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Old 5th November 2013, 11:28 AM   #381
bkercso is offline bkercso  Hungary
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Quote:
Originally Posted by jcx View Post
100 mV is far too much for sensitive, low resisitance iem

for some that level of AC would drive them to >110 dB SPL - will certainly push the coils far off center, increase distortion
But this is not AC, it is DC. It dissipates 0,3 mW on 32 ohm phones. Phones can accept 200..2000 mW electrical power, and >90% of it will be converted into heat. So 100 mV DC does not damage phones.
But I cannot say anything about distortion caused by little constant membrane displacement from center position by DC offset... Somebody measured it?

Last edited by bkercso; 5th November 2013 at 11:30 AM.
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Old 22nd January 2014, 11:09 AM   #382
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Hello All

Thank you all for your kind comments...

I wonder if anyone is still interested in making the JLH Headphone amp ???

Miles
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Old 10th March 2014, 07:50 PM   #383
simcard is offline simcard  Russian Federation
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Originally Posted by MilesCampbell View Post
Hello All

Thank you all for your kind comments...

I wonder if anyone is still interested in making the JLH Headphone amp ???

Miles
Hi.
Yes. Thank you. Very informative.
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Old 12th March 2014, 11:20 PM   #384
bkercso is offline bkercso  Hungary
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Default Power transistors

I experienced this amp has weak bass. I already sold my JLH, but wondering how it sounds with different transistors, mainly in TO220 positions... Anybody tried it?
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Old 13th March 2014, 03:15 AM   #385
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Weak bass compared to what? And with what kind of headphones?

The JLH as suggested has an output impedance of 2.2 ohms, it should sound like a good portable player or somesuch. A typical integrated amp's headphone jack with its much higher output impedance gives a somewhat to considerably "fatter" sound with many cans.

Other than that, the places I would look in case of a real problem (RMAA loopback measurement may identify it) are C4 (the electrolytic in the feedback) and C1 (the input coupling cap). I would not connect an issue with low bass to the choice of output transistors. The amp should play fairly happily with bog standard TIP31A/B/Cs.
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Old 13th March 2014, 04:35 AM   #386
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Originally Posted by bkercso View Post
.....I experienced this amp has weak bass.....
Something must be wrong with your components. I've built this and it has very good bass. It's a very good sounding amp. My output stage was BD139. Worth the trouble building one !

About output offset. I get only a couple of mV. While 100mV might not damage the voice coil of the phones it will displace it quite a bit and cause distortion and also limited excursion in one direction if not anything else. Obviously maximum clean bass response will be reduced. Why do you get so much offset ?
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Old 13th March 2014, 05:42 AM   #387
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Originally Posted by ashok View Post
About output offset. I get only a couple of mV.
I could get a couple of mV from mine, but only after it had been running for an hour and was nice and toasty. On cold start it was easily over 100mv.

Cant say i had any complaints about bass response, overall i was very impressed with mine. Having said that if you bought one of the Chinese kits from eBay the components provided are, well, utter garbage which may be part of your problem. The more bits i replaced on mine the better it got, but i eventually got bored with it and cannibalized it for the parts.
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Old 13th March 2014, 09:04 AM   #388
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If the heat sink runs very hot, you are running too much bias and/or the heat sinks are too small. I ran mine at much lower output stage bias currents too and it still sounds very good ! Worth it putting it into a box and using it !
I plan to add a relay cut out to prevent dc mishaps. For those who do not want relays or ANY dc problems, you could use the single supply version with a capacitor at the output. That sounds very good too. There is a slight difference in how the LF sounds. I thought the split supply goes just a tad deeper and was tighter bass(?) . But if you didn't compare you wouldn't miss anything. Sounds very good too !

100mV start and dropping to a few millivolts is OK but not acceptable as you can do better than that nowadays.
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Old 13th March 2014, 10:36 AM   #389
bkercso is offline bkercso  Hungary
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Originally Posted by ashok View Post
Something must be wrong with your components. I've built this and it has very good bass. It's a very good sounding amp. My output stage was BD139. Worth the trouble building one !
?
I built several amp (approx. 30 different type ones) and JLH has weak bass for my ears. I bought components in a local store in Hungary, BC327/337-40 and TIP41C. My friend build this amp with original parts from eBay KIT and it's bass was similar.
I experienced on many amps that power transistor can effect the bass response significantly. Eg. MJE243/253 has warmer sound than BD139/140.
So change power BJT in JLH was only an idea...
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Old 6th May 2014, 10:37 AM   #390
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Hi,

as of today I am also a proud owner of one JHL from fleabay, thanks to this wonderful thread!

A quick workover (insert feedback cap in right direction, change 0 ohm resistors to proper wire links), and I fired the thing up. Everything seems ok, dc offset after some warm up can be (practically) nulled out. However, upon turn-off, DC offset jumps to about 1.8V amd drops sloooowly to 0V (while discharging reservoir caps?). Has anybody experienced the same behaviour?

Best regards,

hallodeletue
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