I came across this thread about using the NE5534 in a very simple scheme. It is "again" a power boosted op amp as usual except that the output section uses an intermediate stage of the opamp and bypasses the output stage.
Will It make an audible difference ? Can only find out by building it ! This one is really simple and can possibly be used direct coupled ( if there is no dc at the input) and has very few components. Might be interesting to see how it compares against the JLH circuit.
I'll post results when I get it done.
Forgot to post the link :
http://www.diyaudio.com/forums/headphones/162666-very-cheap-but-still-ok-amp.html
Will It make an audible difference ? Can only find out by building it ! This one is really simple and can possibly be used direct coupled ( if there is no dc at the input) and has very few components. Might be interesting to see how it compares against the JLH circuit.
I'll post results when I get it done.
Forgot to post the link :
http://www.diyaudio.com/forums/headphones/162666-very-cheap-but-still-ok-amp.html
Doesn't it make some noise? It's output has low impedance but a preamp usually has high impedance at the output. Is it not a problem?
(I look forward to the PCB's
)
"........ a preamp usually has high impedance at the output....."
I think you mixed it up. Typically a preamp has a high 'input' impedance and low 'output' impedance to enable it to drive the cable and power amp load.
If you wanted a slightly higher output impedance , all you need to do is to add a 100 ohm ( or whatever ohms ) resistor in series with the output .
Cheers.
I think you mixed it up. Typically a preamp has a high 'input' impedance and low 'output' impedance to enable it to drive the cable and power amp load.
If you wanted a slightly higher output impedance , all you need to do is to add a 100 ohm ( or whatever ohms ) resistor in series with the output .
Cheers.
I think that a preamp has high output impedance because typically, power amps have high input impedance (10k-100k). Power amps have low impedance output to be able to drive speakers. But now I don't know, you confused me
>If you wanted a slightly higher output impedance , all you need to do is to add
> a 100 ohm ( or whatever ohms ) resistor in series with the output .
Just don't try it with negative resistance. In theory, that too can be an amplifier.
But reality is walking a phase shift tightrope with oscillation on either side.
Shockley (four layer diode) tried, and sorta got that scheme to work.
But drove him out of business, or maybe when his engineers all quit...
http://semiconductormuseum.com/PhotoGallery/PhotoGallery_Shockley4E30_Page5.htm
> a 100 ohm ( or whatever ohms ) resistor in series with the output .
Just don't try it with negative resistance. In theory, that too can be an amplifier.
But reality is walking a phase shift tightrope with oscillation on either side.
Shockley (four layer diode) tried, and sorta got that scheme to work.
But drove him out of business, or maybe when his engineers all quit...
http://semiconductormuseum.com/PhotoGallery/PhotoGallery_Shockley4E30_Page5.htm
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Hell Ken,
You just confused poor Melorin some more !
Melorin. The preamp has a low output impedance so that it can easily drive the power amp which is not always a high impedance ( unlike tube circuits). It can be as low as 1K ohm in some cases and typically 10k to 20 K ohms. It also needs to drive the interconnecting cable which will have capacitance. With the output impedance of the preamp this becomes a high pass filter. So depending on the value of the capacitance and load impedance you can determine the limiting preamp output impedance to ensure no loss of HF . Often you will find that if a preamp has a 100 ohm output impedance , it is due to a resistor put in series with the output by the designer. The preamp circuit having a very low intrinsic output impedance by itself. It also prevents the preamp from facing a direct capacitive load ( of the cable ) which isn't liked by many circuits.
However this does not mean that a high preamp output impedance will not work ! It will act as a signal divider and will reduce the effective signal available to the power amp and the capacitance loading will have to be looked at very closely to ensure that HF roll off is outside the audio band.
I did some tests with just that. A very high output impedance preamp using tubes. Tube preamp circuits can have ( but not always!) much higher output impedance than solid state circuits. Maybe you should look at my thread about the test I made.
http://www.diyaudio.com/forums/tubes-valves/154850-high-zout-tube-preamps-ss-power-amps.html
You just confused poor Melorin some more !
Melorin. The preamp has a low output impedance so that it can easily drive the power amp which is not always a high impedance ( unlike tube circuits). It can be as low as 1K ohm in some cases and typically 10k to 20 K ohms. It also needs to drive the interconnecting cable which will have capacitance. With the output impedance of the preamp this becomes a high pass filter. So depending on the value of the capacitance and load impedance you can determine the limiting preamp output impedance to ensure no loss of HF . Often you will find that if a preamp has a 100 ohm output impedance , it is due to a resistor put in series with the output by the designer. The preamp circuit having a very low intrinsic output impedance by itself. It also prevents the preamp from facing a direct capacitive load ( of the cable ) which isn't liked by many circuits.
However this does not mean that a high preamp output impedance will not work ! It will act as a signal divider and will reduce the effective signal available to the power amp and the capacitance loading will have to be looked at very closely to ensure that HF roll off is outside the audio band.
I did some tests with just that. A very high output impedance preamp using tubes. Tube preamp circuits can have ( but not always!) much higher output impedance than solid state circuits. Maybe you should look at my thread about the test I made.
http://www.diyaudio.com/forums/tubes-valves/154850-high-zout-tube-preamps-ss-power-amps.html
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Further listening tests as a pre amp.
Some more listening tests with the JLH headphone amp as a preamp.
I raised the gain from x 3.2 ( +10dB) to x 5.7 ( +15 dB) because on some discs the signal level was quite low and and even turning up the volume to max didn't clip the power amp output.
Well, it sounds very good. My best configuration was a Solen cap at the input and with no output cap. The power amp has a Solen at it's input. Sounds very good ! The single supply version isn't very far behind either. Though it has about +6 V dc at it's output we can remove the output cap if the power amp has an input coupling cap , which my amp has.
I'm still listening to this combination!
Some more listening tests with the JLH headphone amp as a preamp.
I raised the gain from x 3.2 ( +10dB) to x 5.7 ( +15 dB) because on some discs the signal level was quite low and and even turning up the volume to max didn't clip the power amp output.
Well, it sounds very good. My best configuration was a Solen cap at the input and with no output cap. The power amp has a Solen at it's input. Sounds very good ! The single supply version isn't very far behind either. Though it has about +6 V dc at it's output we can remove the output cap if the power amp has an input coupling cap , which my amp has.
I'm still listening to this combination!
How did you rais the gain? I am thinking of easing down (?) the gain so that it can be too loud for me (could be if it worked wellSome more listening tests with the JLH headphone amp as a preamp.
I raised the gain from x 3.2 ( +10dB) to x 5.7 ( +15 dB) because on some discs the signal level was quite low and and even turning up the volume to max didn't clip the power amp output.
Well, it sounds very good. My best configuration was a Solen cap at the input and with no output cap. The power amp has a Solen at it's input. Sounds very good ! The single supply version isn't very far behind either. Though it has about +6 V dc at it's output we can remove the output cap if the power amp has an input coupling cap , which my amp has.
I'm still listening to this combination!
).
Alter R13 and R8 from the circuit shown in the post #15.
I had used 3.3K and 1.5K respectively and changed it to 4.7K and 1 K .
To decrease gain you need to increase R8 from 1.5 K to (?) for example 3.3K . In that case the gain will be x 2 = 1+ R13/R8 . removing R8 will give unity gain. Must also check if the circuit is stable . R13 affects the output offset adjustment and you will need to readjust the preset if it is changed.
I think you should always have an extra + 6 dB or more gain to take into account recordings that are at a lower level. Besides I like the volume to max out much before full rotation !
I had used 3.3K and 1.5K respectively and changed it to 4.7K and 1 K .
To decrease gain you need to increase R8 from 1.5 K to (?) for example 3.3K . In that case the gain will be x 2 = 1+ R13/R8 . removing R8 will give unity gain. Must also check if the circuit is stable . R13 affects the output offset adjustment and you will need to readjust the preset if it is changed.
I think you should always have an extra + 6 dB or more gain to take into account recordings that are at a lower level. Besides I like the volume to max out much before full rotation !
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Single supply circuit hum as preamp !
I find the single supply circuit has some hum ( right at the speaker) . I guess the supply will have to be better than what is shown for use as a preamp. However the sound is very smooth. Like a tube preamp. The FFT did show fundamental and second harmonic with higher orders almost burried in the noise which is also very low.
You might want to use the best possible cap at the input. I don't mean by price but by sound. Someone will have to check which type is most suitable.
Off the cuff ( and I could be wrong !) I guess Solen or Jensen PIO's !
This has been a really interesting series of experiments.
I find the single supply circuit has some hum ( right at the speaker) . I guess the supply will have to be better than what is shown for use as a preamp. However the sound is very smooth. Like a tube preamp. The FFT did show fundamental and second harmonic with higher orders almost burried in the noise which is also very low.
You might want to use the best possible cap at the input. I don't mean by price but by sound. Someone will have to check which type is most suitable.
Off the cuff ( and I could be wrong !) I guess Solen or Jensen PIO's !
This has been a really interesting series of experiments.
For use as a preamp only...
You can change R6 ( 22 ohms) shown in the circuit found on page
http://www.diyaudio.com/forums/headphones/159202-jlh-headphone-amp-2.html
Increasing R6 will reduce quiescent current in the output stage and hence the output stage dissipation. Possibly go down to something less than 20mA and avoid a heat sink altogether. R6 could be something like 56 ohms. I used a string of resistors at hand (22+22+10 = 54 ohms) and it worked out fine at low loads ( 1 K ohm) . Maybe still useable with 300 ohm headphones .
Sim says that it will work fine with 300 ohm loads and should be quite listenable with 32 ohm loads at average levels. Distortion figures in the sim might be a bit too good ! Neverthless they shouldn't be too high either.
Will check this out later with music.
Cheers.
You can change R6 ( 22 ohms) shown in the circuit found on page
http://www.diyaudio.com/forums/headphones/159202-jlh-headphone-amp-2.html
Increasing R6 will reduce quiescent current in the output stage and hence the output stage dissipation. Possibly go down to something less than 20mA and avoid a heat sink altogether. R6 could be something like 56 ohms. I used a string of resistors at hand (22+22+10 = 54 ohms) and it worked out fine at low loads ( 1 K ohm) . Maybe still useable with 300 ohm headphones .
Sim says that it will work fine with 300 ohm loads and should be quite listenable with 32 ohm loads at average levels. Distortion figures in the sim might be a bit too good ! Neverthless they shouldn't be too high either.
Will check this out later with music.
Cheers.
More listening tests.
This might sound odd but I've recently been using a LM1875 power amp for testing the JLH headphone map as a preamp. This is because the LM1875 chip has a certain quality about the bass end and mid range that changes dramatically with different front ends as compared to the direct input to the chip.
Especially the tight foot tapping bass changes remarkably with different front ends. Many tubed front ends also 'lost' the bass magic in this setup ! The JLH split supply amp comes very close to being transparent and retaining the quality of the bass end. However it also depends on the input cap on the preamp. Solens do well as do some Epcos caps. Final choice probably depends on personal taste. I find the Epcos slightly smoother ( rolled off a bit ? ) than the Solens. But certainly better than a cathode follower that I tried with a 6DJ8 .
I try very hard to understand why this is so but haven't been able to figure out why. The difference is very audible and I don't just trust my own ears. I ask unsuspecting friend to guess if there is any differenc in what they hear. I don't tell them what's being done. Just ask if the sound is the same or different when switched several times.
This might sound odd but I've recently been using a LM1875 power amp for testing the JLH headphone map as a preamp. This is because the LM1875 chip has a certain quality about the bass end and mid range that changes dramatically with different front ends as compared to the direct input to the chip.
Especially the tight foot tapping bass changes remarkably with different front ends. Many tubed front ends also 'lost' the bass magic in this setup ! The JLH split supply amp comes very close to being transparent and retaining the quality of the bass end. However it also depends on the input cap on the preamp. Solens do well as do some Epcos caps. Final choice probably depends on personal taste. I find the Epcos slightly smoother ( rolled off a bit ? ) than the Solens. But certainly better than a cathode follower that I tried with a 6DJ8 .
I try very hard to understand why this is so but haven't been able to figure out why. The difference is very audible and I don't just trust my own ears. I ask unsuspecting friend to guess if there is any differenc in what they hear. I don't tell them what's being done. Just ask if the sound is the same or different when switched several times.
While listening to this system it occured to me that the dual diode used to bias the input transistor wasn't required if the circuit is used as a preamp as I have used it. This will cause a dc offset of about 1 volt or more depending on the value of the feedback resistor. But as the input to the power amp is capacitor coupled this shouldn't matter.
It sounds very nice and I tried switching between the two schemes ( with at least a two minute time lag ) and I think I hear a difference. I can't be sure if my brain is playing tricks. This needs to be checked with less time lag between the tests. I think I'll try a remote controlled relay.
It sounds very nice and I tried switching between the two schemes ( with at least a two minute time lag ) and I think I hear a difference. I can't be sure if my brain is playing tricks. This needs to be checked with less time lag between the tests. I think I'll try a remote controlled relay.
Thanks Ashok, I have finally built this superb headphone amplifier!
John Linsley Hood and Ashok were right. It's really a great amp!
Ok, I made the single supply version, which is designed by Ashok
It's safe to use my Grados, still sounds very well.
If you want to build a cheap and exellent hp amp, it's a good choice.
If it hadn't been for Ashok, I couldn't have finished with it, so thanks Ashok!
John Linsley Hood and Ashok were right. It's really a great amp!
Ok, I made the single supply version, which is designed by Ashok
It's safe to use my Grados, still sounds very well.
If you want to build a cheap and exellent hp amp, it's a good choice.
If it hadn't been for Ashok, I couldn't have finished with it, so thanks Ashok!
Ashok,
Thanks for your detailed reports! I am also interested in this circuit.
Do you have an update?
What ended up as your final configuration?
Does it work well as a preamp AND headphone amp, or should it be optimized for one or the other?
What PS?
Other observations or comparisons?
Thanks!
Thanks for your detailed reports! I am also interested in this circuit.
Do you have an update?
What ended up as your final configuration?
Does it work well as a preamp AND headphone amp, or should it be optimized for one or the other?
What PS?
Other observations or comparisons?
Thanks!
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