You don't need a PCB.
Just knock it up on some veroboard.
Then sit back and listen to an amazing amplifier, happy with the knowledge that you've saved an absolute fortune by not building a valve amp!
Just knock it up on some veroboard.
Then sit back and listen to an amazing amplifier, happy with the knowledge that you've saved an absolute fortune by not building a valve amp!
Heat SInks
No, but first only the smaller one was present, located at the"back"side. This was not enough, so I added a second pair, putting the smaller ones on the front.
Jos
AndrewT said:
No, but first only the smaller one was present, located at the"back"side. This was not enough, so I added a second pair, putting the smaller ones on the front.
Jos
JLH69 said:
Maybe, but there is much more propensity to do things wrong compared with decent PCB's. Where the ground, rail decoupling etc is pretty much built in. I hear stories of oscillations with transistors which I have used with no problems etc. It must be appreciatted that when you get upto the MHz region/compensation - that layout and all that is a serious problem/issue.
Kevin
Fanuc said:
Oh, I agree with you. However, I've built numerous JLH69s and JLH96s over the years and never had a problem.
I wanted to try to encourage Colin to get stuck in and not be afraid, that's all.
And to quote The Man Himself:-
Jonathan Bright said:
I did email you, Mr. Bright, but haven't received a reply.
Did you receive my email?
JLH69 said:
Hi JLH 69
Yep thank you for the support
I just wanted the PCBs as this makes it a bit easier to build I could make the pcbs but its a bit of a hassle I should point out that this is the headphone version I an about to build same schematic just different resistor values mostly
Hi JLH69, yes I received an email from you ( but under another amp name! mosfet something okay?) and I replied on Sunday the 21st June. The acc' is in my wife's name so the sender "Margaret Bright" might have confused you. Cheers, Jonathan
^^ Nothing received here, perhaps you could try again?
Suggest a subject line such as "JLH Articles"
Suggest a subject line such as "JLH Articles"
Guys, your amps run at about 2A constant current yes? And the JLH96 one is at +/- 22V symmetrical, correct?
If so, it dawned on me that if running them from high current shunt regulators they may sound mega, and still run the shunts just a bit over, and they will not need very big heatsinks for themselves since the shunt current will be on the audio amp bias load all the time. Since the shunt Mosfet is working light enough, I guess that a common 1C/W sink for each shunt will do. You can also use 27-28V DC in for the regs and that cuts 5W dissipation from the CCS Mosfets, VS 30V reg in. You will not need humongous rectification filter capacitors due to the high ripple rejection of the shunt regs. Cuts costs a lot. The parts I put in are very easy to find and logically priced. The TO-247 case Mosfets are tough and need only an isolation pad and metal screw. Don't know, maybe you wanna give it a go. Such regs give an enormous subjective performance boost in my experience. You gotta be sure that your Led string drops 5.4V if you make it, because it can easily give much more current for small variation. Because also the Mosfet Vgs varies from part to part, check the voltage drop on R1 to derive the current. I would have 0.47R,0.56R on hand. The about 2.35A limit is a hard limit due to the CCSed regs. If your speakers need more ceiling you can up the current and sinks by making R1 smaller. The shunt CCS-IbiasJLH difference, is going to be burned on the shunt Mosfet times the Voltage across it if the program is not asking it, i.e. most of the time. So its no good practice if you don't really need it. Don't test them without 2A load current, that will mean 52W on the shunt Mosfet, and the small sink will not help it.
If so, it dawned on me that if running them from high current shunt regulators they may sound mega, and still run the shunts just a bit over, and they will not need very big heatsinks for themselves since the shunt current will be on the audio amp bias load all the time. Since the shunt Mosfet is working light enough, I guess that a common 1C/W sink for each shunt will do. You can also use 27-28V DC in for the regs and that cuts 5W dissipation from the CCS Mosfets, VS 30V reg in. You will not need humongous rectification filter capacitors due to the high ripple rejection of the shunt regs. Cuts costs a lot. The parts I put in are very easy to find and logically priced. The TO-247 case Mosfets are tough and need only an isolation pad and metal screw. Don't know, maybe you wanna give it a go. Such regs give an enormous subjective performance boost in my experience. You gotta be sure that your Led string drops 5.4V if you make it, because it can easily give much more current for small variation. Because also the Mosfet Vgs varies from part to part, check the voltage drop on R1 to derive the current. I would have 0.47R,0.56R on hand. The about 2.35A limit is a hard limit due to the CCSed regs. If your speakers need more ceiling you can up the current and sinks by making R1 smaller. The shunt CCS-IbiasJLH difference, is going to be burned on the shunt Mosfet times the Voltage across it if the program is not asking it, i.e. most of the time. So its no good practice if you don't really need it. Don't test them without 2A load current, that will mean 52W on the shunt Mosfet, and the small sink will not help it.
Attachments
colin.hepburn2 said:
PCBs are available from time-to-time ex-HongKong on that auction site. Indeed, along with kit sets.
Having had both a JLH and a SET amp in the house, I think you'll be happy with the result.
I've been meaning to try either choke input; shunt input or battery supply as the PS is the definite weak point of the '69
thoglette said:
Hi thoglette
Thanks for the info on the pcbs gave you got a link to that auction site
Thanks
colin.hepburn2 said:
The site is Ebay - see item number: 220424767502 for example. A global ebay search for "JLH PCB" shows four items for sale right now.
I am working with JLH high power circuit which is fig.3 in this site: The Class-A Amplifier Site - JLH Class-A Update
I cannot find the VR2 50R in my living place. I am not sure if it can be replaced by a VR 200 ohm or not.
Can anybody give me the answer please ?
Thanks.
I cannot find the VR2 50R in my living place. I am not sure if it can be replaced by a VR 200 ohm or not.
Can anybody give me the answer please ?
Thanks.
In theory yes, in practice assuming the pot is set at 25 ohms that means firstly the adjustment would be super critical with the pot at one end... you could counter that by paralleling with say 68 ohm fixed resistor.
Secondly assuming a pot on it's own, the current in the wiper would be around 30 ma which is to high for a small pot.
Best solution, use a pot, get the adjustment right, then use a pair of fixed resistors instead.
Secondly assuming a pot on it's own, the current in the wiper would be around 30 ma which is to high for a small pot.
Best solution, use a pot, get the adjustment right, then use a pair of fixed resistors instead.
Thanks for your answer.
I have one more question:
Can I use 2SC2500 instead of MJ15003 ? I hear that the 2SC2500 may cause oscillation with this circuit. Is that right ?
I have one more question:
Can I use 2SC2500 instead of MJ15003 ? I hear that the 2SC2500 may cause oscillation with this circuit. Is that right ?
Salas,
You post was excellent. I have ordered some extra hypnotize boards.
Can I use them for the JLH?
Thanks.
You post was excellent. I have ordered some extra hypnotize boards.
Can I use them for the JLH?
Thanks.
My JLH's with 2sc5200, 2sc2922 did not oscillate. (1969 , 2003 update and mathjis's evo)
They ve been in good working for 2 or more years without problem.
They ve been in good working for 2 or more years without problem.