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Old 16th April 2012, 10:31 AM   #1
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Join Date: Apr 2012
Location: Rome, Italy
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Unhappy Sonic Frontiers Power 3 Help!

Hello all!

I have a conundrum. My beloved Sonic Frontiers Power 3's have been in "service" for the past year. Nobody around here can figure out what is wrong with them (this is Italy). I was trying to sell them but everyone got scared off by the noise.

This is my last resort.

Here's the trouble:
As soon as I turn them on a loud burping sound starts - really low frequency and volume - and get louder and higher pitched for about 4 seconds. Then it stops and the amp sounds great. The sound can be compared to a metal ball bouncing on metal.

Both amps do the same thing then sound great.

I have no idea what the local techs did to it, but nothing has changed.
I tried new tubes, swapping tubes, without preamp, changing speakers, I have tried everything.

Here is a link to get the audio files I made of the amps:

HTML Code:
and the other one:

HTML Code:
I would greatly appreciate any help!
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Old 16th April 2012, 09:04 PM   #2
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Location: Cape Cod
It sounds like an oscillation that increases in frequency. You better contact Sonic Frontiers.
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Old 16th April 2012, 09:15 PM   #3
DF96 is offline DF96  England
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Probably caused by failing supply rail decoupling capacitors.
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Old 17th April 2012, 12:33 AM   #4
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Unfortunately Sonic Frontiers as the company that produced Tube amps. pre-Amps, etc. really does not exist. It was bought out years ago and the new company does not produce tube based products or support legacy products...

I know, I currently have a SF Control Amplifier and struck out in getting any assistance or technical info.

Now, I do know that Parts Connexion here in Canada offers some service and retrofitting to the legacy Sonic Frontiers products.

Parts ConneXion - The authority on hi-fi DIY parts and components

Chris Johnson (founder of Sonic Frontiers) who runs? this operation does answer e-mails regarding these products, so perhaps you'll have more luck.

My experience with them has been mixed, however, as were my results with the info they provided...couldn't even get a schematic for the product!

In any event, you may be more fortunate than you despite repeated servicing nothing but problems. When SF products are running smoothly...a lovely product. but when they start acting up..a never ending nightmare of one sonic anomaly after another

Currently mine's acting as a 60 lb boat anchor...replaced by an insanely underwhelming little EL84 SE Amp...that works!

Good luck!
"A problem left to itself dries up or goes rotten. But fertilize a problem with a solution--you'll hatch out dozens." (N.F.Simpson)
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Old 17th April 2012, 01:07 AM   #5
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Do you have the schematic? I have the schematic for the Power 2 which is very similar . Email me if you want it and i'll attach it to the return email..
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Old 17th April 2012, 01:19 AM   #6
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Did anyone work on them? The front end is a solid state current sourced direct coupled tube differential. If they changed the value of the interstage caps after it - it might osciillate at start up or on low frequency notes. also don't change the value of the front end regulators caps and resistors , they are set up to turn on at the correct speed to match the output rising. If someone changed the regulator time constants by changing cap or resistor values that could be the problem.

I put better teflon coupling caps and regulator outputs are film and foil but same value as the originals no problems. I used LM 385. 1.2 voltage references for the regulators.
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Old 17th April 2012, 02:13 PM   #7
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Default Thank you!

Wow. Thank you all so far!

This is the most help I've gotten in years!

I have Chris's email, but the last time I wrote someone else answered for him and told me it was bad tubes (!!!). I got these second hand and this (the past two tech's) is the first time I have had them serviced. They always made this noise, but it was a small burp. Now it is a horrible woofer ripping gargle.

Again, after a few seconds of this, both amps sound great!

Strangely, both amps make the same sound....

I do have the schematic, thanks for the offer, I'll pull it out and have a look at it and see if I can identify the culprit!
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Old 27th April 2012, 10:16 AM   #8
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Hello Skardoman, I have in my shop a pair of Power 3 Sf amp. I have bias reliability problem. Suddenly two tubes went cherry red. Is it possible to get a copy of the schematic diagrams you have.
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Old 30th May 2012, 07:50 PM   #9
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Have the techs check the capacitors on the main board. You may have some that are absorbing
to much current know as dielectric absorption. I use a Sencore LC-120 inductor and capacitor
I am currently working on a Sonic Frontier SFM-160 mono amp. I found most of the electrolytic
capacitors are bad. It was made in April 19 of 1993. Electrolytic caps do have a finite life.

Does any body have a schematic for a Sonic Frontier SFM-160? This amp is blowing the main AC fuse.

I have also found a wire off one of the main amp tube going the the output transformer shorting to a stand off.
I also have noticed that one of the wires coming off the secondary main transformer has about 2.5 ohms to
chassis ground.
Also the push on female connector used to connect the secondary transformer to the main board, are all very loose
to the point that as I was pulling them off the wires came off very easy.

Last edited by nukwar; 30th May 2012 at 08:08 PM.
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Old 31st May 2012, 06:08 AM   #10
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I sold my Anthem preamp to partsconnexion for a fair price considering it had a bad PT. It sounded good but did have a few issues in the 5 years I owned it. It was made in the early - mid 90's and I figure like nukwar's amp it would have more bad parts, and after 20 years it will need re-capping.
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