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Speaker amps for headphones - Page 149

post #2221 of 2719
Quote:
Originally Posted by Gary in MD View Post
 


How about a gold case, nice-looking connectors a shiny display and impressive knobs?

 

To follow this topic a bit further, the Audio-gd M9 appears to use relays for attenuation, and has 100 steps of attenuation. If I am understanding all of this correctly (not likely) that means that there are 100 relays, and one of them is opened for each step, allowing the signal to flow to one of 100 different resistor circuits, thus varying the output signal level.  So the components in the signal path include the open relay and whatever resistors are in the selected circuit.  The relay controller is not technically in the signal chain, since it is simply telling the relays to open and close according to external commands.  And of course this is duplicated for each channel.  Right?

 

Alternatively, if I am understanding the LDR system correctly, the the only thing in the Tortuga signal chain is the LDR, which varies its resistance based on how much light hits it. I assume that means that the LDRs are shut off from all external stray light in the critical wavelengths, and I'm guessing that those wavelengths are well into the optical part of the spectrum, otherwise you would get significant drift due to changes in temperature introducing stray light...???  In any case, the light has to be carefully controlled to ensure proper attenuation, because the LDR response is not perfectly linear with changes in the light. Based on earlier discussions in this thread, the response of each individual LDR is also unique, so you would have to either map each LDR's response and then teach the controller how much light to shine on that particular resistor to get a particular level of resistance, while hoping that it never changes (fat chance) or instead put some sort of feedback loop in to measure the actual output level and adjust the light accordingly in real time.  With the latter, the chain is not perfectly pristine any more, and is definitely not as simple as the relay system, which would seem to me to be a bit more predictable, as long as one assumes the resistors are stable in their performance over time.  

 

So how much of this did I get right?

You are pretty well right on. The LDRs can drift over time, but it's not any more significant than a normal resistor. There's also the benefit of updating the micro-controller at a later date to ensure tight calibration. No feedback loops for the reason you stated.

post #2222 of 2719
Quote:
Originally Posted by Gary in MD View Post
 


How about a gold case, nice-looking connectors a shiny display and impressive knobs?

 

To follow this topic a bit further, the Audio-gd M9 appears to use relays for attenuation, and has 100 steps of attenuation. If I am understanding all of this correctly (not likely) that means that there are 100 relays, and one of them is opened for each step, allowing the signal to flow to one of 100 different resistor circuits, thus varying the output signal level.  So the components in the signal path include the open relay and whatever resistors are in the selected circuit.  The relay controller is not technically in the signal chain, since it is simply telling the relays to open and close according to external commands.  And of course this is duplicated for each channel.  Right?

 

Alternatively, if I am understanding the LDR system correctly, the the only thing in the Tortuga signal chain is the LDR, which varies its resistance based on how much light hits it. I assume that means that the LDRs are shut off from all external stray light in the critical wavelengths, and I'm guessing that those wavelengths are well into the optical part of the spectrum, otherwise you would get significant drift due to changes in temperature introducing stray light...???  In any case, the light has to be carefully controlled to ensure proper attenuation, because the LDR response is not perfectly linear with changes in the light. Based on earlier discussions in this thread, the response of each individual LDR is also unique, so you would have to either map each LDR's response and then teach the controller how much light to shine on that particular resistor to get a particular level of resistance, while hoping that it never changes (fat chance) or instead put some sort of feedback loop in to measure the actual output level and adjust the light accordingly in real time.  With the latter, the chain is not perfectly pristine any more, and is definitely not as simple as the relay system, which would seem to me to be a bit more predictable, as long as one assumes the resistors are stable in their performance over time.  

 

So how much of this did I get right?

 

Quite a lot of it.  The LDR started life (back in the bad "good ol' days" as an open form:  LED over here, light dependent resistor over there.  Box had to be perfectly sealed, or folks were making their own sealed assemblies.  Modern LDR's are integrated into a light tight package.  4 lead package.  2 for driving the LED, 2 for passing the signal through.  

The Tortuga methodology takes a whole slew of LDR's and measures the resistance Vs current drive to the LED and then matches them up.  Software then controls the map of control input to current drive for each device for the desired resistance profile.  What it does not do is compensate for changes in performance of the LDR over time.  I don't know how severe those changes are with time, but since they are non-linear devices, they are bound to change differently relative to each other.

I'm no expert, by any means, and have yet to experience a good stepped attenuator, but versus very good potentiometers as an attenuation device, I give the LDR (even without the microprocessor drive) the win.

Switches used in pre-amps are an interesting topic all by themselves.  I've not found a toggle switch I like.  Reed relays present a more faithful signal across their contacts.  At least when new.  At least at reasonable signal levels.  Careful with too much signal.  Careful with too little signal.  Both cause problems with dry contact reed relays.  More rare, but higher quality for audio are Hg wetted reed relays.  Large cycle lifetime.  Near zero signal degradation with both very low and with moderately high signal levels.  Of course there are problems with them.  You need power to drive the coils when switching (with latching relays) or continuous voltage to the coil in non-latching designs.  They are expensive.  Yes you can still get them, but they are spendy.  And, of course, they are not RoHS compliant, so selling a device with them incorporated is difficult.

 

Perfect pre-amp?  For me it would be 2 - 3 switchable input channels, 2 - 3 switchable outputs.  Switchgear would be decent quality rotary switches driving Hg wetted relays.  Signal attenuation would be handled with an LDR-based attenuator, perhaps followed with a Class A JFET buffer stage for low gain and to provide low output impedance.

post #2223 of 2719

Haha, remember a few weeks back I was telling all you nutty guys to put autoformers between your amps and headphones?

 

Well now McIntosh is in the game with their MHP1000 headphone amp... http://www.whathifi.com/news/mcintosh-introduces-new-compact-amps-media-bridge-and-headphones-at-ces-2014

Quote:
The MHA100 is McIntosh's first dedicated headphone amp. It has four digital inputs to allow playback of music files in a wide variety of formats, while the headphone section uses McIntosh-designed and hand-wound impedance matching Autoformers to deliver "full McIntosh power" into any set of headphones.

Users can choose from three headphone impedance ranges: 8-40ohms, 40-150ohms and 150-600ohms.

post #2224 of 2719
Quote:
Originally Posted by Gary in MD View Post


How about a gold case, nice-looking connectors a shiny display and impressive knobs?

To follow this topic a bit further, the Audio-gd M9 appears to use relays for attenuation, and has 100 steps of attenuation. If I am understanding all of this correctly (not likely) that means that there are 100 relays, and one of them is opened for each step, allowing the signal to flow to one of 100 different resistor circuits, thus varying the output signal level.  So the components in the signal path include the open relay and whatever resistors are in the selected circuit.  The relay controller is not technically in the signal chain, since it is simply telling the relays to open and close according to external commands.  And of course this is duplicated for each channel.  Right?

Alternatively, if I am understanding the LDR system correctly, the the only thing in the Tortuga signal chain is the LDR, which varies its resistance based on how much light hits it. I assume that means that the LDRs are shut off from all external stray light in the critical wavelengths, and I'm guessing that those wavelengths are well into the optical part of the spectrum, otherwise you would get significant drift due to changes in temperature introducing stray light...???  In any case, the light has to be carefully controlled to ensure proper attenuation, because the LDR response is not perfectly linear with changes in the light. Based on earlier discussions in this thread, the response of each individual LDR is also unique, so you would have to either map each LDR's response and then teach the controller how much light to shine on that particular resistor to get a particular level of resistance, while hoping that it never changes (fat chance) or instead put some sort of feedback loop in to measure the actual output level and adjust the light accordingly in real time.  With the latter, the chain is not perfectly pristine any more, and is definitely not as simple as the relay system, which would seem to me to be a bit more predictable, as long as one assumes the resistors are stable in their performance over time.  

So how much of this did I get right?

You don't need 100 relays, you need to have enough relays to generate 100 combinations.
There is a mathematician out there somewhere who can tell us how many relays we need, probably closer to 11 or 12 relays!
Each relay will have two sets of contacts for left and right.
So you don't need to duplicate controllers for each channel.
The relay controller is not in the signal path as it is only telling the relays what to do.
You could also get the controller to operate via remote control.
You could also program the controller and relays to act as left-right balance control.
Edited by Chris J - 1/12/14 at 2:46am
post #2225 of 2719
Quote:
Originally Posted by Armaegis View Post

Haha, remember a few weeks back I was telling all you nutty guys to put autoformers between your amps and headphones?

Well now McIntosh is in the game with their MHP1000 headphone amp... http://www.whathifi.com/news/mcintosh-introduces-new-compact-amps-media-bridge-and-headphones-at-ces-2014

Yeah, Mac has always been a big proponent of using autotransformers on the outputs of their SS power amps.
post #2226 of 2719
Quote:
Originally Posted by Chris J View Post


You don't need 100 relays, you need to have enough relays to generate 100 combinations.
There is a mathematician out there somewhere who can tell us how many relays we need, probably closer to 11 or 12 relays!
Each relay will have two sets of contacts for left and right.
So you don't need to duplicate controllers for each channel.
The relay controller is not in the signal path as it is only telling the relays what to do.
You could also get the controller to operate via remote control.
You could also program the controller and relays to act as left-right balance control.

 

I'm not a mathematician - just a consumer of math, but I found this permutations and combinations calculator, which has revealed the following:

 

2 relays =  4 possible combinations

{a,a} {a,b} {b,a} {b,b}

 

3 relays = 8 possible combinations

{a,a,a} {a,a,b} {a,b,a} {a,b,b} {b,a,a} {b,a,b} {b,b,a} {b,b,b}

 

4 relays = 16 possible combinations

{a,a,a,a} {a,a,a,b} {a,a,b,a} {a,a,b,b} {a,b,a,a} {a,b,a,b} {a,b,b,a} {a,b,b,b} {b,a,a,a} {b,a,a,b} {b,a,b,a} {b,a,b,b} {b,b,a,a} {b,b,a,b} {b,b,b,a} {b,b,b,b}

 

5 relays = 32 possible combinations 

{a,a,a,a,a} {a,a,a,a,b} {a,a,a,b,a} {a,a,a,b,b} {a,a,b,a,a} {a,a,b,a,b} {a,a,b,b,a} {a,a,b,b,b} {a,b,a,a,a} {a,b,a,a,b} {a,b,a,b,a} {a,b,a,b,b} {a,b,b,a,a} {a,b,b,a,b} {a,b,b,b,a} {a,b,b,b,b} {b,a,a,a,a} {b,a,a,a,b} {b,a,a,b,a} {b,a,a,b,b} {b,a,b,a,a} {b,a,b,a,b} {b,a,b,b,a} {b,a,b,b,b} {b,b,a,a,a} {b,b,a,a,b} {b,b,a,b,a} {b,b,a,b,b} {b,b,b,a,a} {b,b,b,a,b} {b,b,b,b,a} {b,b,b,b,b}

 

6 relays = 64 possible combinations

{a,a,a,a,a,a} {a,a,a,a,a,b} {a,a,a,a,b,a} {a,a,a,a,b,b} {a,a,a,b,a,a} {a,a,a,b,a,b} {a,a,a,b,b,a} {a,a,a,b,b,b} {a,a,b,a,a,a} {a,a,b,a,a,b} {a,a,b,a,b,a} {a,a,b,a,b,b} {a,a,b,b,a,a} {a,a,b,b,a,b} {a,a,b,b,b,a} {a,a,b,b,b,b} {a,b,a,a,a,a} {a,b,a,a,a,b} {a,b,a,a,b,a} {a,b,a,a,b,b} {a,b,a,b,a,a} {a,b,a,b,a,b} {a,b,a,b,b,a} {a,b,a,b,b,b} {a,b,b,a,a,a} {a,b,b,a,a,b} {a,b,b,a,b,a} {a,b,b,a,b,b} {a,b,b,b,a,a} {a,b,b,b,a,b} {a,b,b,b,b,a} {a,b,b,b,b,b} {b,a,a,a,a,a} {b,a,a,a,a,b} {b,a,a,a,b,a} {b,a,a,a,b,b} {b,a,a,b,a,a} {b,a,a,b,a,b} {b,a,a,b,b,a} {b,a,a,b,b,b} {b,a,b,a,a,a} {b,a,b,a,a,b} {b,a,b,a,b,a} {b,a,b,a,b,b} {b,a,b,b,a,a} {b,a,b,b,a,b} {b,a,b,b,b,a} {b,a,b,b,b,b} {b,b,a,a,a,a} {b,b,a,a,a,b} {b,b,a,a,b,a} {b,b,a,a,b,b} {b,b,a,b,a,a} {b,b,a,b,a,b} {b,b,a,b,b,a} {b,b,a,b,b,b} {b,b,b,a,a,a} {b,b,b,a,a,b} {b,b,b,a,b,a} {b,b,b,a,b,b} {b,b,b,b,a,a} {b,b,b,b,a,b} {b,b,b,b,b,a} {b,b,b,b,b,b}

 

7 relays = 128 possible combinations

{a,a,a,a,a,a,a} {a,a,a,a,a,a,b} {a,a,a,a,a,b,a} {a,a,a,a,a,b,b} {a,a,a,a,b,a,a} {a,a,a,a,b,a,b} {a,a,a,a,b,b,a} {a,a,a,a,b,b,b} {a,a,a,b,a,a,a} {a,a,a,b,a,a,b} {a,a,a,b,a,b,a} {a,a,a,b,a,b,b} {a,a,a,b,b,a,a} {a,a,a,b,b,a,b} {a,a,a,b,b,b,a} {a,a,a,b,b,b,b} {a,a,b,a,a,a,a} {a,a,b,a,a,a,b} {a,a,b,a,a,b,a} {a,a,b,a,a,b,b} {a,a,b,a,b,a,a} {a,a,b,a,b,a,b} {a,a,b,a,b,b,a} {a,a,b,a,b,b,b} {a,a,b,b,a,a,a} {a,a,b,b,a,a,b} {a,a,b,b,a,b,a} {a,a,b,b,a,b,b} {a,a,b,b,b,a,a} {a,a,b,b,b,a,b} {a,a,b,b,b,b,a} {a,a,b,b,b,b,b} {a,b,a,a,a,a,a} {a,b,a,a,a,a,b} {a,b,a,a,a,b,a} {a,b,a,a,a,b,b} {a,b,a,a,b,a,a} {a,b,a,a,b,a,b} {a,b,a,a,b,b,a} {a,b,a,a,b,b,b} {a,b,a,b,a,a,a} {a,b,a,b,a,a,b} {a,b,a,b,a,b,a} {a,b,a,b,a,b,b} {a,b,a,b,b,a,a} {a,b,a,b,b,a,b} {a,b,a,b,b,b,a} {a,b,a,b,b,b,b} {a,b,b,a,a,a,a} {a,b,b,a,a,a,b} {a,b,b,a,a,b,a} {a,b,b,a,a,b,b} {a,b,b,a,b,a,a} {a,b,b,a,b,a,b} {a,b,b,a,b,b,a} {a,b,b,a,b,b,b} {a,b,b,b,a,a,a} {a,b,b,b,a,a,b} {a,b,b,b,a,b,a} {a,b,b,b,a,b,b} {a,b,b,b,b,a,a} {a,b,b,b,b,a,b} {a,b,b,b,b,b,a} {a,b,b,b,b,b,b} {b,a,a,a,a,a,a} {b,a,a,a,a,a,b} {b,a,a,a,a,b,a} {b,a,a,a,a,b,b} {b,a,a,a,b,a,a} {b,a,a,a,b,a,b} {b,a,a,a,b,b,a} {b,a,a,a,b,b,b} {b,a,a,b,a,a,a} {b,a,a,b,a,a,b} {b,a,a,b,a,b,a} {b,a,a,b,a,b,b} {b,a,a,b,b,a,a} {b,a,a,b,b,a,b} {b,a,a,b,b,b,a} {b,a,a,b,b,b,b} {b,a,b,a,a,a,a} {b,a,b,a,a,a,b} {b,a,b,a,a,b,a} {b,a,b,a,a,b,b} {b,a,b,a,b,a,a} {b,a,b,a,b,a,b} {b,a,b,a,b,b,a} {b,a,b,a,b,b,b} {b,a,b,b,a,a,a} {b,a,b,b,a,a,b} {b,a,b,b,a,b,a} {b,a,b,b,a,b,b} {b,a,b,b,b,a,a} {b,a,b,b,b,a,b} {b,a,b,b,b,b,a} {b,a,b,b,b,b,b} {b,b,a,a,a,a,a} {b,b,a,a,a,a,b} {b,b,a,a,a,b,a} {b,b,a,a,a,b,b} {b,b,a,a,b,a,a} {b,b,a,a,b,a,b} {b,b,a,a,b,b,a} {b,b,a,a,b,b,b} {b,b,a,b,a,a,a} {b,b,a,b,a,a,b} {b,b,a,b,a,b,a} {b,b,a,b,a,b,b} {b,b,a,b,b,a,a} {b,b,a,b,b,a,b} {b,b,a,b,b,b,a} {b,b,a,b,b,b,b} {b,b,b,a,a,a,a} {b,b,b,a,a,a,b} {b,b,b,a,a,b,a} {b,b,b,a,a,b,b} {b,b,b,a,b,a,a} {b,b,b,a,b,a,b} {b,b,b,a,b,b,a} {b,b,b,a,b,b,b} {b,b,b,b,a,a,a} {b,b,b,b,a,a,b} {b,b,b,b,a,b,a} {b,b,b,b,a,b,b} {b,b,b,b,b,a,a} {b,b,b,b,b,a,b} {b,b,b,b,b,b,a} {b,b,b,b,b,b,b}

 

The volume control of my Meier Audio Corda Stepdance has 32 steps, so there must be five relays.

 

If you want to reproduce this via the calculator at the link above, my inputs for the last calculation were:   2, 7, Yes, Yes.

 

Joy!

 

Mike


Edited by zilch0md - 1/12/14 at 6:12am
post #2227 of 2719
Ah, I figured there's got to be an "easy" way to figure this out.
That makes sense!
128 steps is nice, you can increase and decrease volume in 0.5 dB steps.

I'll leave Gary to decide whether the case or the contacts should be gold plated.......
post #2228 of 2719
Quote:
Originally Posted by Armaegis View Post
 

Haha, remember a few weeks back I was telling all you nutty guys to put autoformers between your amps and headphones?

 

Well now McIntosh is in the game with their MHP1000 headphone amp... http://www.whathifi.com/news/mcintosh-introduces-new-compact-amps-media-bridge-and-headphones-at-ces-2014

 

Like this one http://www.enjoythemusic.com/diy/0611/slagle_autoformer_volume_control_modules.htm

post #2229 of 2719

Not the prettiest case work I have ever seen!
Kinda looks like the DIY pre-amp I built in '88.
post #2230 of 2719
Quote:
Originally Posted by Chris J View Post


Not the prettiest case work I have ever seen!
Kinda looks like the DIY pre-amp I built in '88.

 

I know, if I'm going to build one, I'll get a case from this place http://www.modushop.biz/

post #2231 of 2719
Quote:
Originally Posted by wuwhere View Post
 

 

I know, if I'm going to build one, I'll get a case from this place http://www.modushop.biz/

+1 I use them and Lansing :D 

post #2232 of 2719
Quote:
Originally Posted by wuwhere View Post

I know, if I'm going to build one, I'll get a case from this place http://www.modushop.biz/

There stuff looks nice!
No need to hide your DIY from the neighbours or your friends, LOL!
post #2233 of 2719
Quote:
Originally Posted by Chris J View Post


There stuff looks nice!
No need to hide your DIY from the neighbours or your friends, LOL!

LOL, you could always forego the fancy case, and mount them under the floor if you have a basement or something for the ultra-clean look, and get a IR repeater :tongue_smile:

post #2234 of 2719
Quote:
Originally Posted by Chris J View Post


There stuff looks nice!
No need to hide your DIY from the neighbours or your friends, LOL!

 

I have hazy plans to build my next amp into a suitcase...

post #2235 of 2719
Quote:
Originally Posted by Armaegis View Post

I have hazy plans to build my next amp into a suitcase...

good idea.
Send a review sample to CIA weekly digest or NSA monthly magazine or to the Homeland Security blog.

Ooooops.
Nevermind.
I forgot you were Canadian.
CSIS wants to hear it.cool.gif
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