Re: Input Impedance
You could try increasing the the value of the two resistors that together in paralell form the i/p resistor and also you could look around for an i/p transistor with a higher gain.
Other than that, as JLH says, it might be better to decease the o/p impedence of the preamp.
mike
Cheong said:
You could try increasing the the value of the two resistors that together in paralell form the i/p resistor and also you could look around for an i/p transistor with a higher gain.
Other than that, as JLH says, it might be better to decease the o/p impedence of the preamp.
mike
what if you just use a fet as the input transistor? i have used a mosfet there without any problem.
Cheong
The revised input stage that I included in Post #624 (Page 42 of this thread) increases the input impedance of the 1969 version to 100k. Is this high enough to meet your needs?
Geoff
The revised input stage that I included in Post #624 (Page 42 of this thread) increases the input impedance of the 1969 version to 100k. Is this high enough to meet your needs?
Geoff
I would like to know how to calculate the heat given off in the individual transisitors in the output stage of a class-A amp such as the JLH. I assume that the following is known (i) the PS voltage (ii) the standing current (iii) the circuit uses two BJTs such as the 2N3055.
the full voltage rail to rail x the standing current = Total power in each channel. given that the o/p is sitting 1/2 way between the rails the total power will be split equally between the two o/p devices.
cheers
mike
cheers
mike
I haven't noticed any postings here for quite some time. Is it still active or has Millwood successfully killed it? 
😕 😕 😕 😕
😕 😕 😕 😕rclarke said:I haven't noticed any postings here for quite some time. Is it still active or has Millwood successfully killed it?
by your post, I certainly have failed, 🙂
After the loss of our mentor John Linsley-Hood, I came back to see what had been happening here, only to find that one fanatic is still hitting us between the eyes with his egotistical keyboarding.
Millwood. When an ill person makes the effort to freely post information and to help others (on a day when he might be feeling less unwell) your unthinking, but still quite deliberate, comments come over as being particularly galling.
____________________________________________________
In view of the length of this thread, and the now widely spaced photographic postings that were made showing some very fine examples of JLH amplifier construction, is there any way that these could be separately archived for future inspiration, or somehow be edited to a new thread ?
____________________________________________________
The UK Electronics World magazine is running an 'In Memoriam' special edition in the June 04 issue which should be on the shelves during May. Unfortunately many readers of this thread will be unable to obtain a copy.
____________________________________________________
POWER !!! One of the curious aspects of pure class-A is that the output devices dissipate less heat when more energy is being driven into the loudspeaker.
Cheers ............ Graham.
Millwood. When an ill person makes the effort to freely post information and to help others (on a day when he might be feeling less unwell) your unthinking, but still quite deliberate, comments come over as being particularly galling.
____________________________________________________
In view of the length of this thread, and the now widely spaced photographic postings that were made showing some very fine examples of JLH amplifier construction, is there any way that these could be separately archived for future inspiration, or somehow be edited to a new thread ?
____________________________________________________
The UK Electronics World magazine is running an 'In Memoriam' special edition in the June 04 issue which should be on the shelves during May. Unfortunately many readers of this thread will be unable to obtain a copy.
____________________________________________________
POWER !!! One of the curious aspects of pure class-A is that the output devices dissipate less heat when more energy is being driven into the loudspeaker.
Cheers ............ Graham.
Re: Input Impedance
You might try bootstrapping the input resistor, as described in the Self book and online at the Pass website:
http://www.passdiy.com/pdf/a40.pdf
Cheong said:
You might try bootstrapping the input resistor, as described in the Self book and online at the Pass website:
http://www.passdiy.com/pdf/a40.pdf
Graham Maynard said:
I thought you had vowed to leave this place / thread.
whatever brought you back, welcome.
Hi Jam,
Yes, but only part one, which is very general. Four parts already submitted to start with, another possible three parts only in longhand and note form at the moment.
I write more about the problem elements of another most common bipolar topology (circa D Self and Westhost) than about JLH variants which do not suffer the same weaknesses.
Hi slowhands,
The JLH circuit needs a low impedance source for low distortion performance, and this was why, at a time when hollow state pre-amps were common, JLH suggested the external fet stage.
Bootstrapping the bias resistors will help to slightly increase the input impedance as seen by a source, but it will not help the JLH circuit itself, and will not be an optimum solution.
Cheers ............ Graham.
Yes, but only part one, which is very general. Four parts already submitted to start with, another possible three parts only in longhand and note form at the moment.
I write more about the problem elements of another most common bipolar topology (circa D Self and Westhost) than about JLH variants which do not suffer the same weaknesses.
Hi slowhands,
The JLH circuit needs a low impedance source for low distortion performance, and this was why, at a time when hollow state pre-amps were common, JLH suggested the external fet stage.
Bootstrapping the bias resistors will help to slightly increase the input impedance as seen by a source, but it will not help the JLH circuit itself, and will not be an optimum solution.
Cheers ............ Graham.
Picture of JLH
Hi,
until now i build different versions of JLH.
The best one is created with Vishay s102k Resistors, matched 15003`s of ON, Mundorf silver-oil cap as coupling capacitor, Blackgate and Elna Cerafine Cpacitors in Cap-Mult, other transistors matched, too.
Theres the need to say, that JLH is sensitive to parts quality.
With all experiences i and friends of me, made some other amps from Pass, Gainclone, Hiraga...i can tell, that this amp is hardly to beat. Greets to Geoff and the others who helped me...
The Pic is the amp we build with a friend.
Ralf
Hi,
until now i build different versions of JLH.
The best one is created with Vishay s102k Resistors, matched 15003`s of ON, Mundorf silver-oil cap as coupling capacitor, Blackgate and Elna Cerafine Cpacitors in Cap-Mult, other transistors matched, too.
Theres the need to say, that JLH is sensitive to parts quality.
With all experiences i and friends of me, made some other amps from Pass, Gainclone, Hiraga...i can tell, that this amp is hardly to beat. Greets to Geoff and the others who helped me...
The Pic is the amp we build with a friend.
Ralf
Attachments
elaborate please
Hallo Ralf,
very beautiful indeed! Some pictures from the inside would be nice, just curious.
Could you elaborate some more on the differences in your latest version? Which JLH is it? What are the differences you hear with what parts changed? How is the sound different from the Pass and Hiraga etc.
On the site of Geoff some very detailed descriptions can be found on the differences in sound by replacing one component or part of the circuit. You would do many builders a pleasure by sharing this knowledge.
Rudy
Hallo Ralf,
very beautiful indeed! Some pictures from the inside would be nice, just curious.
Could you elaborate some more on the differences in your latest version? Which JLH is it? What are the differences you hear with what parts changed? How is the sound different from the Pass and Hiraga etc.
On the site of Geoff some very detailed descriptions can be found on the differences in sound by replacing one component or part of the circuit. You would do many builders a pleasure by sharing this knowledge.
Rudy
thanks..
..for the complements.
since i have no digicam i cannot show you pics from the inside yet - perhaps later.
..yes i made similar experiences like Tim.
its the "update-Version" of JLH, with Capmult as PSU.
the coupling capacitor makes big influence in sound.
first i used very expensive jensen copper-foil, but the mundorf silver oil has much more resolution. But i cascaded the mundorf by adding a Glimmer and a Kp1832. This made the sound sweeter and smoother.
i and a friend who build the same amps wolud like to say, that the JLH beats the Hiraga Monster, Pass X-SOZ, ZEN, Gainclone.
The JLH has more attack, more fine-resolution, voices are more "human", Pinao is more Piano...
at least at my speakers, and i have more than one pair.
Regards,
Ralf
..for the complements.
since i have no digicam i cannot show you pics from the inside yet - perhaps later.
..yes i made similar experiences like Tim.
its the "update-Version" of JLH, with Capmult as PSU.
the coupling capacitor makes big influence in sound.
first i used very expensive jensen copper-foil, but the mundorf silver oil has much more resolution. But i cascaded the mundorf by adding a Glimmer and a Kp1832. This made the sound sweeter and smoother.
i and a friend who build the same amps wolud like to say, that the JLH beats the Hiraga Monster, Pass X-SOZ, ZEN, Gainclone.
The JLH has more attack, more fine-resolution, voices are more "human", Pinao is more Piano...
at least at my speakers, and i have more than one pair.
Regards,
Ralf
Congrats!
Hi Ralf,
This is one piece of gear that really deserve the name ART!
I would love to see a parts list and the inside. This is really nice.
I can't wait to see/hear more of this piece of ART !
Cheers,
Audiofanatic 😉
Hi Ralf,
This is one piece of gear that really deserve the name ART!
I would love to see a parts list and the inside. This is really nice.
I can't wait to see/hear more of this piece of ART !
Cheers,
Audiofanatic 😉
