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Speaker amps for headphones - Page 112

post #1666 of 2899
Quote:
Originally Posted by zilch0md View Post
 

 

 

 

I certainly agree with Gary's response - the Passport's 12VDC output will allow the MG3 only 10Wpc into 8-Ohm (vs. 24VDC, which allows the MG3 to deliver 32Wpc into 8-Ohm).

 

But I'd like to offer some warnings about my 24VDC battery-powered solution for the MG3.

 

I am currently using this 3600 mAh, 6-cell LiPo to power the MG3 at 25.2V (fully charged) down to 20.4V (when I put it back on the charger):

 

 

 

And I recently purchased this larger, 5300 mAh, 6-cell, LiPo (having the same length as the one above), on sale at the manufacturer's web site:  http://www.gensaceusa.com/98p-30c-5300-6s1p.html

 

 

 

These things are somewhat dangerous, however, as this 30C-rated, 5300 mAh version can supply 159 Amps continuously, without overheating (peak current is much higher still).  

 

Their discharge must be monitored during use, to prevent then from dropping below 3.0V per cell - which can damage the battery and even cause fires that emit toxic soot and smoke, even if they don't burn down your house.  Charging requires some know-how, too, using a "balanced charger" like the Thunder AC6, to ensure that individual cells are not charged to voltages higher than 4.2V, which again, can cause damage and increase the possibility of a fire.

 

 

http://www.amazon.com/Integy-C23212-Voltage-Checker-Warning/dp/B003Y6E6IE

 

 

 

 

 

 

http://www.amazon.com/Thunder-Balance-Charger-Discharger-Software/dp/9269806723

 

In other words, I don't recommend this solution unless you're "into batteries" and can enjoy the ritual of being disciplined in safe handling.

 

 

 

@Chris J - I see this again and again in various articles I've found online: the recommendation to use a 3:1 ratio (where the series resistor has three times the value of the parallel resistor) when designing a 2-resistor network.

 

Can you please tell me what happens sonically, with dynamic headphones especially (as opposed to planar magnetic), when the ratio is increased or decreased?

 

As previously posted, the resistor network that Jan Plummer (of TBI Audio) built for my MG3 amp uses two resistors, but their values have a ratio of 5:1.

 

 

Thanks!

 

Mike

 

Hi Mike,

I just used 3:1 as an example.

With low numbers like this, your amp should sound good with just about any headphone. But it's really just trail and error.  I'm not surprised "the box" sounds good with the HD600, but is disappointing with the LSDs, the power/current/voltage ratios are quite different.

The numbers you show look just as valid, but:

If R1 = 10 Ohm and R2 = 2 Ohms you would only get more attenuation (approx -15.6 dB), i.e less hiss, and also more likely to move you to a "nicer" part of your volume control range.  

I say nicer because we often have to run the volume control way down around 8:30 or 9:30 because the whole chain may have too much gain for headphones when we use speaker amps.

 

I used to have a Yamaha CR-2020 receiver with an output impedance of approx. 120 Ohms (or was it 220?).

Anyway, I had to press the -20 dB button on the receiver to get away from using the very bottom range of the volume control.

Without the -20 dB button pressed in the channel tracking could be a bit dodgy. Irritating!

With the -20 dB button engaged the volume control was more in the range of 9:00 to 11:00 o'clock. Very useful.

 

 

Anyway,

If I was doing this I would do it this way:

1.  try driving phones directly

what do we hear?  too much hiss? do we need to operate the volume control at the bottom end?

 

2.  try values like R1 = R2

still too much hiss?  still problems with volume control?

 

3.  try this:  R1 is three times higher than R2

still too much hiss? bad volume control travel?

 

4.  try R1 is 5 times higher than R2

same questions?

 

5.    if still too much hiss, try R1 is 9 times higher than R2.

this is approx. -20 dB of attenuation.

 

Really what it comes down to is, subjectively, where is the best compromise between low hiss, good volume control travel and hopefully we still have enough power delivered to phones.

As you have found out, sometimes you just can't find a good compromise.

 

Jan must have done a few calculations, but if he doesn't actually have a pair of LCD-2s, it's hard to nail down good real world values for those specific phones. 

Maybe try a lower ratio?

A friend of mine drives LCD-2 straight off the output of a small DECware vacuum tube power amp, I think it's about 10 Watts into 8 Ohms?

 

Chris

post #1667 of 2899
Quote:
Originally Posted by Gary in MD View Post

Balanced outputs as in common ground?

Sorry to be confusing. From the blue circle web site

Most current amplifier designs, even if they have balanced inputs, do not necessarily have true balanced outputs. This means that the positive binding posts have signal but the negative binding posts are actually tied to ground. With this approach the positive binding posts are driving the speaker coils but the negative binding posts are entirely passive.

All Blue Circle amplifiers* employ true balanced output technology. This means both the positive and negative binding posts supply active signal to the speaker voice coils. The advantage This results in the amplifier applying more control over the speaker cone motion than conventional designs.

From the pass labs manual for the 160.5

Please note that, being a balanced output, both of these terminals are electrically live – neither is grounded and should not be treated as ground. This is particularly important if you are using the output of the amp to also drive a subwoofer amplifier or other active component. If there is any question, please contact the manufacturers of the products involved – both they and we will be happy to advise you.

From the inner fidelity review
The unit has a switch on front for selecting pass-through mode which allows the signal to pass through unmolested to your speakers. This allows the WEE to be easily inserted into nearly any system. The only caveat is that the input grounds are tied together, so bridged/balanced amplifiers should not be used (Pass Labs for example).

I have an email from jack at woo audio somewhere responding to my question on the blue circle. Does this make things clearer?
post #1668 of 2899

@ALRAINBOW

 

Quote:

Originally Posted by ALRAINBOW View Post

Email him. He is the guru master of power regulation in this hobby of ours . He devices are the jam in DIY . Ask brunk or someone here will know. He can make you what you need in a box with connectors too. Do not be confused at his website it shows almost nothing I know, but the guy is the jam.

Al D

 

Thanks Al,

 

I've sent Paul Hynes an e-mail explaining that I'd like to limit current output from my LiPo batteries to 4A.  I also asked him if it's possible to do so without consuming current continuously as it does its thing.  Maybe not?

 

Mike

 

@Chris J

 

Quote:
Originally Posted by Chris J View Post
  Warning: Spoiler! (Click to show)


Hi Mike,

I just used 3:1 as an example.

With low numbers like this, your amp should sound good with just about any headphone. But it's really just trail and error.  I'm not surprised "the box" sounds good with the HD600, but is disappointing with the LSDs, the power/current/voltage ratios are quite different.

The numbers you show look just as valid, but:

If R1 = 10 Ohm and R2 = 2 Ohms you would only get more attenuation (approx -15.6 dB), i.e less hiss, and also more likely to move you to a "nicer" part of your volume control range.  

I say nicer because we often have to run the volume control way down around 8:30 or 9:30 because the whole chain may have too much gain for headphones when we use speaker amps.

 

I used to have a Yamaha CR-2020 receiver with an output impedance of approx. 120 Ohms (or was it 220?).

Anyway, I had to press the -20 dB button on the receiver to get away from using the very bottom range of the volume control.

Without the -20 dB button pressed in the channel tracking could be a bit dodgy. Irritating!

With the -20 dB button engaged the volume control was more in the range of 9:00 to 11:00 o'clock. Very useful.

 

 

Anyway,

If I was doing this I would do it this way:

1.  try driving phones directly

what do we hear?  too much hiss? do we need to operate the volume control at the bottom end?

 

2.  try values like R1 = R2

still too much hiss?  still problems with volume control?

 

3.  try this:  R1 is three times higher than R2

still too much hiss? bad volume control travel?

 

4.  try R1 is 5 times higher than R2

same questions?

 

5.    if still too much hiss, try R1 is 9 times higher than R2.

this is approx. -20 dB of attenuation.

 

Really what it comes down to is, subjectively, where is the best compromise between low hiss, good volume control travel and hopefully we still have enough power delivered to phones.

As you have found out, sometimes you just can't find a good compromise.

 

Jan must have done a few calculations, but if he doesn't actually have a pair of LCD-2s, it's hard to nail down good real world values for those specific phones. 

Maybe try a lower ratio?

A friend of mine drives LCD-2 straight off the output of a small DECware vacuum tube power amp, I think it's about 10 Watts into 8 Ohms?

 

Chris

 

Thanks Chris,

 

I was beginning to think there was something "ideal" about the 3:1 ratio. I understand the strategy you've outlined. Thanks for the response!

 

:biggrin:

 

Mike

post #1669 of 2899
I hope he can help with that , but don't you need a low voltage off regulator so you do not go to low on the lipo batteries.

Do you understand what I mean??
post #1670 of 2899
Quote:
Originally Posted by zilch0md View Post
 

 

Thanks Chris,

 

I was beginning to think there was something "ideal" about the 3:1 ratio. I understand the strategy you've outlined. Thanks for the response!

 

:biggrin:

 

Mike

We can only hope that a lower ratio will bring back the dynamics!

post #1671 of 2899

Here's the alpha release of my headphone network calculator: http://robrobinette.com/images/Audio/Headphone_Resistor_Network_Calculator.xls

 

It's an Office spreadsheet created with Libreoffice but Microsoft compatible.

 

Using my HE-500's 32 ohm impedance and 8 ohms for my amp's load impedance it came up with R2 of 6 ohms and R3 of 2 using "Dual Resistor Network A."

 

Those resistors give an amp load of 7.9 ohms, headphone input impedance of 1.3 and amp attenuation of 4.2 times more than the headphones alone.

 

I'm very open to corrections and suggestions. Please don't actually build a network using it until the gurus look it over.

 

Rob


Edited by robrob - 12/1/13 at 9:17pm
post #1672 of 2899
Quote:
Originally Posted by ALRAINBOW View Post

I hope he can help with that , but don't you need a low voltage off regulator so you do not go to low on the lipo batteries.

Do you understand what I mean??

Thanks Al,

Yes, I could ask for that feature as well, but currently, I just use an alarm monitor that I've set to sound when any one cell falls to 3.4V, seen to the right of the amp, in this photo:



I suppose if he could incorporate an automatic shut-off, I'd be willing to pay a little more, but I don't know what the 4 Amp current limiter will cost, yet.

Mike
post #1673 of 2899
Quote:
Originally Posted by robrob View Post

Here's the alpha release of my headphone network calculator: http://robrobinette.com/images/Audio/Headphone_Resistor_Network_Calculator.xls

It's an Office spreadsheet created with Libreoffice but Microsoft compatible.

Using my HE-500's 32 ohm impedance and 8 ohms for my amp's load impedance it came up with R2 of 6 ohms and R3 of 2 using "Dual Resistor Network A."

Those resistors give an amp load of 7.9 ohms, headphone input impedance of 1.3 and amp attenuation of 4.2 times more than the headphones alone.

I'm very open to corrections and suggestions. Please don't actually build a network using it until the gurus look it over.

Rob

Thanks for this, Roberto!

I will dig into it, tomorrow, but as a user, rather than as a QA engineer. I'll let someone smarter than me take that role.

:-)

Mike
post #1674 of 2899
3.4 is way to low for the cells of a lipo. No lower than 3.6 volts ok. Lookup the manufacture of the battery and get there recommendations .

Al D
post #1675 of 2899
Quote:
Originally Posted by robrob View Post
 

Here's the alpha release of my headphone network calculator: http://robrobinette.com/images/Audio/Headphone_Resistor_Network_Calculator.xls

 

It's an Office spreadsheet created with Libreoffice but Microsoft compatible.

 

Using my HE-500's 32 ohm impedance and 8 ohms for my amp's load impedance it came up with R2 of 6 ohms and R3 of 2 using "Dual Resistor Network A."

 

Those resistors give an amp load of 7.9 ohms, headphone input impedance of 1.3 and amp attenuation of 4.2 times more than the headphones alone.

 

I'm very open to corrections and suggestions. Please don't actually build a network using it until the gurus look it over.

 

Rob

 

I'm not too sure what you are getting at with Headphone input impedance?

What is this number supposed to express?

Does it express "apparent output impedance" of the network?

Then delete "amp Impedance" from the formula headphone input impedance formula.

 

Attenuation is more easily understood if the number is inverted, but that's just my opinion and how I think.

I would express attenuation for the 2 resistor version as 0.24.

 

I guess you are neglecting the amp's own output impedance as it is so small?   That makes sense.


Edited by Chris J - 12/2/13 at 4:17am
post #1676 of 2899
Quote:
Originally Posted by Rob80b View Post
 

Hi Chris

 

I bought my current 2BLP pro for the HT also, first for the center channel then it was moved for surround duty, but it was replaced both times with more powerful amps to par with the 4BSST running the mains plus I'm running Dynaudio all round.

 

Robert

 

Hi Robert,

 

That's so funny!

I originally used the 2B-LP as a bridged centre channel amp, then I moved it to centre channel duty.

For centre channel, I replaced it with a Bryston PP 120 Mono Bloc.

One of these days I want to get a 3 channel Pass Labs amp to go with my front channel amp: A Pass Labs X-150.

 

Chris 

post #1677 of 2899
Quote:
 I'm not too sure what you are getting at with Headphone input impedance?

What is this number supposed to express?

Does it express "apparent output impedance" of the network?

Then delete "amp Impedance" from the formula headphone input impedance formula.

Yes, I'm trying to express the "apparent output impedance" of the network--what the headphones see. Should I ignore the amp's impedance or use 0.1 as an estimate?


Edited by robrob - 12/2/13 at 5:58am
post #1678 of 2899
Quote:
Originally Posted by ALRAINBOW View Post

3.4 is way to low for the cells of a lipo. No lower than 3.6 volts ok. Lookup the manufacture of the battery and get there recommendations .

Al D

 

I'm seeing no evidence of phase changes, swelling, failure to charge, etc. taking them down to 3.4V, but I'll research it.  Certainly, they'd be "happier" going no lower than 3.6V, as all rechargeable chemistries prefer to be shallow-cycled rather than deep cycled.  Thanks for the heads-up - I will look into it.

 

Mike

post #1679 of 2899
I think you misunderstood me. They will explode or puff from that kind of use
But what it might do is not charge anymore. This is what I meant.
Also go the an Rc website for battery info. Helifreak.com
post #1680 of 2899
Quote:
Originally Posted by robrob View Post

Yes, I'm trying to express the "apparent output impedance" of the network--what the headphones see. Should I ignore the amp's impedance or use 0.1 as an estimate?

 



As an electrical instructor once told us, "it depends".

My excel on my computer can't edit the formulas. I'm using a work computer right now, maybe I'll see if I can edit the excel at home. Groan......

You could argue that 0.1 Ohms is so small that you can ignore it and simplify the equation in dual resistor version A.......in a typical SS amp.

In dual resistor version B it's extremely important. But in dual resistor version B you could approximate the output impedance seen by the headphones as R2 only if the amp output impedance is very low.

I think most SS amps have an even lower output impedance than 0.1 Ohm.

You could also argue that the output impedance of a vacuum tube power amp is high enough to make a difference, but then you have to know what the output impedance is.....if you can find it! LOL
If it's an SET it may be two or three Ohms....or more!
Edited by Chris J - 12/2/13 at 9:47am
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