I have an Adcom GFA-5400 v1.0 and I am interested in modifiying or upgrading it. Does anyone have any suggestions? Or am I limited to what I can do with this design?
Im thinking about upgrading some of the components. The caps are from 1998, so they have to be needing replacement. There are 12,000uf 63v caps in there now and I was thinking about replacing it with these:
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Last night I was adju8sting the bias and have decided I hate the pots and want to replace them with the more accurate kind, but can not find the exact value. There are 4 4.7k pots and I was thinking about replacing them with:
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Im also thinking about upgrading the bias caps too to better quality.
Any thoughts?
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
Last night I was adju8sting the bias and have decided I hate the pots and want to replace them with the more accurate kind, but can not find the exact value. There are 4 4.7k pots and I was thinking about replacing them with:
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
Im also thinking about upgrading the bias caps too to better quality.
Any thoughts?
I have recived severial caps from that seller and all have been very fine quality. I just got some polycarbonate caps from him a few weeks ago and they were a fraction of the price from Mouser. So far, no fakes, just takes time to get to the US.
Just seen the post on the trimmer replacent. They look like Bourns knock-off's. Anyway, would just go with realy good single turn cermet by Bourns ect.. The bias adjustment moves too much to take advantage of a ten turn pot. Just my 2Cents"
Thanks for all the responses. I am an amateur when it comes to this stuff, but too poor to afford the good stuff. So I am looking to improve what I have. I have learned to adjust the bias and have it adjusted perfectly. Those pots are so touchy.
Is it OK for me to go from a 12000uf 63v cap to a 15000 63v cap? I figure I am just increasing the capacity and keeping the voltage the same. The kendeil caps are going to make it sound so much better.
I also have a Rotel pre that has a left channel a little muted. I read somewhere on this forum it could be the caps, so I took it apart and found the primary caps the tops are pushing up which is a sign. So I ordered new ones as well(same better quality).
This should be a noticeable improvement on the sound.
Is it OK for me to go from a 12000uf 63v cap to a 15000 63v cap? I figure I am just increasing the capacity and keeping the voltage the same. The kendeil caps are going to make it sound so much better.
I also have a Rotel pre that has a left channel a little muted. I read somewhere on this forum it could be the caps, so I took it apart and found the primary caps the tops are pushing up which is a sign. So I ordered new ones as well(same better quality).
This should be a noticeable improvement on the sound.
Changing the caps from 12k to 15k should be no problem. Just be sure that the size of the cap is close to the same. If the cap is PC mounted check you clearance on the board, a few mm can be a deal breaker in dia.
Very nice. I also like the Super Through and Gold caps. As long as you have the room, why not. Keep up the good work!
On the pre, I noticed that most of the caps on the board are marked with a larger circle than the cap installed. It seems almost as if they purposly put cheap caps in, but the board has room for better quality ones. I decided last night to go ahead and upgrade those to ELNA SILMIC II RFS Silk.
I know you can do much better than that. Try using a large Weller soldering gun insted of an Iron. You'll never get the post hot enough for a clean connection.I use the Cardas and I know it took some work to get them right at first. I would also use some liquid flux to assist you. Put a cloth under the work area so you do not get anything on your boards. The rest looks very good. Nice job.
Thanks. The new pots are a lot more accurate and a lot less touchy for adjusting the bias. I'll fix the terminals later. There is a noticeable improvement in the sound quality. I also replaced the IRF9610 and IRF610 Mosfet's on both channels just in case I damaged them from my wiring issue before.
Very nice job! if it sounds good now...wait a few weeks and it will sound even better😉!. I did an upgrade caps in my diy amplifier too. I am using Mundorf audio grade for my power supply and Sonicap for my inputs. it is a big plus the upgrade. The sound is excellent.😉.
Those Adcoms are very well build and sound fantastic!!!
would it be possible to tell me where the bias measurements are taken and if they are the lower set of pots as well? thanks very much
Prior to bias alignment and DC offset check, turn unit on and allow to run at rated output for approximately 5 minutes before attempting adjustments.😀
No load on speaker terminals, no signal input
Adcom manual info for bias adjust:
Measure R675, neg terminal of meter on top, pos on bottom(Closest to the bottom of the amp). Adjust VR 603
Measure R676, neg terminal of meter on top, pos on bottom(Closest to the bottom of the amp). Adjust VR 604
Voltage should be 35mV.
Then connect your voltmeter to the speaker terminals:
Adjust VR601 until you get 0 VDC
repeat for VR602
No load on speaker terminals, no signal input
Adcom manual info for bias adjust:
Measure R675, neg terminal of meter on top, pos on bottom(Closest to the bottom of the amp). Adjust VR 603
Measure R676, neg terminal of meter on top, pos on bottom(Closest to the bottom of the amp). Adjust VR 604
Voltage should be 35mV.
Then connect your voltmeter to the speaker terminals:
Adjust VR601 until you get 0 VDC
repeat for VR602
Waiting for the Rubycon 15K main PSU caps(Shold be here tomorrow!). Nichicon Muse and Fine Gold for the rest of the supply. Elna Silmic for the Amp PCB. Finally get to give this amp some love!😀
I don't know if anyone is still folowing this thread or not, but I'll post my observed results so far. I replaced all of the elctrolytics on the PSU and the caps in the Amp boards. I used Elna silmic II on the amp boards, Rubycons for the main psu caps and Nichicon muse for the secondary psu caps. Still in the burn in proces, but immediately noticable reduction in distortion. the 12k uF caps I removed from the psu are measuring at 9k uF or lower and when shaken have moving parts....lol. I'm extremely pleased to have removed a midrange distortion that I was thinking came from my tweeters being crossed over too low. Sound stage has widened, deepened and moved upward. The imaging seems to be a little more precise. Vocals now seem frighteningly realistic. RTA measurements show improved low frequency response and smoother midrange trasitions. It was warth the two hours it took to replace the caps for sure.😀
I aquired a Adcom GFA 5400 and made a few changes
I may have signed on before, but thinking this is my first post. I recently acquired an GFA 5400 from a friend who was using it to drive two passive subs. It is my second Adcom, the first was a GFA 545II. I liked the build quality of the 545II, but felt it lacked punch at that time. That may have been what I was comparing it to at that time, but it wasn't something I felt a need to hold onto. This GFA 5400 turns out be be very different from the 545II with both being about the same size, with the 5400 having a better power rating, and it having an entire mosfet chain from RCA to speaker outs.
Nice drive initially but something about it bothered me. So far it has a very slight hum, so my starting point was to order and replace all electrolytics. While they are on the way, I put on my tweaking hat and and made a single change that has me really liking this amp now. And that is even before I swap out the caps. Most of the 12,000uf caps have a slight bulge on the top which means that are bad. But the age alone is cause to make the change.
What I've done so far is replace two caps (one on each power board). They are C601 and C602 (390pf). The original looks like a film caps of sorts, and I have played with putting the same or similar type there with no change. The change happened when I swapped in Silver Mica caps of the same value, but things got even better when I put in 330pf instead, and that seems to have bought life to this amp. This may be because of what in using as a source to the amp or even the speakers. But to my ears it is substantial. So I'm wondering if anyone else has tried this..🙂
I may have signed on before, but thinking this is my first post. I recently acquired an GFA 5400 from a friend who was using it to drive two passive subs. It is my second Adcom, the first was a GFA 545II. I liked the build quality of the 545II, but felt it lacked punch at that time. That may have been what I was comparing it to at that time, but it wasn't something I felt a need to hold onto. This GFA 5400 turns out be be very different from the 545II with both being about the same size, with the 5400 having a better power rating, and it having an entire mosfet chain from RCA to speaker outs.
Nice drive initially but something about it bothered me. So far it has a very slight hum, so my starting point was to order and replace all electrolytics. While they are on the way, I put on my tweaking hat and and made a single change that has me really liking this amp now. And that is even before I swap out the caps. Most of the 12,000uf caps have a slight bulge on the top which means that are bad. But the age alone is cause to make the change.
What I've done so far is replace two caps (one on each power board). They are C601 and C602 (390pf). The original looks like a film caps of sorts, and I have played with putting the same or similar type there with no change. The change happened when I swapped in Silver Mica caps of the same value, but things got even better when I put in 330pf instead, and that seems to have bought life to this amp. This may be because of what in using as a source to the amp or even the speakers. But to my ears it is substantial. So I'm wondering if anyone else has tried this..🙂