before the power amplifier is warmed up.

My Aikido's will do the same thing as yours is doing.
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Old 7th May 2007, 11:05 AM   #5
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To answer your question..

Yes, I did kill a SAE2400 about 3 yrs ago when it was on first and I turned on a linestage.

Anything is possible......
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Old 7th May 2007, 12:29 PM   #6
jayme is offline jayme  United States
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If you stiffen up your PSU capacitance, you won't have the thump problem. More capacitance lengthens the time it takes for the B+ to drop, and thus moves the time constant lower.

I have however blown the input fuses on my amp when I turn my aikido off then back on again before it has had time to discharge the PSU fully. I use AC on my heaters, so when the power is turned off, they cool quickly. When it is turned back on, the heaters are still cold, but the partial B+ is then applied directly to the coupling cap and safety resistors....and the rising B+ acts more like a low-freq signal than DC, and thus is passed through the DC coupling cap if it is low enough (I've got a 0.47uF coupling cap, which presents a 3Hz rolloff freq when combined with the amps 100k input impedance).
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