Good built, nice! But I would use shielded coils in output integrators.
How does it sound (eg. vs JLH or vs 30 years old Danish "HP-Amp")?
Tripath TPA series is often used for amp and HP amp too. Here is a Muse one: link. There is a combined version (equivalent with this buit with 6.3 Jack connector in the front) but I don't find that. This is class-T, I don't know exactly what is the difference.
How does it sound (eg. vs JLH or vs 30 years old Danish "HP-Amp")?
Tripath TPA series is often used for amp and HP amp too. Here is a Muse one: link. There is a combined version (equivalent with this buit with 6.3 Jack connector in the front) but I don't find that. This is class-T, I don't know exactly what is the difference.
I se no reasons for shielding the coils, no hum fields inside the cabinet.
This amplifier uses a TPA3122 IC, and the sound is a little thin I think. But the amplifier is well suited for headphone amp because it has common ground at the output, some of these amplifieres does not have this and therfore need rewired headphones. That goes for the Muse also, it is not fit for headphones.
But this amplifier is cheap and very easy to work with and it also runs on a single 12V supply and deliver up to 15W class D.
2 x 15 Watt 8 Ohm Class D Audio Amplifier DIY Kit TPA3122 15W Stereo Amp | eBay
This amplifier uses a TPA3122 IC, and the sound is a little thin I think. But the amplifier is well suited for headphone amp because it has common ground at the output, some of these amplifieres does not have this and therfore need rewired headphones. That goes for the Muse also, it is not fit for headphones.
But this amplifier is cheap and very easy to work with and it also runs on a single 12V supply and deliver up to 15W class D.
2 x 15 Watt 8 Ohm Class D Audio Amplifier DIY Kit TPA3122 15W Stereo Amp | eBay
Hello Miles,
I made the modifications you described and everything worked well. However
there was hum cause the Transformer was to close. I decided to put the transformer in an extra case. When I connected everything and powered up and measured voltages everything was fine. Exept that I could not measure an AC Voltage that shoud double on the both secondaries...
So I put my headphone up and there was the most terribel hum I ever noticed!
I was wondering if I have to connect the earth coming from the mains to the
both secondaries which are combined for 0V.
I made the modifications you described and everything worked well. However
there was hum cause the Transformer was to close. I decided to put the transformer in an extra case. When I connected everything and powered up and measured voltages everything was fine. Exept that I could not measure an AC Voltage that shoud double on the both secondaries...
So I put my headphone up and there was the most terribel hum I ever noticed!
I was wondering if I have to connect the earth coming from the mains to the
both secondaries which are combined for 0V.
You should measure DC offset when amp is warmed up. The offset difference between cold and warm state is about 100mV. Anyway, up to 50-100mV DC is acceptable for headphones.
ahem I'm not so sure about that
I try to stay under 5mV for 'phones and 100mV for speakers.
Take a low impedance headphone of 32 ohm (e.g. Beyerdynamic DT990-32).
Power handling of the headphone is specified at 100mW.
http://europe.beyerdynamic.com/shop/media//datenblaetter/DT990_DB_E_A3.pdf
100mV DC => 0.3mW. So that makes 0.3% of specified power ?
Patrick
Power handling of the headphone is specified at 100mW.
http://europe.beyerdynamic.com/shop/media//datenblaetter/DT990_DB_E_A3.pdf
100mV DC => 0.3mW. So that makes 0.3% of specified power ?
Patrick
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ahem I'm not so sure about that
I try to stay under 5mV for 'phones and 100mV for speakers.
No problem with 100mV also @phones, trust me!
Anyway, it is clipping when switch the amp ON/OFF. For no clipping <10-20mV is desired (depends on phone's impedance and SPL).
I just finished assembling one of these ebay kits and had a few queries, how to adjust the gain (found that), the huge DC offset swing (found that too), and if 60c heatsink temps are normal (confirmed). So after 37 odd pages of this thread it seems i have another evening ahead of me prodding this amp with a soldering iron to work through an extensive list of mods. What a great read this thread was, and what a great forum this is. Cheers all
Well, that's one way of looking at things, if you're concerned only with what offset HP will tolerate before destruction.
If you look at the calculations shown here, which deal with the issue more in terms of fidelity:-
John Conover: Direct Coupled Stereo Headphone Amplifier
...and which are admittedly for a 16 ohm HP with 100dB/mW, then 1, 16-bit LSB in such a system delivering 100dB SPL is 2 microvolts, which puts a very different complexion on the matter IMO, and suggests that output offsets in headphone systems should ideally be <= 1uV. Of course this is not easy to achieve, and offsets of a few (<10) uV are probably more realistic in terms of desirability vs. achievability.
Has anybody got a copy of the board layout, everybody keeps referencing components like R5, C12 etc which i think is from a diagram on the original JLH site link which no longer works
Some JLH schematics can be found here:
JLH headamps
Cheers,
Jacques
Thanks Jacques, those circuit seem to differ but i have figured it out anyway. Removed all the 0ohm links (measured ~5ohms) and replaced with wire, removed those eight 100nf ceramic caps and replaced the gain resistors with 2.2k which has greatly improved the sound of this little amp. I'm actually surprised how clean it sounds now, though the gain is still too high for my source so i might try replacing those 2.2k resistors.
I also have some decent 100uf Panasonic caps here but i'm going to listen to this amp a bit more before i change anything else, some high frequency's sound a bit odd, not sure what i'm hearing yet...
I also have some decent 100uf Panasonic caps here but i'm going to listen to this amp a bit more before i change anything else, some high frequency's sound a bit odd, not sure what i'm hearing yet...
Hi Mcandmar,
Could you post your final schematics?
How did you solve the swinging DC in output which seems to be the biggest problem associated with the JLH design?
Cheers,
Jacques
I don't have any schematic to post, unless you want a pic? Not much to see really that hasn't already been covered in this thread.
I haven't found a solution to the DC offset yet, but its fairly consistent with ~100mv cold start, dropping to ~0mv after 15-20mins.
If i understand it correctly the zener diodes on the board are used as a voltage reference, and that reference changes with temperature? Which has me curious if there is a better method of creating a voltage reference that dosent drift with temperature. Who knows mounting the diodes on the underside of the board may even help, a little pcb with a voltage regulator maybe?
I'm also curious as to why its suggested to remove the variable pot and solder a link onto the board, surly its better to retain the ability to adjust the offset? I also measured mine and both pots are currently set to almost exactly 3k ohms.
I'm not going to spend too much time / effort on this, its really just for fun, and a learning exercise..
I haven't found a solution to the DC offset yet, but its fairly consistent with ~100mv cold start, dropping to ~0mv after 15-20mins.
If i understand it correctly the zener diodes on the board are used as a voltage reference, and that reference changes with temperature? Which has me curious if there is a better method of creating a voltage reference that dosent drift with temperature. Who knows mounting the diodes on the underside of the board may even help, a little pcb with a voltage regulator maybe?
I'm also curious as to why its suggested to remove the variable pot and solder a link onto the board, surly its better to retain the ability to adjust the offset? I also measured mine and both pots are currently set to almost exactly 3k ohms.
I'm not going to spend too much time / effort on this, its really just for fun, and a learning exercise..
100mV does not cause any damages with any headphones. But if you would like to decrease it, set it to -50mV at cold, it will change to +50mV at warm (or inversly?
).
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