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Many AV Receivers/Stereo Integrated amps do NOT use opamp powered headphone jacks - Page 11

post #151 of 221

Another integrated/headphone method...

Here's yet another way to implement the headphone out in an integrated amp. I wrote to Patrick at Glow Audio to ask how their Amp One's headphone jack was implemented. No op amps. No resistors. I won't pretend to understand this. Perhaps someone can explain...

Quote:
The headphone output is tapped directly off the output transformers, the output is 500 mW. See our updated specifications below.
So, I assume that means it is further amplifed to the 5 watts at the speaker terminals after the ouput transformers? What effect would this have on sound?

Tim
post #152 of 221
Thread Starter 
That information is incomplete. 500mw at what impedance?

I chatted with an av engineer about the same idea. He stated that with a 300 ohm load he wouldn't even bother using a resistor since the headphone's large resistance would act like the same way as a resistor in the amp. Of course, he was assuming the power amp was not 1000w.

Perhaps the same assumption has been made by glow?
post #153 of 221
Quote:
Originally Posted by odigg View Post
That information is incomplete. 500mw at what impedance?

I chatted with an av engineer about the same idea. He stated that with a 300 ohm load he wouldn't even bother using a resistor since the headphone's large resistance would act like the same way as a resistor in the amp. Of course, he was assuming the power amp was not 1000w.

Perhaps the same assumption has been made by glow?
Yeah, I guess it depends on what you call complete. I followed up with that question, by the way. But lots of amps don't list an output impedance rating. I did a quick check of Headroom, Woo and HeadAmp, and only Headamp published this number (< 1 ohm). It seems that amp designers, even very good ones, are not nearly as concerned with this spec as many of us are. That tells me that there must be a lot of wiggle room in there for most phones. The other thing that tells me that is the much more common impedance rating for the range of phones the amp will drive. In the Glow's case that's 32 - 600 ohms.

Tim
post #154 of 221
Quote:
Originally Posted by odigg View Post
I chatted with an av engineer about the same idea. He stated that with a 300 ohm load he wouldn't even bother using a resistor since the headphone's large resistance would act like the same way as a resistor in the amp. Of course, he was assuming the power amp was not 1000w.
With a mere 50w RMS @ 8 ohms amplifier, a 300 ohms load will receive 1.3w RMS. I don't know the maximum power handling of 300 ohms phones like HD600/650, but my AKG K501 has a maximum power handling of only 0.2w, and the 250 ohms Beyerdynamic DT880 has 0.1w, I don't imagine the Senns will be much different, which is not a good idea to go without resistors.
post #155 of 221
Thread Starter 
Quote:
Originally Posted by tfarney View Post
Yeah, I guess it depends on what you call complete. I followed up with that question, by the way. But lots of amps don't list an output impedance rating. I did a quick check of Headroom, Woo and HeadAmp, and only Headamp published this number (< 1 ohm). It seems that amp designers, even very good ones, are not nearly as concerned with this spec as many of us are. That tells me that there must be a lot of wiggle room in there for most phones. The other thing that tells me that is the much more common impedance rating for the range of phones the amp will drive. In the Glow's case that's 32 - 600 ohms.

Tim
I think most people aren't concerned with "all that technical stuff" and so many amp makers don't publish them. My time on head-fi has led me to conclude the average person here knows (or cares) perhaps a little more about technical details than the average Joe in Best Buy.

Then again, I don't think this information is left out just because people don't care about it. To me it smells a bit strange, but that's not a theory for this thread.

Quote:
Originally Posted by Navyblue View Post
With a mere 50w RMS @ 8 ohms amplifier, a 300 ohms load will receive 1.3w RMS. I don't know the maximum power handling of 300 ohms phones like HD600/650, but my AKG K501 has a maximum power handling of only 0.2w, and the 250 ohms Beyerdynamic DT880 has 0.1w, I don't imagine the Senns will be much different, which is not a good idea to go without resistors.
The glow amp is 5w. A 300 ohm headphone should cut that down quite nicely
post #156 of 221
Quote:
Originally Posted by odigg View Post
I think most people aren't concerned with "all that technical stuff" and so many amp makers don't publish them. My time on head-fi has led me to conclude the average person here knows (or cares) perhaps a little more about technical details than the average Joe in Best Buy.

Then again, I don't think this information is left out just because people don't care about it. To me it smells a bit strange, but that's not a theory for this thread.



The glow amp is 5w. A 300 ohm headphone should cut that down quite nicely
The Glow is 5 watts at the speaker terminals. 600 mw at the headphone jack.

Tim
post #157 of 221
5 watts @ 8 ohms would give 0.0083 watts @ 300 ohms, about 1.6V rms, probably enough, but seems like on the low side.
post #158 of 221
I found the spec in the email Patrick at Glow sent. Sorry about that. I hadn't opened it and seen that he had attached revised specs. The headphone section is rated 500 mw @ 300 ohms. And here's the whole set he sent me:

Amp One



SPECIFICATIONS



OUTPUT IMPEDANCE
Speakers: 8Ω

Earphone: 32Ω~300Ω

OUTPUT POWER
Speakers: 5W×2 at 1KHz

Earphone: 500mW(300Ω)

FREQUENCY RESPONSE
50Hz-20KHz (±2dB)

T.H.D.
<1% (1W)

S/N
>89dB

INPUT IMPEDANCE
100KΩ

INPUT SENSITIVITY
550 mV~650mV

USB SOUND DECODER
16BitΔ/∑ decoder

USB connection

VACUUM TUBES
6N3×2, EL84×2

POWER CONSUMPTION
52W

POWER REQUIREMENT
115V(60Hz )/230V(50Hz) AC,

AC voltage is switchable.

DIMENSIONS (L x W x H)
238 mm x 138 mm x 148 mm

LINE IN TERMINAL
RCA stereo Connectors x 1

SPEAKER TERMINAL
Binding posts x 2

ACCESSORIES
Power cord x 1

USB cable x 1

HEADPHONE JACK
Stereo (6.35 mm diameter)

WEIGHT
Net Weight: 6.5KG

Shipping Weight: 9KG


Tim
post #159 of 221
Thread Starter 
Quote:
Originally Posted by Navyblue View Post
5 watts @ 8 ohms would give 0.0083 watts @ 300 ohms, about 1.6V rms, probably enough, but seems like on the low side.
Is your math right here? I'm getting 0.133 w @ 300 ohms. 6.3V. I could be wrong as I haven't done this stuff in a while.

Of course, that doesn't explain the glow's 0.5 w. Are they using the transformer to step it up? But there are only two transformers in there. One for each speaker channel...I think.
post #160 of 221
Quote:
Originally Posted by odigg View Post
Is your math right here? I'm getting 0.133 w @ 300 ohms. 6.3V. I could be wrong as I haven't done this stuff in a while.

Of course, that doesn't explain the glow's 0.5 w. Are they using the transformer to step it up? But there are only two transformers in there. One for each speaker channel...I think.
I don't get it either. In fact, I don't even get it enough to ask good questions. But they say the the headphone out is tapped directly off the output transformers, and they rate it at 500 mw into 300 ohms. And they rate the power off the speaker terminals at 5 watts into 8 ohms. And I would think if they were going to lie, they'd exaggerate a bit more .

Tim
post #161 of 221
Thread Starter 
Quote:
Originally Posted by tfarney View Post
I don't get it either. In fact, I don't even get it enough to ask good questions. But they say the the headphone out is tapped directly off the output transformers, and they rate it at 500 mw into 300 ohms. And they rate the power off the speaker terminals at 5 watts into 8 ohms. And I would think if they were going to lie, they'd exaggerate a bit more .

Tim
I'm not sure if doing power/impedance calculations for transformers is the same as what you would use for an amp that doesn't use an output transformer. You can tap an output transformer's secondary winding at different points for different impedances. So I assume the output transformers are tapped at least at 2 points. (8 ohms and 300 ohms).

The power that comes out of such a design is beyond what I know about electronics. Mcintosh uses output transformers, even in their non valve gear - I think. Not a useful bit of info for this thread, but something interesting to me.
post #162 of 221
Quote:
Originally Posted by odigg View Post
I'm not sure if doing power/impedance calculations for transformers is the same as what you would use for an amp that doesn't use an output transformer. You can tap an output transformer's secondary winding at different points for different impedances. So I assume the output transformers are tapped at least at 2 points. (8 ohms and 300 ohms).

The power that comes out of such a design is beyond what I know about electronics. Mcintosh uses output transformers, even in their non valve gear - I think. Not a useful bit of info for this thread, but something interesting to me.
Well, I'll have a Glow in here sometime in the next week or two for a trial run, and I'll be able to test the impedance of my ears, which is the only thing that matters.

Tim
post #163 of 221
just got my gilmore lite and i am doing some comparing with my audiolab integrated amps HP jack. hmm, the glite is a little more civilized than the audiolab and the audiolab seems to have a fakeness to its sound in a direct comparison but I feel the Audiolab got my toes tappin more. Not sure yet if its placebo because of my expectations. Powerwise though, they dont seem to have any problems at all driving my hd600s just like the audiolab. Now I feel that spending for a headphone amp at gilmore lite levels or under is not necessary when one has a good integrated amp
post #164 of 221
Thread Starter 
Quote:
Originally Posted by donunus View Post
just got my gilmore lite and i am doing some comparing with my audiolab integrated amps HP jack. hmm, the glite is a little more civilized than the audiolab and the audiolab seems to have a fakeness to its sound in a direct comparison but I feel the Audiolab got my toes tappin more. Not sure yet if its placebo because of my expectations. Powerwise though, they dont seem to have any problems at all driving my hd600s just like the audiolab. Now I feel that spending for a headphone amp at gilmore lite levels or under is not necessary when one has a good integrated amp
Hey donunus - You have the AD2000 don't you? Can you see how those sound out of the gilmore and the audiolab?
post #165 of 221
Quote:
Originally Posted by odigg View Post
Is your math right here? I'm getting 0.133 w @ 300 ohms. 6.3V. I could be wrong as I haven't done this stuff in a while.
Yes you are right.

Sheesh how do I get that number.
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