Hi Sheldon,
Yes indeed MJL3281/1302 should be fine, also the new OnSemi 4281A/4302A types.
(Mosfet substitutions are likely to adversely affect stability and thus reproduction after stabilisation 'path C's are fitted.)
Design - it is a JLH class-A with class-AB 'helper'.
Put your thumb over the PNP outputs and you have JLH class-A with a high gain Darlingtom configured upper half that others already use, and which JLH himself successfully tried.
My choice is for low C at VAS and drivers to keep loop phase change as being output device defined, no matter what type is fitted.
To maintain stability and what many describe as 'current' feedback via a single input transistor alone, the 10nF and 220nF capacitors remove one differential/mirror phase change from within the NFB loop above high audio frequencies.
Hi Dragon2,
(My health and family health; could be better; thanks for your wishes.)
Okay, I understand your thinking in relation to bass, but the big C is normally paralleled by lesser Cs and there is a series resistance that keeps the response smoothly flat.
Both forward and reverse responses are virtually flat down to 5Hz, probably about five degrees, so any fractional phase distortions extending upwards are unlikely to be audible. Some CD tracks do carry a very low frequency error, and you can see the bass cone fluttering, but the audio itself does not become affected.
I honestly don't think you will improve bass by linking out the big C, besides it helps with zero output voltage control because there is then 100% NFB at dc.
Zero-bias plus resistors introduce a loss of NFB at dc, which means you need greater output error for equivalent control.
Also don't forget that you can still use similar high value 'zero-biasing' resistors connected directly to the divider resistor end of the big C, though the zero itself is not actually a problem to start with.
Most ICs are specified to cope with 1,000 ohm loading. Try 680 ohm in series with the output of your player, that is in series with the cable inner at its output connector. This should isolate the line IC NFB loop from cable C as well as too much amplifier loading.
Cheers .......... Graham.
Yes indeed MJL3281/1302 should be fine, also the new OnSemi 4281A/4302A types.
(Mosfet substitutions are likely to adversely affect stability and thus reproduction after stabilisation 'path C's are fitted.)
Design - it is a JLH class-A with class-AB 'helper'.
Put your thumb over the PNP outputs and you have JLH class-A with a high gain Darlingtom configured upper half that others already use, and which JLH himself successfully tried.
My choice is for low C at VAS and drivers to keep loop phase change as being output device defined, no matter what type is fitted.
To maintain stability and what many describe as 'current' feedback via a single input transistor alone, the 10nF and 220nF capacitors remove one differential/mirror phase change from within the NFB loop above high audio frequencies.
Hi Dragon2,
(My health and family health; could be better; thanks for your wishes.)
Okay, I understand your thinking in relation to bass, but the big C is normally paralleled by lesser Cs and there is a series resistance that keeps the response smoothly flat.
Both forward and reverse responses are virtually flat down to 5Hz, probably about five degrees, so any fractional phase distortions extending upwards are unlikely to be audible. Some CD tracks do carry a very low frequency error, and you can see the bass cone fluttering, but the audio itself does not become affected.
I honestly don't think you will improve bass by linking out the big C, besides it helps with zero output voltage control because there is then 100% NFB at dc.
Zero-bias plus resistors introduce a loss of NFB at dc, which means you need greater output error for equivalent control.
Also don't forget that you can still use similar high value 'zero-biasing' resistors connected directly to the divider resistor end of the big C, though the zero itself is not actually a problem to start with.
Most ICs are specified to cope with 1,000 ohm loading. Try 680 ohm in series with the output of your player, that is in series with the cable inner at its output connector. This should isolate the line IC NFB loop from cable C as well as too much amplifier loading.
Cheers .......... Graham.
Graham, I have got the not so easy to get C3421 and A1358 transistors. Ofcourse, I have loads of C5200/3281 and A1943/1302. Since all components are there as in the original, I'd like to start designing the PCB.
Just a couple of questions. Carlos mentioned about some extra transistor for biasing. Is it apart from what is already in your schematic? The input impedance is a low 600 ohms! If one doesn't mind, NE5534 could be used either as an active gain device or as a buffer since its optimal load is 600 ohms.
Does your design retain the tube like sound of the JLH?
Thanks and wish you and your family speedy recovery and good health.
Just a couple of questions. Carlos mentioned about some extra transistor for biasing. Is it apart from what is already in your schematic? The input impedance is a low 600 ohms! If one doesn't mind, NE5534 could be used either as an active gain device or as a buffer since its optimal load is 600 ohms.
Does your design retain the tube like sound of the JLH?
Thanks and wish you and your family speedy recovery and good health.
My English is confused...the lower NPN transistor, i use to call it extra NPN
Where, in the reality, the other two units, PNP and NPN pair, are the real EXTRA class AB units...i called this way, because it appear as to be lonely in the schematic, others making a NPN to PNP pair (the schematic fast analisis show that...but reality is not exactly this way)... and there is someone alone, lower half cicle amplifier...this one is the class A transistor (the old JLH output transistor work is done by this one!), and you have a trimpot to adjust this one bias.... the current that will cross this transistor, in stand by mode, without signal, depends of its VBE....I suggest a small resistor, alike 0.1 ohms to turn easy this adjustment, measuring the voltage developed over this resistor and entering ohms law to have the current...of course, you can put an ampere meter in series with colector or emitter ...your preference.
This one, is not the main bias adjust, as main bias, is using a VBE multiplier transistor and a 1000 ohms trimpot.
2 Adjustments must be made. and may need a third adjustment to a fine retouch...and you can find, in this thread, very detailed explanations made by Graham, related the way and the sequence of adjustments.
I am sorry to create some confusion.
regards,
Carlos
Where, in the reality, the other two units, PNP and NPN pair, are the real EXTRA class AB units...i called this way, because it appear as to be lonely in the schematic, others making a NPN to PNP pair (the schematic fast analisis show that...but reality is not exactly this way)... and there is someone alone, lower half cicle amplifier...this one is the class A transistor (the old JLH output transistor work is done by this one!), and you have a trimpot to adjust this one bias.... the current that will cross this transistor, in stand by mode, without signal, depends of its VBE....I suggest a small resistor, alike 0.1 ohms to turn easy this adjustment, measuring the voltage developed over this resistor and entering ohms law to have the current...of course, you can put an ampere meter in series with colector or emitter ...your preference.
This one, is not the main bias adjust, as main bias, is using a VBE multiplier transistor and a 1000 ohms trimpot.
2 Adjustments must be made. and may need a third adjustment to a fine retouch...and you can find, in this thread, very detailed explanations made by Graham, related the way and the sequence of adjustments.
I am sorry to create some confusion.
regards,
Carlos
Someone asked something about Star earth.
Here, the ones interested, can capture the meaning.
http://www.diyaudio.com/forums/showthread.php?postid=696439#post696439
regards,
Carlos
Here, the ones interested, can capture the meaning.
http://www.diyaudio.com/forums/showthread.php?postid=696439#post696439
regards,
Carlos
Hi Dragon,
Well that worked !
A couple of weeks back I wrote to the Marie Curie Nurses who should have received a donation from EW.
I informed them what had not been paid.
They sent an invoice to EW for that amount, and it is now being paid.
I'm really chuffed about that. Brilliant!
Thanks Carlos, that was a good reply to Samuel.
Hi Samuel,
If you put a very large output capacitor on the output of the original class-A and increase the other Cs, I believe it amplifies better than a valve amplifier at lower frequencies, though the difference might not be obvious unless you have large loudspeakers. I have also noted better hf definition on a JLH at higher audio frequencies than tube.
I also believe that the 'sound' of a valve amplifier is more related to its 'open' anode - loudspeaker coupling, which gives different driving/damping characteristics to a solid state 'closed' NFB amplifier, even when both are class-A.
It is though extremely difficult to tell which amplifier is which when good ones are amplifying at lower levels, and the GEM is no different in that regard.
And yet to get an amplifier that is clean from low through to higher lounge listening levels is not as easy whether it is hollow or solid-state; but I no longer feel the need to be searching any more!
Well that worked !
A couple of weeks back I wrote to the Marie Curie Nurses who should have received a donation from EW.
I informed them what had not been paid.
They sent an invoice to EW for that amount, and it is now being paid.
I'm really chuffed about that. Brilliant!
Thanks Carlos, that was a good reply to Samuel.
Hi Samuel,
If you put a very large output capacitor on the output of the original class-A and increase the other Cs, I believe it amplifies better than a valve amplifier at lower frequencies, though the difference might not be obvious unless you have large loudspeakers. I have also noted better hf definition on a JLH at higher audio frequencies than tube.
I also believe that the 'sound' of a valve amplifier is more related to its 'open' anode - loudspeaker coupling, which gives different driving/damping characteristics to a solid state 'closed' NFB amplifier, even when both are class-A.
It is though extremely difficult to tell which amplifier is which when good ones are amplifying at lower levels, and the GEM is no different in that regard.
And yet to get an amplifier that is clean from low through to higher lounge listening levels is not as easy whether it is hollow or solid-state; but I no longer feel the need to be searching any more!
I use to talk with Hugh almost every day..he is very busy
Those days, as he is having some problems with suppliers and some dead lines to send some kits.
Also he is expanding the factory, and instructing one more employee.
Aksa amplifier are wonderfull, i cannot leave without them, despite full range with good power, i love them to my tweeters, in that position they are very hard to beat.
There are many hidden secrets in Aksa, i think it is very difficult to have the schematic, and having it, i am afraid that will not have the Aksa sound. Many models where done, and upgrades too, so, having one schematic, if not the last one....will loose something.
In the Aksa case...have to put hands inside the pocket, you may have a finger hurted because the mice trap you may have installed, inside your pockets,Ahahahaha!.... to avoid spend money, have to buy them or visit someone that have those kits...now a days, having some thousands sold, will not be difficult to find someone that have it, and as i could see, the Aksophiles use to have more than one model.
But i am sure, the one will not show you the schematic, if not a brother or a very close parent, as people is clearly advised not to inform or provide schematic copies....the product has registration.
regards,
Carlos
Those days, as he is having some problems with suppliers and some dead lines to send some kits.
Also he is expanding the factory, and instructing one more employee.
Aksa amplifier are wonderfull, i cannot leave without them, despite full range with good power, i love them to my tweeters, in that position they are very hard to beat.
There are many hidden secrets in Aksa, i think it is very difficult to have the schematic, and having it, i am afraid that will not have the Aksa sound. Many models where done, and upgrades too, so, having one schematic, if not the last one....will loose something.
In the Aksa case...have to put hands inside the pocket, you may have a finger hurted because the mice trap you may have installed, inside your pockets,Ahahahaha!.... to avoid spend money, have to buy them or visit someone that have those kits...now a days, having some thousands sold, will not be difficult to find someone that have it, and as i could see, the Aksophiles use to have more than one model.
But i am sure, the one will not show you the schematic, if not a brother or a very close parent, as people is clearly advised not to inform or provide schematic copies....the product has registration.
regards,
Carlos
Hi Stocker,
Indeed, Hugh might be watching, and yet I feel sure that he will be too modest to clarify that his amplifier is the result of several updates that were determined via repeated 'music' reproduction auditions.
This is more audiophile than those who simulate and measure to design and then persuade themselves that the resultant sound must be good.
Every amplifier sounds different, and each one will have its own niche according to personal likes and dislikes, thus it cannot be assumed that any one design, including mine, is going to automatically sound 'better' than another within any given specific reproduction system!
I think we need to watch ourselves here in Sgt Carlos' thread, in case we find ourselves on the receiving end of a dose of reality.
****Aha, I just find that Carlos and Hugh were watching too.****
Cheers .......... Graham.
Indeed, Hugh might be watching, and yet I feel sure that he will be too modest to clarify that his amplifier is the result of several updates that were determined via repeated 'music' reproduction auditions.
This is more audiophile than those who simulate and measure to design and then persuade themselves that the resultant sound must be good.
Every amplifier sounds different, and each one will have its own niche according to personal likes and dislikes, thus it cannot be assumed that any one design, including mine, is going to automatically sound 'better' than another within any given specific reproduction system!
I think we need to watch ourselves here in Sgt Carlos' thread, in case we find ourselves on the receiving end of a dose of reality.
****Aha, I just find that Carlos and Hugh were watching too.****
Cheers .......... Graham.
Hi,
I have purchased the parts for GEM, is the following capacitors voltage rating sufficient for +/- 36V operation?
C6 - 4,700uf 25V
C8 - 2,200uf 25V
C3 - 220uf 50V
C9, C10 - 10uf 50V
C11,C12 - 10,000uf 50V
All my resistors are 0.5 w except R10-R13 (0R1) which is 5w. Is it safe to use 0.5w for R14 (2R5) ? Thanks
I have purchased the parts for GEM, is the following capacitors voltage rating sufficient for +/- 36V operation?
C6 - 4,700uf 25V
C8 - 2,200uf 25V
C3 - 220uf 50V
C9, C10 - 10uf 50V
C11,C12 - 10,000uf 50V
All my resistors are 0.5 w except R10-R13 (0R1) which is 5w. Is it safe to use 0.5w for R14 (2R5) ? Thanks
Hi Peter,
Cs and Vs.
4m7-25V should have decently low impedance.
2m2-25V is right on the voltage limit. I have used 25V here and it does work fine, but I would go for the next voltage rating for long working life in a finished construction.
Parallel each of these capacitors, also C11 and C12, with one 220u-50V each, and something like 0.47u-63V just to be sure that circuit impedances are low.
Rs.
Where I have shown 2.5 ohms in the output Zobel, this represents four 10 ohm NON-WIREWOUND resistors about half inch long in parallel with something like a 0.6W to 1.0W rating each.
Do not go for modern subminiature resistors here, because they fail far too easily, and this is one resistor you don't want to fail.
The series 390 ohm and 820 ohm bootstrap resistors have 36 volts across them, so they get HOT. I would recommend about 2W for both.
Cheers .......... Graham.
Cs and Vs.
4m7-25V should have decently low impedance.
2m2-25V is right on the voltage limit. I have used 25V here and it does work fine, but I would go for the next voltage rating for long working life in a finished construction.
Parallel each of these capacitors, also C11 and C12, with one 220u-50V each, and something like 0.47u-63V just to be sure that circuit impedances are low.
Rs.
Where I have shown 2.5 ohms in the output Zobel, this represents four 10 ohm NON-WIREWOUND resistors about half inch long in parallel with something like a 0.6W to 1.0W rating each.
Do not go for modern subminiature resistors here, because they fail far too easily, and this is one resistor you don't want to fail.
The series 390 ohm and 820 ohm bootstrap resistors have 36 volts across them, so they get HOT. I would recommend about 2W for both.
Cheers .......... Graham.
Speaker output
Hi Graham,
After a heavy week at home and at work I am now back on the revised PCB....
One question if I may, can you advise the preferred method of creating the speaker positive output? I note in your last schematic you have a connection on the control PCB rather than the heatsink mounted components. Have I understood this correctly?
Many thanks
Hi Graham,
After a heavy week at home and at work I am now back on the revised PCB....
One question if I may, can you advise the preferred method of creating the speaker positive output? I note in your last schematic you have a connection on the control PCB rather than the heatsink mounted components. Have I understood this correctly?
Many thanks
Hi Barry,
Yes that is correct.
The voltage output sensing NFB resistor should not come from the end of a track that carries high frequency currents, but from where the loudspeaker potential is taken off, also where the Zobel acts. The output device connections should also be brought back to this point.
This is the same as for the mirror, which should be independently fed from the positive rail, not at the end of a track simultaneously carrying high frequency output device currents. In some amplifiers the mirror supply has independent filtering.
Cheers .......... Graham.
Yes that is correct.
The voltage output sensing NFB resistor should not come from the end of a track that carries high frequency currents, but from where the loudspeaker potential is taken off, also where the Zobel acts. The output device connections should also be brought back to this point.
This is the same as for the mirror, which should be independently fed from the positive rail, not at the end of a track simultaneously carrying high frequency output device currents. In some amplifiers the mirror supply has independent filtering.
Cheers .......... Graham.
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