I am using an Adcom GFP-565 preamp and a modified GFA-545 mk II amplifier. I also have another matching GFA-545 mk II as well as a GFA-535 mk II amp. The 545 amps are modified by altering the negative feedback with a series resistor and bypass capacitor, and running the bias hotter at around 12mV across the emitter resistor instead of the factory 7 mV. This requires monitoring the output transistors with a infrared thermometer making sure the transistors do not exceed 45 degrees C, or 113 degrees F of the hottest one on that channel. Check after 30 minutes minimum idle time. I was running 16mV but ran into thermal runaway in the summer time, so I backed it down to 12mV. This mod was recommended by Nelson Pass who designed these as a sonic improvement. This is what I am using for my high end setup.
I have just repaired this GFP-555 model and I am amazed on how good it sounds, it rivals my APT Holman preamp modified by me with Analog Device IC, I had to change a phono IC which is labeled as 5E, Adcom mark the IC's in order to hide what they use but I did a research and the original 5E should be a Burr Brown OP27 which can handle 21.5 volts but I put a NE5534 and can handle 21.5 also and is working fine
I have the GFP565 bought it second hand it is still performing very good, also bought new old stock of GFA555 mk2. It was stored in the original box never opend for more then 25 years, it perform flowessly, i have checked first the bias and dc offcet was good 👍. This is very good stereo system that outperforms many new stuff that sold this days
I followed your repair work on the GFP-555. Thank you!. Very helpful. Fuses are all OK. power on indicator light is working. Circuit board traces all look OK. I had no 21 + or 21 - voltages at the two test points you pointed out. The relay is also not functioning. I'm wondering if the next logical step is to replace the relay? Any input would be appreciated. Thank you. R.E.McD
@@VintageAudioFan I did find a source for the relay which is good because I could replace that for sure, however I've since determined that the relay has no DC voltage on its coil, so that is probably the issue and not a bad relay. It seems like I have AC power up to the rectifier, but nothing after that on the DC side. I'm having a bit of trouble finding where the relay is in the circuit. It seems like they show the relay and rectifier as one big block of circuitry. I can read schematics and have good mechanical and soldering skills, but I'm afraid diagnosing where the breakdown is in the power supply section may be beyond my skill level. Do you still have a repair service by any chance?
If there is no voltage on relay, it seems the problem is in the power supply based on your descriptions. I suggest to check the bridge rectifier W02/PB153M and voltage regulator power transistors Q901 (2SB633) and Q902 (2SD613). These components are the most suspicious area for the the cause of power supply malfunctions.
Happy to find this video, as I recently pulled my Adcom GFP-555 and GFA-535 out of storage. The were in a closet for 20 years! In any event, I finally have the space to be able to use them, and hooked them up to run my iTunes library through a pair of ELAC UB-5s. The sound is quite good, but unfortunately, I am getting a more frequent intermittent loss of 80% of one channel, accompanied, at times by static and crackle. It plays fine in Mono though, and I've traced the problem back to the Line Out on the Pre-Amp (both the Normal and Lab outputs; the problem also displays on headphones). At this age, I would not be surprised if a solder joint may be loose, but I don't have the courage or confidence to open it up. Any ideas, VAF (or any readers)???
It sounds like the issue is either in the relay (RY901), mono switch or solder joints. However, I suggest checking or replacing the relay first. Because these relays tend to built up the residue on their contact surfaces due to the age. Specially, when you stored it for a long period of time. If the problem persists after replacing the relay, then I suggest check the mono switch and the solder joints. Thanks for the comments and let me know if it works.
@@VintageAudioFan Thanks very much for you response. I wish I had the expertise to tackle the problem! I think your overall premise is correct though - the years of disuse have created the need for a good cleaning, and testing, starting with the points you mentioned. If I can find a reputable tech to work on it, that should be my next step, otherwise look for one on the used market, as I do like the sound
I like your workaround. I have the exact same problem on my GFP-555. Patching around the Signal in and out Processors worked for me, as well. However, these connections are designed to put an equalizer in place. They come after the selector circuit, but before the tone control circuit. This means none of the tone controls works. Where should I start looking to find out where the fault is, so I can restore the units original functionality?
Does the unit has the outputs when you switch off the Tone-In control? If the tone control is not working but you still have outputs from the pre-out, then you have a defective tone control circuit which is powered by an IC (NJM2041DD). You can try replacing it. But before you do that, I also suggest you to check the contact of Tone-In switch, cold joints at underside of PC board and all the wire soldering joints. It will be more efficient by using a signal generator and oscilloscope to trace the signal path. You can also check out my other videos for troubleshooting procedure.
Dear sir I am watching your videos I like them how you trace faults in electronics Can pls suggest as I have bought an old Yamaha C4 preamp it is working properly can pls suggest how much it is important to recap the unit as it's quite vintage Pls share any video of recapping of preamp in future if you get one Regards Guru
Definitely, it will improve the sound quality and extend the expectancy of good performance of C-4 preamp. Currently, I am working on a repair of Marantz 2230 receiver which I need to recap the power amplifier due to the deteriorate capacitors. I will publish it as soon as it is completed. Thanks.
I have a Adcom GFP 565. When I plug the headphones into the jack, the speakers will not shunt (turn off). The sound comes out of the speakers and headphones.
GFT 565 is a preampifier which is separate from the power amplifier (connected to the speakers). The use of headphone is designed for monitoring the sound output of the preamplifier. So plug into to the headphone jack of DFP 565 has nothing to do with the speakers.
Hello I have the adcom gtp400 with the tuner. Iv had if for 30years. I also have the 555ll amp with a pair if heresy ll speakers. My system sounds great. I had the adcom 6 carousel cd player but not anymore. I just play music from my phone...mp3 and flac files. Maybe you can help me? I wanted to get a Dac for my adcom and not sure what to get. I just want a great dac to make my mp3 and other music files to sound better but do not know what to get. Can I get a dac and still keep my gtp400? Do I get a dac that plugs into my gtp400? Maybe you can help me in the right direction with some links on amazon...show me some good dacs that I can choose that i would be able to add to what I have. I know there are Dac players like phones that do it...is that the way to go? Should I have a dac..maybe a blue tooth one that is always hooked up at home plus I was also planning on getting one of the dac mp3 players...can I use both? I will eventually get a single cd player but for now I just play mp3 and flac files and also stream on RUclips. Any help you can give me on dac and how I would hook to my gtp400 would be much appreciated. I could spend up to $500 max on this addition.
Yes. You can keep your GTP400 and use it's Aux input connecting to DAC's RCA output jacks. I'll recommend the Schiit Modi 3 DAC for the beginner - see attached link for more information: ruclips.net/video/ih0EqxsTBq8/видео.html
@@VintageAudioFan and your opinion is that that schiit Dac makes the sound of mp3 files...digital files sound better? You can hear the difference easily?
@@VintageAudioFan If he can get a GCD-750 which have a input to use internal DAC to decode an external source and maintain his ADCOM gears would be great
![Noob To Max With DRAGON REWORK In Blox Fruits [FULL MOVIE]](http://i.ytimg.com/vi/LnBMOinoOvA/mqdefault.jpg)
Never gave much respect to Adcom but your video has opened my eyes !
Great video !!
Adcom is surprisingly good stuff, not to be underestimated.
I am using an Adcom GFP-565 preamp and a modified GFA-545 mk II amplifier. I also have another matching GFA-545 mk II as well as a GFA-535 mk II amp. The 545 amps are modified by altering the negative feedback with a series resistor and bypass capacitor, and running the bias hotter at around 12mV across the emitter resistor instead of the factory 7 mV. This requires monitoring the output transistors with a infrared thermometer making sure the transistors do not exceed 45 degrees C, or 113 degrees F of the hottest one on that channel. Check after 30 minutes minimum idle time. I was running 16mV but ran into thermal runaway in the summer time, so I backed it down to 12mV. This mod was recommended by Nelson Pass who designed these as a sonic improvement. This is what I am using for my high end setup.
I liked your video and I greatly respect your methodical approach!
I have just repaired this GFP-555 model and I am amazed on how good it sounds, it rivals my APT Holman preamp modified by me with Analog Device IC, I had to change a phono IC which is labeled as 5E, Adcom mark the IC's in order to hide what they use but I did a research and the original 5E should be a Burr Brown OP27 which can handle 21.5 volts but I put a NE5534 and can handle 21.5 also and is working fine
I have the GFP565 bought it second hand it is still performing very good, also bought new old stock of GFA555 mk2. It was stored in the original box never opend for more then 25 years, it perform flowessly, i have checked first the bias and dc offcet was good 👍. This is very good stereo system that outperforms many new stuff that sold this days
Thanks for your sharing.
Thanks for sharing, great video.
The little factory signal processor loop jumpers were missing. Easy fix! 🤘
I followed your repair work on the GFP-555. Thank you!. Very helpful. Fuses are all OK. power on indicator light is working. Circuit board traces all look OK. I had no 21 + or 21 - voltages at the two test points you pointed out. The relay is also not functioning. I'm wondering if the next logical step is to replace the relay? Any input would be appreciated. Thank you. R.E.McD
A defective relay will significantly impair the output sound quality of amplifier. I suggest to find a new relay to replace it.
@@VintageAudioFan I did find a source for the relay which is good because I could replace that for sure, however I've since determined that the relay has no DC voltage on its coil, so that is probably the issue and not a bad relay. It seems like I have AC power up to the rectifier, but nothing after that on the DC side. I'm having a bit of trouble finding where the relay is in the circuit. It seems like they show the relay and rectifier as one big block of circuitry. I can read schematics and have good mechanical and soldering skills, but I'm afraid diagnosing where the breakdown is in the power supply section may be beyond my skill level. Do you still have a repair service by any chance?
If there is no voltage on relay, it seems the problem is in the power supply based on your descriptions. I suggest to check the bridge rectifier W02/PB153M and voltage regulator power transistors Q901 (2SB633) and Q902 (2SD613). These components are the most suspicious area for the the cause of power supply malfunctions.
Anyone know the first track at 1:30? Sounds like Pat Metheny....
Happy to find this video, as I recently pulled my Adcom GFP-555 and GFA-535 out of storage. The were in a closet for 20 years!
In any event, I finally have the space to be able to use them, and hooked them up to run my iTunes library through a pair of ELAC UB-5s. The sound is quite good, but unfortunately, I am getting a more frequent intermittent loss of 80% of one channel, accompanied, at times by static and crackle. It plays fine in Mono though, and I've traced the problem back to the Line Out on the Pre-Amp (both the Normal and Lab outputs; the problem also displays on headphones). At this age, I would not be surprised if a solder joint may be loose, but I don't have the courage or confidence to open it up. Any ideas, VAF (or any readers)???
It sounds like the issue is either in the relay (RY901), mono switch or solder joints. However, I suggest checking or replacing the relay first. Because these relays tend to built up the residue on their contact surfaces due to the age. Specially, when you stored it for a long period of time. If the problem persists after replacing the relay, then I suggest check the mono switch and the solder joints. Thanks for the comments and let me know if it works.
@@VintageAudioFan Thanks very much for you response. I wish I had the expertise to tackle the problem! I think your overall premise is correct though - the years of disuse have created the need for a good cleaning, and testing, starting with the points you mentioned. If I can find a reputable tech to work on it, that should be my next step, otherwise look for one on the used market, as I do like the sound
I like your workaround. I have the exact same problem on my GFP-555. Patching around the Signal in and out Processors worked for me, as well. However, these connections are designed to put an equalizer in place. They come after the selector circuit, but before the tone control circuit. This means none of the tone controls works. Where should I start looking to find out where the fault is, so I can restore the units original functionality?
Does the unit has the outputs when you switch off the Tone-In control? If the tone control is not working but you still have outputs from the pre-out, then you have a defective tone control circuit which is powered by an IC (NJM2041DD). You can try replacing it. But before you do that, I also suggest you to check the contact of Tone-In switch, cold joints at underside of PC board and all the wire soldering joints. It will be more efficient by using a signal generator and oscilloscope to trace the signal path. You can also check out my other videos for troubleshooting procedure.
i need your help please i have adcom gfp 565 it the relays shut down after some miunutes
Please send your inquires to my email. The email address is listed under "Above" in my RUclips home page.
Dear sir
I am watching your videos I like them how you trace faults in electronics
Can pls suggest as I have bought an old Yamaha C4 preamp it is working properly can pls suggest how much it is important to recap the unit as it's quite vintage
Pls share any video of recapping of preamp in future if you get one
Regards
Guru
Definitely, it will improve the sound quality and extend the expectancy of good performance of C-4 preamp. Currently, I am working on a repair of Marantz 2230 receiver which I need to recap the power amplifier due to the deteriorate capacitors. I will publish it as soon as it is completed. Thanks.
I have a Adcom GFP 565. When I plug the headphones into the jack, the speakers will not shunt (turn off). The sound comes out of the speakers and headphones.
GFT 565 is a preampifier which is separate from the power amplifier (connected to the speakers). The use of headphone is designed for monitoring the sound output of the preamplifier. So plug into to the headphone jack of DFP 565 has nothing to do with the speakers.
Hello
I have the adcom gtp400 with the tuner. Iv had if for 30years.
I also have the 555ll amp with a pair if heresy ll speakers. My system sounds great.
I had the adcom 6 carousel cd player but not anymore.
I just play music from my phone...mp3 and flac files.
Maybe you can help me?
I wanted to get a Dac for my adcom and not sure what to get. I just want a great dac to make my mp3 and other music files to sound better but do not know what to get. Can I get a dac and still keep my gtp400? Do I get a dac that plugs into my gtp400? Maybe you can help me in the right direction with some links on amazon...show me some good dacs that I can choose that i would be able to add to what I have. I know there are Dac players like phones that do it...is that the way to go? Should I have a dac..maybe a blue tooth one that is always hooked up at home plus I was also planning on getting one of the dac mp3 players...can I use both?
I will eventually get a single cd player but for now I just play mp3 and flac files and also stream on RUclips. Any help you can give me on dac and how I would hook to my gtp400 would be much appreciated. I could spend up to $500 max on this addition.
Yes. You can keep your GTP400 and use it's Aux input connecting to DAC's RCA output jacks. I'll recommend the Schiit Modi 3 DAC for the beginner - see attached link for more information: ruclips.net/video/ih0EqxsTBq8/видео.html
@@VintageAudioFan and your opinion is that that schiit Dac makes the sound of mp3 files...digital files sound better? You can hear the difference easily?
@@VintageAudioFan If he can get a GCD-750 which have a input to use internal DAC to decode an external source and maintain his ADCOM gears would be great
Great Music, Dave Brubeck. After great successful repair. Good sounding, but not as nice as the NAD sound.