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Speaker amps for headphones - Page 117

post #1741 of 3116
Quote:
 The "Attenuation Only" scenario: formula for amplifier attenuation is incorrect, it should ignore R3 entirely. I think that's why Mike was getting funny numbers; it looks like it's calculating stuff the same way as "preferred" scenario.

I thought I fixed that. It is using the incorrect formula from the "Preferred" scenario.  

post #1742 of 3116

fixed equations...

 

load resistor for tube amps (p.s. this should be for transformer coupled tube amps)

=1/(1/Res1 + 1/HeadImp)

=1/(1/AmpOut + 1/Res1)

None

 

 

preferred headphone interface

=IF(Res3=0, R2+HeadImp, Res2+1/(1/Res3+1/HeadImp))

=IF(R3=0, Res2+AmpOut, 1/(1/Res3 + 1/(Res2+AmpOut)))

ugh not gonna dig through the last one

 

 

attenuation only

=Res2+HeadImp

=AmpOut+Res2

 

 

 

Blargh that's all that I can do for now. We could get rid of those logic statements entirely if you created some hidden hash variables somewhere and used

Res1actual = IF(Res1=0, 1000000000, Res1)

Res2 shouldn't change

Res3actual= IF(Res3=0, 1000000000, Res3)

 

Then use the Res#actual in your formulas

post #1743 of 3116
Quote:
Originally Posted by Chris J View Post
 

 

Yes, fellas, resistor noise is irrelevant in this application.

It will be utterly swamped by the noise from your power amp.

 

And perhaps in most cases, the thermal noise of the voice coils in your headphones.

 

se

post #1744 of 3116

What is the attenuation formula for the "Attenuation Only" scenario with only R2?

 

Is it 20*log(HeadImp/R2+HeadImp) ?

post #1745 of 3116

Yes

post #1746 of 3116
Quote:
Originally Posted by robrob View Post
 

What is the attenuation formula for the "Attenuation Only" scenario with only R2?

 

Is it 20*log(HeadImp/R2+HeadImp) ?

Actually, isn't it  20*log(HeadImp/(R2+HeadImp))?

post #1747 of 3116

Thanks again Armaegis, beta8 is now up and has the correct attenuation only formulas. I know the nested DIV0 protection statements could be done much more elegantly but they work.

 

I'm going to flesh out the instructions to cover all the scenarios you and Chris mentioned.

post #1748 of 3116
Quote:
Originally Posted by potterma View Post
 

Actually, isn't it  20*log(HeadImp/(R2+HeadImp))?

Yes, good catch on the missing ( )

 

The spreadsheet has them in place.


Edited by robrob - 12/4/13 at 7:50pm
post #1749 of 3116

alternate dual resistor network, formulas:

=IF(Res1=0, Res2+HeadImp, 1/(1/Res1 + 1/(Res2 + HeadImp)))

=IF(Res1=0, Res2+AmpOut, Res2+1/(1/Res1 + 1/AmpOut))

=20*LOG(HeadImp/(HeadImp+Res2))

post #1750 of 3116

In Libreoffice

 

Tools --> Macros --> Organize --> Libreoffice Basic

click edit

type this in:


 

Quote:

Function par(a, b)
par=1/(1/a + 1/b)

End Function

 

 

Now anywhere in the spreadsheet, you can type

=par(Res3, HeadImp)

and it will give you the parallel'd calculation

post #1751 of 3116

Booyah!

post #1752 of 3116
Quote:
Originally Posted by Armaegis View Post
 

Now anywhere in the spreadsheet, you can type

=par(Res3, HeadImp)

and it will give you the parallel'd calculation

Nice!

post #1753 of 3116
Quote:
Originally Posted by Gary in MD View Post

 

So is this why Mike's HD600s sound great with a resistor box initially designed for the low-impedance LCD-2s?

 

Gary,

 

Playing with Rob's spreadsheet, with values entered for the MG3 and and Jan Plummer's choice of 10-Ohm and 2-Ohm resistors, changing the headphone impedance from 50 Ohms (LCD-) to 300 Ohms (HD600) has almost no affect on attenuation.  And this jives with something Jan Plummer told me on the phone one day (paraphrasing): "Selecting the series resistor [the one that attenuates voltage] is more about considering the intended headphone's sensitivity than its impedance."  

 

That's obviously correct, now that I'm playing with the spreadsheet.  To answer your question, since the attenuation caused by Jan's resistor box, is effectively the same with the HD600 as it is with the LCD-2 (since they are both enjoying the same voltage), it must be the HD600's greater sensitivity that allows it to exploit the available power more than the less sensitive LCD-2.

 

Mike

post #1754 of 3116

Makes sense... which should scare you, since I've been watching this spreadsheet-building frenzy with great fascination, but haven't been to follow it all that well.  You guys clearly speak a different language than us non engineers, and that's great.

 

In fact I find this whole episode to be very uplifting.  You folks don't know each other, live in different states, different countries, etc. but got together and produced an excellent product that will serve the community well.. and all for the love of the hobby.  High fives to all of you, except my arms aren't that long...


Edited by Gary in MD - 12/4/13 at 9:30pm
post #1755 of 3116
Quote:
Originally Posted by zilch0md View Post
 

Yes, thanks Rob for trailblazing this spreadsheet!

 

Compare this to the results shown for my current TBI dual-resistor network:

 

 

[snip]

 

 

That's much better!  And now, to test it with my ears, expecting to hear -6 dB attenuation, instead of -15.8 dB...

 

:o

 

Mike

 

OK...  

 

Here's the short version:  I can still hear hiss in the MG3 to LCD-2, with the 50-Ohm series resistors in place (for -6.0 dB attenuation).  But the dynamics are wonderful!  The LCD-2 have come to life!  

 

Sadly, the hiss is still just too obvious during quiet passages.  And, as many MG3 owners are already aware, you can hear the hiss as soon as you turn on the amp  -and- it does not vary when turning the volume knob.  

 

So...

 

I serially combined my two 50-Ohm resistors on one channel - to get 100 Ohms (for -9.5 dB attenuation, instead of -6.0 dB) - the hiss was both detectable and tolerable, but it's not gone entirely, as is the case with Jan Plummer's resistor box, that applies -15.8 dB attenuation.

 

Conclusion - I'm done trying to use the LCD-2 with the MG3.  Killing the hiss effectively = effectively killing the dynamics.  

 

So...  My MG3 is now going to be used  with my Definitive Technology SM45 near-field monitors and my HD600 (via Jan's resistor box) - which is marvelous - and the LCD-2 are still in search of an amp with lots of power.  I guess I'll start saving up for an Odyssey Cyclops.

 

Thanks for all the help, everyone - I've learned a LOT!

 

:L3000:

 

Mike

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