NAIM NAP 140 CLONE vs JLH 1996 Class A (30W per Channel (4ohm)) - Page 3 - diyAudio
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Old 24th July 2008, 09:46 PM   #21
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Hi Panelhead
Excellent advice, I hadn't thought of that. My speakers have been configured for biamping so that is certainly an option.
However, if I take your approach, It will cost quite a bit more.
I think I would prefer to match the amp for a 4ohm load and then I would have extra money to purchase top quality components.
However, if you would like to donate $500 to my cause then I will definitely carry out this setup .
Thanks
Jeff
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Old 25th July 2008, 10:10 AM   #22
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Default DIY is not cheap

Building your own gear is not very cost effective. You could save money by purchasing used hi-end gear.
I would think it is possible to build two JLH amps for 500.00. This would be great, two nice amps.
My suggestion for passive bi-amping is just another way to drive a speaker with a low power amp. If you notice, most comments here have been along the lines of needed current and voltage swing for your speakers.
Good luck in your build!

George
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Old 25th July 2008, 10:24 AM   #23
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Hi Panelhead
I did think your idea was a good one. At the moment though I will build just one dual mono setup, and if I feel it is lacking then I will probably do as you have suggested (ie biamping) sometime in the future when I have saved up enough.
Thanks for the encouragement, this is going to be my first build.
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Old 25th July 2008, 05:29 PM   #24
sreten is offline sreten  United Kingdom
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Hi,

Well I will simply state some things :

For the drivers used in the Usher 2.5 speaker a 2.5 way will be
around 87-89dB/2.83V@1m and in real watts terms 84-86dB/W.

Panelhead is talking about dumping 20A into speakers.
The JLH topolology stops dead in its tracks at 2 times the set current.

For those speakers you would need to optimise power into 3R, not 4R.
A 30W per channel class A amplifier will be rather large.
30W into 3R is a fairly puny amplifier, compared to class AB.

You cannot simply add another one for bi-amping. Well you can
if it is still current limiting, if its not you would need to change
the transformer to get more voltage swing into 8 ohms.

You should IMO consider a more suitable amplifier for your speakers.

You say you are a bass player, so am I, I'm telling you that you will very
likely be not happy with the JLH giving up the ghost on the bass end.

/sreten.
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Old 25th July 2008, 06:02 PM   #25
AndrewT is offline AndrewT  Scotland
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Hi Sreten,
it's worse than you state.
The JLH is single ended and the ClassA hard limits at the bias current, not double.
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Old 25th July 2008, 06:42 PM   #26
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by AndrewT
Hi Sreten,
it's worse than you state.
The JLH is single ended and the ClassA hard limits at the bias current, not double.
Hi AT,

No.
The top can produce plenty of current by turning full on.
The bottom the current is modulated ~ turning off at
the positive limit, and ~ doubling at the negative limit.
The bias current = 1/2 required peak current.
It hard limits negatively at ~ twice the bias current.

/sreten.
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Old 25th July 2008, 06:50 PM   #27
Geoff is offline Geoff  United Kingdom
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Quote:
Originally posted by AndrewT
Hi Sreten,
it's worse than you state.
The JLH is single ended and the ClassA hard limits at the bias current, not double.
The JLH is not single ended neither is it true push-pull. The peak output current depends on the characteristics of the output transistors used and, from simulation, will normally be between 1.3 and 1.4 times the quiescent current.

When developing the DoZ, which has a similar output stage, Rod Elliott determined empirically that the optimum quiescent current was 0.75 times the required peak output current.
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Old 25th July 2008, 07:14 PM   #28
sreten is offline sreten  United Kingdom
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Hi,

Oh well, half right .......

It is worse than I described, but not as bad as single ended.

The class A site has article on a high current version for the ELS57.

The built version is massive - its fine for the ELS57 because they
cannot take much voltage swing and it takes them very near
the maximum volume they can do, which is not much.
So for them it is probably as good as gets.
Also note the ELS57 are very easy to drive in the bass.

A similar amplifier driving a typical 2.5 way speaker ?

There are better choices.
If class A is a must (most of the time) a push pull output stage should
be used IMO, it does not hard current limit for low impedance loads.

/sreten.
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Old 26th July 2008, 12:55 AM   #29
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Hi Geoff
Could you please come to the defence of this amp. I know that a lot of what has been said has not been 100% accurate and by people who have never built this amp.
If they are right please tell me as I am just about to spend a lot of money on this amp. So far I have the PCBs.
My wife won't allow me to play music loud anyway (about as loud as you might listen to tv that is it) so I won't be pushing this amp hard, but the bass response is absolutely critical.
Please have a look at the impedance plot (See PDF attachment below). The only time it drops below 4ohms is at about 2.5kHz which is above the xover freq (so will be handled by the tweeter).
Thanks

Does anyone know how to contact Joe DAppolito, I really would like some trustworthy advice?

Anyway this post was for advice about the sound difference between the JLH and Naim NAP 140, which no one has really talked about. There must be someone who has heard both of these amps.
Attached Files
File Type: pdf usher2w5s3 impedance plot.pdf (81.5 KB, 55 views)
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Old 26th July 2008, 03:11 AM   #30
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Default Doubt it

All the JLH I have seen built are lower power, current than the one you are planning. 10 or 20 watt are 8 ohms usually. When I had Lowthers this was plenty of output.
I have never seen anyone build those Naim clones. From comments, there are tricks in the Naim gear that make the factory units better sounding than the clones. Course, owners of factory Naim would always say a clone could not match up.
Build your JLH. I good friend MikeW built several and compared to Aleph's, X's, and a lot of other designs. He said the JLH was better than most. This was driving an average two way speaker.
Liike you he played average load speakers at sane levels and the 10 watt JLH worked fine. At 30 watter should be even better.

George

SRETEN,
Mine condition is even worse than you state, the amps CAN deliver about 20 amps per channel. Passive bi-amping, this is 40 amps per speaker. For what ever reason, the single channel driving the 2.5 way did not have as smooth mids, and did break up more at high bass levels. I suspect when driven with one amp, the bass driver was getting away. With a dedicated amp, the bass driver must be controlled a little better.
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