[Teerawit]

No fair 98venom, you got a pre-machined case!

 

[rickcr42]

BTW Generic Bread Man (

),this may help you visualise the input to headphone amp w/ volume control part a bit better :

http://www.stereophile.com/images/ar...rt/scan35.html

on the output just add whatever slectors you need.even a simple DPDT "two output" selector works for most systems (headphones/speaker amp send)

 

[98venom]

Quote:

Originally Posted by Teerawit No fair 98venom, you got a pre-machined case!

Hey, it is a nice one though.......

I was considering a Parmetals case, but for the price, I decided on this one.....

 

[amb]

I added a diagram to the M³ website illustrating a way to implement a preamp, reproduced here:

 

[rickcr42]

Seems to me there was a HUGE deal made by a couple of members here who spent 2 months trying to design a simple A/B switch for three channel headphone amps yet here is a simple dual pole switch on the output of the amp recommended by the amp designer ?

What gives ?

Either switched grounds ARE or they ARE NOT important for this topology since the attack on Ray Samuels A/B switch was solely based on it as was the assault on anyone who even hinted at using a two pole switch on the output and that includes simple muting relays which also took on a voodoo aspect here.

it seems the answer is not only inconsistant but all over the map and it would be nice to have clarity.A definitive answer for future reference

 

[Whitebread]

This really is excellent, thanks a ton guys!!

 

[Whitebread]

Quote:

Originally Posted by rickcr42 Seems to me there was a HUGE deal made by a couple of members here who spent 2 months trying to design a simple A/B switch for three channel headphone amps yet here is a simple dual pole switch on the output of the amp recommended by the amp designer ? What gives ? Either switched grounds ARE or they ARE NOT important for this topology since the attack on Ray Samuels A/B switch was solely based on it as was the assault on anyone who even hinted at using a two pole switch on the output and that includes simple muting relays which also took on a voodoo aspect here. it seems the answer is not only inconsistant but all over the map and it would be nice to have clarity.A definitive answer for future reference

I was also wondering about this. Despite all the confusion, isn't switching the grounds as simple as changing the wiring slightly and running the gound amp channel to the ground output portion of the input selector switch? I guess I'm saying that, if in doubt, just switch the grounds because its only a little more expensive for the 4 pole rotary and extra wiring, plus you'll eliminate any chance to develope hum (at least due to the pre-amp), correct?

 

[rickcr42]

Quote:

guess I'm saying that, if in doubt, just switch the grounds because its only a little mor expensive for the 2 pole rotary and extra wiring, plus you'll eliminate any chance to develope hum (at least due to the pre-amp), correct?

I wish it were that simple.There have been a few complaints by three channel amp users on "ground bleed" when using non-ground switched sources and there has also been some nastiness directed to others who use more conventional two pole switching but there ARE downsides to both ways as well as good points.

The downside to switching the grounds AND signal is if you use a break-before-make switch (ALL toggle switches and some rotary switches) you can get a "pop" through your system because there is no ground present during that moment of switching yet here we see a simple toggle switch with unswitched grounds on the output and if it is in fact a make-before break rotary or a three pole toggle then it should show that for clarity and why I originally went to such great lengths in this thread to add in the "unless ou have a three channel amp" part.

I personally do not like or use this topology but many do and when they ask a simple question I think it is a disservice to have answers that change instead of definitive answers .One that do not change weekly or confuse.


MY opinion is yes,the grounds should be switched or any common ground load will be in fact always present at the output of the amp no matter what actual output is selected.For instance power amp input ground still connected to the third channel even though headphone out was selected.

And since I feel this is most likely the better way that means toggle or rocker or slide switches are off the list as are break-before-make rotary switches because having an "open" ground even for an instant can lead to pops and clicks when changing the switch.The only thing left is the 3 Pole make-before break rotary switch that switches left channel/right channel/synthesized ground channel simultaneously.


No big deal to me personally though it does make trying to help people get a simple answer no easy deal and it would just be nice to have clarity on this issue once and for all for those who may in future want to do something similiar and after doing a search come away more confused than informed.

The information is all over the map.When a simple "let's build and A-B switch" thread a year or so ago ran for WEEKS and nothing ever was actually ironed out because most involved were actually clueless as to THE answer yet were actually pissed when anyone that had the answer even attempted to clue them even though it was as simple as the above all along

 

[amb]

Rick, I would hope that you look at the diagram more closely before attacking my post. There is no need to switch the ground for the headphone output and preamp output here because of the way they are wired. The headphone output jack here is referenced to the output of the ground channel whereas the preamp output is referenced to the input signal ground. They are not to be used interchangeably. It is also assumed that the preamp out will be connected to a high-impedance input stage of a power amplifier which is a very light load with very little return current, therefore there will be virtually no signal ground pollution. Headphones on the other hand (especially low-Z ones) cause much higher ground return currents, and are thus handled by the active output ground channel.

Since you mentioned our headphone amp A/B switch, it must have switched grounds because it is used to switch between two headphone amps to a common headphone load. The two amps could have different output ground topologies (i.e., one being a 3-channel with active output ground and the other being "passive" common ground, or between two amps each with active grounds). Not having a switch would create a short circuit condition on the 3-channel amp(s) across the signal ground and output ground, because the two amps are usually hooked up to a common source which shares the input signal ground.

Same thing with dummy load boxes. These are often used in RMAA loop-back testing and thus the output ground must be lifted on the return back to the sound card, or else a short circuit condition will occur on 3-channel amps.

The A/B switch and dummy load scenarios do not apply to the immediate subject at hand here (wiring the amp to serve as a preamp and headphone amp).

 

[rickcr42]

Quote:

Rick, I would hope that you look at the diagram more closely before attacking my post.

I was hoping maybe you would surprise me just this once but did not really expect it.Anything not in full agreement or questioning past statements for clarity is an attack on you while anything you say is "just an opinion" right ?

no wonder there is still so much confusion on this topic and no one can get a straight answer that remains the same answer.......

Quote:

They are not to be used interchangeably. It is also assumed that the preamp out will be connected to a high-impedance input stage of a power amplifier which is a very light load with very little return current, therefore there will be virtually no signal ground pollution. Headphones on the other hand (especially low-Z ones) cause much higher ground return currents, and are thus handled by the active output ground channel

that is not the opinion stated in past threads if I read them correctly.In THOSE threads it was said that any switches not also switching grounds were not good because there was a continuous connection to the active ground channel to any other amp/gear connected to the jacks and that THIS effected the sonics so was not a good idea.

Not my words.just repeating earlier posts.

So for Ultimate clarity and the final definitive answer on this topic

1-No need for switched grounds using a 3-CH amp with a high load impedance
2-You must use switched grounds with a low impedance load

so far on target right ?

Finally-shorting rotary or "any" switch with enough poles to do the job ?
I beleive switching grounds and signal can be dangerous if the volume levels are high and the "pop" load enough when the ground integrity is gone for that instant of switching but your amp so what is the actual truth on that ?

Is a 3-pole toggle switch that is used to switch the output signal AND grounds pop free even though it is a "break first" switch ?

These questions are not "fluff" or personal even though you would have it that way for whatever reason but serious questions to finally nail down exactly what the requiremnts are so there are no more misconceptions.
And trust me man,there ARE misconceptions and the threads over time have proven that out with no one true answer yet so maybe this is the one to point to as the final word on the subject ?

 

[Whitebread]

Input Selector Switch
This input selector switch is the non-shorting type. Does this mean that it "disconnects, then reconnects" and would cause a pop if the grounds were switched?

Also, My original question was weither I should switch the grounds of the input sources and then just feed 2 ground wires (1 per channel) to a common ground with the ground channel of the M3. Now I'm wondering if I should switch the grounds of the pre-amp output also. I mean, is the ground channel of the M3 meant to JUST drive the common ground of the heaphone and not the power amp?

 

[rickcr42]

Quote:

This input selector switch is the non-shorting type. Does this mean that it "disconnects, then reconnects" and would cause a pop if the grounds were switched

non shorting means "BreakBefore Make" or in simple terms no contact between switching so could cause "pops" though to be honest not having a 3-CH headphone amp am waiting for the definitive answer before saying this is an absolute.

Usually the answer would be use a shorting switch like the very inexpensive Lorlin.one of the few commonly available shorting rotary switches.

Quote:

Also, My original question was weither I should switch the grounds of the input sources and then just feed 2 ground wires (1 per channel) to a common ground with the ground channel of the M3.

I personally would go with simple there and use the normal type 2-pole rotary switch to select the left and right channel signals while leaving the ground alone.
There are lucid arguments for both ways but the alternative usually means adding extra resistors across every single switch contact to avoid switching transients and that to me is ovecomplicating the simple to cure a problem not usually there

Quote:

I mean, is the ground channel of the M3 meant to JUST drive the common ground of the heaphone and not the power amp?

it is an "active" ground rather than the typical passive-wire ground buss style ground connection and can be looked at as any other active circuit.
That is with a hi-Z input impedance and lo-Z output impedance (typical of active stages) so the input requirements WAY easier to accomodate than the output which can be loaded down in extreme cases like any amp could be.


I would not stress the input but treat it as any amp while paying attention to the output in the attempt to avoid any potential problems before they actually become a problem and thus requireing a fix.

DIY means you have the option to plan your attack and get it right before building the actual "thing" under consideration with the forum allowing options from various sources to make your life digfficult

 

[rickcr42]

Pretty much the "affordable" standard in shorting multi-pole rotary switches :

http://www.lorlin.co.uk/a.htm

Easily found at most major parts suppliers

 

[Whitebread]

Quote:

Originally Posted by rickcr42 non shorting means "BreakBefore Make" or in simple terms no contact between switching so could cause "pops" though to be honest not having a 3-CH headphone amp am waiting for the definitive answer before saying this is an absolute. Usually the answer would be use a shorting switch like the very inexpensive Lorlin.one of the few commonly available shorting rotary switches. I personally would go with simple there and use the normal type 2-pole rotary switch to select the left and right channel signals while leaving the ground alone. There are lucid arguments for both ways but the alternative usually means adding extra resistors across every single switch contact to avoid switching transients and that to me is ovecomplicating the simple to cure a problem not usually there it is an "active" ground rather than the typical passive-wire ground buss style ground connection and can be looked at as any other active circuit. That is with a hi-Z input impedance and lo-Z output impedance (typical of active stages) so the input requirements WAY easier to accomodate than the output which can be loaded down in extreme cases like any amp could be. I would not stress the input but treat it as any amp while paying attention to the output in the attempt to avoid any potential problems before they actually become a problem and thus requireing a fix. DIY means you have the option to plan your attack and get it right before building the actual "thing" under consideration with the forum allowing options from various sources to make your life digfficult

Alright,
For now I'll bet on the shorting type switch, but I'll wait for the definite answer, as you are. And I'll just switch the + and wire grounds together.

One thing, though, why would I need to wire resistors to every switch tab? I know you said to avoid switching transcients, but what does that mean specifically?

And thanks for the link to the shorting rotary.

 

[rickcr42]

Quote:

One thing, though, why would I need to wire resistors to every switch tab? I know you said to avoid switching transcients, but what does that mean specifically?

The resistors provide a path to ground that is otherwise absent and what causes the "pops' and/or "clicks" when you move the switch from one position to another.Those sounds are known as switching transients which is used to describe any noisy type of switching operation

The way it is wired is a resistor from each and every input lug on the switch to input circuit ground so no matter what the position or if the switch is "opened up" every source is still terminated to a stable ground.

Personally seems to me a long way to go when you set out to fix a thing then need to fix the fix

Quote:

For now I'll bet on the shorting type switch, but I'll wait for the definite answer, as you are. And I'll just switch the + and wire grounds together.

Seems a smart move.This is not the last time this will come and would be nice to get it nailed down once and for final.........