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Old 26th August 2009, 08:52 PM   #1
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Default Am I Going to Kill This Amp?

First a question:

I have a set of high efficiency speakers. They have an MSRP of $6500, and I've been using them with a handful of VERY cheap amplifiers. As in under $200. I've been into audio for twenty years, and I've never heard an audible improvement between amplifiers, interconnects, or speaker wire. I have owned three tube amps. The first tube amp I bought was audibly inferior to a cheap solid state amp, the bass was really bloated. The second that I purchased was clean, but didn't sound any better than a solid state. And it broke down. The third tube amp I bought was for my headphones. It *did* sound really nice, better than the other two. But I had nothing to compare it to; it's the only headphone amp I've ever owned.

The other day I noticed an Adcom GFA-555 II at a pawn shop, and I was thinking about buying it. As I noted, I've never heard an audible improvement from replacing an amp, but using a $150 amplifier with a set of $6500 speakers IS a bit ridiculous.

On a whim, I hooked up the headphone amp to my high efficiency speakers.

Oh sh!t, why did I do that? Now I'm totally screwed. It transformed the speakers.

And I don't mean that I sat there listening for four hours, and thought that there was a subtle improvement. I sat down for 30 seconds, everything sounded different, and I literally got up off the couch and started checking wires. I thought for sure I must have plugged in something wrong. I spent ten minutes changing the polarity on the speakers, double checking that the RCA plugs were firmly seated, checked the gains on the output, etc...

This sounded completely different.

So...

Will I blow up my headphone amp doing this?

It's an Antique Sound Labs MG-SI15DT. I've heard that it's a clone of the Decware Zen amp. It puts out 0.15 watts into 10 ohms. Admittedly, that's a ridiculously small amp, but my speakers have an efficiency of 104db. So it's no different than using a 5 watt amplifier with speakers that have an efficiency of 89db.

Here's the amp:

http://www.tubehifi.com/amp/amp/mgheaddt.html

And the speakers that it's powering:

http://www.ai-audio.com/products_esp15.html
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Old 26th August 2009, 09:05 PM   #2
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hard to say, but at a nominal 8 ohms, you can be sure the impedance of the speaker dips pretty dramatically at some point. If your amp is designed for 10 ohm headphones (which typically are less inclined to wild swings of impedance) you MAY have an issue in the long term. Meantime, try and figure out what it is about the sound that you are enjoying!
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Old 26th August 2009, 10:14 PM   #3
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Are you using the amp in triode or pentode mode? Searching the model bring up lots of favorable write-ups. Looking at: http://www.affordableaudio.org/ASL-MG-SI-15-DT.pdf it seems your doing nothing wrong or damaging. Enjoy!
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Old 26th August 2009, 10:17 PM   #4
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Quote:
Originally Posted by Listens2tubes View Post
Are you using the amp in triode or pentode mode? Searching the model bring up lots of favorable write-ups. Looking at: http://www.affordableaudio.org/ASL-MG-SI-15-DT.pdf it seems your doing nothing wrong or damaging. Enjoy!
That was the first amp I bought from ASL. Really sounded terrible. Loose tubby bass, and it broke after less than a month of use.

Sold it on Ebay.

The one I'm listening to at the moment is their *headphone* amp... with a set of Summas.
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Old 26th August 2009, 10:53 PM   #5
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Sounds like you need one of those new-fangled T-amps... but that is a topic for a different forum.
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Old 27th August 2009, 08:52 AM   #6
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Quote:
Originally Posted by Patrick Bateman View Post
I have a set of high efficiency speakers. They have an MSRP of $6500, and I've been using them with a handful of VERY cheap amplifiers. As in under $200. I've been into audio for twenty years, and I've never heard an audible improvement between amplifiers, interconnects, or speaker wire. I have owned three tube amps. The first tube amp I bought was audibly inferior to a cheap solid state amp, the bass was really bloated. The second that I purchased was clean, but didn't sound any better than a solid state. And it broke down. The third tube amp I bought was for my headphones. It *did* sound really nice, better than the other two. But I had nothing to compare it to; it's the only headphone amp I've ever owned.
You get what you pay for. In the first case, I'd guess the design was open loop pentode final. Probably something like a SE 50C5 running open loop. That'll really sound hideous. The second amp: probably a Big Box offering: too much gNFB, poor open loop deisgn. Of course, it'll sound just like a SS amp. Now, I've done solid state designs that come very close, but they aren't there yet, and hollow state sounds better. Of course, I design 'em right.

As for that headphone amp, I'd be more worried about poofing the $6,500 speeks, especially if it's an OTL design that might put voice coil destroying DC offsets through them.
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Old 27th August 2009, 10:31 AM   #7
Klimon is offline Klimon  Belgium
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Those speakers just scream for diy flea-powered amps (vt-25, 12b4a, 6ah4, 71a.......)

BTW, What are you wearing, mr. Bateman?

Simon
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Old 27th August 2009, 11:37 AM   #8
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This may be an output impedience issue. A typical amp ment to drive 4 or 8 ohm speakers will typicaly have an output impedience of ~.1 ohm if it's solid
state or maby ~3 ohms for a single ended tube amp don't hold me to these
figures. Your headphone amp says it has either a 10 or 600 ohm output impedience. If it realy have a 10 ohm output impedience this can alter
the frequency responce of the speaker. You might try one of your solid state
amps again but this time with a 8 ohm resistor in seriese with the speaker cables. If this helps you might also look at the Pass F2 amp.
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Old 27th August 2009, 06:57 PM   #9
pointy is offline pointy  United Kingdom
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i see your name is Bateman which is the same surname as Terry on a forum about Leak amps

>http://tech.groups.yahoo.com/group/hjleak/<

he/they may be able to help you as well as this site.
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Old 27th August 2009, 09:28 PM   #10
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Quote:
Originally Posted by Miles Prower View Post
You get what you pay for. In the first case, I'd guess the design was open loop pentode final. Probably something like a SE 50C5 running open loop. That'll really sound hideous. The second amp: probably a Big Box offering: too much gNFB, poor open loop deisgn. Of course, it'll sound just like a SS amp. Now, I've done solid state designs that come very close, but they aren't there yet, and hollow state sounds better. Of course, I design 'em right.

As for that headphone amp, I'd be more worried about poofing the $6,500 speeks, especially if it's an OTL design that might put voice coil destroying DC offsets through them.
Here's the circuit. I don't know enough about amps to comment much. It uses the same tubes as the Decware Zen (6BQ5 instead of EL84). There have been a few articles noting that Antique Sound Lab is in the habit of cloning other brands designs...

Click the image to open in full size.

Last edited by Patrick Bateman; 27th August 2009 at 09:32 PM.
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