Adcom GFA-5800 amp cooling?

John in MA
John in MA Posts: 1,010
edited April 2008 in Electronics
Here's a odd one for you guys. Anyone familar with when the cooling system of an Adcom GFA-5800 is supposed to fully kick in? The design has two horizontal heat sink tunnels with fans mouned on the ends. No external heatsinks or provisions for convection.

For some reason the right channel's temperature sensor appears to be set lower than the left (marked 40 vs 60) and a rather disinterested fellow at Adcom confirmed this. The right fan will kick in once the amp is at normal operating temperature, but I have yet to see the left one turn on even when driven heavily. The design does not allow both channels to be cooled by one fan.

I'm a little curious about this since just sitting at idle the left side of the amp is getting uncomfortably hot. I'm going to check the bias when I get a chance, and I also might see about putting a lower temp sensor on that side if I have to.
Post edited by John in MA on
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  • danger boy
    danger boy Posts: 15,722
    edited April 2008
    is there a fuse that might be burned out on that side? just a possible idea.
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  • venomclan
    venomclan Posts: 2,467
    edited April 2008
    This is a Ben question. He has dismantled every Adcom amp ever made. :)
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  • Rays_Fan
    Rays_Fan Posts: 7
    edited April 2008
    engtaz tells me Ben and H9 Adcom experts.

    Rays_Fan
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  • John in MA
    John in MA Posts: 1,010
    edited April 2008
    Don't think there's a fuse for the fan system. They're two low-voltage 120mm box fans running off some kind of thermistor controlled solid-state power source. I'm going to check voltages when I have some time.
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  • heiney9
    heiney9 Posts: 25,421
    edited April 2008
    More than likely the thermistor for the channel that doesn't turn on is out of spec. It's my understanding that under normal operating situation neither fan should run. It's been a long time since I've been around a 5800 however.

    A great resource for Adcom's and older gear in general is the DIY Audio forum. Lots of knowledgeable and very experienced people on there. Lots of Adcom info available over there. Check it out.
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Puritan Audio PSM136 Pwr Condtioner & Classic PC's | Legend L600 | Roon Nucleus 1 w/LPS - Tubes add soul!
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  • ben62670
    ben62670 Posts: 15,969
    edited April 2008
    I have one in GA. I will look into it for you in a week. I can drive my custom SDA at 2 ohms. 19 drivers per channel should get it hot enough to kick in the fans.
    I'll shoot you a PM with my number. BTW mine has more airflow on one side than the other. I'll see if it sucks in one side, and blows out the other.
    H9 you out there?
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
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  • ben62670
    ben62670 Posts: 15,969
    edited April 2008
    heiney9 wrote: »
    More than likely the thermistor for the channel that doesn't turn on is out of spec. It's my understanding that under normal operating situation neither fan should run. It's been a long time since I've been around a 5800 however.

    A great resource for Adcom's and older gear in general is the DIY Audio forum. Lots of knowledgeable and very experienced people on there. Lots of Adcom info available over there. Check it out.

    There you are:D
    +1 on DIYaudio.com
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
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    Ben
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  • John in MA
    John in MA Posts: 1,010
    edited April 2008
    I've been meaning to spend some time over there. The 5800 is Nelson Pass's favorite Adcom, too.

    I think at least some fan action would be required whenever it's been running a while. This sucker's hot, and there's no natural cooling. I believe both tunnels are supposed to blow out the back, and I think you're right about more airflow on one side. I wonder what Adcom had in mind with this setup.
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  • ben62670
    ben62670 Posts: 15,969
    edited April 2008
    Well thanks for the motivation to tear it apart:) Mine never has had even airflow on both sides. I think this is probably due to having 2 thermal resistors. This amp is quite impressive. I have had many Adcom's including the 585, and 565's. The 5800 is definitely the hardest hitting amp I have owned. No harshness to the sound either. It kinda sucks. I am most likely going to have to sell mine:(
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • John in MA
    John in MA Posts: 1,010
    edited April 2008
    That's the part of the design that makes me wonder. If you have two identical channels, both producing about the same amount of heat, why put a higher temp sensor and a faster fan on one side? I know that's the way they designed it, just don't know why.

    If they were thinking that the fan on one side could draw enough air through the other channel at lower temperatures, I think someone must have miscalculated. All the airflow goes through the chassis top grate.
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  • ben62670
    ben62670 Posts: 15,969
    edited April 2008
    I am guessing that one of the fans turns on slightly earlier than the other. If one starts it will draw some air over the other channels outputs therefore the other channels fan will not kick in till it reaches a higher temp than the opposite channels fan can cool. It also could have have something to do with the mounting of the thermal resistor. Mine never got real hot on either channel. I will check when I get up north.
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • heiney9
    heiney9 Posts: 25,421
    edited April 2008
    John in MA wrote: »
    I've been meaning to spend some time over there. The 5800 is Nelson Pass's favorite Adcom, too.

    I think at least some fan action would be required whenever it's been running a while. This sucker's hot, and there's no natural cooling. I believe both tunnels are supposed to blow out the back, and I think you're right about more airflow on one side. I wonder what Adcom had in mind with this setup.

    It is a Nelson Pass design (until Adcom engineers put their grubby little paws on it :p). It's a great sounding amp, but I'm with you; why have a heavily biased amp with enclosed cooling fins. It was stupid move and that's part of the reason the 5800 had a fairly short run and the 5802 was introduced.

    Those fans, IIRC, should be controlled by a thermistor attached to the heat sinks and they should either be variable speed of have 3 distinct speeds based on the temp of the heat sinks. Generally in the real world if bias is set properly, etc. both sides should run at about the same temperature.

    First thing I would do, if you are capable, is find out what the idling temp is of each bank of heat sinks. If they are both close then it has something to do with the actual fan sensing circuit. I briefly looked over at DIY because I seem to remember someone inquiring about the fan circuit of the 5800 last year. Didn't find it.

    I have not heard of too many issues with the fans on the 5800 not working properly. If you don't find any info at DIY make a post about it and if Chris (Anatech) answers, he's the man. He is very knowledgeable about Adcom issues and he knows his stuff, nice guy too. Ask Ben about Chris, he helped him repair his 565's.

    The only other thing is if you are not going into thermal protection then you're probably alright. But if your like me, you want things to work like they are supposed to.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Puritan Audio PSM136 Pwr Condtioner & Classic PC's | Legend L600 | Roon Nucleus 1 w/LPS - Tubes add soul!
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  • John in MA
    John in MA Posts: 1,010
    edited April 2008
    I haven't posted on DIY yet but I spent some time with the amp. An AK member also has one of these and said his fans start with the amp, and increase in speed as the thing warms up.

    On my amp, after being on about 20 minutes my right fan header measures 3.8v and the left is 3.2. At this point neither fan shows any signs of life. The AK guy's 5800 already has both fans spinning at these voltages. Heatsinks are quite warm but I can keep my hand on them. I didn't leave it on long enough to see at what voltage my right fan was turning on with.

    I'm not sure what the bias procedure is for this amp, but measuring across R64, I get 45mv on the right and 56mv on the left. The other main resistors each have their own unique measurements without much of a pattern. The left channel is warmer than the right.
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  • heiney9
    heiney9 Posts: 25,421
    edited April 2008
    You definitely have an issue; how serious it is is anyones guess. Ben has spent some time inside the Adcoms so maybe he can give you some guidance.
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Puritan Audio PSM136 Pwr Condtioner & Classic PC's | Legend L600 | Roon Nucleus 1 w/LPS - Tubes add soul!
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  • ben62670
    ben62670 Posts: 15,969
    edited April 2008
    John in MA wrote: »
    On my amp, after being on about 20 minutes my right fan header measures 3.8v and the left is 3.2. At this point neither fan shows any signs of life.
    I'm not sure what the bias procedure is for this amp, but measuring across R64, I get 45mv on the right and 56mv on the left.

    H9 is right. There is an issue. I don't have the service manual for that one yet. I'll get it;) It is bias a little hot. Some guys do that on purpose thinking they are getting more out of their amp:confused: Why you would want more out of an amp like that I do not know. What is the fan label have on it for voltage? 12v? even at 3.8v they should be spinning. Post in DIYaudio.com There are some very knowledgeable guys their including the men that designed the amp. Something like "Fan issue Adcom GFA-5800". Actually I'll post it for you under the same screen name I have here, and post the link.
    Ben

    Edit
    link
    http://www.diyaudio.com/forums/showthread.php?s=&threadid=121301
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • John in MA
    John in MA Posts: 1,010
    edited April 2008
    I appreciate the gesture, but I was going to post a properly thought out description of the issue in a day or two. I'm still investigating here.

    Edit: The fans themselves are functional. When connected to a battery they spin right up. I don't know what the specs are, the fans are unmarked. They appear to be fairly high quality.
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  • ben62670
    ben62670 Posts: 15,969
    edited April 2008
    Hey John.
    Its something I would like to know for myself too. Even slight friction will impede correct fan operation especially with lower voltages. I like to collect Adcom service manuals too:)
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • John in MA
    John in MA Posts: 1,010
    edited April 2008
    The fans spin very freely. When they're connected to the amplifier while it's showing 3-4V they don't seem to show any inclination to move, even when spun by hand.

    A wild guess would be that the fan driver isn't delivering the required power when actually loaded with a fan, but at point I have no clue.
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