I am a new member, thank you very much if you can help me!
I finally got a USED GFA-555 II from AudioGon, In the hope to improve my Monitor 10B's sound quality, unfortunately it doesn't. Here is the story:
I hook it up with Harman Kardon HK-3490's preout
I find the sound from the GFA-555II lacks some clarity compare the sound directly from the HK3490 receiver's speaker out. It's not very easy to describe the difference. it likes a very mild noise in the high end. something like Sibilance, I have to listen to it carefully, then I can notice it.
In term of volume, the volume from GFA-555II even slightly smaller than the volume from the HK3490's speaker out. I expect GFA should and can produce bigger or much bigger volume.
Finally, when I turn off the power in GFA, it still sounds for a few seconds, first the left channel fade out, and then is the right, is this means anything wrong.(is this normal?)
I think I used a very good Monster cable, I also tried Luna 6 cable to connect the HK3490 preout and GFA , I got the same thing.
If listen this GFA-555II AMP alone, it seems it works fine, but just by comparing with the output from the HK3490 receiver. I feel this AMP does not fully work but I am not sure.
Please help me to sort out the situation,
Thanks a lot in advance!
I finally got a USED GFA-555 II from AudioGon, In the hope to improve my Monitor 10B's sound quality, unfortunately it doesn't. Here is the story:
I hook it up with Harman Kardon HK-3490's preout
I find the sound from the GFA-555II lacks some clarity compare the sound directly from the HK3490 receiver's speaker out. It's not very easy to describe the difference. it likes a very mild noise in the high end. something like Sibilance, I have to listen to it carefully, then I can notice it.
In term of volume, the volume from GFA-555II even slightly smaller than the volume from the HK3490's speaker out. I expect GFA should and can produce bigger or much bigger volume.
Finally, when I turn off the power in GFA, it still sounds for a few seconds, first the left channel fade out, and then is the right, is this means anything wrong.(is this normal?)
I think I used a very good Monster cable, I also tried Luna 6 cable to connect the HK3490 preout and GFA , I got the same thing.
If listen this GFA-555II AMP alone, it seems it works fine, but just by comparing with the output from the HK3490 receiver. I feel this AMP does not fully work but I am not sure.
Please help me to sort out the situation,
Thanks a lot in advance!
How long does it take to remove the cover? 5 min tops?
It takes about the same amount of time to discharge the filter caps remove the bad and replace with new. You have to remember when you purchase something used that has some age to it there are bound to be potential problems. While your at it you might as well replace the small caps(electrolytic) in the signal path as well. As mentioned by DJK its got thirty years on it. You cannot expect new performance on any piece regardless of where it was purchased.
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Finally, when I turn off the power in GFA, it still sounds for a few seconds, first the left channel fade out, and then is the right, is this means anything wrong.(is this normal?)
Yes, any amp without a relay on the speaker output will continue to put audio out until the power supply voltage goes down.
I would't put a lot of value on the audio from the HK piece its not high quality. There are much better pieces out there.
It takes about the same amount of time to discharge the filter caps remove the bad and replace with new. You have to remember when you purchase something used that has some age to it there are bound to be potential problems. While your at it you might as well replace the small caps(electrolytic) in the signal path as well. As mentioned by DJK its got thirty years on it. You cannot expect new performance on any piece regardless of where it was purchased.
Quote:
Finally, when I turn off the power in GFA, it still sounds for a few seconds, first the left channel fade out, and then is the right, is this means anything wrong.(is this normal?)
Yes, any amp without a relay on the speaker output will continue to put audio out until the power supply voltage goes down.
I would't put a lot of value on the audio from the HK piece its not high quality. There are much better pieces out there.
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It s not a matter of supply caps..
Does anyone think that the sibilance is due to bad supply filtering.???.
Just pointing out the amplifier has age and therefore the caps should be changed. I sincerely doubt the amplifier has any problems. The flaw probably lies in the fact the HK piece sounds very colored and I'm being nice. In other words garbage in garbage out. I'd like the opinion of the poster if he mated the amplifier up to a decent preamp.
More likely, this amp is not well designed stability wise , as corroborated
by the numerous threads about its flaws...
Everything has some type of flaws. The Adcom has had a fairly decent track record. I base this on the first 5 or so years after it came out. One cannot expect amplifier to perform the same as it did day one.
It s not a matter of supply caps..
Does anyone think that the sibilance is due to bad supply filtering.???.
Just pointing out the amplifier has age and therefore the caps should be changed. I sincerely doubt the amplifier has any problems. The flaw probably lies in the fact the HK piece sounds very colored and I'm being nice. In other words garbage in garbage out. I'd like the opinion of the poster if he mated the amplifier up to a decent preamp.
More likely, this amp is not well designed stability wise , as corroborated
by the numerous threads about its flaws...
Everything has some type of flaws. The Adcom has had a fairly decent track record. I base this on the first 5 or so years after it came out. One cannot expect amplifier to perform the same as it did day one.
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yer still on some personal crusade against this amp. Stability problem based what? on some hobbyist's flawed transistor models and simulations. There lot's of repair threads because there are lots of these amps sold with some folks wanting to learn to fix and keep them up and running. Yes sadly some people break them, they are not bullet proof to stupidity.
Thank you all very much for all the valuable inputs, I have some updates...
I hope HK3490 is the problem but unlikely as the external preout is also used internally by the HK 3490 power amplifier portion and it ends up a better sound. If the preout of HK-3490 is noisy, the sound of its speaker output should be noisy too. This is my logic so far.
I means 'Better' just by comparing the sound from GFA-555II, not means the sound from HK-3490 is perfect, it can considered colored or something else.
I have sent the AMP to a nearby repair store to check as they are in promotion period for free check.
They have used Oscilloscope to check the wave form to detect distortion, they did found distortion, they are in the process to further diagnosis which component cause the distortion, I hope the problem is caused by some dry out caps rather than the bad design of Adcom itself!
Thank you all and have a very nice weekend.
I hope HK3490 is the problem but unlikely as the external preout is also used internally by the HK 3490 power amplifier portion and it ends up a better sound. If the preout of HK-3490 is noisy, the sound of its speaker output should be noisy too. This is my logic so far.
I means 'Better' just by comparing the sound from GFA-555II, not means the sound from HK-3490 is perfect, it can considered colored or something else.
I have sent the AMP to a nearby repair store to check as they are in promotion period for free check.
They have used Oscilloscope to check the wave form to detect distortion, they did found distortion, they are in the process to further diagnosis which component cause the distortion, I hope the problem is caused by some dry out caps rather than the bad design of Adcom itself!
Thank you all and have a very nice weekend.
Quote:
They have used Oscilloscope to check the wave form to detect distortion, they did found distortion,
Good for you. Since your repair shop found the amplifier incapable of reproducing a sine wave correctly I am hopeful they have the expertise to repair it. It would have been interesting to run the amplifier into a distortion analyzer for a true reading of how much distortion it was making. Like I said you cannot expect an amplifier of that age to reproduce like it was day one. I am hopeful that you repair this amplifier and beg or borrow a decent preamp so that you will be able to experience what a good preamp coupled with a good power amplifier do sound like.
Someone here on this forum seems to feel that the Adcom 555 II is plagued with problems.
Quote:
More likely, this amp is not well designed stability wise , as corroborated
by the numerous threads about its flaws...
I was unable to dig up any information or numerous threads to this effect. I will repeat the amplifier is around 30 yrs old and therefore will not and cannot be expected to perform like day one. This is why you can find all kinds of used amplifiers on different sites for sale on the internet. If its got a problem they put it up for sale and unfortunately you got one of them. To be perfectly honest here I would repair the 555 and send the HK down the road. The HK is a cost effective piece for someone wanting to do home theater on a budget.
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I hope HK3490 is the problem but unlikely as the external preout is also used internally by the HK 3490 power amplifier portion and it ends up a better sound. If the preout of HK-3490 is noisy, the sound of its speaker output should be noisy too. This is my logic so far.
Well I don't agree 100% with your logic. I once owned a Dunlap Clarke Fet 10 preamp and matching power amplifier. Together they sounded good but when I mated the pre with a different power amp it sounded shrill with the sound of breaking glass in the highs. There was nothing I had that I could mate with the preamp and come up with a winning combination it sounded best with its mate piece. My experience of owning probably 100 different preamps and power amps is that this does come up rarely. In your situation you did hear something out of the ordinary (the distortion) the 555 was making. My suggestion is to repair the 555 so it reproduces signal to factory specifications and a competent shop should be able to do that. When that is done you can replace the caps a mentioned and have something that will provide years of enjoyment.
They have used Oscilloscope to check the wave form to detect distortion, they did found distortion,
Good for you. Since your repair shop found the amplifier incapable of reproducing a sine wave correctly I am hopeful they have the expertise to repair it. It would have been interesting to run the amplifier into a distortion analyzer for a true reading of how much distortion it was making. Like I said you cannot expect an amplifier of that age to reproduce like it was day one. I am hopeful that you repair this amplifier and beg or borrow a decent preamp so that you will be able to experience what a good preamp coupled with a good power amplifier do sound like.
Someone here on this forum seems to feel that the Adcom 555 II is plagued with problems.
Quote:
More likely, this amp is not well designed stability wise , as corroborated
by the numerous threads about its flaws...
I was unable to dig up any information or numerous threads to this effect. I will repeat the amplifier is around 30 yrs old and therefore will not and cannot be expected to perform like day one. This is why you can find all kinds of used amplifiers on different sites for sale on the internet. If its got a problem they put it up for sale and unfortunately you got one of them. To be perfectly honest here I would repair the 555 and send the HK down the road. The HK is a cost effective piece for someone wanting to do home theater on a budget.
Quote:
I hope HK3490 is the problem but unlikely as the external preout is also used internally by the HK 3490 power amplifier portion and it ends up a better sound. If the preout of HK-3490 is noisy, the sound of its speaker output should be noisy too. This is my logic so far.
Well I don't agree 100% with your logic. I once owned a Dunlap Clarke Fet 10 preamp and matching power amplifier. Together they sounded good but when I mated the pre with a different power amp it sounded shrill with the sound of breaking glass in the highs. There was nothing I had that I could mate with the preamp and come up with a winning combination it sounded best with its mate piece. My experience of owning probably 100 different preamps and power amps is that this does come up rarely. In your situation you did hear something out of the ordinary (the distortion) the 555 was making. My suggestion is to repair the 555 so it reproduces signal to factory specifications and a competent shop should be able to do that. When that is done you can replace the caps a mentioned and have something that will provide years of enjoyment.
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You should check better , as regularly there s a GFA 555 owner that
pop up to ask for some help.
One can suppose that this is some kind of lemon that goes from one
hand to another until it find someone willing to fix it definitly.
Quote:
You should check better , as regularly there s a GFA 555 owner that
pop up to ask for some help.
One can suppose that this is some kind of lemon that goes from one
hand to another until it find someone willing to fix it definitly.
I'm wondering if you have a hard on for this amplifier. Have you ever heard, seen, or had the top off one before?
You should check better , as regularly there s a GFA 555 owner that
pop up to ask for some help.
One can suppose that this is some kind of lemon that goes from one
hand to another until it find someone willing to fix it definitly.
I'm wondering if you have a hard on for this amplifier. Have you ever heard, seen, or had the top off one before?
The Adcom GFA 535 and 545 and their Mk II "improved version" models were designed by Nelson Pass. They are widely regarded as very good amplifiers, especially for the relatively low prices that used ones now fetch. I would assume that the 555 and 555 II were also designed by Nelson Pass.
I have two Adcom 545 MkII amps, that I bought earlier this year, on eBay, for around $180 each, after reading many, many good reviews and user testimonials about them. They have excellent build quality and the sound quality is basically perfect (according to my Magnepan MG-12/QR speakers). Their sound quality is nowadays considered to be at least "entry-level audiophile", which isn't bad.
The 545 II is rated at 100 W/ch @ 8 Ohms and 150 W/ch @ 4 Ohms.
I like them quite a lot.
Tom
I have two Adcom 545 MkII amps, that I bought earlier this year, on eBay, for around $180 each, after reading many, many good reviews and user testimonials about them. They have excellent build quality and the sound quality is basically perfect (according to my Magnepan MG-12/QR speakers). Their sound quality is nowadays considered to be at least "entry-level audiophile", which isn't bad.
The 545 II is rated at 100 W/ch @ 8 Ohms and 150 W/ch @ 4 Ohms.
I like them quite a lot.
Tom
This sounds like a very interesting topic, as the "problems" this Adcom seems to have are generic to many commercial amps around.
The good thing about buying a second hand amp is usually the price, and you should know you are taking some risks. But you could also be buying it to upgrade and/or modify what needs to, and then the risks should be less of a problem.
Some years ago there was an article on The Audio Amateur, where Kit Ryan designed a high current regulated supply for another Adcom amp: the 545. In fact that regulator could be applied on practically every power amp around, then and today. An Adcom owner mailed a letter that he built the regulator and took the chance to also improve on all the passive parts on it, with very good audio quality improvement.
The 545 model had been recently released back then, so aging problems were not still present. If you take a commercial product like that Adcom or yours, and put it under a "how to make it better" microscope, you see that there are areas for improvement, even more after so many years since it was made.
If you start with all the passive parts (resistors, film capacitors, small and large electrolytics, cabling) and some active parts (supply diodes), you can solve not only the aging problem but also improve on what commercial compromises made Adcom pick the parts they did back then. That could get some improvements and at least bring the amp back to its original specs.
One main difference in the 555 is that it has a DC servo, so special attention has to be attended to the parts around it. Do get a Service manual. I got mine here:
Adcom Diagrams, Schematics and Service Manuals for FREE
The only thing I would add up front for now is a good quality volume pot, at least 10K log, so you could go in directly with different sources, like CD or DVD player, to see if the HK 3490 is not colouring the audio quality.
Don't pick very exotic/expensive parts for the upgrading, or things can get very expensive and crazy.
After this first stage I would try other improvements, like low current or high current regulators, like Kit Ryan's, or others. But go slowly and you will see if things improve.
I do think the Adcom is a good product to start with, and it's worth improving on.
The good thing about buying a second hand amp is usually the price, and you should know you are taking some risks. But you could also be buying it to upgrade and/or modify what needs to, and then the risks should be less of a problem.
Some years ago there was an article on The Audio Amateur, where Kit Ryan designed a high current regulated supply for another Adcom amp: the 545. In fact that regulator could be applied on practically every power amp around, then and today. An Adcom owner mailed a letter that he built the regulator and took the chance to also improve on all the passive parts on it, with very good audio quality improvement.
The 545 model had been recently released back then, so aging problems were not still present. If you take a commercial product like that Adcom or yours, and put it under a "how to make it better" microscope, you see that there are areas for improvement, even more after so many years since it was made.
If you start with all the passive parts (resistors, film capacitors, small and large electrolytics, cabling) and some active parts (supply diodes), you can solve not only the aging problem but also improve on what commercial compromises made Adcom pick the parts they did back then. That could get some improvements and at least bring the amp back to its original specs.
One main difference in the 555 is that it has a DC servo, so special attention has to be attended to the parts around it. Do get a Service manual. I got mine here:
Adcom Diagrams, Schematics and Service Manuals for FREE
The only thing I would add up front for now is a good quality volume pot, at least 10K log, so you could go in directly with different sources, like CD or DVD player, to see if the HK 3490 is not colouring the audio quality.
Don't pick very exotic/expensive parts for the upgrading, or things can get very expensive and crazy.
After this first stage I would try other improvements, like low current or high current regulators, like Kit Ryan's, or others. But go slowly and you will see if things improve.
I do think the Adcom is a good product to start with, and it's worth improving on.
Ryan's Regulators for Power amps
I actually built a pair of Kit Ryan's regulators and used them for years in my B&K ST-202+. The improvement was not modest. The regulated amps had far, far more clarity and detail in the music. Only problem I had was a very faint buzz probably due to improper grounding or my amateurish production of the PC board. If the Mosfets are still around, and particularly if you could get the boards professionally manufactured, and also if there's heat sink real estate enough to add them, I strongly recommend them. I later fried one channel board of the B&K, and it's been in the garage waiting ever since. Considering buying a couple of the L7 mosfet amp kits on ebay, and using them with the regulators and power supply/chassis. Anyone have a thought to share here?
Bill Boyd
Cary, NC
I actually built a pair of Kit Ryan's regulators and used them for years in my B&K ST-202+. The improvement was not modest. The regulated amps had far, far more clarity and detail in the music. Only problem I had was a very faint buzz probably due to improper grounding or my amateurish production of the PC board. If the Mosfets are still around, and particularly if you could get the boards professionally manufactured, and also if there's heat sink real estate enough to add them, I strongly recommend them. I later fried one channel board of the B&K, and it's been in the garage waiting ever since. Considering buying a couple of the L7 mosfet amp kits on ebay, and using them with the regulators and power supply/chassis. Anyone have a thought to share here?
Bill Boyd
Cary, NC
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