Transformer Headphone Attenuator

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John Chapman

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Transformer Headphone Attenuator
« Reply #20 on: 11 Jun 2003, 05:02 pm »
Jazz,

That ASL box you link above might be just the trick. It does just what we have been talking about. At it's price I have to think we might be able to make a no holes barred version that would use better quality switches and transformer core materials, etc but the general principle is the same. I'll have one on the way to me soon as I have a couple amps being shipped here anyway. I'll mess with it here and then send it down to you to play with and try if you'd like.

Many Thnaks!

John Chapman
www.bentaudio.com

JaZZ

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Transformer Headphone Attenuator
« Reply #21 on: 11 Jun 2003, 06:19 pm »
John...

...that's a great offer! I'd be glad to accept it. But are you aware that I live in Switzerland? (Shipping charge!) :?

I've already tried to contact Divertech via e-mail – without success, their account seems to be out of action. Do you know a valid e-mail address of them? I was about to order one of the Reference Tool boxes, but now that you plan to design an improved and maybe more esthetic version, I'm hooked on your virtual product.

BTW, are you a professional manufacturer and/or representative of an enterprise (Bent Audio?)? How would you rate the sonic differences between resistor- and transformer-based passive pre-amps in not too critical cases, e.g. DAC2 out 20 ohm, Metaxas Solitaire in 100 kOhm? I use a simple Alps 10 kOhm pot, and it seems to work fine... (after having used a switched attenuator) but I'm interested in a transformer approach for the speaker rig, too. But don't the immense cable lengths in such devices make them sound a bit like long cables? I mean: do you have to choose between cable-induced smearing effects and resistor-induced impedance/capacitance effects (frequency response!)?

 JaZZ

John Chapman

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Transformer Headphone Attenuator
« Reply #22 on: 11 Jun 2003, 08:57 pm »
Jazz,

I do this audio stuff full time (and then some!) and all the products and parts I sell through my company Bent Audio.  I also do it for fun. Can't get enough of it. I usually bow out of talking online about how stuff I make sounds. Since most likely everyone but us has left this monster of a thread by now I'll make an exception.

The TX102 does have lots of wire in it. I don't understand why but it does not seem to be any problem at all. You are likely getting good results with the pot you have and resistor stepped attenuators can work quite well. All the work I did on my TAP system originally was with resistor based passives. Where I find the transformer to be ahead of the resistors is in terms of the body of the music. The resistors can sound a bit thin. Always extremely clear and transparent but sometimes lacking body. My first reaction on listenning to the TX102 was that it had a more organic quality to it. It very well could be that this is a distortion but the transformers measure extremely well (Dead Flat to about 100Khz and THD numbers like < 0.005%) so on the bench they are very close to the resistor based units. This is a surprise to many who expect transformers to measure awful! It was a pain for me to change from the resistors I'd spent years with but the transformers have been a lot of fun.

You are I'm sure aware of it but with a 10K pot the low output impedance of your sources is only really there from the amps 'point of view' when the pot is all the way up. As the pot is turned down the series resitance introduced becomes the source impedance the amp see's and it will be very much higher than the source's low output impedance.

I was just sent a link to a short write-up about a new product using the TX102. It is here:

http://www.ultraaudio.com/home.shtml

Caught my eye as he uses the same dac I use and I too find the connection through the transformer better then direct.

I did not spot that you were over there but I think I have a plan for the ASL box.  Shoot me an e-mail at john@bentaudio.com and I'll explain....

BTW - Divergent's page has been down for a day or two - some net hosting trouble....

Many Thanks!

John

JaZZ

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Transformer Headphone Attenuator
« Reply #23 on: 12 Jun 2003, 04:49 pm »
John...

...it's highly interesting and a pleasure to talk to you. Instead of answering my question concerning the sonic impact of the long wires the way you did, you could have stated: «The bandwidth of the TX102 is ..., so within the audio band it's perfectly linear, and there's no degradation of sound.» But you seem to know exactly what I'm talking about; I appreciate that a lot.  

As to the «more organic» sound of the transformer or the thin sound of resistors, resp.: what do you think is the cause, especially for the latter? When I hook up my HD 600 or my DT 880 to the DAC2's line-out without any resistor in between, I get the same sound as with the potentiometer. Doesn't this mean the transformer adds some euphonic coloration to it? Don't get me wrong: I'm ready to accept this, as long as it sounds better, and I don't expect it to cause such important sound alterations as from amplifiers. But still there's the mystery why the direct connection (be it with speaker amps or headphones) doesn't automatically sound more credible and natural, rather the opposite. Do you think, apart from this consideration, that resistor-based attenuators do something fundamentally wrong to cause this typical thin and incoherent sound, exaggerately said? Or would you agree with the assumption that there's something fundamentally wrong with the signal from high-level output stages, in other words: today's state of digital technique? It's easily imaginable how amps can mask the «digital» aftertaste of digital sources, the same way CDs, heard through a radio tuner, sound nothing similar to the sterile digital sound, due to the masking of the digital artifacts (or maybe the effects from the sharp low-pass cut-off, resp.!) by the produced distortion.

Yes, I'm aware that the 10 kOhm pot increases the actual source impedance seen by the amp, but it should be far beyond any critical value anyway (say 5 kOhm to 100 kOhm), although I know nothing about the impedance curve of my Metaxas nor the capacitance of my cables.

JaZZ

John Chapman

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Transformer Headphone Attenuator
« Reply #24 on: 12 Jun 2003, 05:43 pm »
Jazz,

The resistors and transformers measure very close so I don't know if one can be said to be particularly more 'accurate' than the other. I love my test gear and believe stuff has to behave pretty well but as everyone knows that does not tell much of the story when it comes to how something sounds. The organic quality may be a form of inaccuracy but it seems to restore something that is missing sometimes with straight resistor passives (at least in my playing around). Even with resistor passives the type of resistor has an effect on the sound. Vishay's for instance are very transparent and clear but could end up a bit edgy if the system had a tendency to be that way. Tantilum films are more forgiving and a lean a bit toward the transformers sound. Which resistor might fit best would be a system / listenning preference kind of thing. I don't think it is that resistors do anything wrong at all - it's just that in most systems I have played with the transformers seem to result in a bit more body to the sound that I like. . This organic quality could also be related to the impedance situation being so different from resistors to transformers.


Your amp will have a flat input impedance (just a resistor) so there would not be an impdance 'curve' like the headphones (and speakers) have.

Thansk!

John

JaZZ

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Transformer Headphone Attenuator
« Reply #25 on: 12 Jun 2003, 10:25 pm »
John...
Quote
The organic quality may be a form of inaccuracy but it seems to restore something that is missing sometimes with straight resistor passives...

[/i]...the question is: what is it that is missing and has to be «restored», and where has it gotten lost? Do you think, like me (after my corresponding experiences), that the perfectly accurate signal doesn't sound appealing enough? And why is it so? Of course I don't really expect the final answer from you, but maybe you have an idea...

BTW: «organic quality» sounds quite appealing... even more so than «accuracy»...

JaZZ

John Chapman

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Transformer Headphone Attenuator
« Reply #26 on: 13 Jun 2003, 01:17 am »
JaZZ,

These are tough questions! As I mentioned I really like stuff to behave pretty well on the test bench but I find I am less and less concerned with have the most 'accurate' sound. I don't know what exactly is at work with the parts of the system but everyone (well - almost everyone) would agree that the goal is to have the sum of the be a pleasure to listen to! I have heard truly great systems with resistor passive pre-amps and I also am like'n what the transformers do in many systems so I don't think it's a 'contest' between them so much as picking what best fits your system and your listening preferences. In many systems there seems to be a slight thinness and a like of rythmic drive that the transformers (or a really nice tube line stage) seems to restore. If the system has that body and drive in spades then a passive resistor pre-amp (matched to a source and amp that fit the needed impedances) can do a good job I think.

Going back to the headphones we might find that the transformer behaves the same way in that enviroment - giving back a bit of the body and drive that folks like in their active headphone amps. This would be the only case for taking that route over the resistor based units you have built. The transformer passive headphone arrangement will place some restrictions on which sources and which headphones will best suit this arrangement but should be much more forgiving than the resistor passive circuit. This is similar to the transformer pre-amp which behaves from an electrical point of view very much like an active pre-amp - having a high input impedance and a low output impedance.


Thanks!

John

JaZZ

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Transformer Headphone Attenuator
« Reply #27 on: 13 Jun 2003, 01:11 pm »
John...

Quote
....I find I am less and less concerned with have the most 'accurate' sound.

Does this mean you're gonna built active amps in the near future? :) But seriously: a certain interest in what's real and what's fake you surely have, no? I have to confess that I even prefer headphone amps to the direct drive, just because the missing «organic» quality is restored with them. But that doesn't keep me from being curious about what's wrong with the pure original signal. You have no idea?

Quote
Going back to the headphones we might find that the transformer behaves the same way in that enviroment - giving back a bit of the body and drive that folks like in their active headphone amps.

I like your wording! It's true, «folks» do want some meat on the bones...:lol:, me included. But again: how come that it's missing in the original signal (to a certain degree)?

I have managed to compensate for the dryness «caused» by my passive pre-amp by fine-tuning my speaker's crossover network – something that usually can't be done with headphones. Interestingly I don't have to fine-tune them to my tuner or turntable sound; those are much less critical in this regard.  

JaZZ

John Chapman

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Transformer Headphone Attenuator
« Reply #28 on: 13 Jun 2003, 03:08 pm »
JaZZ,

I have no plans to build any active pre-amps! Nothing against them as some are very good - just too busy with all the passive stuff on the go!

I still don't think with the passive resistor pre-amp there is anything 'wrong' with the signal as such. I think the situation is different in different systems and the fact that sometimes they work very well follows from this. The only things that I can think of causing this tendency toward thinness with them is that:

1- Impedance issues are causing it. The large series impedance (compared to transformers or active pre-amps) could be an issue some of the time.  These series impedances are not helping in any stage of the signal path and particularly where they are followed by cables and an input stage of the amp to drive. This, however,  is not what is at work all the time because a direct connection from a source with a built in level control (and presumably a buffered output with constant and lowish impedance) can still sometimes display this tendency - although not to the same degree in my experience.  

2- Some systems have this 'sound' and so choosing a component that adds a bit of body or organic quality (like an active curcuit with tubes or a transformer passive) helps to ballance things out and results in a more real sounding and fun to listen to system. The same could be said for going with a tube amp vs. a solid state amp and there are many fans of both - neither is really right or wrong. Which fits best depends on the tendency of the rest of the system and, most important, the system owner's preference.

3- A combination of #1 and #2 - likely  to be the case sometimes (may much of the time??) as well.



Many Thanks!

John

Czilla9000

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Transformer Headphone Attenuator
« Reply #29 on: 14 Jun 2003, 01:19 am »
Hi, it is me.


I am confused. I still listen to my headphones passively but I am confused to whether or not it is better (objectively).


So basically, what conditions must be met inorder for a passive headamp to be better than an active one? How does one make sure it is better?

John Chapman

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Transformer Headphone Attenuator
« Reply #30 on: 14 Jun 2003, 02:54 am »
Hello!

Welcome back with us! Much of this thread has talked about how we can not really predict if a passive headphone level control will be better than an active one. Our next step in this is to build some stuff and play with some stuff and see how it is working. JaZZ is ahead of us as he has already been experimenting with this stuff!! If it turns out we prove out that a passive control can be made to work well it does not mean at all that it will be better than an active one in all cases. For one thing you can be sure that some setups and some listeners will prefer active headphone amps - For them the active units will do what it takes to make them happy with the sound. Also we can pretty much predict that for high output impedance sources (almost certain) OR low impedance headphones (maybe) that an active circuit would be prefered. That likely leaves a small group of users that the passive solution might be best for.

I think there is not a way to analyze it and come to a conclusion. It also seems that there are a lot of opinions but little real experiments happening so far. For yourself I'd suggest getting a modest active unit (used) or maybe scooping one of these little ASL passive transformer headphone units (called "Reference Tools"). Then you'll have some stuff to listen to and play with and compare to the passive unit you have now. If our testing develops into something we think is working really well then if your system suits the passive system then we can get one down for you to play with.  The only way to 'make sure'  it is better for you is to experiment with some of the alternates and see which works best. in your setup

Sorry for all the confusion but we are just at the front end of this thing and don't have a lot of answers yet!

Many Thanks!

John

Czilla9000

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Transformer Headphone Attenuator
« Reply #31 on: 14 Jun 2003, 04:59 am »
Has the impedence problem been solved?


How do I build something of the like?


Have you come to any sort of conclusion to whether or not a transformer is better than a resistor?



Thank you.

John Chapman

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Transformer Headphone Attenuator
« Reply #32 on: 14 Jun 2003, 01:22 pm »
Hello!

These are easier questions! They are kind of related but I'll take each one at a time.

----------------------------
>Has the impedence problem been solved?
------------------------------
Sort of... Given high (or highish) impedance headphones and a lowish impedance source (say 200 ohms or less) we can with a transformer (or autoformer) get impedance ratio's that are comparable to what many amp/speaker ratio's are like (for things like triode amps and OTL's). Since many folks including myself have had good results with these kind of ratio'd in-room I'd think that they'd work pretty well for headphones.  

--------------------
>Have you come to any sort of conclusion to whether or not a transformer is better than a resistor?
--------------------
From an impedance point of view this is a 'no brainer'. The transformer solution killls the resistor and this is why we even bother considdering the Transformer/autoformer solution. Once we step down a few ticks from the top level the output impedance goes down very fast. This impdeance does not go down in a 'linear'way because it's related to the sqaure of the turns ratio on the transformer. The table at the S site referenced earlier in the thread shows this impedance for a typical pre-amp application so the absolute numbers in the table don't fit what we'd do for headphones. The rate they drop off would be the same though.

---------------------------------
>How do I build something of the like?
---------------------------------
A bit tricky to home brew right now - since no-one I know of makes transformers or autoformers for just this application. It could be that a speaker level autoformer (radioshack?) might be a way to play with it and I'll check the next time I am near one. I don't know if these things would have the inductance to give an easy to drive load to the source though...  If you want to play with something along this line soon get an ASL box. For $150.00 or so you could not buy decent parts to home brew a similar unit.  

Whatever Bent Audio might have to offer will come after months of testing and only if we think we have come up with something that does something better than the other options out there (active or passive).



Many Thanks!

John Chapman
www.bentaudio.com





[/quote]

JaZZ

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Transformer Headphone Attenuator
« Reply #33 on: 14 Jun 2003, 09:14 pm »
Hi... and welcome back, Czilla!


(Czilla9000)  «Have you come to any sort of conclusion to whether or not a transformer is better than a resistor?»
--------------------
(John Chapman)  «From an impedance point of view this is a 'no brainer'. The transformer solution kills the resistor and this is why we even bother considering the resistor/autoformer solution...»


I guess this applys primarily to the attenuators used instead of preamps. IMO, for headphone direct-path application you don't have to apply the same rigid measure. Even a 100- or 150-ohm line out can provide a sufficiently appropriate source for direct drive – apart from the reduced sensitivity. You may know that transformerless tube amps have output impedances around 100 ohm, and they work well, at least with high-impedance cans. My Earmax Pro even is designed to drive low-impedance headphones as well.

Nevertheless, the high serial resistance has in fact a certain impact on the frequency response, though, dependent on the headphone's impedance curve; but it's all but dramatic – otherwise you had to remove OTL tube amps from the list of usable amps. There are even certain headphones which benefit from high output impedances and are recommended to be used with 120 ohm serial resistance (Beyer DT 931, 831), and BTW 120 ohm are an official norm for headphone amps (don't ask me where this is codified).

Futhermore keep in mind that an additional voltage-divider attenuator in the signal path on the one hand indeed decreases the load impedance «seen» by the line-out amp, but on the other hand also causes a considerable smoothing of the impedance curve – minimizing the corresponding coloration potential. So in reality the problems with the resistance approach are far less important than they appear initially.

So the main issue is its (overrated) frequency-response twisting potential. But such a behavior is something that can't clearly be rated as a sound degradation in the context of the whole system – it may just as well be in favor of the final frequency response provided by the headphone. This in contrast to amps: the signal degradation they cause has more to do with harmonic distortion and transient-response corruption – and is irreversible by nature.

So from this point of view, John, with reference to your statement that the transformer approach is the more forgiving and possibly less accurate variant, its theoretical advantage over the resistor approach in terms of the impedance proportions has to be put into perspective.

That said, like you I'm mostly interested in a credible and natural presentation and less in a theoretically correct sound. So if the transformer provides the «better» result, I'll favor it over my potentiometer solution. And I would be glad if it could combine the euphonic («organic») qualities of amps with the direct path's transparency and transient speed.

After all there's just one question left. You answered that «...there's nothing wrong with the signal as such in a passive preamp». Whereas my question actually was: «What's wrong with the original signal that it needs some subtle modification to restore its "organic quality"?» Well, that's my standpoint after my experiences with different sources and headphones as well as from different preampless speaker rigs. And this mystery – why a degraded signal sounds more appealing and natural than the accurate one – is my main motive for my occupation with the direct path. Could the digital technique bear the blame? With analog sources I never had the same impression.

 JaZZ

John Chapman

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Transformer Headphone Attenuator
« Reply #34 on: 15 Jun 2003, 02:17 am »
Hello!

I had a typo in that quote and have changed the original post - It should read "Transformer/autoformer" instead of "resistor/autoformer".

Good point with the OTL amps - that example and the SE amp stuff  is why I thought the tranformer might be able to get impedance down to acceptable levels. One of main diferences between active and passive solutions to this is the impedance issue and the fact that transformers have an impedance behavior more in-line with active headphone amps make me have some hope for this approach meeting some success and possibly acceptance. For example when we are driving a pair of headphones from a 2V source with a 200 ohm output impedance (typical CD player or DAC) the output impedance at a 0.5V listening level would be in the order of 15 ohms or so I'd estimate.

I am afraid I can not anwer to the question of what might be missing or 'wrong' with the original signal - other than I don't think it really can be talked of in terms or right and wrong only in terms of what fits a particular system/listener and what does not.  I think maybe a good way to think about it is if you hooked up a system without the pre-amp and listen to it that'd be it's sound. Then from that sound you can choose a level control (pre-amp) that best fits what's needed to ballance out the sound. Some will need a dynamic kick and some, for instance, might need some of this organic stuff....


Many Thanks!

John Chapman
www.bentaudio.com

JaZZ

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Transformer Headphone Attenuator
« Reply #35 on: 15 Jun 2003, 04:36 pm »
John...

...thanks for your comments so far! See you later...

 JaZZ