Amplifier ground problem

[Viktor277]

Replaced my old Harman Kardon PM645, with a bit less old Adcom Gca 510. Sufficient upgrade over the 645,especially in terms of detail and massive control over the speakers thanks to 400 damping factor, practically no distortion.

The issue i have is that when you touch the 510 the speakers buzz, like a static noise, which i dont remember happening with any amp i encountered before.

As i understood this unit has no protection and no ground because *design philosophy*. I don't know if this is a potentially bad thing but id appreciate any comment/advice. I had this unit cleaned since the left channel was going out frequently, to be expected of a 30yo unit, but it was a simple fix. Now its working fine other than that odd buzzing, which was present before and after i took it for cleaning.

If its about something that cant catch on fire on its own then i dont care about it, but if someone says otherwise ill look into it. Just wanna stay safe.

[kb5zue]

I figure there is a 99.9% chance it's a grounding problem.  Does it have a three-prong grounded power cord?  I can't tell by the pictures on the internet.  If you feel safe about it, open the case and verify that it is grounded thru the power cord.  There are several other things you can do to check it out.  How about installing a grounding cord yourself if it doesn't have one.  You can try using a volt meter to see if voltage is going thru the case.  

 

Sorry, all I can  think of tonight.   Take Care and good luck.

 

[Viktor277]

2 hours ago, kb5zue said:

I figure there is a 99.9% chance it's a grounding problem.  Does it have a three-prong grounded power cord?  I can't tell by the pictures on the internet.  If you feel safe about it, open the case and verify that it is grounded thru the power cord.  There are several other things you can do to check it out.  How about installing a grounding cord yourself if it doesn't have one.  You can try using a volt meter to see if voltage is going thru the case.  

 

Sorry, all I can  think of tonight.   Take Care and good luck.

 

Its a european style connector, but i think it is 2-prong cable, i think that seller mentioned that. This is a 220v model.

[H713]

It's not too uncommon for power amplifiers to have a 2-prong cord.

 

It's not really a wanky "design philosophy", it's a solution to the ground loop problem that is a common problem with power amplifiers. If the chassis (and thus RCA shield) is tied to mains earth, and your preamplifier is built the same way, then both ends of the RCA shield (which is one of your signal conductors!) are independently tied to mains earth through separate power cables. This creates a loop, and any changing magnetic fields within that loop induce a current. This is one of the main sources of hum in audio systems Some people make things even worse by plugging their power amp into a different circuit from their preamp. By not tying the chassis to mains earth, they're breaking one end of the ground loop.

 

As a manufacturer, there are ways of accomplishing this while still meeting electrical safety requirements.

 

As a warning, some people (including some electricians and less-practical engineers) will immediately "check for safety" and try to measure the potential of the enclosure with respect to mains earth using a DMM, then freak out when they see that it's not 0V. The mistake they're making is that a DMM has a high (10M) input impedance, so even small parasitic capacitance is enough to make it look like there's 50 V on the case. It doesn't present a safety hazard, however, because the maximum current available is measured in microamps. Some fancier (hint: expensive) DMMs have a "low Z" measurement mode that is supposed to alleviate this error. If you measure with a really high impedance probe, like a 1000:1 HV probe, you'll see almost the full line voltage on the case. This doesn't even remotely present a safety issue, but it does seem to freak out people who don't know what they're looking at. 

 

Most of this parasitic capacitance is in the transformer itself, though there could be some Y capacitors for EMI filtering contributing as well. While not impossible to eliminate, it's both difficult and expensive. 

 

What are you driving this amplifier with? Is it a floating source like your phone? This amplifier would have been designed with the idea that its source was ground referenced. Of course, with issues like this it should go without saying to check cable connections - a bad RCA cable can cause all of these problems. In any case, what you're describing doesn't sound like a safety issue.

 

I don't recommend modifying the grounding scheme of amplifiers unless you have a pretty solid understanding of how that particular amplifier works. Usually the engineers who design audio power amplifiers plan out the grounding pretty carefully. If they specify a slew rate above, say, 70 V/us, then you really don't want to mess with it.

 

[Viktor277]

On 7/7/2023 at 7:34 AM, H713 said:

It's not too uncommon for power amplifiers to have a 2-prong cord.

 

It's not really a wanky "design philosophy", it's a solution to the ground loop problem that is a common problem with power amplifiers. If the chassis (and thus RCA shield) is tied to mains earth, and your preamplifier is built the same way, then both ends of the RCA shield (which is one of your signal conductors!) are independently tied to mains earth through separate power cables. This creates a loop, and any changing magnetic fields within that loop induce a current. This is one of the main sources of hum in audio systems Some people make things even worse by plugging their power amp into a different circuit from their preamp. By not tying the chassis to mains earth, they're breaking one end of the ground loop.

 

As a manufacturer, there are ways of accomplishing this while still meeting electrical safety requirements.

 

As a warning, some people (including some electricians and less-practical engineers) will immediately "check for safety" and try to measure the potential of the enclosure with respect to mains earth using a DMM, then freak out when they see that it's not 0V. The mistake they're making is that a DMM has a high (10M) input impedance, so even small parasitic capacitance is enough to make it look like there's 50 V on the case. It doesn't present a safety hazard, however, because the maximum current available is measured in microamps. Some fancier (hint: expensive) DMMs have a "low Z" measurement mode that is supposed to alleviate this error. If you measure with a really high impedance probe, like a 1000:1 HV probe, you'll see almost the full line voltage on the case. This doesn't even remotely present a safety issue, but it does seem to freak out people who don't know what they're looking at. 

 

Most of this parasitic capacitance is in the transformer itself, though there could be some Y capacitors for EMI filtering contributing as well. While not impossible to eliminate, it's both difficult and expensive. 

 

What are you driving this amplifier with? Is it a floating source like your phone? This amplifier would have been designed with the idea that its source was ground referenced. Of course, with issues like this it should go without saying to check cable connections - a bad RCA cable can cause all of these problems. In any case, what you're describing doesn't sound like a safety issue.

 

I don't recommend modifying the grounding scheme of amplifiers unless you have a pretty solid understanding of how that particular amplifier works. Usually the engineers who design audio power amplifiers plan out the grounding pretty carefully. If they specify a slew rate above, say, 70 V/us, then you really don't want to mess with it.

 

I do not have required expertise to mess with such schematics.. As per recommendation from a friend, i took it to a guy that repairs all sorts of amps and is actually doing it right, consulted with bunch of people that already took it to him, some that actually know quite a bit more than me about technicalities of amplifiers, and all agreed that pops is doing a good job. I try to sound as professional and fluent as i can since english isn't my first language, pardon me if something doesn't make sense at first glance.

Turns out the problem was in ''ground mass''. He didn't care to explain to me what that is but the problem is fixed, took him only a hour to do so as well.

Since you mentioned slev rate, that is the only specification that isn't mentioned on the spec sheet of amplifier, also a first time that i got a owners manual with a amp lol, its what it is when u buy used, mostly. If rise time is releated, its 1.5us, supposedly its good? Im impressed with the specs as well, mostly with the damping factor of 400 for such a small amp, massive control and practilly no distorsion, the seller said, and i can confirm it. Read somewhere that it used to get compared to much more expensive amps of the day in '93, sticker price of 499, adjusted for today's dollars is around 1000. A killer amp truly, made such a difference that it made me realise that the problem all these years wasn't in the speakers.

[Viktor277]

[X]

[Viktor277]

On 7/7/2023 at 7:34 AM, H713 said:

It's not too uncommon for power amplifiers to have a 2-prong cord.

 

It's not really a wanky "design philosophy", it's a solution to the ground loop problem that is a common problem with power amplifiers. If the chassis (and thus RCA shield) is tied to mains earth, and your preamplifier is built the same way, then both ends of the RCA shield (which is one of your signal conductors!) are independently tied to mains earth through separate power cables. This creates a loop, and any changing magnetic fields within that loop induce a current. This is one of the main sources of hum in audio systems Some people make things even worse by plugging their power amp into a different circuit from their preamp. By not tying the chassis to mains earth, they're breaking one end of the ground loop.

 

As a manufacturer, there are ways of accomplishing this while still meeting electrical safety requirements.

 

As a warning, some people (including some electricians and less-practical engineers) will immediately "check for safety" and try to measure the potential of the enclosure with respect to mains earth using a DMM, then freak out when they see that it's not 0V. The mistake they're making is that a DMM has a high (10M) input impedance, so even small parasitic capacitance is enough to make it look like there's 50 V on the case. It doesn't present a safety hazard, however, because the maximum current available is measured in microamps. Some fancier (hint: expensive) DMMs have a "low Z" measurement mode that is supposed to alleviate this error. If you measure with a really high impedance probe, like a 1000:1 HV probe, you'll see almost the full line voltage on the case. This doesn't even remotely present a safety issue, but it does seem to freak out people who don't know what they're looking at. 

 

Most of this parasitic capacitance is in the transformer itself, though there could be some Y capacitors for EMI filtering contributing as well. While not impossible to eliminate, it's both difficult and expensive. 

 

What are you driving this amplifier with? Is it a floating source like your phone? This amplifier would have been designed with the idea that its source was ground referenced. Of course, with issues like this it should go without saying to check cable connections - a bad RCA cable can cause all of these problems. In any case, what you're describing doesn't sound like a safety issue.

 

I don't recommend modifying the grounding scheme of amplifiers unless you have a pretty solid understanding of how that particular amplifier works. Usually the engineers who design audio power amplifiers plan out the grounding pretty carefully. If they specify a slew rate above, say, 70 V/us, then you really don't want to mess with it.

 

As for speakers, it's driving JBL Professional 8330, 91db, efficient and easy to drive.

Here are the specs if you're interested.

[Heats with Nvidia]

Does the same happen when you touch other parts of the amplifier? I once had a similar problem with an amp and in this case it was a broken ground connection within the amplifier.

 

By the way, if you are comfortable disclosing it, what is your firs language? There is at least a chance that we can use that, because english isn`t my first language either.

[HenrySalayne]

On 7/7/2023 at 7:34 AM, H713 said:

As a warning, some people (including some electricians and less-practical engineers) will immediately "check for safety" and try to measure the potential of the enclosure with respect to mains earth using a DMM, then freak out when they see that it's not 0V. The mistake they're making is that a DMM has a high (10M) input impedance, so even small parasitic capacitance is enough to make it look like there's 50 V on the case. It doesn't present a safety hazard, however, because the maximum current available is measured in microamps. Some fancier (hint: expensive) DMMs have a "low Z" measurement mode that is supposed to alleviate this error. If you measure with a really high impedance probe, like a 1000:1 HV probe, you'll see almost the full line voltage on the case. This doesn't even remotely present a safety issue, but it does seem to freak out people who don't know what they're looking at. 

Devices with an AC cord but without a PE connection are appliance class II. Especially for devices with a metal case, this requires double insulation around anything carrying dangerous voltages.

Most older HiFi devices and even some newer things manufactured in Asia are not built with reinforced / double insulation. They are indeed a safety hazard and should be avoided / thrown away or only be used on a RCD protected outlet.

[Heats with Nvidia]

17 hours ago, HenrySalayne said:

Devices with an AC cord but without a PE connection are appliance class II. Especially for devices with a metal case, this requires double insulation around anything carrying dangerous voltages.

Most older HiFi devices and even some newer things manufactured in Asia are not built with reinforced / double insulation. They are indeed a safety hazard and should be avoided / thrown away or only be used on a RCD protected outlet.

Or you just change that and ground the case. I have done that regularly with older but quite valuable equipment to bring it up to a higher safety standard. It was mostly Synthesizers.

[H713]

On 7/31/2023 at 12:16 AM, HenrySalayne said:

Devices with an AC cord but without a PE connection are appliance class II. Especially for devices with a metal case, this requires double insulation around anything carrying dangerous voltages.

Most older HiFi devices and even some newer things manufactured in Asia are not built with reinforced / double insulation. They are indeed a safety hazard and should be avoided / thrown away or only be used on a RCD protected outlet.

It's not uncommon to see this kind of equipment built double-insulated. It continues to be quite common on AV receivers, and has been for quite some time.

 

I have not dug especially deep into how they're achieving their double insulated rating on newer models. My suspicion is that they're already using a custom transformer design and are getting their double insulation there.

 

 

Stuff from the 70s and 80s often is not compliant with current standards. I tend not to be too worried about most 80s and 90s power amps and receivers, as I don't run across too many that are especially sketchy in this regard. It's the 60s tube amps and RF test equipment that I get nervous about. As bad as a chassis hot with 120 is, a chassis hot with 4 kV is a hell of a lot worse. 

 

On 7/29/2023 at 11:18 PM, Viktor277 said:

As for speakers, it's driving JBL Professional 8330, 91db, efficient and easy to drive.

Here are the specs if you're interested.

Slew rate is quoted, just in a really stupid way. 65 V square wave with a 1.5 us rise time. That's ~43 V/us, which is on the faster side of normal for an amplifier of this size. It's sort of an idiotic brochure meant to sell an amplifier, since it lists a lot of useless specs (the number of semiconductor devices in the amplifier, for example) and two almost completely redundant distortion specs (50 W and 75W). They also boast about two things that contribute to mediocre reliability: A lack of current limiting (so they're relying on mechanical relays to protect the transistors) and a lack of output inductors (some amplifiers can get away with this, but given how marginal the stability of some audio amplifiers is, it makes me nervous). 

 

I only brought the issue of slew limiting up because there are some amplifiers from the 80s that were pushing >250 V/us and > 1 MHz bandwidths. With a matching transformer, you could literally use some of these as RF amplifiers. Small amounts of ground and power supply inductance in these amps is a surefire way to end up with an RF oscillator. I managed to get the output stage on one to oscillate at 60 MHz. You won't know about this unless you have a spectrum analyzer or relatively fast scope. 

 

[Viktor277]

On 8/4/2023 at 6:45 AM, H713 said:

It's not uncommon to see this kind of equipment built double-insulated. It continues to be quite common on AV receivers, and has been for quite some time.

 

I have not dug especially deep into how they're achieving their double insulated rating on newer models. My suspicion is that they're already using a custom transformer design and are getting their double insulation there.

 

 

Stuff from the 70s and 80s often is not compliant with current standards. I tend not to be too worried about most 80s and 90s power amps and receivers, as I don't run across too many that are especially sketchy in this regard. It's the 60s tube amps and RF test equipment that I get nervous about. As bad as a chassis hot with 120 is, a chassis hot with 4 kV is a hell of a lot worse. 

 

Slew rate is quoted, just in a really stupid way. 65 V square wave with a 1.5 us rise time. That's ~43 V/us, which is on the faster side of normal for an amplifier of this size. It's sort of an idiotic brochure meant to sell an amplifier, since it lists a lot of useless specs (the number of semiconductor devices in the amplifier, for example) and two almost completely redundant distortion specs (50 W and 75W). They also boast about two things that contribute to mediocre reliability: A lack of current limiting (so they're relying on mechanical relays to protect the transistors) and a lack of output inductors (some amplifiers can get away with this, but given how marginal the stability of some audio amplifiers is, it makes me nervous). 

 

I only brought the issue of slew limiting up because there are some amplifiers from the 80s that were pushing >250 V/us and > 1 MHz bandwidths. With a matching transformer, you could literally use some of these as RF amplifiers. Small amounts of ground and power supply inductance in these amps is a surefire way to end up with an RF oscillator. I managed to get the output stage on one to oscillate at 60 MHz. You won't know about this unless you have a spectrum analyzer or relatively fast scope. 

 

Well, at least they didn't try to hide any specs. As is, it sounds very good, with my set up, better than some 3x expensive amps. They cut corners in right places. I don't think this brochure is meant to sell the amp, it's literally a manual. I don't think it's stupid to quote literal specs of a unit, considering that most companies aren't bothered to list any detailed specs other than basic specs than can be understood by average consumers, and are hiding behind the 1khz measurements which give the best results, as can be seen in this manual too.