Hi,
I have recently bought a Tascam LM-8ST line mixer, which has a headphone output on the front. However when I use my Beyerdynamic DT 250 headphones with it, the output is far too loud - and I end up only using the very bottom of the volume control.
DT 250 Impedance: 80 Ω
LM-8ST Headphone Output: 250 mW + 250 mW (32Ω)
While I know that beyerdynamic also make a high-impedance version of the headphones - I am slightly surprised by the how big a mismatch there is.
I would like be able use the full range of the headphone control (without destroying my ears). Would some kind of attenuator circuit work? How do I calculate the resistor values?
Thanks!
njh.
I have recently bought a Tascam LM-8ST line mixer, which has a headphone output on the front. However when I use my Beyerdynamic DT 250 headphones with it, the output is far too loud - and I end up only using the very bottom of the volume control.
DT 250 Impedance: 80 Ω
LM-8ST Headphone Output: 250 mW + 250 mW (32Ω)
While I know that beyerdynamic also make a high-impedance version of the headphones - I am slightly surprised by the how big a mismatch there is.
I would like be able use the full range of the headphone control (without destroying my ears). Would some kind of attenuator circuit work? How do I calculate the resistor values?
Thanks!
njh.
250mW is quite a bit of power for headphones!
You might be able to do a simple voltage divider to cut the levels, but I don't know how that might affect distortion etc. Perhaps a buffer? Depends how much effort you are looking to expend.
But more importantly... how an earth does your 'Join Date' say Jan 1970???
You might be able to do a simple voltage divider to cut the levels, but I don't know how that might affect distortion etc. Perhaps a buffer? Depends how much effort you are looking to expend.
But more importantly... how an earth does your 'Join Date' say Jan 1970???
Simply inserting a resistor in serie is the easiest way to proceed but might alter the frequency response of your headphones.
If it is a problem, you need a resistor divider with a fairly low output impedance. If the mismatch is that bad, I would start with 33ohms from output -12 ohms to ground (about -12dB).
If it is a problem, you need a resistor divider with a fairly low output impedance. If the mismatch is that bad, I would start with 33ohms from output -12 ohms to ground (about -12dB).
Someplace I saw plots that demonstrated that headphones had a better response when driven from a low-impedance source. Anyway, here's a page with some attenuator ideas:
Headphone attenuation adapter | DIY-Audio-Heaven
I used 3.6 ohms across the headphones (since that's what I had two of), and the rest of the attenuator involves the headphone volume pot (and jack) from a scrapped stereo component. If I was building from scratch, I'd use a 2-pole rotary switch and a selection of series resistors.
Headphone attenuation adapter | DIY-Audio-Heaven
I used 3.6 ohms across the headphones (since that's what I had two of), and the rest of the attenuator involves the headphone volume pot (and jack) from a scrapped stereo component. If I was building from scratch, I'd use a 2-pole rotary switch and a selection of series resistors.
1) 250mW@32 ohm=100mW@80 ohm, so not that much.
That said,why attenuate Headphone OUT?
Just don´t drive it that hard; attenuate signal reaching Headphone Volume pot instead.
If at all possible, we want to keep/increase Headroom, not waste it.
Open unit, read what´s printed on phone volume stereo pot, specially ohm and taper, say A10k or something, post it here for suggestions.
In principle you locate the tracks feeding pot HOT terminal, cut them nearby and add a series attenuation resistor there, much better to attenuate Signal than Power.
User Manual block diagram shows a stereo pot controlling Stereo Earphone amp, said Stereo pot is fed from a selector switch , maybe you can add the resistor there.
If at all possible, try to get the Schematic (ask Tascam) ; if not post a closeup picture of the pots and switch area so we know what you have there.
In principle attenuate signal by around 10dB (3X) which should give you a way more controllable pot range.
Series resistors should be ~3X the pot value; for example IF pot is 10K you would need a 22k to 33k resistor.
If too much or too little attenuation, new values can be suggested but we need pot value to start.
If no label or it´s on an unreadable place, set volume to 0 (always with Mixer OFF and unplugged for some time) and measure end to end resistance, not *exact* because it´s in circuit but it will give us a value to work with.
That said,why attenuate Headphone OUT?
Just don´t drive it that hard; attenuate signal reaching Headphone Volume pot instead.
If at all possible, we want to keep/increase Headroom, not waste it.
Open unit, read what´s printed on phone volume stereo pot, specially ohm and taper, say A10k or something, post it here for suggestions.
In principle you locate the tracks feeding pot HOT terminal, cut them nearby and add a series attenuation resistor there, much better to attenuate Signal than Power.
User Manual block diagram shows a stereo pot controlling Stereo Earphone amp, said Stereo pot is fed from a selector switch , maybe you can add the resistor there.
If at all possible, try to get the Schematic (ask Tascam) ; if not post a closeup picture of the pots and switch area so we know what you have there.
In principle attenuate signal by around 10dB (3X) which should give you a way more controllable pot range.
Series resistors should be ~3X the pot value; for example IF pot is 10K you would need a 22k to 33k resistor.
If too much or too little attenuation, new values can be suggested but we need pot value to start.
If no label or it´s on an unreadable place, set volume to 0 (always with Mixer OFF and unplugged for some time) and measure end to end resistance, not *exact* because it´s in circuit but it will give us a value to work with.
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you probably have increased the output level above +4dBu which reads 0dB on the LED. lower the ST1 level and increase the gain of your amp to meet the specs.
Another possibility is to switch the phones to ST2 aux and lower the aux level to not have too much gain.
Usually the pots are in a centre position if levels are correct
Another possibility is to switch the phones to ST2 aux and lower the aux level to not have too much gain.
Usually the pots are in a centre position if levels are correct
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The impedance of the DT 250 is quite flat across the frequency spectrum :
Measurement's report Beyerdynamic DT 250 80 ohm test and graphs - Reference Audio Analyzer
So post #3 is good advice.
But the first thing I would want to find out is how much you want to attenuate.
This you can do by trial & error with just a series resistor.
33R will give you -3dB; 82R -6dB; 180R -10dB; 360R-15dB, 750R -20dB.
If it is anything more than 6dB, then maybe you should consider the potential divider solution.
And I would consider using 68R instead of 33R, as it will half the load on the headphone amp.
This ususally also means lower distortion.
Patrick
Measurement's report Beyerdynamic DT 250 80 ohm test and graphs - Reference Audio Analyzer
So post #3 is good advice.
But the first thing I would want to find out is how much you want to attenuate.
This you can do by trial & error with just a series resistor.
33R will give you -3dB; 82R -6dB; 180R -10dB; 360R-15dB, 750R -20dB.
If it is anything more than 6dB, then maybe you should consider the potential divider solution.
And I would consider using 68R instead of 33R, as it will half the load on the headphone amp.
This ususally also means lower distortion.
Patrick
The world (in unix) started 1/1/1970. If the Join Date has been corrupted to "zero" it may display that way.
And _then_ +/- your local time zone. Which may put you back in 1969.
