Headphone distortion when monitoring DR-40

[Geoffrey Kolbe]

I find that if I have the headphone volume anything higher than 'quiet' then I get distortion on the sound. I do not know the impedance of the headphones, but I suspect that the cause of the distortion is that the impedance of the headphones is 'low'.

Since the headphones are plugged into the line-out of the DR-40, I suspect that high impedance headphones are needed to avoid distortion.

Has anyone else had this problem?

Any recommendations on the best type of headphones for monitoring the DR-40?

Thanks

 

[Arjan P]

Hi Geoffrey, and welcome! I don't know the DR-40 very well (I have a DR-100 myself), but from what I see the output has the headphones symbol / line out (slash in between).

That suggests to me that you need to change a setting to make it either a headphones output OR a line out. Should be in the menu system somewhere.. It's an (educated) guess, but I hope I'm right!

 

[Geoffrey Kolbe]

Thanks Arjan.
So, this prompted me to go and look at the manual (how sad is that?) and the specification for the headphones/line-out jack is: output impedance 12 ohms. Maximum output is into a 32 ohm load. There is nothing in the manual to say there is a switch from headphones to line-out.

This is all relatively low impedance stuff, and I would not expect distortion if I were to put, say, an 8 ohm load by way of headphones.

Anybody else with any experience of using headphones to monitor the DR-40...?

Thanks

 

[Art Anderson]

I just slapped on some headphones to see what my experience is. Yes, I was surprised that it can get ugly really quickly. I hardly ever use headphone monitoring or playback on the DR-40 and I'm coming up on 4 years of ownership. I probably made that choice early on and forgot why. Neither handheld or internal mics is my typical mode of use.

So tonight what I got was that with the headphone level indicator having 4 clear bars at the right extreme, it sounded OK. Setting it anywhere higher than that it can break up very quickly.
I tried to keep the recording level bars at the -12dB triangle marker just for an easy reference for this discussion. Meanwhile the numerical value was usually around -08 dB and the bar meter left tell tale full limit marks.

The headphones are cheap @$$ Sony MDR-ZX110 or some such. The $25 things that fold flat.

 

[Geoffrey Kolbe]

Thanks for your confirmation Art. Sounds like it is a generic problem with the DR-40 and not just a specific problem with my machine.

I have ordered a very expensive pair of Beyerdynamic DT 770 PRO Studio Headphones, for the reason that they are 32 ohm input impedance and so should be a perfect match to the DR-40. They come on Saturday. I will report back on what happens next....

 

[JSchmo_Bass]

My experience is that the headphones out never sounds that great compared to the actual WAV file.

I use my DR-40X to capture my bands rehearsals (2 internal mikes plus 2 externals from the PA) in 24/48 4 channel mode.

After each band practice I sit with the unit and headphones to review, set marks between the “good bits”, auto divide and then mix down to 2 channels to balance the internal and external signals into a pleasant scratch mix of the key songs.

I then transfer the files via USB to my laptop and send them to the rest of band (sometimes compressing to mp3 on my laptop with a converter at this point so they can be emailed).

I am always amazed at how much better the files sound at the end of this process than at the headphone stage.

However it’s all good. can’t beat the efficiency of do all those quick cut and mix spots right on the DR, sitting on the couch, riding in a car or anywhere really.

if it was a special keeper track I might bring all 4 files into a DAW for perfect edits and mastering, but for workaday... I love this device!

 

[Art Anderson]

Until last year I was using mine every Friday and Saturday for a few years, recording small bands, duos, soloists playing at a cafe. That would be two hours each session. I didn't use that technique you describe of marks and auto divide because I was taking the files into my PC, eventually synced up to the video I'd been taking at the same sessions.

Like you said JSchmo-Bass, the files sound very good compared to the headphones. That is what I was inferring when I wrote I don't use the headphones. I just had 2 possible ways I'll set up my gear and I became confident in the system. I'd check with headphones during setup at the beginning, not to monitor. The headphones hung unused but at the ready the rest of the night.

The DR-40 hasn't let me down but I did dismiss the usability of headphone monitoring long ago. And the little speaker on the back? LOL. Good luck with that.
I bought a DR-70D last year but it hasn't seen any action yet.

 

[Geoffrey Kolbe]

Thanks to everyone for their input

I went out and bought myself some very expensive Beyerdynamic DT 770 PRO Studio Headphones, which have a 32 ohm input impedance, and I am glad to say these work well without any attendant distortion, even with the volume turned right up.

I think the lesson is that the DR-40 is somewhat sensitive to the output impedance and cheap headphones tend to have 4 ohm or 8 ohm input impedance, which is obviously not matching the DR-40 well.

Anyhow, for anyone else looking for the answer to this question, high impedance headphones seems to be the answer and 32 ohm headphones would seem to be the perfect match, according to the manual.

 

[Number41]

Glad I found this thread, I got my dr40 second hand and used my cheap-ish sony headphone to monitor it right away from the first try, needless to say that it caused a lot of frustrations when the sound keep distorting even when I'm nowhere near the suggestion mark and the peak light indicator never showed once. I looked up the specs for my headphones and it's already 16ohm and I don't feel like investing in a hi end headphones atm, all I want to use it for really is to monitor the level/distortion not to check the sound quality.. If the suggestion mark & the peak indicator is sufficient then I guess I'll just go with that.

 

[BazzBass]

I run the line out into my little mixer,then into monitors and/or headphones. Haven't encountered any issues using this method. Glad you have it sorted

 

[Geoffrey Kolbe]

I don't feel like investing in a hi end headphones atm,

I guest the headphones don't have to be expensive to be 32 ohm headphones. I guess you could put a 39 ohm resistor across the 'phones plug....?

 

[Number41]

I actually just found a decent jbl that's 32ohm, not sure that the impedance is the only thing that caused the problem but I'll just take the tascam to the store and try it out. Will confirm back soon.

 

[tzdvl]

The pertinent specifications for using headphones with the DR-40 are:
Output impedance: 12Ω
Maximum output: 20 mW + 20 mW (when connected to headphones, 32Ω load)

I would interpret this to mean that the DR-40 is capable of driving headphones of 32Ω at full power output of 20mW in each channel.

It sounds like the DR-40 might be designed to be similar in output to portable music players (iPods, etc.), which often are optimized for use with 32Ω headphones.

Lower impedance 'phones (less than 32Ω) would probably require more output current than the output stage is capable of producing, causing overload and increased distortion. I don't know of any good "modern" headphones that are less than 32Ω, anyway.

Higher impedance 'phones would use less current, but would require more voltage for full volume. Portable players can't provide much output voltage, so they often come with 32Ω 'phones, and supply more current for higher wattage (volume).

This morning I tried my DR-40 with four different sets of headphones. I tried a set of older Apple earbuds (32Ω)
Sennheiser HD 280 Pro (64Ω)
Sennheiser HD 600 (300Ω) and
Sennheiser HD 420 (600Ω).

Maybe I'm lucky (and I don't like to blow my ears out), but I got decent clean output using all four 'phones. The output level got uncomfortably loud with all of them before I heard obvious distortion. The Apple earbuds sounded the worst (very bright and tinny), but I don't know if that is due to their low impedance or their "quality" .

I got good volume levels at around "halfway" on the volume indicator with the 32Ω and 64Ω 'phones, and about 3/4 level with the 300Ω 'phones. The 600Ω 'phones were JUST loud enough at full volume.

I looked at the output waveform on my oscilloscope (I was powering the DR-40 with three fresh Duracell alkaline batteries).
The output voltage clipped at about 3 volts peak-to-peak with the 32Ω and 64Ω 'phones, and at just under 4 volts p-p with both the 300Ω and 600Ω 'phones.

All but the 600Ω 'phones were far too loud to keep on my ears at clipping level. The 600Ω Sennheiser HD 420s were tolerable at full volume, which was right at clipping.

So, if you're hearing excessive distortion from your DR-40 I would try using 'phones of at least 64Ω, and preferably higher, up to 300Ω or so). The DR-40 just can't adequately drive 600Ω 'phones.

And make sure you're using fresh batteries.

Of course, you will get MUCH better sound if you plug your DR-40 into a mixer or headphone amp, and plug the phones into that!

 

[Geoffrey Kolbe]

That is really good information TZDVL, thanks for sharing it with us.

 

[Number41]

Thanks so much for a very detailed reply!

 

[Cosmic]

I have a DR-70, and, like previous portables in similar price ranges, the headphone amp is underpowered crap. If you feel like it, get a compact external Lithium-powered headphone amp and tape it to the unit. I use a Topping amp which is flat in shape and which (in my case) fits on top of the DR-70 with double-sided tape. The Topping takes the "line out" feed from the DR-70 and, while no award-winner, it at least has quite a bit more power than the silly circuit in the recorder.

 

[tzdvl]

The DR-40 does have pretty marginal capability for use with headphones.

The output voltage is limited to around 4 volts peak-to-peak due to the 4.5 volt supply (three 1.5 volt batteries). Maybe a bit more when on USB power (5 volts)?

And the output current capability is wimpy. Notice that even using headphones between 32Ω and 64Ω caused the available output voltage to drop from 4 volts to 3 volts.

Since higher output power (milliWatts = volume) and low distortion requires both decent voltage AND current, you shouldn't expect much from a device like the DR-40.

That said, the fact that the DR-40 has ANY ability at all to drive headphones, from what is really a line output, should be appreciated!

I'm sure the designers just wanted to provide a way to check the basic quality and balance of a recording. Similar to, but much better than, the silly little internal speaker. It's just there to tell you "yeah, the levels are OK, and I'm recording in both channels, but I probably have the mics too close to that ventilation fan..."

It is useful, but don't expect to use it for live monitoring or mixing and mastering!

 

[skier]

This is all relatively low impedance stuff, and I would not expect distortion if I were to put, say, an 8 ohm load by way of headphones.

Actually, that's not true. While 8 ohms seems like an appropriate load because it's the most common nominal impedance for most speakers, the DR-40 manual explicitly states the output is "20mW + 20mW (32Ω load)" - I read that as 20mW for each ear cup. If you use headphones with, for example, a 16 ohm impedance, then twice as much current will flow and it will overload the DR-40 headphone amp and distort. 8 ohm phones would draw four times the current. You need to present a load of at least 32 ohms impedance to avoid distortion and possibly overheating the built-in headphone amp. That said, the audio level will be lower at a higher impedance than 32 ohms, so you may not find the level high enough.

I guest the headphones don't have to be expensive to be 32 ohm headphones. I guess you could put a 39 ohm resistor across the 'phones plug....?

NO! Putting any resistor value across the the plug will actually lower the impedance further causing more current to flow and more distortion - you could even overheat and burn out the headphone amp depending in how the circuit was designed. In this case, if you've got a set of cans with too low an impedance value, your only option other than using the correct impedance phones would be to place a resistor "in series" with the left cup and another resistor of equal value in series with the right-side cup. Doing this, the phones will present a higher impedance to the amp and it should not distort unless the impedance is still too far below 32 ohms. If it is around 32 or higher, the maximum audio level available to you will be lower than if you actually were using cans rated at 32 ohms because you'll be losing some of the power across the resistors. If the amp has enough power to provide an adequate sound level even though it's losing some power to the resistors, it may still be loud enough for you to use. But if the amp has little extra reserve, it may not be enough.

No matter how you look at it, using phones of the proper impedance will give you the best flexibility of better volume and avoiding distortion.

 

[tzdvl]

One thing to keep in mind: the output impedance of the DR-40 is specified as "12Ω".
I would assume that the designers have placed a 12 ohm resistance in line with the output, to protect the output stage from short circuits (or 8Ω headphones ).

So, whatever headphones you plug in, they are going to have 12 ohms added to their actual impedance. Using 32Ω 'phones, the amp is going to actually "see" 44Ω.

That means that if you do plug in 8Ω headphones, the amp will be driving 20Ω. It may not sound great, but you probably won't kill it!

Now (WARNING. Boring tech-y stuff ahead!) ...
According to the online headphone "geeks and gurus", headphones should sound and work best when "the output impedance of the amp is less than about 1/8th the impedance of the headphones".

When you plug headphones into a headphone amp, the amp is going to be driving both the output resistor and the 'phones, in series. The power produced by the amp will be "divided" proportionally between them, according to their resistance.

So with 32Ω 'phones and a 12Ω output resistor , about 2/3 of the power is being used by the 'phones, and 1/3 is "wasted" by the resistor (as heat). With 8Ω 'phones 2/3 of the power goes to the resistor!
With 300Ω 'phones, only 4% of the power goes to the resistor.

In addition, the actual impedance of most headphones, like loudspeakers, is NOT equal at every frequency. The frequency response of the 'phones will be influenced by that "dividing" of the power between the 'phones and the output resistor. If the impedance of a set of 'phones varies a lot over the audible frequency range, a higher output impedance can cause significant frequency response irregularities, especially with low-impedance ‘phones.

So anyway, according to the geeks, 32Ω headphones would "prefer" an output impedance of, at most, 32/8 = 4 ohms.

Given that the DR-40 has an output impedance of 12Ω, headphones of more than 96Ω should be optimum. Assuming, of course, that the amp can supply enough voltage to drive them.

And my experiment in my first post above shows that the DR-40 can easily drive headphones up to 300Ω to uncomfortable volume levels!

So if I were going to buy a set of headphones specifically to use with the DR-40, I would shoot for a set with an impedance between 100 and 300 ohms.

 

[skier]

@tzdvl, your logic is sound - this is all just simple Ohm's Law. I don't have a schematic or an actual DR-40, so I can't measure anything. The real question as you said is: is the amp output voltage enough to drive high impedance phones, and that will depend on the phones. And more importantly as you also stated, the actual impedance of any audio output transducer varies with frequency. We don't know what the inductive or capacitive characteristics are with any specific phones unless we measure it across the frequency spectrum at which they're designed to operate, and my experience is that those characteristics can be all over the place, especially the cheaper varieties. A good set of phones will cost more, but will also be more consistent across the line and provide better fidelity.