I installed everything. It's a complete retrofit, PS, preamp, amp. Only thing original is the input/tuner board which I haven't gotten to yet.
None of the pads under any of the mounting screws provide a ground connection. The preamp is on a separate transformer. I was using a portable DAC for testing so no ground there. Hmmm...
Seems like poor design to not have the input and output grounds connected right on the board. Thinking I'll solder a jumper on the underside.
None of the pads under any of the mounting screws provide a ground connection. The preamp is on a separate transformer. I was using a portable DAC for testing so no ground there. Hmmm...
Seems like poor design to not have the input and output grounds connected right on the board. Thinking I'll solder a jumper on the underside.
No, it's a good design to have separate common connections. Very common in fact.
So ... what do the installation instructions say?
So ... what do the installation instructions say?
I once tore my hair out troubleshooting a PCB. It turned out that some external fault had caused a huge current to flow through one of the board traces, to the point that the trace basically evaporated. It escaped my attention for a long time until I bit the bullet and started following the board connections. After replacing the components that were also damaged by the event, adding a jumper to replace the board trace fixed the problem.
You might be looking at a similar kind of thing. All the grounds on that board have to be connected together for it to work right.
Still......why both of them?? I'd check the voltage between the ground lines before doing anything else. With the power supply turned on, of course.
You might be looking at a similar kind of thing. All the grounds on that board have to be connected together for it to work right.
Still......why both of them?? I'd check the voltage between the ground lines before doing anything else. With the power supply turned on, of course.
They are connected at an electrically quiet point. Separating them aims to keep the signal common clean from noise caused by heavy currents. So ou should measure a low impedance between the two. Some tmes up to about 100R resistors are installed between the two points to discourage ground loops. There is no current flow to speak of, or shouldn't be. Therefore no problem It depends on the design.
Now, what exactly do the installations instructions for those modules say?
When is ground not a ground? Not all "grounds" are the same, learn to call them by different names to help keep it clear in your head.
Now, what exactly do the installations instructions for those modules say?
When is ground not a ground? Not all "grounds" are the same, learn to call them by different names to help keep it clear in your head.
Unfortunately, the only instructions are how to set the bias.
There's ~1meg between input and output common.
There's ~1meg between input and output common.
Maybe you had some kind of inadvertent ground configuration that permitted the boards to work?
You may be able to find some online info on how to correctly wire up those boards -- if that's how they were laid out, surely some other folks have encountered the same problem.
You may be able to find some online info on how to correctly wire up those boards -- if that's how they were laid out, surely some other folks have encountered the same problem.
I have had multiple issues with silicon Insulators just as you describe. Pull them go back to mica and problem solved
I sent an email to the place I bought them inquiring about the lack of connectivity between the input and output commons. Hopefully I'll get a response.
Pay attention to your speaker returns as well. Normally they go to the common on your main filter caps. The common has a return to the power transformer. Then make a separate common between them where everything else in the world goes. The one to the power transformer has scary large current spikes in it.
I got a response. This is good news and totally explains everything.
"Hi David.
This amplifier uses the "Ground Separation" technique. This helps to greatly reduce noise and hum. The ground for the input signal and the ground for the power supply are separated by a 2.2 Ohm resistor - see attachment.
The downside of "Ground Separation" is that when switching the input signal or speaker or experimenting with the amplifier on, the current through this resistor can be very large and the resistor burns out. You need to change this 2.2 Ohm resistor.
In the future, please switch the signal and speakers only with the amplifier off."
"Hi David.
This amplifier uses the "Ground Separation" technique. This helps to greatly reduce noise and hum. The ground for the input signal and the ground for the power supply are separated by a 2.2 Ohm resistor - see attachment.
The downside of "Ground Separation" is that when switching the input signal or speaker or experimenting with the amplifier on, the current through this resistor can be very large and the resistor burns out. You need to change this 2.2 Ohm resistor.
In the future, please switch the signal and speakers only with the amplifier off."
Burning that resistor is rare, but it can happen. You have to run a huge amount of current through it, and that should never happen.
Never change connections to an amplifier unless it is off, else you may be repairing it shortly.
Never change connections to an amplifier unless it is off, else you may be repairing it shortly.
Yes, large transient noises are bad. I discovered that at a young age when I was wrestling with my brother and sent the needle skidding across Deep Purple Machine Head and fried our Dad's Marantz 2245.
I probably bumped a connection on the test bench and zapped it.
Assuming this also provides a measure of protection so I wouldn't want to replace it with a higher wattage one?
It should never pass any real current - ever. It is a reference for the audio signal only. The easiest way to wipe that out is touch the speaker return wire to the audio "ground". If the amp is off, no problems. If you have that much differential current between your sources and the amplifier, you have very real, very big problems. In that case, this resistor is the "canary in the coal mine". A very good warning.
You can increase the power rating if you feel the need, but make darned sure the part is not inductive. Looks like a 1/4 W or maybe 1/2 W resistor depending on the brand and model.
You can increase the power rating if you feel the need, but make darned sure the part is not inductive. Looks like a 1/4 W or maybe 1/2 W resistor depending on the brand and model.
Hi totally analogue,
Unplugging inputs on any amplifier while it is running is very unwise. If it has level controls, you can turn them to minimum and that makes it safe - usually. It is very bad practice, audio lesson 101. Even on the bench I follow those rules and I disconnect speakers or loads.
Without level controls, you open the input circuit and a direct coupled amplifier sees a sudden open, and any offset is just like a signal. Additionally the centre pin breaks contact last, so you lose common first (and shielding). You really want to do that? You may pick up RF (AM Radio, CB or HAM operator, or these days a cell phone. Some amps will demodulate the RF, again not what you want. Other amplifiers may become unstable due to the capacitance on the diff pair.
So basic rule for all amplifiers is real simple. Turn it off if you're going to change connections. I do get damaged amplifiers in for service and that is all they did. They are typically mystified, too bad no one trained them. Although, ever single owners manual I have seen tells you to turn the amplifier or receiver off to make connections. Could be something in that.
Unplugging inputs on any amplifier while it is running is very unwise. If it has level controls, you can turn them to minimum and that makes it safe - usually. It is very bad practice, audio lesson 101. Even on the bench I follow those rules and I disconnect speakers or loads.
Without level controls, you open the input circuit and a direct coupled amplifier sees a sudden open, and any offset is just like a signal. Additionally the centre pin breaks contact last, so you lose common first (and shielding). You really want to do that? You may pick up RF (AM Radio, CB or HAM operator, or these days a cell phone. Some amps will demodulate the RF, again not what you want. Other amplifiers may become unstable due to the capacitance on the diff pair.
So basic rule for all amplifiers is real simple. Turn it off if you're going to change connections. I do get damaged amplifiers in for service and that is all they did. They are typically mystified, too bad no one trained them. Although, ever single owners manual I have seen tells you to turn the amplifier or receiver off to make connections. Could be something in that.