[vvanrij]

That my NAD receiver's headphone out sounds almost the same, actually a little bit better, than my MKIVse. I hope that I'm wrong because I paid alot of money for the MKIVse.

 

[pp312]

Well, if you paid a lot of money for it you could probably get a good bit back-- and let's face it, a receiver is a more convenient item than a receiver + HP amp. Also, I suggest that if you haven't yet decided which is better, then there's no appreciable difference--but I think you already know that.

 

[KonstantinT]

Hi!
Did anyone power high impedance headphones by a (vintage or modern) NAD preamplifier?
I´m confused with the impedance matching and mismathing.
I own a 20 years old NAD 3240PE integrated (speaker) amp with the well-known handicap: the phones out has a high impedance (220 Ohms). My Sennheiser HD565 have 150 Ohms. I think this impedance mismatch is the reason why it doesn´t sound better than the same phones connected to a portable CD-Player.
When I´m home I mainly enjoy music at night using my headphones and I mainly hear vinyl discs. Therefore I think a preamplifier with a good phono input stage and a decent phones output would help to improve sound quality for small money and by the way saving energy when no speakers power is needed. In this case, I would use my 3240PE only on demand as a loudspeakers power amp (via its main in sockets).
NAD offered a similar looking preamp named 1240. The phono stage has more features and better specs than the 3240PE´s one. And the headphones output has only 100 Ohms.
Do you think it would improve the headphone sound, if I go for the 1240 preamp?
I intend to get a Sennheiser HD650 later (when the ministry of finances allowes). It has 300 Ohms. If a change from the 3240PE´s 220 Ohm jack to the 1240´s 100 Ohms output improves the sound of the 150 Ohms HD565, shall I expect that it will result to the same improvement with a high impedance-headphone?

Thanks in advance!
Konstantin

 

[scompton]

I believe, from looking at the schematic, that my NAD 3155 has an headphone out impedance of 740 ohms. I don't have many low impedance headphones. The KSC 75 is lousy out of it. The DT831, 250 ohms, is fantastic. My AKG K601, 150 ohms, sounds good too.

I don't have a dedicated amp to compare it with. I'm about to build a Starving Student Millet Hybrid, so how fully soon I'll have a comparison.

 

[pp312]

Quote:

Originally Posted by KonstantinT /img/forum/go_quote.gif Hi! Did anyone power high impedance headphones by a (vintage or modern) NAD preamplifier? I´m confused with the impedance matching and mismathing. I own a 20 years old NAD 3240PE integrated (speaker) amp with the well-known handicap: the phones out has a high impedance (220 Ohms). My Sennheiser HD565 have 150 Ohms. I think this impedance mismatch is the reason why it doesn´t sound better than the same phones connected to a portable CD-Player.

Personally I think the reason is that you probably don't listen at high volume, so you aren't testing the limits of the portable CD player. The CD player may have a decent HP amp inside, but only usable at low volume. That after all is what an amplifier is all about: amplifying.

Quote:

Originally Posted by KonstantinT /img/forum/go_quote.gif When I´m home I mainly enjoy music at night using my headphones and I mainly hear vinyl discs. Therefore I think a preamplifier with a good phono input stage and a decent phones output would help to improve sound quality for small money and by the way saving energy when no speakers power is needed. In this case, I would use my 3240PE only on demand as a loudspeakers power amp (via its main in sockets). NAD offered a similar looking preamp named 1240. The phono stage has more features and better specs than the 3240PE´s one. And the headphones output has only 100 Ohms. Do you think it would improve the headphone sound, if I go for the 1240 preamp?

A preamp must use a dedicated amp for its HP jack, possibly op amp based.
The quality of that amp is unknowable without trying it, but it will be electronically different from the integrated in that the integrated will use a resistor network from the main amp out. But who knows? It may not even sound different. NAD are not slackers, and it's likely they've made certain all their HP jacks sound decent.

Quote:

Originally Posted by KonstantinT /img/forum/go_quote.gif I intend to get a Sennheiser HD650 later (when the ministry of finances allowes). It has 300 Ohms. If a change from the 3240PE´s 220 Ohm jack to the 1240´s 100 Ohms output improves the sound of the 150 Ohms HD565, shall I expect that it will result to the same improvement with a high impedance-headphone? Thanks in advance! Konstantin

You know you'll only get a headache trying to match impedances like that, don't you? It just confuses you (and me!) and tells you nothing about the sound. Get your Senn 650s (they're worth it) and try plugging them into a few likely amps. And forget about impedance matching.

 

[tfarney]

Quote:

Originally Posted by scompton /img/forum/go_quote.gif I believe, from looking at the schematic, that my NAD 3155 has an headphone out impedance of 740 ohms.

740 sounds awfully high and I believe NAD's standard is 220 ohms. I'd check again.

Tim

 

[scompton]

Quote:

Originally Posted by tfarney /img/forum/go_quote.gif 740 sounds awfully high and I believe NAD's standard is 220 ohms. I'd check again. Tim

Typo, it's 470. Which is also very high. I can't find anything in the schematic other than in line 470 ohm resistors. The schematic has 2 pages of specs. Just about the only thing not documented is the headphone out impedance.

 

[KonstantinT]

Scompton,
first, I thank you for giving me advise again.
About the phones jack impedance of your 3155:
470 Ohms are high indeed. Does "470 Ohms" stay on the schematics? Else, the number 470 could be only a part number, not the Ohms value.
I found the schematics of the 3240PE (my NAD amp). The resistors (opne fpr each channel) at the phones output are named "R503" and "R504", but the value "220 Ohms" is mentioned there and on the parts list too.
Or are there two 470 Ohms resistors for each channel in parallel? This would result to 235 Ohms for each channel. But imo it doesn´t make sense to use to resistors in parallel.
My english is not very fine (I´m Greek and live in Germany) but I hope you understand me.
Anyway, I think you are satisfied with your 3155 and that´s what counts. Impedance matching means headaches, like pp312 wrote.
Konstantin

 

[scompton]

The headphone out impedance is not documented anywhere. I have a copy of the schematic. The headphone jack is next to the speaker selector switch. From what I can see in the schematic, the leads to the headphone jack branch off of the leads to the speaker selector switch. There are 470 ohm resistors in series. I can't see any resistors in parallel. From what I've read this makes the output impedance 470 ohms. I've not taken the top off and looked. That might be easier to see. Then again it might not. From the schematic, the switch and jack are board mounted. If the resistors are on the underside, I won't be able to see anything.

I tend to believe the 470 ohms for a couple of reasons. First, because they didn't document it in the user guide or service manual. 470 ohms sounds bad enough that they might not have wanted to document it. The schematic has 2 pages of specs. I documents output impedance of the speaker outs, preamp out, and tape outs, but no headphone out.

The other reason is in the articles linked on one of these integrated amp threads. The Meier article shows 2 graphs, one at 120 ohm and one at 470 ohm. This makes me think that some amps are 470 ohm.

The other article, on making an adapter for speaker outs, shows using a 470 ohm resistor in series as the first part, with a 120 ohm resistor in parallel, and finally, another in series with the appropriate value to make the whole network near 120 ohms. Either I'm not seeing these other resistors on the schematic or they don't have them. I imagine that if they are there, they'll be on the board with the switch and jack. That's not a complicated board and they're not there, at least in the schematic.

Does anyone know how to measure the headphone output impedance with a DMM?

 

[Navyblue]

Quote:

Originally Posted by scompton /img/forum/go_quote.gif Does anyone know how to measure the headphone output impedance with a DMM?

Just connect one probe to either left or right channel and another to ground.

 

[scompton]

Quote:

Just connect one probe to either left or right channel and another to ground.

I can't believe I didn't think of that

I have a couple of spare plugs because I have some headphones that need to be reterminated. I plugged on in. It measures 420 ohms with my cheap DMM.

 

[Navyblue]

Interesting, so higher impedance may not be something so bad after all? I've been asking this for ages, but I am going to ask again if any one knows.

How does amp output impedance matter?

I wonder if I should break my 120 ohms barrier for my headphone adapter that I imposed on myself.

As a side note for those integrated amps that have bad headphone jack implementation or does not have a headphone jack at all, I highly recommend to build one of those. The more I listened the more I think that there probably aren't anything else that is significantly better.

 

[scompton]

Low impedance headphones sound really bad out of the NAD. By low impedance, I mean 32-50 ohm like the KSC75 and PX100. I just use these straight out of my iPod anyway. I wonder how it would effect the K701. There's a DC area meet next month and I'm taking the NAD. Hopefully, someone will have a K701 to test with.

It does really boost the bass with my Beyer DT831. They're 250 ohms and have anemic bass with portable amps, which is the only other thing I have. Interestingly, it doesn't appear to boost the bass much with the DT880 or K601, both of which sound very nice.

Even stranger, it makes my HD580 shrill and Grado like. They're almost unlistenable with any music that has a lot of treble.

I'm hoping to try an experiment with adapters. I've bought a bunch of 2 watt resistors and I'm going to use a plug board to build a speaker terminal headphone adapter. I'll be able to switch impedance by switching 1 wire. If it works I might solder one up.

 

[KonstantinT]

Hi, few days ago I decided to "tune" the phones output of my NAD 3240PE (sharing the speakers out) using almost the simplest way. Why should I accept the 220 ohms output impedance? A look on the schematics told me, that there is one 220 ohms part on each channel. So I got new, 100 ohms metal film resistors with 1% tolerance (the old are metal too, but 5% tolerance). Changing required either disassembling of some parts, what I didn´t dare, or handling with pliers. The resistors are just behind the jack, under the cables going to the mains switch. I had to take away the bottom plate to access the soldering points, else I would melt up the board.
With 100 ohms out I have to turn the volume a bit down, "8 o´clock" instead of "9 o´clock", else it gets a little louder on my 150 ohms Sennheiser HD565 ovation. I hope the increase of resistance in the volume adjust (variable resistor) is not as much as the decrase I did achieve.
How does it sound with 100 ohms? Well, I think it´s a bit brighter and clearer, but probably it´s only the EXPECTED effect, not the ACHIEVED.
Am I crazy? I don´t know. Anyway, it costed only 0,20 Euros for material, a small amount of silver soldering wire and about 5 Wh of electric energy.
Bye!

 

[musiclover45]

hello,

To me, it just makes sense to have a dedicated headphone amp. With the MKV, you have two selectable inputs, so you could listen to another source without turning on your main system. Having that flexibility is very nice indeed. The MKV is going to sound better than a standard headphone jack setup. It has much more power and was built to be quiet and very dynamic.
Do you think your source is lacking? I have no idea.

thanks !!