Hi mjraudio,
Ground resistors seem to blow in some, but not all installations. Normally these are not a problem. Don't increase the size (wattage) or resistance as we do want these to blow in a fault condition.
Go ahead and replace those components. I was only trying to set your mind at ease.
-Chris
Ground resistors seem to blow in some, but not all installations. Normally these are not a problem. Don't increase the size (wattage) or resistance as we do want these to blow in a fault condition.
Go ahead and replace those components. I was only trying to set your mind at ease.
-Chris
Status
Okay guys, I borrowed a digital multi-meter from a friend and tested the resistors on the soft start board, they measure approximately to their ohms ratings and should work fine.
One of the filter cap PCBs had a disgusting solder job where two solder points which were not supposed to be touching were shorted. I cleaned up the connection and now it should be great.
Just waiting on the new rectifier and filter caps to arrive, then I will plug them in and hope the unit doesn't blow up!
Now that I have DMM, on my other working GFA-565, I plugged it in and warmed up the unit with (and without speakers) attached, and measured the DC offset at the speaker terminals. It hovered at around 250-270 mV: not good!
I see no electrolyte on the PCB board, and the electrolytic caps look fine.
A NOTE OF INTEREST! On my working 565, when I blew air lightly on the transistor heatsinks (Q111 and Q112), the DC leakage onto the speaker terminals dropped about 50mV, the more air I blew onto the sinks, the lower the leakage dropped, when i let it stand again (with or without a signal coming through to the speakers, and with or without speakers attached) the DC leakage onto the speaker terminals rose up to about 240 mV after a little bit.
When playing, you can hear the hum/buzz from the leaking DC, but it's not enough to significantly thump my speakers on powerup and shutoff, and there are no thumps while playing.
Eventually I want to remove the entire board, solder faston, pin, or quickconnectors onto any wire-solder points so I can disconnect the board easily in the future, remove all electrolytic and film caps, clean the PCB, replace them with black gate electrolytic caps and auricap film caps, and then rewire everything.
The DC servo circuit has several parts to it amongst which are the op-amp IC (Adcom 2A), several Panasonic film capacitors (can I replace all film caps with Auricaps?) and the Adcom matched transistor pairs (MPS-A13 and MPS-A63). Would it be a good move to just replace everything in that circuit? I want to upgrade all electrolytic and film caps to audio-grade ones, and have a stable unit that will not fail in the future. I'm also considering the possibility of installing a very small and quiet cooling fan on top of the input stage to help cool the Q111 and Q112 transistors to prolong life, improve stability and potentially keep DC leakage on to the speaker terminals to a minimum.
Okay guys, I borrowed a digital multi-meter from a friend and tested the resistors on the soft start board, they measure approximately to their ohms ratings and should work fine.
One of the filter cap PCBs had a disgusting solder job where two solder points which were not supposed to be touching were shorted. I cleaned up the connection and now it should be great.
Just waiting on the new rectifier and filter caps to arrive, then I will plug them in and hope the unit doesn't blow up!
Now that I have DMM, on my other working GFA-565, I plugged it in and warmed up the unit with (and without speakers) attached, and measured the DC offset at the speaker terminals. It hovered at around 250-270 mV: not good!
I see no electrolyte on the PCB board, and the electrolytic caps look fine.
A NOTE OF INTEREST! On my working 565, when I blew air lightly on the transistor heatsinks (Q111 and Q112), the DC leakage onto the speaker terminals dropped about 50mV, the more air I blew onto the sinks, the lower the leakage dropped, when i let it stand again (with or without a signal coming through to the speakers, and with or without speakers attached) the DC leakage onto the speaker terminals rose up to about 240 mV after a little bit.
When playing, you can hear the hum/buzz from the leaking DC, but it's not enough to significantly thump my speakers on powerup and shutoff, and there are no thumps while playing.
Eventually I want to remove the entire board, solder faston, pin, or quickconnectors onto any wire-solder points so I can disconnect the board easily in the future, remove all electrolytic and film caps, clean the PCB, replace them with black gate electrolytic caps and auricap film caps, and then rewire everything.
The DC servo circuit has several parts to it amongst which are the op-amp IC (Adcom 2A), several Panasonic film capacitors (can I replace all film caps with Auricaps?) and the Adcom matched transistor pairs (MPS-A13 and MPS-A63). Would it be a good move to just replace everything in that circuit? I want to upgrade all electrolytic and film caps to audio-grade ones, and have a stable unit that will not fail in the future. I'm also considering the possibility of installing a very small and quiet cooling fan on top of the input stage to help cool the Q111 and Q112 transistors to prolong life, improve stability and potentially keep DC leakage on to the speaker terminals to a minimum.
Hi mjraudio,
Sorry, strip and clean once your other one is running properly.
-Chris
Electrolyte is normally not visable. It doesn't take much to cause a problem.
Sorry, strip and clean once your other one is running properly.
Still, it's a leakage issue. I'll bet the servo is just in range (or just out).
No, Auricaps are too large. Why change those? Just replace the electrolytics.
Too hard to match. Leave them alone unless you have a proble with them.
-Chris
Thanks for your reply anatech! 🙂
Once I get both units repaired I will begin the very huge job of removing the input stage, cleaning and replacing the electrolytic caps.
There is one large film cap at the back of the board that I want to replace with an Auricap in the hopes of improve sound a little. Could I get better filtration or even better sound with just one Auricap where the Roederstein 100V/4.7uF (C101) cap is?
Also, I do not like how hot the transistors get on the input board, when I eventually disconnect the board and clean it, I will remove the sinks and regrease them with a better thermal compound (I come from a deep IT background where CPU grease is important). Since I do not have a balanced input stage, there is space above the unbalanced audio input board for a small (and necessarily quiet) fan. With some custom work I might be able to install one. Does this seem like a bad idea or the unit benefit from some form of active cooling to help prolong life and promote stability.
NOTE: The large AC continuously variable fan never turns on with an 8 ohm load at moderate volumes. I think it will only turn on when I push the amp to the extremes (never going to happen because my speaker cones would go long before the amp distorted).
Once I get both units repaired I will begin the very huge job of removing the input stage, cleaning and replacing the electrolytic caps.
There is one large film cap at the back of the board that I want to replace with an Auricap in the hopes of improve sound a little. Could I get better filtration or even better sound with just one Auricap where the Roederstein 100V/4.7uF (C101) cap is?
Also, I do not like how hot the transistors get on the input board, when I eventually disconnect the board and clean it, I will remove the sinks and regrease them with a better thermal compound (I come from a deep IT background where CPU grease is important). Since I do not have a balanced input stage, there is space above the unbalanced audio input board for a small (and necessarily quiet) fan. With some custom work I might be able to install one. Does this seem like a bad idea or the unit benefit from some form of active cooling to help prolong life and promote stability.
NOTE: The large AC continuously variable fan never turns on with an 8 ohm load at moderate volumes. I think it will only turn on when I push the amp to the extremes (never going to happen because my speaker cones would go long before the amp distorted).
Hi mjraudio,
-Chris
Yup, sorry you need to do that.
I honestly don't see that changing anything but your bank balance in a small way. 😉 The original is a good part.
Use normal grease and do not over tighten the screws. Special grease will not help in the least. Carefully flattening the heatsink surface would make a far larger difference. I built and rebuild voice mail servers, I flatten those heatsinks too. 😉
Air currents normally will cause noise in low level stages. Run a 12 VDC fan at 5V if you want. Two of those 1" jobbies might do the trick, aimed to avoid the input section.
-Chris
The amp is DC-coupled from start to finish (with the possible exception of the input, since I don't know if this is a bipolar input or FET). Regardless, BlackGate caps work well for interstage coupling, but all your caps are being used for filtering duties. I'd use Panasonic FC/FM or Nichicon HE/PW. They'll last much longer than any BG cap, and very likely do a better job.
Hmm interesting. Well I just replaced the electrolytic caps on the AC Input/Bias Time-delay (soft start) boards in BOTH my amps with shiny and brand new Mallory electrolytic caps, as well as the bridge rectifiers with higher quality HVCA models. My functioning amp worked flawlessly with the new electronics installed and I have high hopes that my broken 565 will work great as soon as I receive and install the new 100V 36,000uF filter capacitors that I ordered ($106).
But I just wanted to confirm that replacing the electrolytic capacitors on the soft start circuit with Mallory electrolytics and replacing the bridge rectifier with THIS unit worked perfectly fine in the GFA-565. I recommend that HVCA manufactured bridge rectifier especially because although it is glass encased, the bottom and sides are metal, which can conduct heat better and pass its own heat to the heatsink to which it is attached to in the 565. An excellent unit.
I also replaced the two electrolytic capacitors on the output stage with Mallory caps.
If the broken amp is fixed I will not only throw the biggest party ever, but plan to completely fix the input stage next.
If the fix/rebuild works, I will have spent $140 to fix the broken amp having replaced both filter caps, new bridge rectifiers in BOTH amps, and new electrolytic capacitors all around.
I am cautiously optimistic 🙂 ... and to think that a repair shop quoted the previous owner $400 to fix the unit.
I have no immediate plans to do so, but what would it take to replace the transformer in the GFA-565? Is the 565's transformer a custom unit designed by Adcom specifically for the 565? Or could I order THIS unit (if it fits) and install it?
My current transformer makes a humming noise, is also two decades old (literally), and has nasty stains on the outside which make it look like one of those circular blocks of cheese. I'm thinking about long-term upgrades I can eventually make to upgrade and mod the amp for either higher performance (whatever that means), better quality (if possible), or to simply get rid of the hum and rebuild the amp for fun!
But I just wanted to confirm that replacing the electrolytic capacitors on the soft start circuit with Mallory electrolytics and replacing the bridge rectifier with THIS unit worked perfectly fine in the GFA-565. I recommend that HVCA manufactured bridge rectifier especially because although it is glass encased, the bottom and sides are metal, which can conduct heat better and pass its own heat to the heatsink to which it is attached to in the 565. An excellent unit.
I also replaced the two electrolytic capacitors on the output stage with Mallory caps.
If the broken amp is fixed I will not only throw the biggest party ever, but plan to completely fix the input stage next.
If the fix/rebuild works, I will have spent $140 to fix the broken amp having replaced both filter caps, new bridge rectifiers in BOTH amps, and new electrolytic capacitors all around.
I am cautiously optimistic 🙂 ... and to think that a repair shop quoted the previous owner $400 to fix the unit.
I have no immediate plans to do so, but what would it take to replace the transformer in the GFA-565? Is the 565's transformer a custom unit designed by Adcom specifically for the 565? Or could I order THIS unit (if it fits) and install it?
My current transformer makes a humming noise, is also two decades old (literally), and has nasty stains on the outside which make it look like one of those circular blocks of cheese. I'm thinking about long-term upgrades I can eventually make to upgrade and mod the amp for either higher performance (whatever that means), better quality (if possible), or to simply get rid of the hum and rebuild the amp for fun!
Hi mjraudio,
-Chris
The original rectifiers were okay, but you didn't hurt anything. Mallory caps are historically good quality. I see no faults with your choices.
You will probably be successful. Now you can see why the shop estimated this figure.
Yup. Don't go higher in voltage to attempt to increase the power. You don't need the extra heat. You could go a little higher in current rating if you want without hurting anything.
-Chris
This is why old owner sold this amp. Probably the repair shop gave him an estimate around $250 or more 😱
Are you shure the output transistors are good?
/Peter
Are you shure the output transistors are good?
/Peter
Hi Peter,
I've seen pretty high estimates from shops based on weight and value rather than any knowledge of the inner workings.
-Chris
I've seen pretty high estimates from shops based on weight and value rather than any knowledge of the inner workings.
-Chris
anatech said:
I AM SUCCESSFUL 😀
Works beautifully, except the 670mV of DC offset at the speaker terminals...I will redo the input boards in about a month.
Complete workup:
Both amps: new bridge rectifiers, new electrolytic caps on soft start circuit and output stages (Mallory electrolytics), cleaned up internals.
Previously broken amp: new filter caps, cleaned up Adcom's messy solder job.
Result? Two beautifully functioning Monobloc amplifiers. Now I just need to wire in another circuit as I'm having to power one with an extension cord from the other room, lol.
A note of interest, my replacement capacitors were 100V, 36000uF 105degree rated, and are 2.5" in diameter and measure about 3" tall. How is this possible when the originals weighed a ton and were 5" tall?
Updated capacitor design in the last 20 years? Or did I get ripped off with a mislabeled capacitor. The 22,000uF capacitors are this size.
I also ordered spade connectors for my 0.5M (1.5ft) CAT6 16-conductor (12 AWG aggregate) prototype speaker cables....and I'm also building a custom lighting system with black light neon tubes to go behind my audio racks. I like to listen in low light 🙂
I will post pics of my system in the next few weeks.
Good job!
However, that is far too much offset. I wouldn't recommend using the amp(s) until you get that issue resolved.
No, you weren't ripped on the caps. Insulation has improved vastly over the last 20 years and as a result package sizes have continued to shrink.
Glad it's working! First step down...
Again, great job!
However, that is far too much offset. I wouldn't recommend using the amp(s) until you get that issue resolved.
No, you weren't ripped on the caps. Insulation has improved vastly over the last 20 years and as a result package sizes have continued to shrink.
Glad it's working! First step down...
Again, great job!
Thanks Apogee! I couldn't have done it without everyone's help here on the diyAudio.com, you, anatech, and the others too..THANKS! 🙂 This thread is certainly a "diy success story."
Now I can look at these big black boxes and know what is inside of them. I feel like an educated audiophile now, one that constantly has to improve upon the design.
I'll order parts I need to fix the input boards this week and I'm also going to replace the opamps with Analog Devices OP97FS ICs as per Walt Jung's recommendation. I will also install an IEC inlet on each amp. Could the introduction of such a power receptacle introduce noise or degrade the power feed in any way?
Oh, and also, I am now using the APPROPRIATE Bussman-model ABC-12 and 15 fuses for the amps, identical on each unit.
Now I can look at these big black boxes and know what is inside of them. I feel like an educated audiophile now, one that constantly has to improve upon the design.
I'll order parts I need to fix the input boards this week and I'm also going to replace the opamps with Analog Devices OP97FS ICs as per Walt Jung's recommendation. I will also install an IEC inlet on each amp. Could the introduction of such a power receptacle introduce noise or degrade the power feed in any way?
Oh, and also, I am now using the APPROPRIATE Bussman-model ABC-12 and 15 fuses for the amps, identical on each unit.
Hi mjraudio,
Peter is right. Far too high an offset. We know something is wrong and it will not get any better with time. Fix it properly now please.
Sorry, I know you're dying to listen to some serious tunes, but now is not the time.
-Chris
Peter is right. Far too high an offset. We know something is wrong and it will not get any better with time. Fix it properly now please.
Sorry, I know you're dying to listen to some serious tunes, but now is not the time.
Yup! 😉
-Chris
anatech said:
You won't believe this but I just measured the offset on the previously broken amp and it measured 5-7mV (very temperature sensitive).
The amp that was never broken measures 270mV.
I am still nervous about using the other amp now, I think 270mV is way too high! I will fix it this week and switch back to my GFA-545 II until I have them both working right.
Isn't that something? The amp that was once broken has nearly perfect operation and better than the other one that wasn't "bad."
Take that previous owner! Take that!
On switching on the previously broken GFA-565, the offset is 670mV, after 30 minutes of listening, it is around 5-7mV.
Does it usually take half an hour to settle down?
Does it usually take half an hour to settle down?
MJR: Nice job.. these guys all helped me with my Threshold.. and still are.. they were WAY easier on you though 🙂 hehehe.. tough group but they are smart so I cut em some slack..
Isn't it a great feeling of accimplishment to wake up a dead amp? I am having a blast!
Isn't it a great feeling of accimplishment to wake up a dead amp? I am having a blast!
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