Head-Fi.org › Forums › Summit-Fi (High-End Audio) › High-end Audio Forum › Speaker amps for headphones
New Posts  All Forums:Forum Nav:

Speaker amps for headphones - Page 119

post #1771 of 3125
Quote:
 If the amp has true common ground, then you wouldn't need the R5 resistors. Just connect the headphone ground to one of the speaker grounds and be done with it.

 

So just use the standard "preferred" two resistor network or single series resistor?

post #1772 of 3125

If you live in USA try to grab Dynaco ST35. Im using it wit E5LE straigt from speaker taps witout any combination of resistors and sound is fantastic. Rigt now its connected troug potentiometer to Sabre DAC from Audio GD.

Generally tese amps need some attention but after tis it just play pure music.

post #1773 of 3125
Quote:
Originally Posted by robrob View Post
 

 

So just use the standard "preferred" two resistor network or single series resistor?

 

Use whatever resistor arrangement works for you. Use none if you don't have noise issues and have enough control of the pot.

 

My advice is this: if your headphone wiring only has L/R/G, then ONLY connect it to an amp that has a true shared ground. If your amp does not have a shared ground, meaning it has separate L+/L-/R+/R- outputs, then ONLY connect it to a headphone that has separate L+/L-/R+/R- wiring.

 

Worst case scenario: your amp has inverted differential outputs and you're trying to tie the negatives together with resistors. Boom. Well not really boom, but bad mojo.


Edited by Armaegis - 12/5/13 at 1:30pm
post #1774 of 3125
Quote:
Originally Posted by Armaegis View Post
 

 

Careful with the wording. Using "speaker load" here isn't quite correct. "Recommended load" would be better, as specified by the manufacturer and/or output tap on the amp.

 

And the reason you need it is to protect the transformer itself. While I can't explain it properly (I have a good idea, but don't want to muck it up for others), the simplified gist of it is that a transformer coupled tube amp expects a load to be connected to it at all times otherwise the transformers will risk damage. 

 

This is only true of transformer coupled amplifiers which use negative feedback, and some non-feedback pentode amplifiers where the tranformers can oscillate.  The explanation can be found here:

 

http://www.bottlehead.com/smf/index.php/topic,5097.0.html

 

A triode without negative feedback would be fine.

post #1775 of 3125
Quote:
Originally Posted by robrob View Post

I believe it's to reduce crosstalk. Without the pair of R5 resistors R3 would connect to L- and R-.

 

Armaegis, I assumed this network would only be used with amps with true common ground, meaning continuity between chassis and black speaker terminal. Do you have a suggested network?

 



If it's a single ended amp, then signal common will be the same as L- and R-.

There may not be a direct connection between signal ground and chassis ground (enclosure ground).
Chassis ground is often the third pin on the AC cable.

But in a Single Ended amp, there should be a direct connection between L- and R-, they should be at the same point.

The network you show actually looks like a network you might use if you want to connect a pair of headphones with a three wire system (like an AKG Q701) or Beyer DT880) to a power amp with a balanced output.

Someone will object and say, "but you can convert these headphones to balanced?"
Yes you can, if you want to remove the original cable and install a 4 wire cable.

But if you don't do that, I think this network can be used to do that.
post #1776 of 3125
Quote:
Originally Posted by Armaegis View Post

 

I really *really* do not like this network. The R5's do not add additional attenuation. They create a fake ground, but only sorta-not-really works if the two negative amp terminals are "roughly" ground but aren't.

 

Ugh, ok this is what happens when you have an amp circuit that pumps out the + and - simultaneously, and - is supposed to be ground but isn't tied to it, so really kinda floats. Likely there's some offset/noise in both that cancels out when you connect them across a load, which is fine because that's how they're meant to operate. But the offset/noise from the R and not necessarily the same as the L. Smashing the L- and R- together with resistors kinda-but-not-really works because they're sorta close to ground, so the resistor joint just creates a middle point. The big no-no is that this isn't true ground, and now L+ and R+ aren't referencing to their proper respective negatives anymore.

 

If you're lucky, things works out because the negatives were close enough to proper ground that it works out. But very likely you'll also just create a mess of things. It (probably) won't wreck your headphones, but you would potentially hear even more noise. I know there is at least one member here with a TBI amp and that exact box, and his noise is worse with the adapter.

 



I don't see why L- and R- would kinda float.
If it's a single ended amp then L- and R- are signal ground.

If t's balanced out then L- and R- are Inverting outputs and are not to be tied to any ground.

Must be a Manitoba thing......................LOL!
post #1777 of 3125
Quote:
Originally Posted by Chris J View Post
 
If it's a single ended amp, then signal common will be the same as L- and R-.

There may not be a direct connection between signal ground and chassis ground (enclosure ground).
Chassis ground is often the third pin on the AC cable.

But in a Single Ended amp, there should be a direct connection between L- and R-, they should be at the same point.

The network you show actually looks like a network you might use if you want to connect a pair of headphones with a three wire system (like an AKG Q701) or Beyer DT880) to a power amp with a balanced output.

Someone will object and say, "but you can convert these headphones to balanced?"
Yes you can, if you want to remove the original cable and install a 4 wire cable.

But if you don't do that, I think this network can be used to do that.

Chris, here's a single-ended amp with balanced (non-common ground) output:

The term "single-ended amp" refers to the amplification topology, not the input or output. A SE amp can have balanced input and output.

 

I have seen negative speaker terminals that use resistors to ground to balance the + and - capacitance for common mode noise rejection from the speaker wires.


Edited by robrob - 12/5/13 at 2:37pm
post #1778 of 3125
Quote:
Originally Posted by Chris J View Post
 
Quote:
Originally Posted by Armaegis View Post
 

 

I really *really* do not like this network. The R5's do not add additional attenuation. They create a fake ground, but only sorta-not-really works if the two negative amp terminals are "roughly" ground but aren't.

 

Ugh, ok this is what happens when you have an amp circuit that pumps out the + and - simultaneously, and - is supposed to be ground but isn't tied to it, so really kinda floats. Likely there's some offset/noise in both that cancels out when you connect them across a load, which is fine because that's how they're meant to operate. But the offset/noise from the R and not necessarily the same as the L. Smashing the L- and R- together with resistors kinda-but-not-really works because they're sorta close to ground, so the resistor joint just creates a middle point. The big no-no is that this isn't true ground, and now L+ and R+ aren't referencing to their proper respective negatives anymore.

 

If you're lucky, things works out because the negatives were close enough to proper ground that it works out. But very likely you'll also just create a mess of things. It (probably) won't wreck your headphones, but you would potentially hear even more noise. I know there is at least one member here with a TBI amp and that exact box, and his noise is worse with the adapter.

 



I don't see why L- and R- would kinda float.
If it's a single ended amp then L- and R- are signal ground.

If t's balanced out then L- and R- are Inverting outputs and are not to be tied to any ground.

Must be a Manitoba thing......................LOL!

 

While I can't speak for all designs, I've seen some Class D/T amps that have the weird "sort of ground but not really" negative terminals. They're not inverting, but they aren't true ground either and you shouldn't tie them together.

post #1779 of 3125
Quote:
Originally Posted by robrob View Post
 

Chris, here's a single-ended amp with balanced (non-common ground) output:

The term "single-ended amp" refers to the amplification topology, not the input or output. A SE amp can have balanced input and output.

 

I have seen negative speaker terminals that use resistors to ground to balance the + and - capacitance for common mode noise rejection from the speaker wires.

 

 

Oh no!  :eek:

Not this argument again! :eek:

Somehow audiophiles made up their own private definition of balanced.

Single ended and balanced refer to how the amplifier transmits and receives information.

If you ground one side of the secondary side, then it's a SE output amp.

If you ground the centre tap on the secondary side, then it's a balanced output amp.

If you saw + and - output tied to common via resistors then it must be a transformer coupled output?

 

The other issue with this is you'll probably have to solidly ground the secondary side of the output transformer to meet electrical code in many countries. Especially with a rather high voltage on the primary side.

 

Sure, there are many different way to build an amp with balanced input and output.

But just because the balanced input signal is converted to single ended and converted back into balanced output doesn't mean the designer is cheating or "it's not really balanced".

post #1780 of 3125
Quote:
Originally Posted by Armaegis View Post
 

 

While I can't speak for all designs, I've seen some Class D/T amps that have the weird "sort of ground but not really" negative terminals. They're not inverting, but they aren't true ground either and you shouldn't tie them together

 

 

Oh man, I would love to see that topology!

Do you have a link or something?

What's going on?

 

 

My guess: each output has common mode chokes for filtering.

That's all I got! :o


Edited by Chris J - 12/5/13 at 4:21pm
post #1781 of 3125

LOL it never fails :P

post #1782 of 3125
Quote:
 Single ended and balanced refer to how the amplifier transmits and receives information.

 

Single-ended refers to an amplifier topology (push-pull and differential are "double-ended") but it is commonly, but incorrectly, used to describe unbalanced cables. Balanced and unbalanced refers to circuit and component interconnects with balanced impedance. I defer to the Wizard: http://www.valvewizard.co.uk/se.html


Edited by robrob - 12/5/13 at 6:43pm
post #1783 of 3125
Quote:
Originally Posted by Armaegis View Post
 

 

Use whatever resistor arrangement works for you. Use none if you don't have noise issues and have enough control of the pot.

 

My advice is this: if your headphone wiring only has L/R/G, then ONLY connect it to an amp that has a true shared ground. If your amp does not have a shared ground, meaning it has separate L+/L-/R+/R- outputs, then ONLY connect it to a headphone that has separate L+/L-/R+/R- wiring.

 

Worst case scenario: your amp has inverted differential outputs and you're trying to tie the negatives together with resistors. Boom. Well not really boom, but bad mojo.

Maybe not BOOM, but you might let the magic smoke out!

 

(don't ask how I know....)

post #1784 of 3125
Quote:
Originally Posted by brunk View Post
 

@potterma My LDR-3X HiZ upgrade chip shipped today, so i should be receiving it some time next week. They had a delay because they found another tweak to apply :)

 

LDRx graphic (Click to show)

EDIT: This was the tweak applied: Substantially increased input impedance with a nominal 10k ohm impedance floor

 

That looks better... Got rid of the "bathtub wall" on the low attenuation end.  On the other end, it doesn't matter much.  

 

Now for the listening test... :popcorn:

post #1785 of 3125
Quote:
Originally Posted by potterma View Post
 

Maybe not BOOM, but you might let the magic smoke out!

 

(don't ask how I know....)

 

Also, very important to not inhale the magic smoke. That's definitely bad mojo.

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: High-end Audio Forum
Head-Fi.org › Forums › Summit-Fi (High-End Audio) › High-end Audio Forum › Speaker amps for headphones