DarkHorse said:failed with Post #1440 circuit!
it works normally,but it sounds not in my taste...
bass is too loose,mid is not sweet,treble is too gray...
so I'm not satisfaction,tonight I will replace the bootstrap to CCS,perhaps it will be good.
mid n treble sounds like power supply noise
n how u ever get tight bass with a cap on output ???
these are my guess's on this
Hi,mikelm:
because I didn't add the NFB,so it's bass certainly is loosely.
do you know what kind sound I favourite with audio circuit,
is clearly,sweetly & trippingly.some thing like TV's sound,I have a TV set,it is so cheap,but it sounds good!
with my puzzle,one duty off day,I guess I will disassembly it and have a look with it's audio amp sections...
come back to current case:I still trying to find my dream AF amp circuit
regards
WINCO
mikelm said:
mid n treble sounds like power supply noise
n how u ever get tight bass with a cap on output ???
these are my guess's on this
because I didn't add the NFB,so it's bass certainly is loosely.
do you know what kind sound I favourite with audio circuit,
is clearly,sweetly & trippingly.some thing like TV's sound,I have a TV set,it is so cheap,but it sounds good!
with my puzzle,one duty off day,I guess I will disassembly it and have a look with it's audio amp sections...
come back to current case:I still trying to find my dream AF amp circuit
regards
WINCO
Re: J-amp 2003 rail voltages hum
You could hear a little hum.
Fired up the scope,
situation 1 : clipped the gnd connector of the scope to the ''negative' output and BANG: humming increased enormous. Humming stayed when I put the signal probe to the positive o/p.
Strangely when reversing the probe and gnd connector even the tiny hum disappeared.
Back to situation 1: Looking into more details of the hum the scope revealed a verid solid 1.8Mhz oscillation with 6.4 V pp.
More Tinkering time next week....
Well, today I put my 'humming' JLH on the bench. Shorted the input and hooked a 6Ohm bookshelf speaker up to it.dutch diy said:
You could hear a little hum.
Fired up the scope,
situation 1 : clipped the gnd connector of the scope to the ''negative' output and BANG: humming increased enormous. Humming stayed when I put the signal probe to the positive o/p.
Strangely when reversing the probe and gnd connector even the tiny hum disappeared.
Back to situation 1: Looking into more details of the hum the scope revealed a verid solid 1.8Mhz oscillation with 6.4 V pp.
More Tinkering time next week....
More regarding hum
In addition to the previous post some final comments.
The oscillation occured when chassis of amp an chassis of scope were connect via the mains connection, (I used an 4way earth extension cord but did not plug that into an earthed wallsocket)
Studing the scope picture of the situation where I had no big hum revealed another point for research.
Something that looked like the remaining noise did, under more details, look like 2 - 3 periods of a 'decaying oscillation' however, i was not quite abble to record 'the fequency at which this was repeated'.
Next step is to prepare for some tinkering (get things for zobel / q3/q4 coupling) and make a list of more detailed readings I want next time.
In addition to the previous post some final comments.
The oscillation occured when chassis of amp an chassis of scope were connect via the mains connection, (I used an 4way earth extension cord but did not plug that into an earthed wallsocket)
Studing the scope picture of the situation where I had no big hum revealed another point for research.
Something that looked like the remaining noise did, under more details, look like 2 - 3 periods of a 'decaying oscillation' however, i was not quite abble to record 'the fequency at which this was repeated'.
Next step is to prepare for some tinkering (get things for zobel / q3/q4 coupling) and make a list of more detailed readings I want next time.
Back at the start of the Class A thread mrfeedback suggested using MJL3281A's. Has anyone tried? (haven't read all posts...too many!)
These would appear to solve the main problems with JLH's original. Gain is consistent between devices, gain is flat from 50 mA to 5A, fT 30 MHz etc....
Simulation of a JLH 10watter with 470 ohm bootstrap pair/BD139 driver and 1k/100 ohm feedback needed 22 pF stab. cap. across 1k ... but that's it. Gain 11x to 4 MHz. 2nd h distortion 0.1% at 20 kHz/10V.
Seems good.
Cheers
John
These would appear to solve the main problems with JLH's original. Gain is consistent between devices, gain is flat from 50 mA to 5A, fT 30 MHz etc....
Simulation of a JLH 10watter with 470 ohm bootstrap pair/BD139 driver and 1k/100 ohm feedback needed 22 pF stab. cap. across 1k ... but that's it. Gain 11x to 4 MHz. 2nd h distortion 0.1% at 20 kHz/10V.
Seems good.
Cheers
John
Summary ?
Dear all,
I finally have time to start building a new version of a JLH amp. So I reread this entire thread (yes, really
) to find out which version suits my abbilities and needs best.
T be hounest I can't find my way in this myriad of versions corrcted mistakes and mod's to versions. I have the feeling that I'm not the only one with this problem.
Is there a (short) summary or is there someone who is willing to write one, which asseses the following issues:
- the major versions
- the "state of the art" basic schema version
- advised mods
- suitability for which application
- pros/cons
It would be great if this became avaiable to the diy audio community.
greetings, MArco
Dear all,
I finally have time to start building a new version of a JLH amp. So I reread this entire thread (yes, really
) to find out which version suits my abbilities and needs best.T be hounest I can't find my way in this myriad of versions corrcted mistakes and mod's to versions. I have the feeling that I'm not the only one with this problem.
Is there a (short) summary or is there someone who is willing to write one, which asseses the following issues:
- the major versions
- the "state of the art" basic schema version
- advised mods
- suitability for which application
- pros/cons
It would be great if this became avaiable to the diy audio community.
greetings, MArco
Re: Summary ?
there are two on here that would be close to the top my my list
http://www.tcaas.btinternet.co.uk/jlhupdate.htm
and from my memory of this thread I would recommend the mosfet version developed by tschrama here:
http://www.diyaudio.com/forums/showthread.php?postid=287957#post287957
mike
deduikertjes said:
there are two on here that would be close to the top my my list
http://www.tcaas.btinternet.co.uk/jlhupdate.htm
and from my memory of this thread I would recommend the mosfet version developed by tschrama here:
http://www.diyaudio.com/forums/showthread.php?postid=287957#post287957
mike
short summary
Well it is a short summary. In my earlier reading I've overlooked the mosfet version and it looks interesting indeed. What I find difficult about it that it is followed by a difficult discussion but very little detail about building, power supply voltage, etc. I'll dig into this further.
I've two torroidial transformers waiting to be put in a JLH, altough they might not be ideal. They are identical 160 VA 0-19 V transformers. Which JLH design is best suited to this, or are they insufficient?
I maybe could arrange them to be 19-0-19 and drive to channels of the jhl-update or jhl-esl from it.
But it is maybe also possible to use 1 for left and 1 for right channel and find a version which runs on that. Or is the voltage than way to low. Any advices?
Marco
Well it is a short summary. In my earlier reading I've overlooked the mosfet version and it looks interesting indeed. What I find difficult about it that it is followed by a difficult discussion but very little detail about building, power supply voltage, etc. I'll dig into this further.
I've two torroidial transformers waiting to be put in a JLH, altough they might not be ideal. They are identical 160 VA 0-19 V transformers. Which JLH design is best suited to this, or are they insufficient?
I maybe could arrange them to be 19-0-19 and drive to channels of the jhl-update or jhl-esl from it.
But it is maybe also possible to use 1 for left and 1 for right channel and find a version which runs on that. Or is the voltage than way to low. Any advices?
Marco
Wiring your transformers as a 19-0-19 VAC transformer with a full wave bridge will run two channels of the JLH just fine. See Geoff's table at the bottom of
http://www.btinternet.com/~tcaas/jlhupdate.htm
This table assumes regulated supplies, so with a 18-0-18 he expects +/- 18VDC. This would get you 16W into 8 ohms. Plenty.
http://www.btinternet.com/~tcaas/jlhupdate.htm
This table assumes regulated supplies, so with a 18-0-18 he expects +/- 18VDC. This would get you 16W into 8 ohms. Plenty.
Well, Paulb,
Thank you for your reply. I'm getting more hope. 2 more questions:
you state
why does the table assume regualted supplies? Will a Capacitance Multiplier power supply also do?
Will the resulting 19-0-19 transformer made from two 0-19 160 VA wired in series be large enough or do I need more VA's for a proper performance (I actually never quit understood why these transfomers have to be that large in a Class A circuit).
Thanks, MArco
Thank you for your reply. I'm getting more hope. 2 more questions:
you state
why does the table assume regualted supplies? Will a Capacitance Multiplier power supply also do?
Will the resulting 19-0-19 transformer made from two 0-19 160 VA wired in series be large enough or do I need more VA's for a proper performance (I actually never quit understood why these transfomers have to be that large in a Class A circuit).
Thanks, MArco
A capacitance multiplier will also drop some voltage. It uses this to smooth out the ripple in the supply. It will be less than a regulator. I do recommend the multiplier; read the notes at Geoff's site on it for more detail. I have big caps in my JLH (2x68000uF per channel) so am not using one. My transformers are 18-0-18 VAC.
I've seen recommendations that the transformer VA rating should be double the DC power required. Part of that is because you get higher DC voltage than the AC "RMS" input voltage.
You should get maybe +/-26VDC from your transformers if wired 19-0-19. At 2A bias current per channel, this is (26+26)*2A*2ch = 208W. Doubling this is 416VA, so your 320VA is a little light. But it will work, if the transformers get hot just drop the bias current a little. I predict that you will run into problems anyway just getting the amp's output transistors properly heatsinked with that much power. I recommend doubling the output transistors as Geoff's schematic of the higher power version shows. I'm using doubled output transistors, 2A bias, and even with big heatsinks I have to add a fan to keep the transistors' temperature below 60C.
Geoff had provided me with a PCB pattern that you can use if you like. He also described a bias setting procedure that worked very well to get things running. I'll try to dig this up and post it when I get a chance.
I've seen recommendations that the transformer VA rating should be double the DC power required. Part of that is because you get higher DC voltage than the AC "RMS" input voltage.
You should get maybe +/-26VDC from your transformers if wired 19-0-19. At 2A bias current per channel, this is (26+26)*2A*2ch = 208W. Doubling this is 416VA, so your 320VA is a little light. But it will work, if the transformers get hot just drop the bias current a little. I predict that you will run into problems anyway just getting the amp's output transistors properly heatsinked with that much power. I recommend doubling the output transistors as Geoff's schematic of the higher power version shows. I'm using doubled output transistors, 2A bias, and even with big heatsinks I have to add a fan to keep the transistors' temperature below 60C.
Geoff had provided me with a PCB pattern that you can use if you like. He also described a bias setting procedure that worked very well to get things running. I'll try to dig this up and post it when I get a chance.
Well Paulb,
from your info it looks as if it is possible to build a decent JLH with my two transformers. I'll start (of course) with the power supply.
I'm interested in both PCB and bias setting procedure. I'd really appreciate if you dig it up...
From your posts I understand that you've build a JLH according to the jlhupdate scheme. Is that correct?
thanks, MArco
from your info it looks as if it is possible to build a decent JLH with my two transformers. I'll start (of course) with the power supply.
I'm interested in both PCB and bias setting procedure. I'd really appreciate if you dig it up...
From your posts I understand that you've build a JLH according to the jlhupdate scheme. Is that correct?
thanks, MArco