artto Posted June 25, 2004 Share Posted June 25, 2004 OK. I'm going to reveal some of my electronics ignorance. Can a stereo headphone output jack that has variable volume control, on a CD or SACD player for instance, be used to drive tube power amps (and not lose any sound quality)? Quote Link to comment Share on other sites More sharing options...
mike stehr Posted June 25, 2004 Share Posted June 25, 2004 You might have some issues with gain, either too much or not enough.(Probably not enough, I dunno....) I always wondered about that as well... Rig up a headphone jack to RCA jacks, and give it a shot. If your trying to bypass a pre-amp or get things more simplified for some reason,(I have no idea of what you have going) a stepped attenuator is a nice option. And you won't have to find a DVD/CD/SACD with a decent quality volume control circuit. A real PITA, IMO. Quote Link to comment Share on other sites More sharing options...
fini Posted June 25, 2004 Share Posted June 25, 2004 ---------------- On 6/25/2004 4:15:28 PM artto wrote: OK. I'm going to reveal some of my electronics ignorance. Can a stereo headphone output jack that has variable volume control, on a CD or SACD player for instance, be used to drive tube power amps (and not lose any sound quality)? ---------------- Wow, are my baubles pooped. How are we going to be able to respect your opinions now that you've asked such a silly question? (thanks, artto! I've wondered about that, too...) Quote Link to comment Share on other sites More sharing options...
Number 9 Posted June 25, 2004 Share Posted June 25, 2004 The mW output of headphone jacks varies considerably. Anywheres from 150mw to as high as 1 Watt. So it will likely be too high of an output. Also, unless you have a dedicated headphone amplifier, the quality is not going to be as great as going from the RCA jacks, because you not only have an extra processing layer, but a less than stellar one. Most headphone jacks are powered by cheap op-amps. You will also have impedance mismatch issues. Again, if driven by opamps, the impedance output is likely to be around 0 Ohms. Quote Link to comment Share on other sites More sharing options...
artto Posted June 25, 2004 Author Share Posted June 25, 2004 You're kind of right on track Mike. I'm trying to get some volume control while connecting the SACD player directly to the power amps. The Music Hall Maverick I bought, I thought had volume control, but it doesn't, and after several weeks I've gotten conflicting answers from reputable sources as to when, if at all, this feature went into production. I'm getting tired of researching it. And I'm getting tired of looking for an acceptable unit with volume control. The Shanling SCD-T200 has it but I really don't need the tube output (although it can be used with both its normal SS output or the tube section) & the disc top load mechanism just takes up/requires a lot more shelf space. Cool looking unit though. The new Sony SCD-XA9000ES & SCD-XA777ES have headphone outputs on the front with a volume control. Both of these units seem to be up there with the best of them sound wise. So if I can use the stereo headphone output jack, run that to my phantom center channel box, and from there to the power amps, I can run the power amps with their level controls at 12 o'clock which is where they sound best. The other alternative is, I guess I could make a new center channel box with level controls on it for the flanking speakers too (I was going to do that eventually anyway). Maybe the easiest solution is to just get the Shanling. I'll have the volume control on the remote. And I just won't use the tube output, except maybe for CD. Quote Link to comment Share on other sites More sharing options...
artto Posted June 25, 2004 Author Share Posted June 25, 2004 Number9, yeah, I was concerned about the impedance issue screwing up the sound or mismatching the ability to drive the amps. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted June 25, 2004 Share Posted June 25, 2004 "The other alternative is, I guess I could make a new center channel box with level controls on it for the flanking speakers too (I was going to do that eventually anyway)." You would have more control of level, and not restricted to one source unit. "Maybe the easiest solution is to just get the Shanling. I'll have the volume control on the remote. And I just won't use the tube output, except maybe for CD." Yeah, and the tube buffer on the output helps those worthless recorded CD's. A remote is a nice option as well. I guess you could always flog the Shanling on Audiogon if you hate it. Quote Link to comment Share on other sites More sharing options...
garymd Posted June 25, 2004 Share Posted June 25, 2004 I did that exact thing with my MkIIIs and 555ES before the blueberry arrived. Sounded pretty good. Works well as a temporary solution but I wouldn't use it full time. Quote Link to comment Share on other sites More sharing options...
Marvel Posted June 26, 2004 Share Posted June 26, 2004 The output impedance won't be 0 ohms, but will be low as to drive headphones. Normally they would be between 8 and 600 ohms. This can still work quite well when feeding into a high ompedance input on the amp. Sure works better that way that the reverse, where the source is way higher that second device. If the source and load are equal impedance, you will have the maximum power transfer. If the headphone output were 50mw, the amp (if the same impedance as the phone amp) would only get 25mw. As the load impedance increases, the efficiency will go up, but the power transferred will actually decrease. IOW, you probably won't get too high a signal to the power amp, considering the high impedance of the amplifier input. I have fed 10 watt film projector amp speaker outputs into line level mixer inputs with no problems. Marvel Quote Link to comment Share on other sites More sharing options...
Number 9 Posted July 1, 2004 Share Posted July 1, 2004 >> The output impedance won't be 0 ohms, but will be low as to drive headphones. Normally they would be between 8 and 600 ohms. Well ... you are saying two different things. Yes, headphone amp outputs are designed to DRIVE headphone impedances that can run from 32 Ohms (Grados) to 600 Ohms (some Beyers, AKG and Sennheisers). However, the output impedance of the amp itself should be near 0 Ohms. There are some exceptions such as tube amps, or opamps where a resistor has been specifically put in the path to raise the impdedance. But it is generally acknowledged that a properly designed headphone output impedance should be close to zero to provide the best damping giving the length of most headphone cable runs. Check out headwize.com and some posts made by Peter Millett and David Berning on headphone amp designs from a few years ago. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 2, 2004 Share Posted July 2, 2004 Artto, The Sony Headphone outputs will work with no problems but will be a compromise in sound quality. Craig Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 2, 2004 Share Posted July 2, 2004 "The output impedance won't be 0 ohms, but will be low as to drive headphones. Normally they would be between 8 and 600 ohms." Yeah, my brain filled in the gaps. I should have said: "The output impedance won't be 0 ohms, but will be low as to drive headphones. Normally they (headphones) would be between 8 and 600 ohms, so the headphone amp output impedance would have to be at least lower than the phones." The rest is still valid. Marvel Quote Link to comment Share on other sites More sharing options...
gerbache Posted July 2, 2004 Share Posted July 2, 2004 ---------------- On 6/26/2004 1:08:53 PM Marvel wrote: If the source and load are equal impedance, you will have the maximum power transfer. If the headphone output were 50mw, the amp (if the same impedance as the phone amp) would only get 25mw. As the load impedance increases, the efficiency will go up, but the power transferred will actually decrease. IOW, you probably won't get too high a signal to the power amp, considering the high impedance of the amplifier input. This is a standard textbook way of looking at impedance matching, but in general, amplifiers like this don't follow this rule. Normally, you want your amplifier output impedance to be considerably lower than the load impedance. In addition, you can find headphones that range anywhere from 32 to 600 ohms, so it would be next to impossible to design a headphone amplifier such that it is "matched" to the headphones. It turns out that if you look at the way these amplifier circuits work, you actually generate maximum power when your output impedance of the amplifier is as low as possible. That being said, some years ago, a "standard" was designed proclaiming that all headphones should be able to expect a 120 ohm output impedance regardless of the impedance of the headphones themselves. I'm not sure how often amplifier manufacturers follow this standard, but nonetheless, many headphones are designed with this in mind. Quote Link to comment Share on other sites More sharing options...
Marvel Posted July 4, 2004 Share Posted July 4, 2004 I have read that most amps have an actual output impedance of around .7 to 1.5 ohms (SS amps). If the amp had a 120 ohm output, a lot of headphones (or speakers for that matter) wouldn't properly load the amp. Are you trying to confuse me? I did cite from a textbook, but you don't want the load impedance to be lower than the source impedance. I've seen people try that, and it isn't a pretty sound. I guess from your response, you think I am saying the impedances should match. Nope, not at all. I remember getting my Sennheisers back in the early '70s. I couldn't believe they had a 600 ohm impedance as most phones at the time really were between 8-32 ohms. I still have them in a box somewhere. Marvel Quote Link to comment Share on other sites More sharing options...
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