JLH class A or penultimate zen for driving low sensitivity speakers?

[gregjpeters]

Helllo all,

I'm contemplating constructing either a penultimate zen or JLH class a amp, and from what I've read, it sounds like I would be pretty happy with either (though if anyone has a strong opinion of why one is better then the other I would like to hear it) . My question is which one would sound better with relatively generic, low sensitivity speakers? It seems that this "audiophile quality" amp can be made with a poor person's budget, but the high quality speakers are still out of reach.

Your advice is appreciated,

Greg.

[PMoreton]

Well, I'm building a JLH now, and so I'm biased toward it. But cost wise, these are not cheap to build. Sure, you can add up the pcb component prices and come to just a few pounds. However, the reservoir electrolytics, output devices, heatsinks and PSU transformers can cost you a small fortune.

(My design is in fact a colaborative project called the JLH-2005, which updates the original JLH to use more modern parts and tecniques. We will publish the schematic and PCB layout once I have tested it!)

[sreten]

Hi,

As stated its the cost of the hardware that decides the budget.
Single ended, or the option of, requires lots of heatsinking.
Other choices are Elliot's "Death of Zen" and Pass's PLH (JLH-u-like).

Suitable speakers would use a highish sensitivity 8" (smaller drivers
generally
do not hit the sensitivity with decent bass) +1" dome in a largish vented box.
Such drivers are getting rarer .....

/sreten.

[PMoreton]

Attached are first photos of the nearly completed JLH-2005 pcbs. The off-board power transistors are not connected yet, but it's getting there!

The JLH-2005 is an implementation of John Linsley-Hood's famous Class-A amplifer, using modern parts.

[Nelson Pass]

As nice as both those designs are, it is possible that you
will want more muscle than they provide. I would guess the
tipping point is probably about 88-90 dB/watt or more sensitivity
in your drivers.

[gregjpeters]

Well last night I finally lashed together my +/-22v dual rail JLH 2000 prototype, as shown in the photos (same as 1996 version but with constant current sources). The entire thing (minus power supply and output transistors) fits on a 3 x 3.5" PCB. You'll notice the 330pF input filer cap is missing as I didn't have one handy, but will add it soon. It uses generic transistors and capacitors throughout, and CCSs for the input and output transistors, as suggested by fellow forum members. The CCS/input transistors are BC560s, and BC560/BD140 + BD139 for the output stage. It worked right first time. How does it sound? Well, this is my first homebuilt amp, and I was a little sceptical of all you audiophiles with your transparency, authority, soundstage, etc mumbo jumbo. I was a bit scared I'd turn it on and think it was all a waste of time and no better than my pioneer home theatre amp, but I have to say it sounds unbelievable! It brings out parts of the music I never knew were there, like the little scratches of the guitarist's hands on the frets and imperfections in the singer's voice. Ok, I'm no audiophile, but it sounds better than any amp I have heard in a shop. I replayed the songs on my other amp and realised the sounds are there, but this amp actually makes you notice them. They don’t fall into the blur of the music. I can't wait to make a proper power supply and housing. Also, the 10-15 watt is more than adequate for "reasonable" listening levels, even with my insensitive home theatre speakers. Highly recommended to anyone.

[jerishi]

I'm very interested in your updated version... And look forward to seeing a published pcb . I built a version some yrs. ago and was impressed. Thanks-

[gregjpeters]

I used this schematic from the class-A amplifier site, except I changed the 2SA970s for BC560s, the 2SA1358 for BD140, and the 2SC3421 for a BD139, selected for high gain using a cheap multimeter transistor tester. Power supply caps aside, I spent probably $AUD20, ($US13) on the whole thing. It really does sound very good. I'll email you the board design if you like. It's my first ever PCB, so the layout may leave a bit to be desired.

[jerishi]

Hi greg, I'd appreciate your pcb design. I've already built the power supply , still functional but (currently) 'unemployed' (like myself... so... I've time on my hands and need new project. It looks good. Thanks- (am working on wifes computer) ..hmmm which begs question, can you (at other end) see my e-mail? If not, let me know.

[Nelson Pass]

Originally posted by gregjpeters
Well, this is my first homebuilt amp, and I was a little sceptical of all you audiophiles with your transparency, authority, soundstage, etc mumbo jumbo. I was a bit scared I'd turn it on and think it was all a waste of time and no better than my pioneer home theatre amp, but I have to say it sounds unbelievable! It brings out parts of the music I never knew were there, like the little scratches of the guitarist's hands on the frets and imperfections in the singer's voice

Congratulations.