This forum is always so helpful, I have a question. I have a friend who just bought a pair of Polk Audio SDA-SRS 2.3tl's. These are the speakers that have a cable running between them that cancel out interaural cross talk. So a signal from the left speaker is sent to the right and vice versa. With the cable provided the power amp connected can only be a common ground amp. He is going to use an ADCOM GFA-5800 to power them. He is being told that it is a NON-COMMON Ground amp and that he will damage the speakers.
Maybe someone can explain how the Adcom 5800 series is Non-common ground, becasue I thought only true mono-blocks or possible dual-mono (in 1 chassis) were the only Non-common ground designs. What makes the 5800 a non-common ground amplifier?
Thanks
Brock
Maybe someone can explain how the Adcom 5800 series is Non-common ground, becasue I thought only true mono-blocks or possible dual-mono (in 1 chassis) were the only Non-common ground designs. What makes the 5800 a non-common ground amplifier?
Thanks
Brock
Hi Heiney9,
A stereo amplifier can easily have a non-common ground by having seperate power supplies for the two amplifier channels, so everything LEFT is referenced to the ground for the LEFT channel which appears at the outside ring of the input RCA and the black speaker post. The RIGHT channel will reference to it's power supply and appear at it's in/out terminals likewise. The two MAY share a common transformer but with duplicate secondary windings.
Cheers,
Greg
A stereo amplifier can easily have a non-common ground by having seperate power supplies for the two amplifier channels, so everything LEFT is referenced to the ground for the LEFT channel which appears at the outside ring of the input RCA and the black speaker post. The RIGHT channel will reference to it's power supply and appear at it's in/out terminals likewise. The two MAY share a common transformer but with duplicate secondary windings.
Cheers,
Greg
Hi Heiney9,
The GFA-5800 is not bridged. Each channel is referenced to ground with a 100R resistor. Measure between the two negative speaker terminals and make sure you read about 200 ohms. If not, fix this.
To use these speakers you will need to short the two negative terminals together. Then enjoy the music. You may have some additional back ground noise by defeating the resistive connection between channels but it shouldn't be serious.
-Chris
The GFA-5800 is not bridged. Each channel is referenced to ground with a 100R resistor. Measure between the two negative speaker terminals and make sure you read about 200 ohms. If not, fix this.
To use these speakers you will need to short the two negative terminals together. Then enjoy the music. You may have some additional back ground noise by defeating the resistive connection between channels but it shouldn't be serious.
-Chris
Chris,
I think his issue is more the output ground , not input ground (which as you correctly point out is 100R). Question is, can he tie the 2 grounds of the speaker posts?
I know I have run loads of either ground (channel a and channel b while the hot side in both cases was channel a) on a GFA-5802 (300wpc also single Toroid) with no issues but that was testing. Not sure I can state he will be fine long term. If I were to take a guess, I'd say he will be ok because the SDA's are connected together via 2 huge coils with DCR or 2 ohms each. So in series, they will present a 4 ohm load to tie the grounds which in my opinion will have little or no effect of the GFA's pseudo ground (i.e. 2 secondaries one for each channel). I think he can use the 5800 with the 2.3tl.
What do you think?
I think his issue is more the output ground , not input ground (which as you correctly point out is 100R). Question is, can he tie the 2 grounds of the speaker posts?
I know I have run loads of either ground (channel a and channel b while the hot side in both cases was channel a) on a GFA-5802 (300wpc also single Toroid) with no issues but that was testing. Not sure I can state he will be fine long term. If I were to take a guess, I'd say he will be ok because the SDA's are connected together via 2 huge coils with DCR or 2 ohms each. So in series, they will present a 4 ohm load to tie the grounds which in my opinion will have little or no effect of the GFA's pseudo ground (i.e. 2 secondaries one for each channel). I think he can use the 5800 with the 2.3tl.
What do you think?
Hi Arif,
No, in this amp, the channel grounds are referenced independently to chassis ground through a 100 ohm resistor each. If the amp is run into the Polk's without shorting the two ground terminals, Brock's friend may burn out the two 100 ohm resistors.
There is but one transformer with independent windings supplying power to each channel. Each amp is treated as if it's a mono block. If you look at the schematic, it shows the main ground for each channel connected to chassis ground through this 100 ohm resistor. Neat idea eh (Canadian)?
I didn't even have to look for the input ground. The inputs are referenced to the channel ground first.
-Chris
No, in this amp, the channel grounds are referenced independently to chassis ground through a 100 ohm resistor each. If the amp is run into the Polk's without shorting the two ground terminals, Brock's friend may burn out the two 100 ohm resistors.
There is but one transformer with independent windings supplying power to each channel. Each amp is treated as if it's a mono block. If you look at the schematic, it shows the main ground for each channel connected to chassis ground through this 100 ohm resistor. Neat idea eh (Canadian)?
I didn't even have to look for the input ground. The inputs are referenced to the channel ground first.
-Chris
Hi Arif,
No. The chassis will then be 50 ohms away from the circuits instead of 100 ohms. Each amplifier will now have a short ground to ground to the other. This is what we want for these speakers. Better use something greater than 22 GA here.
There is no normal reason for the output currents to flow into the chassis ground, they are returned to the power supplies.
-Chris
No. The chassis will then be 50 ohms away from the circuits instead of 100 ohms. Each amplifier will now have a short ground to ground to the other. This is what we want for these speakers. Better use something greater than 22 GA here.
There is no normal reason for the output currents to flow into the chassis ground, they are returned to the power supplies.
-Chris
Thanks very much for the responses. For some reason I'm not getting e-mail notifications when someone replies to a thread I'm subscribed to 
.
I'm pretty sure I understand now how an amp with secondary windings can actually not have a common ground.
Hi Chris we've corresponded before about a Nak SR-3A problem, as always you are knowledgeable and helpful. Also, K-amps you've been helpful in the past as well. I'm not a tech and though I do understand some electronics theory, I don't know my around the insides of units. It's also been along time since I could read and interpret a schematic.
I have another question I need some input/opinion. It's about Adcom which I know you 2 are familiar with. I've owned a GFA-545 since new in about 86-87. I use it pretty much daily and it's now getiing to be almost 20 years old. It seems in the past the unit ran warm, I could always feel a little heat (nothing excessive) coming from the unit, which is normal. Lately I've noticed that the amp is a bit lean in the sound it puts out and doesn't seem to have the oomph it once had. This is very slight, but since I've owned the sytem for 18 years I can notice subtle differences pretty quickly. The unit doesn't seem to put out any heat at all anymore. I can reach under the chassis and feel the heat sinks and they are almost ice cold. I'm thinking maybe a bias issue?
Is it typical to take these in at this age and have it cheked to make sure everything is in spec? Is it possible it needs to be refreshed and will it make it sound better? This may all be my imagination, but something just seems off with my system and I find it odd that the amp once ran warm and now seems to run very cold.
Any opinions or advice or stories about what could cause this would be appreciated. I heistate to take it to the local repair shop because the guy there has no manners and is not willing to even discuss what could be wrong and possible fixes. You basically drop it off tell him what's wrong and he tells you what it costs and he'll be in touch. I'm sure he can do the work properly, but then again since he's not very social it's hard to get a good read on him.
TIA
Brock
.I'm pretty sure I understand now how an amp with secondary windings can actually not have a common ground.
Hi Chris we've corresponded before about a Nak SR-3A problem, as always you are knowledgeable and helpful. Also, K-amps you've been helpful in the past as well. I'm not a tech and though I do understand some electronics theory, I don't know my around the insides of units. It's also been along time since I could read and interpret a schematic.
I have another question I need some input/opinion. It's about Adcom which I know you 2 are familiar with. I've owned a GFA-545 since new in about 86-87. I use it pretty much daily and it's now getiing to be almost 20 years old. It seems in the past the unit ran warm, I could always feel a little heat (nothing excessive) coming from the unit, which is normal. Lately I've noticed that the amp is a bit lean in the sound it puts out and doesn't seem to have the oomph it once had. This is very slight, but since I've owned the sytem for 18 years I can notice subtle differences pretty quickly. The unit doesn't seem to put out any heat at all anymore. I can reach under the chassis and feel the heat sinks and they are almost ice cold. I'm thinking maybe a bias issue?
Is it typical to take these in at this age and have it cheked to make sure everything is in spec? Is it possible it needs to be refreshed and will it make it sound better? This may all be my imagination, but something just seems off with my system and I find it odd that the amp once ran warm and now seems to run very cold.
Any opinions or advice or stories about what could cause this would be appreciated. I heistate to take it to the local repair shop because the guy there has no manners and is not willing to even discuss what could be wrong and possible fixes. You basically drop it off tell him what's wrong and he tells you what it costs and he'll be in touch. I'm sure he can do the work properly, but then again since he's not very social it's hard to get a good read on him.
TIA
Brock
Hi Brock,
I am in agreement with Arif. Also coupling caps. There may be a problem since the bias current shouldn't change that much over time.
As far as your local service guy is concerned, I would need to know he's competent before I would put up with the attitude. I don't believe this fella is interested in anything more than making it "go". You need to find someone who enjoys amps and music as a technician.
-Chris
I am in agreement with Arif. Also coupling caps. There may be a problem since the bias current shouldn't change that much over time.
As far as your local service guy is concerned, I would need to know he's competent before I would put up with the attitude. I don't believe this fella is interested in anything more than making it "go". You need to find someone who enjoys amps and music as a technician.
-Chris
Agree with Chris,
You dont necessarily need a techchie, just someone who loves this type of stuff. Chris, I do not remember the older 545 having couplling caps, thats why in today's world, some of the older Adcoms sound better than the Mk.II's because the Mk.II's have caps that may be drying up or weakening or whatever.
You dont necessarily need a techchie, just someone who loves this type of stuff. Chris, I do not remember the older 545 having couplling caps, thats why in today's world, some of the older Adcoms sound better than the Mk.II's because the Mk.II's have caps that may be drying up or weakening or whatever.
Thanks for the quick responses...seems the e-mail notification is working again.
K-amps I live in Illinois about an hour west of Downtown Chicago.
Chris, I agree with trying to find a tech that actually cares about what he is doing. This guy may actually be pretty good, but his attitude is so bad. He's been in business a very long time and says he specializes in vintage audio restoration. He won't even look at anything unless it cost $150 or more new. I don't blame him for not wanting to repair some of the low-budget crap out there today. If it's crap to begin with he will send you on your way.
The key IS finding someone you can trust to do the repair and make some suggestions about maybe tweaking things a bit or discussing things like weakness in an original design or perhaps soemthing that is commonly done to improve this or that. That's why having a running discussion with him about his experiences would help me better understand and have more confidence in what he is doing.
My brother bought an Adcom Gcd-575 (cd player) off e-bay for a 2nd system. When it arrived it skipped on many cd's, so the seller agreed to pay for 1/2 the repair bill. My brother took it to the above guy (only place in town) who had repaired several of them in the past. He cleaned it re-aligned, reset the laser assembly. The cost about $70. The unit still skips occasionally, though much better than it was. However, my brother has it sitting in a closet because he doesn't want to use it and he won't resell it with the issues it has.
Not exactly a ringing endorsement. My brother should have taken it back to have it repaired again....but he never did (his own fault).
I could send my amp back to Adcom for repair, but I've heard that it is very expensive and I hate sending stuff in the mail if I can avoid it..too many horror stories. Anybody have any recommendations about a good repair shop....Geez I'm rambling
Brock
K-amps I live in Illinois about an hour west of Downtown Chicago.
Chris, I agree with trying to find a tech that actually cares about what he is doing. This guy may actually be pretty good, but his attitude is so bad. He's been in business a very long time and says he specializes in vintage audio restoration. He won't even look at anything unless it cost $150 or more new. I don't blame him for not wanting to repair some of the low-budget crap out there today. If it's crap to begin with he will send you on your way.
The key IS finding someone you can trust to do the repair and make some suggestions about maybe tweaking things a bit or discussing things like weakness in an original design or perhaps soemthing that is commonly done to improve this or that. That's why having a running discussion with him about his experiences would help me better understand and have more confidence in what he is doing.
My brother bought an Adcom Gcd-575 (cd player) off e-bay for a 2nd system. When it arrived it skipped on many cd's, so the seller agreed to pay for 1/2 the repair bill. My brother took it to the above guy (only place in town) who had repaired several of them in the past. He cleaned it re-aligned, reset the laser assembly. The cost about $70. The unit still skips occasionally, though much better than it was. However, my brother has it sitting in a closet because he doesn't want to use it and he won't resell it with the issues it has.
Not exactly a ringing endorsement. My brother should have taken it back to have it repaired again....but he never did (his own fault).
I could send my amp back to Adcom for repair, but I've heard that it is very expensive and I hate sending stuff in the mail if I can avoid it..too many horror stories. Anybody have any recommendations about a good repair shop....Geez I'm rambling
Brock
K-amps said:Agree with Chris,
You dont necessarily need a techchie, just someone who loves this type of stuff. Chris, I do not remember the older 545 having couplling caps, thats why in today's world, some of the older Adcoms sound better than the Mk.II's because the Mk.II's have caps that may be drying up or weakening or whatever.
I know in the literature they always used the term "direct coupled" maybe that means no coupling caps?
The MkII's use a triple darlington output and have dc servo's which many believe (so I;ve read) contribute the lesser sonic signature compared to the original 545.
Brock
But the 545ii beats the 545 in sonics hands down!
I have owned both... As far as mail, no biggie, fed-ex ground and UPS have not lost or damaged a single amp I sent through them in the last 3 years and I have sent a lot... only thing is pack it well such that if you dropped it on a concrete floor, it would survive... that means a minimum of 2" styrofoam on all sides and bubble wrap between the SF and the amp.
Cheers!
I have owned both... As far as mail, no biggie, fed-ex ground and UPS have not lost or damaged a single amp I sent through them in the last 3 years and I have sent a lot... only thing is pack it well such that if you dropped it on a concrete floor, it would survive... that means a minimum of 2" styrofoam on all sides and bubble wrap between the SF and the amp.
Cheers!
Hi Brock, Arif,
There are some supply decoupling caps to be replaced, and one across the bias circuit I think. You may want to bypass these with some 1~10 uF foil jobs. I don't remember all the values, but replacing a 1uF electrolytic with a foil cap can sometimes sound amazing. I'm not talking BG's or anything ridiculous.
I agree with K-amps. Shipping a well packed product is generally not a problem. I just really hate the customs people. Actually, I hate most paperwork to be honest about it!
-Chris.
There are some supply decoupling caps to be replaced, and one across the bias circuit I think. You may want to bypass these with some 1~10 uF foil jobs. I don't remember all the values, but replacing a 1uF electrolytic with a foil cap can sometimes sound amazing. I'm not talking BG's or anything ridiculous.
I agree with K-amps. Shipping a well packed product is generally not a problem. I just really hate the customs people. Actually, I hate most paperwork to be honest about it!
-Chris.
Yup the bias bypass cap can affect sonics, as can the feedback decoupling cap. I am not much of an exotic parts person, but I have had experience with clearly observing the benefits of ditching electrolytic caps in anything in the signal path in favor of silver micas, polypropylenes and al foil types.
If you don't beleive me, try using a 50uF np cap in series with one of your speakers (disregarding the LF roll-off) you will notice congestion of sound especially as the volume goes up, this will become VERY appearant when you remove the lytic and put in a polypropylene of the same value.... my jaw dropped the first time I tried it.... I only trust my own ears and I'd expect you'd do the same.
Arif
If you don't beleive me, try using a 50uF np cap in series with one of your speakers (disregarding the LF roll-off) you will notice congestion of sound especially as the volume goes up, this will become VERY appearant when you remove the lytic and put in a polypropylene of the same value.... my jaw dropped the first time I tried it.... I only trust my own ears and I'd expect you'd do the same.
Arif
Hi Brock,
Now you have to decide where to send your amplifier for service. There is a consensus on what to do, with your input of course. If you send it to the right person I feel you will be very pleased for a number of years in the future.
Arif, now about speaker crossovers ..... Nah, that's a whole new thread and has likely been done before.
-Chris
Now you have to decide where to send your amplifier for service. There is a consensus on what to do, with your input of course. If you send it to the right person I feel you will be very pleased for a number of years in the future.
Arif, now about speaker crossovers ..... Nah, that's a whole new thread and has likely been done before.
-Chris
Thanks guys....I really appreciate your input and I'm going to be making a decision very soon. I do really like this amp, in fact I've always liked it and I see no reason not to freshen it up a bit. I still need to think on it a while and do some more whole system evaluation as funds are limited. But the input by both of you has really helped.
I still think these older Adcoms are better than the new ones. What do you guys think? I know the newer 5xxx series are Mos-Fet so that changes the tonal characteristic. There is just something about the simplicity of design with the original series that appeals to me. But what about design, build quality and part quality of the newer generation of Adcoms? Just wondering what your opinion's are?
Brock
I still think these older Adcoms are better than the new ones. What do you guys think? I know the newer 5xxx series are Mos-Fet so that changes the tonal characteristic. There is just something about the simplicity of design with the original series that appeals to me. But what about design, build quality and part quality of the newer generation of Adcoms? Just wondering what your opinion's are?
Brock
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.