Budget USB interface also for general use? (headphone output power)

Mack Caster said:
I use the Power-play Pro 8 pictured below and love it. It has two inputs so you can feed both sources you are needing. I run one from my AI and one from my mixer. I simply push the input selector on the front panel for what device I am listening to. For $149.00, it will power whatever you need. If you have 7 buddies show up, they can bring their own cans and listen as well.

FEATURES


  • 8-channel headphone distribution amplifier
  • Eight totally independent stereo high-power amplifier sections
  • 2 separate main inputs
  • 2 headphone outputs per channel
  • Dedicated direct input for each channel
  • Highest sonic quality with virtually all types of headphones



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I will say that the HA8000 is loud and cheap. Used it for years. But once I moved on to better I realized how noisy and distorted the unit was. I now have a Presonus HP60 which is 3 times the cost. But man it is nice to hear clean signal.

Just saying...
 
Ok Spitzzy' ! Let's get this impedance thing sorted out! (what follows might be a sticky but no matter)

ALL electronic audio devices have an input impedance* which imposes a load, i.e. draws current from the source driving it. Naturally we want to keep that current as low as possible because it robs signal VOLTAGE from the system which will have to be made up by amplification which increases noise.

Typically the LOWEST input Z you should find on any 1/2 decent bit of audio kit is 10,000 Ohms (aka R).

The output impedance of gear such as a line OP of an AI should be low, typically 100R. So, a piece of kit with an OPZ of 100R feeding a 10k input would suffer a signal loss of just 0.08dB, totally undetectable. Of course, not everything will be as low as 100R but so long as Zin is around 10X Zout all will play happily.
We can therefore dispose of any consideration of the INPUT Z of any H/P amp? So long as it is AT LEAST 10k, it does not matter a fig.

Now, a headphone OUTPUT is rather different from an AI line OP in that is has to deliver much more current. The amplifiers are therefore mini power amps and to (attempt) equalize the drive levels into the crazy range of can impedances the amp is made to have a high enough VOLTAGE delivery for high Z (sort of!) but sufficient current to drive low Z units (again, low cost designs make a brave attempt)

They accomplish this technical marvel by the clever dodge of inserting a resistor of between 33 and 100 Ohms in the output circuit. The resistor also performs the other vital function, that of protecting the mini amp from a short circuit!

As to amplifiers sounding "shit"? Just people being deliberately hyperbolic. The world and his uncle seems happy with the sound quality delivered from phones, pods and laptops. The amplifiers in my HA400 are better than any of those. Yes, with an impeccable source and $1000 headphones I guess a $2000 cans amp stands out! But not a lot in practice.

*In practice, electronic AUDIO devices have a virtually pure input RESISTANCE, i.e. there is no change of load with frequency (yes! Even for transformer inputs) Outputs too are virtually resistive but peeps like to talk about 'impedance'!

Dave.
 
mjbphotos said:
I just realized I need something like that Powerplay - but smaller (not so many outputs).
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They make a Power Pro 4 that is $20.00 cheaper than the Pro 8 and the 4 is actually nicer for mixing and mastering. The only problem is, it is set up to run from your amps in, to your amps out, keeping everything in line with only 1 input option. The 4 outs have low,mid and high eqs. I bought the pro 8 so I could run from my US 16 x 8 AI as well as my PC. I am making a 8 plug patch bay that will be recessed in the wall of my track room.

That way I can feed headphones to 7 people behind the glass. Another thing I like about the pro 8 is that I can hook into each channel in the rear, feed that to the patch bay and still use the front inputs, if anyone else wants to listen in the control room. I have two 8 bay XLR recessed inputs that will be tied into the 16 x 8 as well, they have 2 1/4 inch outs per box and I will run my mains into those, once I choose my speakers/surround sound for my track room/home theater/guest bedroom. My next project is building a Murphy bed with bookshelves when it is in the up position. Boat baby! Bust Out Another $1,000.00! :laughings:
 
ecc83 said:
ALL electronic audio devices have an input impedance* which imposes a load, i.e. draws current from the source driving it. Naturally we want to keep that current as low as possible because it robs signal VOLTAGE from the system which will have to be made up by amplification which increases noise.Dave.
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We need to get a MOD to sticky this post. See, now we don't need no stinkin headphone forum! (Just Playin with the OP). But, that really explains everything you need to know before your drop some $$$ on a set of high dollar cans. Thanks Dave!
 
jimmys69 said:
I will say that the HA8000 is loud and cheap. Used it for years. But once I moved on to better I realized how noisy and distorted the unit was. I now have a Presonus HP60 which is 3 times the cost. But man it is nice to hear clean signal. Just saying...
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You make a very valid point Brother. When you crank anything that carries a audio signal to the max, it will add the noise as well. I record mostly Gospel, Classical Instrumental and Bluegrass. Very seldom do I have to go over 25% on the pots for the Artist, which in turn, keeps the noise to a min.

The HP60 is no doubt a Superior unit for meeting louder demands used for head bangers. I love the fact it has the TB feature as well. Now if Bat Biten Ozzy was coming over, he would probably WOHD and fry my little Pro 8 unit.

Ozzy says: :wtf:Mack, I can't ear my bloody self sing! :laughings:


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I made the decision to move from the HA after a friend gave me his old Samson S Phone. It had such a better clean and full sound. But died a couple months later. So that when I just decided to get comparable at more cost. The Presonus was next up the price scale with the aux inputs.

I must say the sound quality change is really noticeable. I cant say that it is as loud as the HA, but it is still very quiet at loud volumes. In my drum room I send directly to a mixer there so drummer can kill his hearing as he desires and have more of whatever he wants. They all different. Shit, I likely should have them sign a release form.... lol
 
jimmys69 said:
In my drum room I send directly to a mixer there so drummer can kill his hearing as he desires and have more of whatever he wants. They all different. Shit, I likely should have them sign a release form.... lol
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This is from my 5th paragraph in my contract. I can PM you a copy if you want something to reference. You will need to check Co state law but it may give you a starting point. In 2017, even when we do what's right, someone may try and sue due to their own ignorance.

Paragraph 5. Hearing Loss. It is expressed that I am fully responsible for any hearing loss or damage due to my own negligence for requesting, or by my own hand, increasing the amplification of any audio signal during my performance via speakers, monitors or headphones. I further acknowledge that I am fully aware that loud noises can effect my hearing and possibly cause non repairable hearing damage or loss of hearing. I hereby acknowledge that D and L Studio LLC has offered to provide me with hearing protection, if I decide it will be needed to protect my hearing. I also acknowledge that D and L Studio LLC has given me the opportunity to read on-line information provided by 21st Hearing Center concerning hearing loss of Musicians, located at:
Musician Hearing Loss and Prevention | 21st Century Hearing
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Mack Caster said:
This is from my 5th paragraph in my contract. I can PM you a copy if you want something to reference. You will need to check Co state law but it may give you a starting point. In 2017, even when we do what's right, someone may try and sue due to their own ignorance.
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Thanks man! Not sure I need to sign contracts as I only work with friends/friends of friends. My studio is not really a business. More of a hobby that I enjoy doing since I gave up trying to be a rock star...

Though I wonder if I should take this more seriously. One greedy poor musician could screw me with a frivolous lawsuit... Hmm...
 
jimmys69 said:
Though I wonder if I should take this more seriously. One greedy poor musician could screw me with a frivolous lawsuit... Hmm...
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I know I don't have to tell you about how people sue someone when 99.9% of the population said they could never win. Yet they do. Commonsense has no bearing on written law. If a defense attorney can smell a buck, all bets are off. I am not using you as an example, but it could go something like this:

Attorney to Defendant: Are you aware that loud noises causes hearing loss or damage? How long have you been playing/recording music? How many dbs does your system provide? Have you ever made any money doing this? Are you licensed to do this? Do you inform people that you record as well as provide an amplified signal to that they could receive hearing damage by using your system? Have you had any official training using sound systems? Plus a hundred more.
 
Hmm... that stuff reminded me of another thing I've been wondering specifically concerning headphones. A (long) while ago I measured the peaks of some drum hits. With the decibel meter hanging at maybe an arms length away, maybe slightly closer from the top of the snare drum, I managed to get over 140 dB hitting a full power rimshot.

Now what does that have to do with headphones? Well... I was simply thinking, how could a teeny tiny headphone element possibly get anywhere near that loud without shattering into pieces? How could it even get to let's say 100 dB? I'm probably massively misunderstanding something about the numbers and units, but the actual sound pressure of the headphone an inch away from my ear can't possibly reach a level comparable to playing a drum set loud without hearing protection no matter how many times I crank the output of my laptop to 100% and listen to a close-to-zero peak recording. Or can it? Seems impossible. If I would drive my K182's at exactly one Volt from an ideal source at peak signal level, would it actually shoot 112 decibels right into my ear, from that distance?

Also a bit more about those USB interfaces built-in headphone outs... in case they are basically the output jack itself and an x Ohm resistor connected to an op-amp, wouldn't it be pretty easy to change the resistor to a more suitable one if the problem is there, or possibly even also replace the op-amp with a better one (are there some that provide more gain than others)? Requires modding and might not be worth it but I would imagine it would be feasible. It it's too much for myself, I could ask someone more skilled to do it for me... I've heard of people replacing all 8 of their ADA8000's pre op-amps...

P. S. I know I don't know anything about electronics and I know I'm a fool so it's useless pointing that out at this point :)
 
The numbers do go up alarmingly for very high sound levels. Say you had guitar speakers like the Celestion V30s that deliver 100dB/W at a mtr. To get 140dB you would need a 10,000W amplifier (and a lot of speakers!) . So, how does a snare drum produce such a level? Because it is VERY efficient. I have no idea what power the human (or even a drummers) arm produces but I would guess at a few watts. Those watts are concentrated into a tiny spot and that small deflection is coupled/transformed into the air by a large radiator. The snare hit also only lasts milliseconds.

Headphones can produce high levels in the ear because they do are pretty efficient. Very light diaphragm with a relatively large magnet, much bigger magnet to mass ratio than any MC speaker. Then, it is VERY close to the ear canal and sound falls off as the square of the distance* like light.

Modding a headphone amp? Not practical, the build out resistor is optimum for the power the chip can deliver. The chip is not the constraining factor in a AI, the supply voltage is.

Chip swapping in the ADA? Don't know off hand what they are but knowing Berries, be cheap so MAYBE a better jfet chip could give lower noise. If the circuit is suitable NE5532s would be good, LM4562s even better. But in truth the noise improvement would be small, 3dB maybe. MOST of the noise in such circuits comes from the resistors, in fact you can often design LOWER noise devices by using MORE chips!

If you look you will read a LOT of bollox about certain chips 'sounding better' than others. It is almost always tweaky,bearded Russ Andrews disciples peddling their subjectivist cobblers.

*But only where the radiator is MUCH smaller than a wavelength. When it is not...Gets complicated!

Dave.
 
I guess I could try to figure out where that measuring mic thing (what is the proper name for it anyway?) is and measure the loudness of my headphones. Maybe I'll learn something interesting.

Now however, I'm actually going back to my original 'quest'... I think. I just went through the thought process of: okay, I'll get that interface (2 inputs, main out and headphone out), then run these cables from the main out to the speakers with that adapter there, then... hold on. I don't have the main outs anymore so the only possible place to connect a headphone amp to is the interface's headphone out jack, using the hp amp as a "booster"! Or did I miss something? Does it really work properly that way?

BTW, to me it looks like a MA400 would be a better headphone amp. I have no need for the multiple outputs in the HA400, and the MA400 looks to have a lower output impedance and slightly but substantially more power (30R vs. 100R and 60 mW vs. 40 mW). The MA400's TS/TRS input is labeled "monitor" instead of "line" but I don't suppose that would make a difference? Wouldn't the "monitor" inputs actually even be a better match for a headphone level signal than the "line" inputs in an HA400?

It's funny, I've forgotten so much stuff if I ever even knew it in the first place.
 
Yes, the 'Monitor' input on the MA400 would be fine, the 10dB (x3) gain would probably be enough GAIN boost but. The MA has only ONE monitor/line type input, the other two are microphone ins and you don't want those.

The power hike, 60 from 40mW is hissall, less than 2dB. You need a 10dB (X10) boost in power to get the sort of levels I think you are talking about. In any case the MA uses the same 12volt supply as my HA400 so, not going to be much louder.

I am convinced that the only compact and low cost solution to this problem is a small mixer (I can recommend the Berry X802). The BIG question yet to answer is if such a mixer will give you the HP drive you want? Two options:..

Go to a store armed with cans and get a salesman to let you try one. Or, order one and invoke the 'Distance Trading Regulations' if they apply to you if it does not meet your needs.

Oh! There is a third option? BUILD yourself a 'State of Art' super powerful headphone amp with multiple inputs, something I might well do myself if I get any deafer! Ah! Jusfort! If you buy a S/H integrated amplifier/receiver (20Wpch is plenty) you could use the HP sckt on that. OR make an attenuator unit to drive cans from speaker terminals (care needed there) Such an amp will surely have at least AUX and Tape inputs.

Dave.
 
Naah, it's more like I don't need the mic in, and even that's not necessarily true... and the HA400 also has only one line in. Besides, remember that I already HAVE an HA8000... I'll figure out later whether I need another distribution amp.

I agree completely that the power difference is minimal, but I don't see a downside to it. Maybe I'll decide to get some 600 Ohm phones in the future or something so it's always good to have it in reserve, even if it's just a tiny bit. The main thing I'm interested in right now is, will plugging the headphone amp into the interfaces headphone out jack distort the signal in any meaningful way or is this again a case of it all balancing itself out nicely due to the huge impedance difference between the AI hp out jack and the HP AMP input?

Also, at this point I don't even know. Maybe the AI's own headphone amp will be loud enough after all. Regardless, I'm going to buy the hp amp because I might need it, and it's so cheap that who cares if I don't, in the end. A compressor/limiter at some point in that chain would be mighty useful but I can't seem to find anything like that online. One of my spontaneous crackpot ideas involves a bass guitar comp/limiter pedal that I have... maybe I could stick that in there right before the hp amp and enjoy the loud, crystal clear but SAFE sound ;)
 
spitzer said:
Naah, it's more like I don't need the mic in, and even that's not necessarily true... and the HA400 also has only one line in. Besides, remember that I already HAVE an HA8000... I'll figure out later whether I need another distribution amp.

I agree completely that the power difference is minimal, but I don't see a downside to it. Maybe I'll decide to get some 600 Ohm phones in the future or something so it's always good to have it in reserve, even if it's just a tiny bit. The main thing I'm interested in right now is, will plugging the headphone amp into the interfaces headphone out jack distort the signal in any meaningful way or is this again a case of it all balancing itself out nicely due to the huge impedance difference between the AI hp out jack and the HP AMP input?

Also, at this point I don't even know. Maybe the AI's own headphone amp will be loud enough after all. Regardless, I'm going to buy the hp amp because I might need it, and it's so cheap that who cares if I don't, in the end. A compressor/limiter at some point in that chain would be mighty useful but I can't seem to find anything like that online. One of my spontaneous crackpot ideas involves a bass guitar comp/limiter pedal that I have... maybe I could stick that in there right before the hp amp and enjoy the loud, crystal clear but SAFE sound ;)
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Oooo! You got some strange idea and misconceptions Spitz! Hearing damage is proportionate to loudness and duration therefore if you COMPRESS a signal it STAYS louder for longer! A peak limiter might seems useful but the hugely important factor is the level AT THE EARDRUM and you have no way to determine that.

The only way to stay 'safe' as you put it is to monitor your own reactions. Do you go a bit deaf after a session? (called a Temporary Threshold Shift. CAN become permanent!) If so, level are to high/to long.
Ringing in ears? Headaches?

BTW the bit of kit whose name you could not recall is a Sound Level Meter. Get one, make sure it has a C weighting scale then hunt up Massive Masters article about calibrating monitors. Do that and you will forever have a reference as to how loud you should listen and for how long (safe'ish is 8 hrs at 85dBSPL)

Forget 'impedance' when coupling gear together. LEVEL is all that matters. No modern gear will be damaged if you get it wrong. (BIG power amps excepted!). You also need to be aware that headphone amps are essentially stereo devices and mic inputs mono (and XLR!) Playing around with mono and stereo connections can lead to weird results. Need to know what you are doing!

Dave.
 
...and I have no idea what's going on :D

A "peak limiter" is a compressor with the parameters set a certain way, is it not? Also a compressed signal sounds louder than a raw one, so you can turn the volume down accordingly. Finally, I was kind of making a joke there, although I don't see why it wouldn't work provided I could feed that limiter at the proper levels for it.

ecc83: What sort of listening levels do you think I am talking about by the way?

And still most importantly as of presently, could someone briefly explain what actually DOES happen to the signal when it's fed through a "headphone level" output into a "line level" input, then into a pair of headphones after some gain (voltage?) is applied? Okay, impedance doesn't matter at all. What about the levels then? Would things be somehow mismatched in other ways? Would there be notable distortion?

thanks in advance.
 
ecc83 said:
I cannot see where I have used the contraction 'Dr'? Are you using it to mean 'Doctor'? If so, doctor of what? Medicine? Divinity? Dave.
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I will not know how to answer that, till I know the name of the Doctor.

spitzer said:
...and I have no idea what's going on :D. Finally, I was kind of making a joke there
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Me To! :laughings:The picture below should make everything clear, once you click on it.

View attachment 100880
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spitzer said:
...and I have no idea what's going on :D

A "peak limiter" is a compressor with the parameters set a certain way, is it not? Also a compressed signal sounds louder than a raw one, so you can turn the volume down accordingly. Finally, I was kind of making a joke there, although I don't see why it wouldn't work provided I could feed that limiter at the proper levels for it.

ecc83: What sort of listening levels do you think I am talking about by the way?

And still most importantly as of presently, could someone briefly explain what actually DOES happen to the signal when it's fed through a "headphone level" output into a "line level" input, then into a pair of headphones after some gain (voltage?) is applied? Okay, impedance doesn't matter at all. What about the levels then? Would things be somehow mismatched in other ways? Would there be notable distortion?

thanks in advance.
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You have to look at electronic devices as 'Black Boxes' (in the first instance at least, otherwise that way madness lies) . They have an input defined by its impedance (resistance) and a maximum input level defined as 'X' dBV, dBu or volts rms or peak to peak. Output level will be similarly defined as dBu etc and (if you are lucky!) a source impedance given. As mentioned, you can ignore impedances almost always and just look at levels.
Obviously, if a bit of kit has a max Vin of +10dBu and you hit it with +12dBu it will distort!

In an ideal world ALL audio devices (where appropriate) would have a maximum output not less than +22dBu (10V rms) and have gain ranges such that they could be inserted anywhere in the audio chain and work at their optimum level which for 'proper' studio kit is +4dBu (abt 1V rms).

Butty-but-but! Such levels and head rooms are only possible if the gear has decently high internal supply voltages, + and -15V being about the minimum and that is costly and in fact, to interface with a computer is simply an overkill.

So, how do you proceed? Bit like a gaggle of guitar pedals, plug 'em in and see w'appen.

Oh yes! What level do I THINK you need? No idea but I suspect a bit more than is good for you!

Dave.
 
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