Issues with Adcom GFA-545

Hello all,

I am fairly new here and a very amateur tinkler, so please be nice, I need help. Here is my issue: My GFA-545 is in perfect cosmetically and sonically for the most part. The inside is spotless without a single sign of any cap leakage, or burn out. The fuses are all original and have never been tripped. It is mint looking, and sounding. The off-sets are .5 on both channels, and the bias are perfect as well. So here is my worrisome issue: when I shut the amp off, there is a short winding sound for about 2 seconds. Any ideas?

Thanks,

Carlos:)
 
Hello cayovelez, it the sound you are hearing upon turning off the amp a new sound, or has it done this since you got it. If it's been doing it since you bought it, then it's most likely just the Electrolytic Caps in the power supply discharging after power is disconnected. If it's something fairly recent, then you do have a failing component(s), most likely a cap(s) somewhere.

I know that the Adcom GFA-6000 I own would make a staticy whining noise when I powered it off, and it did this since I bought it when it was about 3 months old. Any amp that doesn't have a relay to disconnect the speaker from the amp when the power is shut off can do this. And the larger the capacity of the cap, then the more likely it will do this, and the longer the noise may last.

Peace,

Dave Gerecke
 
The issue never happened with the amp on its own, there are no weird sound on its own at all, however when I pair it to my gfa-555mkii for bi-amping is when it happens. I have tried 2 different pre-amps an adcom gfp555mkii and a conrad johnson pf-1. Both amps sound fantastic, and their offset are around .5. When I shut the 555 no issues, only when I shut the 545 that I get the weird wind down like noise only in my upper Panels that it amps. I tried both amps on their own, and no issues at all what o ever. What gives?
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi cayovelez,
Dave is right on most counts there. Most amplifiers that do not disconnect the speakers when turning off or on will become unstable and make some kinds of noises.

These amplifiers have issues where some capacitors can leak - a defect in the original parts. The electrolyte is not visible to the naked eye, and it's extremely corrosive. If your amp is truly untouched, get it into a really good audio technician for repair right away! This tech will probably not repair TVs / VCRs / Microwaves - just audio. They will also be older, past 40 for sure. You may find this person working out of home, rather than in a service shop these days.

If they are dried out, how come the amp sound great otherwise, and the DC offsets are right up to specs? I don't understand.
Because djk is an experienced technician and you are not. Defective capacitors still have some capacitance, and this should not affect the DC offset anyway. The readings you get would then depend on whether the amp is oscillating or not, and how your meter reacts to high frequency AC on a DC scale.

Are your DC offsets 0.5 mV or 0.5 V? What is the bias current sitting at, how and when did you measure them? What meter did you use, and are you aware of the accuracy of that range and whether it's ever been calibrated or not?

I'm not trying to be hard on you, just explaining some things that are important that I don't think you are aware of. When you are measuring in the mV range, the quality of the meter you use becomes important, as is your understanding of whether the LSD means anything or not. With a cheap 3 1/2 digit meter, the last digit is often pure fiction. Is that 0.5 really 0.9, 0.1, 1.3 mV? When measuring 1.9000 VDC, a reading of 1.98 may be in tolerance for some meters. Imagine one of these that is out of tolerance and was never checked or calibrated! Just because you have 3 1/2 digits does not mean they are significant.

-Chris
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi cayovelez,
What is the resistance between the input jack grounds to the chassis, to each other? I don't have this schematic, so I can't say. Other models used a 100 R resistor between signal common and the high current ground. Other amplifiers have the ground connection continuous between signal and output stage / power supply common.

The issue never happened with the amp on its own
Okay, so now you know the issue is not with the amp itself - right?

Are you using an electronic crossover? Doesn't sound like it. Are there any common connections between the woofer and high frequency speakers (dangerous)? Are these amps both plugged into the same power bar or outlet?

Remember that the chassis of each amp are connected to AC ground in your house, and also the grounds between RCA shells are connected. That's a ground loop, and probably the cause of your problems. You may have to modify the chassis ground to circuit common connection in order to break that loop. Do not run the system with an AC ground interrupted!

-Chris
 
Anatech, Thanks for your comment. My meter is a good old trusty Simpson 461 freshly calibrated, a buddy of my that works for the air force as an electronics tech calibrates it for me often. My dc offsets on my 545 is .5mV on one channel and .7mV on the other, both freshly turned on and after a while on. The bias are very close to spec considering it's age, the channel with .5mV the bias is 10.2mV and the one with .7mV was 11.4mV. So I adjusted both of them to spec after some warm up and kept on re-checking them and after 5 plus hours of warming up and playing tunes the bias kept at 10mV. The next day I checked again my DC offset and the same, and the Bias was steady at 10mV. The noise only come on when I bi-amp running the 545 for ESP and the 555 for the lower. Each amp on their own sounds fantastic, the 545 only acts up when bi-amping.
 
Hello Carlos, Don't feel stupid about grounding issues. They are actually some of the most common, and also difficult problems to work on. Many people, including experienced EE's, get tripped up by ground loops.

Peace,

Dave

P.S. Any info from Anatech is worth it's weight in gold. From reading a little of his bio, scattered throughout diyaudio.com, he's got an incredible amount of hands on experience with just audio equipment.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi cayovelez,
Thank you, I'm really happy you sorted this out. Your experience will provide direction for many others having similar issues. Dave's right, grounding problems are hard to sort out sometimes.

Hi Dave,
Now you're making me blush. My experience only means I've suffered - much. :)

-Chris
 
Hello Carlos, the power conditioner isn't going to hurt things any, at least not in a general sense, but when it comes to grounding, all the fancy technology in the world won't fix a ground issue. It really takes some knowledge, thought, and some of the more basic technology out there to solve grounding problems.
Ground issues are why most pro audio systems use balanced systems, with transformers. Balanced audio helps solve some ground and hum issues, and having a transformer on the input helps break ground loops, since the primary and secondary of the transformer are isolated. But even these two things don't fix everything. Sometimes it's as simple as having patch cords that have the ground connected at the sending device, and not connected at the receiving device. And sometimes that can be more harm than good. No two situations with ground issues are ever quite the same. Just look around at some of the comments from people like anatech, Nelson Pass, and John Curl, among many here. They have all been through the ringer with ground issues.

Peace,

Dave

P.S. Chris(anatech) no blushing necessary, I have an associates in EET and I have still been reminded of things I forgot, and learned new things from your writings. Knowledge learned from experience (i.e. doing it wrong) is the most valuable. I can introduce you to people with PhD's in EE that I wouldn't trust near the circuits you understand.
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Dave, Carlos,
I disagree with the statements that power line conditioners will not cause any problems. First, it depends on what the line conditioner does to achieve it's published goals. When considering a power amplifier, you need to have as little impedance in the AC mains feed as is reasonably possible. That eliminates the use of filters, sine wave regeneration (especially!) and center tapped AC balancing schemes. Constant voltage type transformers also do things to the AC waveform that make it normally unsuitable for audio use.

Most everyone will have a story about someone else who solved all their problems with a pet product, but those are the exceptions I think.

In general, use good sockets and direct lines to your power mains if possible. Nothing else goes in line between any higher powered amplifier and it's AC power source. Any type of power regeneration system would be about the worst thing you could use. Variable frequencies out to the amplifier power makes this even more problematic.

For signal source type equipment (preamps, tuners, CD players ...), a power line conditioner can certainly help. My preference would run to line filters with over-voltage protection. A really good AC filter, implying larger chokes, might be what you are looking for. Many years ago, Adcom sold something called an ACE-515 (?) for that purpose. This worked very well, and I'm pretty sure there are others that are as good or better. Once the noise and spikes have been attenuated, you have gone as far as what I would think as reasonable unless there are abnormal circumstances in your area.

One very important point to remember is that the power supply that was designed inside your products (amplifiers, pre-amplifiers or whatever) is supposed to isolate the internal power supply voltages from the outside world. If a power conditioner makes a difference for real, I strongly suspect the equipment was not designed well, or you have a special situation in your area. Believe me when I say that finding substandard power supplies in equipment is the normal situation. Oddly enough, most decent mass market brands do a far better job in power supply design than "higher end products" on average. That may come down to larger companies having larger R&D budgets with more classically trained engineers on staff.

The last point that should be repeated is that if you supply any extra power line feeds to your audio system, make very sure they are on the same phase of your mains supplies. Most North American homes are supplied two circuits out of phase. Between these two hot terminals, you have the familiar 208 VAC for your electric stove and clothes dryer. Each supply phase should be around 120 VAC to ground, called common. The other safety ground is not intended to carry any current (GFIs sense this as a fault condition and trip). This is where the ground pins on three wire AC plugs connect to.

-Chris
 
Hello Chris, once again you demonstrate why I said what I did about your input. You brought up issues I hadn't thought about. The logic is there, and makes sense.

I do remember the power line conditioner from Adcom you refer to, I believe that it was the ACE-515. Occasionally they show up on ebay, but if they are still effective after years of use, I can't say. I don't know how much age and usage effects the components inside, or what they use for conditioning. I personally only have a signal conditioner on the Preamp, etc. The power amps just go through a surge protector.

In regards to the AC incoming, if I remember things correctly, on conventional house wiring, there are two 120 volt legs, 180 degrees out of phase, thus providing the 240 volts for appliances. This is done by grounding the center tap on the secondary of the step down transformer from the power company. If you tap between the one of the "hot" leads and the neutral line in the breaker box, you get 120 volts. If you connect between the two 120 volt legs, you get 240 volts. (Remember that I said neutral, and not safety ground. The safety ground should have no current on it, unless there's a fault, then the fuse should blow).
If you are getting 208 vac, that indicates a three phase system, as the 120 volt signals are 120 degrees out of phase with each other. It's be a long time, but if you do the math of the voltages times the phase angle you get 208 volts.

I also agree one should be careful with which leg of the 120 volts you use, for different reasons. From the stand point of the audio system, you would be better served to hook everything between the Neutral and one 120 volt leg. From the stand point of power balancing (the power companies desire) you would be better to balance the load between the two legs.

One thing that I am curious about, with Carlos specific issue, he only has the strange noise upon power down when he has the amps hooked up to Bi-Amp his speakers. This might indicate a ground loop on the outputs of the power amps, which would indicate the possibility of the negative terminals on the input of the speaker crossover being hooked together. I would think it would be best if when in Bi-Amp setup, the hi pass and low pass crossover sections were completely separated.

Peace,

Dave
 
Wayward Adcom GFA-545: What's all the buzz about

Hey guys. I am very new to DYI, and new with regards to mods, repairs, etc. In fact, I don't have any real formal electronics repair training, so this line of questioning is more for educational purposes, than for me actually trying any repairs myself. I saw this thread and thought it would be a great place to get some help with my particular problem. And please forgive my crude non technical terminology
icon_e_smile.gif
As a pro bassist by trade, I have built bass guitars, electronics and all. But the most complex thing I've done with audio gear is upgrade rca inputs and binding posts. Lol. Like I said...REAL new.

Anyway, I just acquired a GFA-545 (the first series, not the mkII) that is very pristine inside and out, like it was tucked away in an AV install. But when I hooked it up, there was slight distortion coming from the speakers, particularly the left side. The audio signal comes thru as it should, and no front panel lights are indicating any problems, yet the sound has a fuzzy quality to it. I already own two 535 II’s so I am quite familiar with the sound of this series of Adcom amps, and would like to benefit from the extra power of the 545.

I'm not looking for a super mod. I just want to replace (or have replaced) the most likely culprit(s) of the problem. I really have enjoyed reading this thread, and it has given me some great insight on how this whole mod world works. But frankly, at this point a lot of this stuff is above my pay grade. If I tackle this myself, where should I start? I’m not looking to fry a perfectly good amp, and if I get someone to do the work, I’d like to know what they are telling me needs to be done.

If it's any help, I did start out by replacing all the fuses, and measuring the bias at the speaker terminals. Left and right channels were 5.6mV and 5.5mV respectively. Close to spec, I think.

So what’s next?