Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: RMAA Headphone Amp Tests (Read 13915 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

RMAA Headphone Amp Tests

Reply #25 –
Quote
I'm not sure what you're asking... if you mean test procedure, I used a splitter from the headphone out jack to go to a pair of headphones (HD600) and also to the soundcard's input jack.

That is just what I wanted to know.
 

RMAA Headphone Amp Tests

Reply #26 –
Revo measurements, including soundcard baseline, at http://www.kikeg.arrakis.es/measurements/R...lutionHD580.htm

As you can see, frequency response is much better, but, as it was possible to happen, IMD value is not very good, and worse than in DoobAmp, due to low-freq. distortion, which is due to lack of power reserve.

Frequency response problems at both headamps would be clearly audible, but low freq. distortion at Revo output is not very likely to be, in my opinion.

With the SantaCruz soundcard, which seems to have a dedicated transistor output stage (Revo has just 2 paralelled opamps), it's possible that distortion figure is better.

And, using the resistor voltage divider at the output of a decent speaker amp would yield nearly perfect measurements.

Edit: however, if poor frequency response at the DoobAmp is due to crossfeed circuitry, quite likely it would be fixed just disabling or removing this crossfeed.

RMAA Headphone Amp Tests

Reply #27 –
Quote
There was some speculation on the Head-Fi thread that the frequency response variations of the Meta42 could be caused by the crossfeed circuit -- who knows.

I mixed frequency response curves at the original post, I just edited it. The problems at the Meta42 are very likely to be caused by the crossfeed circuitry, as you say. The problems at Creek amp are the ones due to a too high output impedance.

RMAA Headphone Amp Tests

Reply #28 –
KikeG, what amp do you have? Have you tried doing tests with a split cable?

RMAA Headphone Amp Tests

Reply #29 –
Quote
Very good performance is possible to achieve for any kind of headphone, just using a simple voltage divider with the adequate resistor values, at the speaker outputs of a minimally decent receiver or speaker amp.

Wouldn't this rise the output impedance level and negate the benefits of having a good headphone amplifier (besides 'I can play LOUD man!' one)? AFAIK one would want output impedance as low as possible.

RMAA Headphone Amp Tests

Reply #30 –
Quote
Quote
There was some speculation on the Head-Fi thread that the frequency response variations of the Meta42 could be caused by the crossfeed circuit -- who knows.

I mixed frequency response curves at the original post, I just edited it. The problems at the Meta42 are very likely to be caused by the crossfeed circuitry, as you say. The problems at Creek amp are the ones due to a too high output impedance.

I got rid of the "DoobAmp" (sold) and got another Meta42 instead... it seems like a good design in a headphone amp (albeit on the expensive side).  Hasn't arrived yet, but will test it eventually when it does.

Today I did something interesting (and risky) -- removed/jumpered the headphone jack output resistors (470 ohms per channel) from my ca. late 80's Sony TA-AX205 speaker amp.  This evened out the frequency response of my HD-580s greatly, but now I have to be careful plugging/unplugging the jack, and make sure to do it with power off (so it won't be shorted out even briefly).  Also, the range of the volume control is more restricted.  No big deal on either point, it was well worth it... sounds better, bass hump is gone, neutrality is greatly improved.



Picture of headphone jack from inside with resistors removed/jumpered.  The remaining resistor grounds the headphone jack to the case.

RMAA Headphone Amp Tests

Reply #31 –
Quote
... I have to be careful plugging/unplugging the jack, and make sure to do it with power off (so it won't be shorted out even briefly).

Make sure that you wait at least 20-30 seconds after turning the amplifier off to allow the big power supply filtering capacitors to discharge (if the amp design doesn't completely cut off power supply to output stages AFTER the capacitors).

RMAA Headphone Amp Tests

Reply #32 –
Quote
Quote
... I have to be careful plugging/unplugging the jack, and make sure to do it with power off (so it won't be shorted out even briefly).

Make sure that you wait at least 20-30 seconds after turning the amplifier off to allow the big power supply filtering capacitors to discharge (if the amp design doesn't completely cut off power supply to output stages AFTER the capacitors).

The amp contains a relay which I believe shuts off almost immediately when power is turned off.  It takes about 4 seconds to engage after power on (which I assume happens after the PSU filter caps charge up -- they're really large ones).

RMAA Headphone Amp Tests

Reply #33 –
Quote
KikeG, what amp do you have?

I don't understand what you mean. Do you mean speaker amp?

Quote
Have you tried doing tests with a split cable?

My measurements of the Revo output were done with a splitter connector at the Revo output. That's the only way of evaluating real output performance when driving headphones.

RMAA Headphone Amp Tests

Reply #34 –
Quote
Wouldn't this rise the output impedance level and negate the benefits of having a good headphone amplifier (besides 'I can play LOUD man!' one)?

Not if you pick adequately the resistor values. An output impedance equivalent to a few ohms is easy to achieve. The 20 ohm/2 ohm divider, for example, works well in this sense. The only thing you need to be careful is that the 20 ohm resistor is rated several watts.

RMAA Headphone Amp Tests

Reply #35 –
Quote
I don't understand what you mean. Do you mean speaker amp?


I thought you performed a headphone amp test.

Quote
My measurements of the Revo output were done with a splitter connector at the Revo output. That's the only way of evaluating real output performance when driving headphones.


I disagree. Normal listening does not include a splitter cable that leaches current away from the headphones (Kirchhoff). I agree it can be useful to see if the amp can take the load.

RMAA Headphone Amp Tests

Reply #36 –
Quote
I disagree. Normal listening does not include a splitter cable that leaches current away from the headphones (Kirchhoff). I agree it can be useful to see if the amp can take the load.

HD580  impedance is ~300Ohms. Input impedance is 10Kohms+ so after a Kirchhoffian calcualtion you'll realize that the input added load is negligible.

RMAA Headphone Amp Tests

Reply #37 –
I see.

RMAA Headphone Amp Tests

Reply #38 –
lucpes is right. As to my test, I just measured performance of my Revo built-in headphone output.

RMAA Headphone Amp Tests

Reply #39 –
Quote
lucpes is right. As to my test, I just measured performance of my Revo built-in headphone output.

Those were some damn nice results. Did you use your Audiophile to do the recording? I can't get anywhere near those results when doing a loopback with my Revo:

http://medlem.spray.se/urt/Revolution/2444.../Comparison.htm

RMAA Headphone Amp Tests

Reply #40 –
Quote
Those were some damn nice results. Did you use your Audiophile to do the recording? I can't get anywhere near those results when doing a loopback with my Revo:

No, I used the Revo input. If I use the Audiophile input, I get a nice ground loop that causes a lot of low-freq. noise.

As to your measurements, they show low frequency hum noise (50 Hz and its harmonics). It could be caused by a long cable or defective connector picking this 50 Hz hum noise. Try using a different, shorter cable, and move it around till the hum dissapears or gets lower. If it doesn't, it could be kind of an internal ground loop caused by the same card, maybe a semi-defective unit? Still, the noise is quite low level, and may happen just in loopback tests, not when playing music.

RMAA Headphone Amp Tests

Reply #42 –
I tried rmaa-ing my Creek 11se w/obh-2. I don't have a splitter so I'm wondering if my results therefore are not comparable with yours...?

M-audio revo with 3.5mm -> 2xrca connected to the amp, AKG K-501 connected to output 1 and output 2 connected back to the revos line-in.

The results