Headphone amp technology ?

[Rico67]

Why some headphoneamps have caps in the signal path (Cmoy , grado RA1etc..) and others like RSA haven't ?
Thank you for informations.
I'don't understand the reason why.

[Daroid]

You're not interested in amplifying DC voltages since they heat up the coils of the headphones.

A capacitor has an impedance caracterized by Z=1/jw*C, where C is the capacitance and w is the angular frequency in rad/sec. For DC, i.e. w=0, impedance reaches infinity.
The impedance is not always so because differenct capacitors have different equivalent circuits, but it is a very good asumption for DC and up to a few MHz.

RSA probably use some different topology i'm sure. There are other ways to detect DC which does not involve coupling capacitors, which effectively can shut off the amplifier if the dc voltage input is too high.

[ericj]

Analog audio is always alternating current - AC. Most audio devices have some DC offset -- this means that there's a portion of the signal that ls always above or below 'ground' even during complete silence.

When the DC offset is low, it's not a big deal. But a large DC offset reduces the incursion or excursion of the driver by moving the 'neutral' position of the driver in or out from where it would normally be at 0 volts.

If the DC offset is large enough, it can overheat the coil in the headphone driver or cause the driver to exceed it's maximum excursion, which ruins the driver.

Capacitors block DC voltage. Some amplifiers have input coupling capacitors because if you have a source with a DC offset of 10mv and an amp with a voltage gain of 11 (and no DC servo on the output), you end up with 110mv of DC offset at the output of the amplifier - which starts to be a problem.

It's unavoidable that an input (or output) coupling capacitor can color the sound, and some people prefer to avoid their use wherever possible.

So, some amps are built without coupling capacitors. And many of those have no DC servo either. There is always some chance of a bad DC offset at the output of the amp with these, depending on the DC offset of the source.

But most good sources don't have any significant dc offset in their output.

[ericj]

Originally Posted by Daroid

RSA probably use some different topology i'm sure. There are other ways to detect DC which does not involve coupling capacitors, which effectively can shut off the amplifier if the dc voltage input is too high.

Without having seen an RSA Hornet board or a schematic for one in person, I can't say what protection methods it may have.

It's entirely possible that it doesn't have any DC offset protection. The Mini3v2 for example does not. But it's a portable amp, and most portable sources have capacitor-coupled output or a headphone driver with it's own offset zeroing methods.

Nearly all of my amp knowledge is in DIY amps - but the truth is that commercial amps are very similar in design, and sometimes far less ambitious in design. Sometimes, it's the same flippin circuit in a pretty box with a high price tag.

Some amps, like the dynalo / gilmore lite (same thing) have a circuit that actively zeroes out the offset on the output. This is called a DC servo.

Some amps, especially tube amps but some solid-state designs as well, have output coupling capacitors.

And some are designed to have a stable ground reference but not to protect against DC offset on the input - these are referred to as DC-coupled amps. Sometimes these run without protection of any kind like my Rotel integrated amp, and sometimes they have DC offset and clipping detection, like my Akai power amp.

The protection circuits detect offset a variety of ways, but generally all of them use relays to open or close the circuit.

If you have a DC-coupled amp with no protection circuit, you can add a protection circuit to it. AMB Labs sells a DIY board for that which works quite well.

[b0dhi]

It's easy enough just to accurately set the bias on the amp so that the DC offset is very low. I easily adjusted my bal. M^3 to less than 0.5mV offset at full volume, I'm sure the builders of high end direct coupled amplifiers do the same thing. Unless your source has a high DC offset, it won't be any issue, and it's better not to have the capacitor in the signal path.

[Rico67]

Thank you for all informations.
I was talking about that because i use an Imod and made some test with direct coupling with different portable amps.
The result was that Imod didn't need special caps cables with Grado RA1, but need one with RSA Hornet.
I think, it's important to know what we do when we use caps on the imput of an amp.
because if you spend a lot of monay in external great caps (C1) and plug it on an amp with an internal poor caps (C2), result 'll be :
(C1XC2) / (C1+C2) = < at the minus cap.
And result'll be quite disapointed !

[SierraHotel01]

[QUOTE=Rico67;3828897]Why some headphoneamps have caps in the signal path (Cmoy , grado RA1etc..) and others like RSA haven't ?

One of the reasons Ray's portable amps need 500 hours of burn-in, is to "form" the capacitors. (Ask a EE for more detailed explanation). Sonically, a "well-formed" capacitor extends and sharpens bass response, while, at the same time, extending and sweetening high frequency response. Some listeners notice a dramatic psycho-acoustic difference after burn-in.

Ray builds state-of-the-art amps, and is one of the nicest, most reputable people you'll ever meet. Encourage you to search this forum and/or check out his website to learn more about his design philosophy.

Ray's Hornet portable amp certainly does have a capacitor in the signal path. Check out the quote below:

Sam Tellig (Stereophile) wrote about the Hornet in September 2006 (Vol.29 No.9):

"The Hornet is a marvel of miniaturization—there's good stuff inside: tantalum and film capacitors, 0.1% Vishay resistors, a milspec OFC printed-circuit board. A 15,000µF filter capacitor buffers the Hornet's op-amp chip with a secret circuit about which Ray Samuels keeps mum. (It's astonishing that Ray can get sound this good from an op-amp—a mere integrated circuit.)"

I've got an RSA Tomahawk. Built like a tank. Elegant design. But most importantly, it synergizes really well with my 3G Nano & headphones (SE530 / SR325i). You've just gotta hear it yourself, and decide if that's a sound signature you enjoy.

Wouldn't even consider listening to my iPod without connecting it to Ray's Tomahawk, via an Audio Line Out (ALO) Cryo Dock Cable. Add your favorite low impedance headphones, and "Off you go".

But then again, since all of this audiophile stuff is such a subjective experience, YMMV. Listen to what your own head tells you.

(N.B.: I also use SRS Labs iWOW, an audio enhancer plug-in for iTunes / iPod on a Mac. iWOW makes a DRAMATIC difference in an iPod or iTunes signal train. SRS Labs is a spin-out of Hughes Aircraft. They implement serious "rocket science" when it comes to audio signal processing. Check them out yourself. You can get a free 14 day demo of iWOW on their website, then if you like it, buy it for $19.95. They also have a version for PC's - I think it's called SRS Sandbox. What they did to all those 1's & 0's before they hit the DAC is very impressive. iWOW is quite appropriately named, IMHO. With such a phenomenal product, I'm surprised at their [lack of] marketing campaign. Oh yeah, they come from a military / aerospace business culture. If you like the iWOW result, pass the word along to your friends. That's what I'm doing.)

[SierraHotel01]

[QUOTE=Rico67;3828897]Why some headphoneamps have caps in the signal path (Cmoy , grado RA1etc..) and others like RSA haven't ?

One of the reasons Ray's portable amps need 500 hours of burn-in, is to "form" the capacitors. (Ask a EE for more detailed explanation). Sonically, a "well-formed" capacitor extends and sharpens bass response, while, at the same time, extending and sweetening high frequency response. Some listeners notice a dramatic psycho-acoustic difference after burn-in.

Ray builds state-of-the-art amps, and is one of the nicest, most reputable people you'll ever meet. Encourage you to search this forum and/or check out his website to learn more about his design philosophy.

Ray's Hornet portable amp certainly does have a capacitor in the signal path. Check out the quote below:

Sam Tellig (Stereophile) wrote about the Hornet in September 2006 (Vol.29 No.9):

"The Hornet is a marvel of miniaturization—there's good stuff inside: tantalum and film capacitors, 0.1% Vishay resistors, a milspec OFC printed-circuit board. A 15,000µF filter capacitor buffers the Hornet's op-amp chip with a secret circuit about which Ray Samuels keeps mum. (It's astonishing that Ray can get sound this good from an op-amp—a mere integrated circuit.)"

I've got an RSA Tomahawk. Built like a tank. Elegant design. But most importantly, it synergizes really well with my 3G Nano & headphones (SE530 / SR325i). You've just gotta hear it yourself, and decide if that's a sound signature you enjoy.

Wouldn't even consider listening to my iPod without connecting it to Ray's Tomahawk, via an Audio Line Out (ALO) Cryo Dock Cable. Add your favorite low impedance headphones, and "Off you go".

But then again, since all of this audiophile stuff is such a subjective experience, YMMV. Listen to what your own head tells you.

(N.B.: I also use and highly recommend SRS Labs iWOW, an audio enhancer plug-in for iTunes / iPod on a Mac. iWOW makes a DRAMATIC difference in an iPod / iTunes signal train. SRS Labs is a spin-out of Hughes Aircraft. They implement serious "rocket science" when it comes to audio signal processing. Check them out yourself. You can get a free 14 day demo of iWOW on their website, then if you like it, buy it for $19.95. They also have a version for PC's - I think it's called SRS Sandbox. What they do to all those 1's & 0's before they hit the DAC is very impressive. iWOW is quite appropriately named, IMHO. With such a phenomenal product, I'm surprised at their [lack of] marketing campaign. Oh yeah, they come from a military / aerospace business culture. If you like the iWOW result, pass the word along to your friends. That's what I'm doing.)