I don't mind seeing a question posed, but the goading really detracts from the direction of any thread. It's a big job for the mods, but this should be important. No one likes to be mocked. We are all grown up, aren't we?
I think SteveA made a good point. The more experience on the board, the better it is for all of us.
Now we are really off topic.
-Chris
I think SteveA made a good point. The more experience on the board, the better it is for all of us.
Now we are really off topic.
-Chris
Graham is a little bit tired, not only those small problems faced here, he has more
problems, related his personal life, some health problems inside family...all those things turns people too much sensitive.
Let's give time... a break to him, i think he will return.
He is perceiving forum permissive, loosing some control, having room to some excesses, in his opinion....mine too.
I think he will finally give up.
But i already have some belief that good winds will refresh his mind, and this will be good for all of us.
He is a very good researcher...a real scientist that can "see some movie inside his brain"...related amplifier working dinamically.
He explained me once, and was a fantastic travell.
Well, i like this guy!.... i have enormous respect and confidence on him, and i am his friend, also i am prepared to do everything he wants me to do, as i have not the tradition to leave my friends alone when they are down.
regards,
Carlos
problems, related his personal life, some health problems inside family...all those things turns people too much sensitive.
Let's give time... a break to him, i think he will return.
He is perceiving forum permissive, loosing some control, having room to some excesses, in his opinion....mine too.
I think he will finally give up.
But i already have some belief that good winds will refresh his mind, and this will be good for all of us.
He is a very good researcher...a real scientist that can "see some movie inside his brain"...related amplifier working dinamically.
He explained me once, and was a fantastic travell.
Well, i like this guy!.... i have enormous respect and confidence on him, and i am his friend, also i am prepared to do everything he wants me to do, as i have not the tradition to leave my friends alone when they are down.
regards,
Carlos
mastertech said:
WOW Masterpiece, I dont know that you even specialize in Class-A..Thats really great!
Cheers to you too,
K a n w a r
It is time to say thanks to forum friends support, and to say good bye.
It is with my heart broken in many pieces, that I have the obligation to
Tell all forum friends, that my dear friend Graham Maynard is presenting
his excuses to give up from this thread and also the entire forum.
His life is tormented by his mother disease, and he is needing a rest to
recompose his forces, severily weekened, as a result of a cruel predestination;
The need to assist his beloved mother day after day growing weekness.
He has not more energy to face some forum turbulences.
One more “David” win “Goliath”… but I have some fear that this “David” has not
The same value as had the ancient David.
We had long conversations, and avoiding the emotions of the moment, we could see that
The best thing to do is to remove our participation of our forum, turning only spectators, alike hundreds that already did that, and no one could detect, or even realised, that may have something not correct related rules and actitudes.
My friend going out from this thread, giving up, will produce in myself the imperative to Stand at his side, as I support his criticisms and point of views, beeing mine his point of views to.
This way, as the thread is complete related informations needed by our friends, I will unsubscribe of it.
Also I will not open more threads, as a single guy can destroy the harmony.
details are here:
http://www.diyaudio.com/forums/showthread.php?postid=745163#post745163
But will be moved...as usually happens... when someone disagree
Needing some help, go directly to my mail:
nanabrother@yahoo.com
It is with my heart broken in many pieces, that I have the obligation to
Tell all forum friends, that my dear friend Graham Maynard is presenting
his excuses to give up from this thread and also the entire forum.
His life is tormented by his mother disease, and he is needing a rest to
recompose his forces, severily weekened, as a result of a cruel predestination;
The need to assist his beloved mother day after day growing weekness.
He has not more energy to face some forum turbulences.
One more “David” win “Goliath”… but I have some fear that this “David” has not
The same value as had the ancient David.
We had long conversations, and avoiding the emotions of the moment, we could see that
The best thing to do is to remove our participation of our forum, turning only spectators, alike hundreds that already did that, and no one could detect, or even realised, that may have something not correct related rules and actitudes.
My friend going out from this thread, giving up, will produce in myself the imperative to Stand at his side, as I support his criticisms and point of views, beeing mine his point of views to.
This way, as the thread is complete related informations needed by our friends, I will unsubscribe of it.
Also I will not open more threads, as a single guy can destroy the harmony.
details are here:
http://www.diyaudio.com/forums/showthread.php?postid=745163#post745163
But will be moved...as usually happens... when someone disagree
Needing some help, go directly to my mail:
nanabrother@yahoo.com
destroyer x - hope the sun will shine after everything and that we can enjoy Your endless energy and experience .... that also goes to Mr. Graham...... every life has dark spots in it..... also where there is dark there must be light..... happy diy and happy listening.....sunny
Sorry Friends, but i need to speak to Carlos in portuguese
Carlos,
Fica nessa porra de fórum! Todos nós sabemos o quanto você é legal, não saia por causa de uma pessoa de merda!
Você tem muitos ensinamentos para dar aqui! Ajuda o pessoal, todos nós sabemos que você podeo ajudar muita gente! Todos nós sabemos que você deve ficar! Fica rapaz!
Carlos,
Fica nessa porra de fórum! Todos nós sabemos o quanto você é legal, não saia por causa de uma pessoa de merda!
Você tem muitos ensinamentos para dar aqui! Ajuda o pessoal, todos nós sabemos que você podeo ajudar muita gente! Todos nós sabemos que você deve ficar! Fica rapaz!
Graham & Carlos
Hi,
I have just returned from holiday and have been reading the recent postings.
I am very shocked and sad to read about Graham and Carlos.
This forum relies heavily on individuals who are prepared to share their knowledge/ideas and lead those who are less experienced through the forrest of DIY Audio. Without them I fear we will quickly lose our way.
Barry
Hi,
I have just returned from holiday and have been reading the recent postings.
I am very shocked and sad to read about Graham and Carlos.
This forum relies heavily on individuals who are prepared to share their knowledge/ideas and lead those who are less experienced through the forrest of DIY Audio. Without them I fear we will quickly lose our way.
Barry
I thank you all...very kind intentions, i am negotiating with Graham
And i am jumping alike pop corn inside hot can...doing all i can to have him back.
I cannot stay, stand ahead this thread, as it was openned to Graham, as some aid to him that had not time and had intentions to show his amplifier, to offer it to our community.
And i did it, but i have not his knowledge, i cannot hold this thread alive as i have not know how to that...a lot of questions need to be answered by Graham....his presence is something that is a need here in this thread.
Also i cannot dennie he has a good reason to give up, and those things are beeing negotiated with him, i am showing that some offenses could not be exactly something with bad intention...and that we failled too, related to ignore some strikes, as we can do that, our forum has "a ignore switch" to avoid us to face that sittuation.
Alike some toy, we accepted the batteries the guy put on us.... he installed batteries and we start to move against him...forum rules say that we cannot loose good education, that we have to be polished...when the guy insert batteries (provocations) inside us...we move the way the stricker wanted...he was much more clever than we were...our failure i think... we gave him room to that.
So, those things, may move Graham a little.
I simply cannot turn my back to Graham.... think about that.... a friend is offended related something you made together with him...he decide to give up related that job you were doing with him...will you stand and continue working?
Sorry, this may be enormous ignorance for many of you, citizens you are from more developed country, that had better education than i could have...but in my third world place, if a good friend is challenged, we stand beside him to figth...i cannot do different...this is some kind of coward actitude that i am not allowed by myself to do.
But i am still at our forum.... not contributing opening threads for a while as something need some adjustment, i do not want to be exposed this way again...and my direct mail adress is yours to use if need something....hehe...i will ask Graham and will return you.
Trying to go around obstacles...to turn around problems guys..give us some time...i will try to revert all this thing.
Mod Evil, put a link to your personal mail adress... there's a moderator that have many Brazilian friends, he speak many languages, and he can understand your text...it is dangerous to talk this way my dear... too much clear and true...avoid that...i thank you because a friendly message, but this may create problems to you.
regards,
Carlos
And i am jumping alike pop corn inside hot can...doing all i can to have him back.
I cannot stay, stand ahead this thread, as it was openned to Graham, as some aid to him that had not time and had intentions to show his amplifier, to offer it to our community.
And i did it, but i have not his knowledge, i cannot hold this thread alive as i have not know how to that...a lot of questions need to be answered by Graham....his presence is something that is a need here in this thread.
Also i cannot dennie he has a good reason to give up, and those things are beeing negotiated with him, i am showing that some offenses could not be exactly something with bad intention...and that we failled too, related to ignore some strikes, as we can do that, our forum has "a ignore switch" to avoid us to face that sittuation.
Alike some toy, we accepted the batteries the guy put on us.... he installed batteries and we start to move against him...forum rules say that we cannot loose good education, that we have to be polished...when the guy insert batteries (provocations) inside us...we move the way the stricker wanted...he was much more clever than we were...our failure i think... we gave him room to that.
So, those things, may move Graham a little.
I simply cannot turn my back to Graham.... think about that.... a friend is offended related something you made together with him...he decide to give up related that job you were doing with him...will you stand and continue working?
Sorry, this may be enormous ignorance for many of you, citizens you are from more developed country, that had better education than i could have...but in my third world place, if a good friend is challenged, we stand beside him to figth...i cannot do different...this is some kind of coward actitude that i am not allowed by myself to do.
But i am still at our forum.... not contributing opening threads for a while as something need some adjustment, i do not want to be exposed this way again...and my direct mail adress is yours to use if need something....hehe...i will ask Graham and will return you.
Trying to go around obstacles...to turn around problems guys..give us some time...i will try to revert all this thing.
Mod Evil, put a link to your personal mail adress... there's a moderator that have many Brazilian friends, he speak many languages, and he can understand your text...it is dangerous to talk this way my dear... too much clear and true...avoid that...i thank you because a friendly message, but this may create problems to you.
regards,
Carlos
mod_evil said:
To quote Robin Williams :
There ain't nothing like a good bowel movement.
Then flush it.
Graham and DX, are self suicided for this thread, and we were buried under this stone
I am unsubscribed related the thread.
Personally, i will help everyone that need some help about GEM, using direct mail.
Will not post nothing in this thread.... Graham gave up.... Dx will giving up too.
If you did not understood our reasons..... time will show you...do not run to understand...go living in this sweet dream, till you will face the hard reality...things of the life.
I will be helping MikeB, another lovely friend, will defend the quality of units that i have tested, and will protect my friends, the same way i wish my friends stand by aside me, to help me in the good and bad days.... a Friend is a Friend, a Banana is a Banana, a friend is precious, the banana is a fruit!
I am not sorry...i am doing what i have to do....and if everybody do what they have to do, this problem would never happened.
Good by, farewell, be happy boys
Carlos
I am unsubscribed related the thread.
Personally, i will help everyone that need some help about GEM, using direct mail.
Will not post nothing in this thread.... Graham gave up.... Dx will giving up too.
If you did not understood our reasons..... time will show you...do not run to understand...go living in this sweet dream, till you will face the hard reality...things of the life.
I will be helping MikeB, another lovely friend, will defend the quality of units that i have tested, and will protect my friends, the same way i wish my friends stand by aside me, to help me in the good and bad days.... a Friend is a Friend, a Banana is a Banana, a friend is precious, the banana is a fruit!
I am not sorry...i am doing what i have to do....and if everybody do what they have to do, this problem would never happened.
Good by, farewell, be happy boys
Carlos
Attachments
![diyaudio[1].jpg](/community/data/attachments/38/38128-99b7185455ec260ed0376e8efc4f34a6.jpg?hash=mbcYVFXsJg)
While I have been visiting this board for quite some time, I rarely post. I am posting now because of my concern over the recent events in this forum. I would like to believe that this forum, as well as the entire board, has room for Grahm and tfl, for subjectivist and objectivist and for the softspoken as well as the outspoken. Grahm's work is not easy for me to understand, we think differently, and tfl's questioning and poking has helped me sort some things out. Both Grahm and tfl stick to their beliefs with strong determination and strongly defend them, each with a different style. It is allowing these strong beliefs and determined efforts to understand and to explain that makes DIYAudio so special. Hopefully, time will let the dust settle and a new appreciation of the diverse points of view and styles will emerge.
I am not blessed with the golden ears of many on this board, usually having difficulty hearing differences between amplifiers, yet being overwhelmed that my system simply does not sound like the concert I enjoyed. OTOH I am blessed with fair mathematical and technical ability and can understand circuit differences and measurements so I lean to the objectivist side of things and enjoy seeing the debate between what is heard and what is measured get resolved. Shunning folk because we are not comfortable with their style will only result in this debate becomming one sided .. then we all lose. As long as the we stick to the technical and stay away from personal assaults I am comfortable. Just wanted to express my (long winded) opinion.
Bill 😉
I am not blessed with the golden ears of many on this board, usually having difficulty hearing differences between amplifiers, yet being overwhelmed that my system simply does not sound like the concert I enjoyed. OTOH I am blessed with fair mathematical and technical ability and can understand circuit differences and measurements so I lean to the objectivist side of things and enjoy seeing the debate between what is heard and what is measured get resolved. Shunning folk because we are not comfortable with their style will only result in this debate becomming one sided .. then we all lose. As long as the we stick to the technical and stay away from personal assaults I am comfortable. Just wanted to express my (long winded) opinion.
Bill 😉
AKSA said:
You may have a point...
On the other hand, positions taken that merely demand participant's acceptance at face value,....
.....on the grounds that one's experiance is neccesary and sufficient for the evokation of blind faith,
.....are not condicive to fruitfull exploration, and in my view, are simply untenable...
Hi mikeks,
True, but there is no need to take a disagreement to a personal level.
Requesting proof of a statement is merely a learning process. This is where I think some members run into trouble. They see a technical disagreement as a personal attack and respond in kind.
-Chris
True, but there is no need to take a disagreement to a personal level.
Requesting proof of a statement is merely a learning process. This is where I think some members run into trouble. They see a technical disagreement as a personal attack and respond in kind.
-Chris
I have been a mute witness to the developments; initially I felt terrible that these unfortunate events came about as a sequel to my initial experience of oscillation with the GEM amp. Issues regarding caveats necessary to stabilize this amp were raised more evidently, though these were buried all along in this thread, but the tone of these statements could have been milder. Graham need not have treated the comments made as personal attack, which many members have pointed out.
It is true that Graham Maynard has generously shared with the members of this forum the result of his 30 long years of work. He was certainly not obliged to make available an official PCB layout that takes care of parasitic issues.
However, it might have helped many constructors who went ahead of me but also experienced initial output device failures, if only at the very outset a short list of guidelines could have been published.
Since Graham and Carlos have resigned from this thread, I would like to mention the following few guidelines to potential constructors; before long let me add that the GEM amp that I constructed using my own layout is working very well for the past 72 hours.
1. Remember that the GEM amp is a very high bandwidth amplifier. If properly done, it can also be used as a Video amp; hence, using RF techniques for (PCB) layout would help.
2. Keep input components and tracks about 2 inches away from output devices and tracks.
3. Tie all ground points together using star topology.
4. For a start, use 47pf capacitor between Base and Collector of VAS; if found stable, try reducing it in steps and possibly completely eliminating it. At every step of change reduce both Class A and AB bias to minimum and start all over again.
5. Bypass all large electrolytic caps with smaller caps and film caps to reduce inductance.
6. If at all necessitated by layout, use very short wires for connecting all transistors that mount on heatsink; given the nature of the GEM amp, it is wiser to use a layout wherein all transistors on heatsink also connect directly on to the PCB without the use of extra wiring.
7. In the case that direct mounting on PCB is used, as mentioned in (6) above, use separate wires to connect the leads of the Vbe multiplier transistor. Using the leads of the transistor directly on to the PCB will transfer some heat on to the PCB tracks; since most of the types to be used in this position nowadays come in insulated package, thermal tracking may be insufficient.
8. As far as possible, use non-inductive resistors for output devices and Zobel network. 1E 1Watt x 10 resistors for 0.1E and 10E 2 Watt x 4 resistors for 2.5E is one possible method if single non-inductive resistors in high wattage packages are not available. A better alternative is to use Metal Oxide Power Resistors.
9. Before powering up, check that the 100E Class A bias trimpot is set to a short and the 1K Class AB bias trimpot is set to 50% ie., 500E each between Base/Collector and Base/Emitter of Vbe multiplier.
10. Connect output leads to a Voltmeter and 22E resistors in both power rails; do not insert fuses at this time. Use + - 36 volts, adequate heatsinking and power up. Watch for any signs of fire or smoke, excessive heating of devices and output DC voltage which should be within a few millivolts.
11. If all is well, remove the 22E resistors in power rails, insert 2 Amp fast blow fuses and an Ammeter in the negative supply line. I found that the Class A bias tracking with the ammeter in the positive rail had a bit of lag, whereas in the negative rail it was spot on. (Alternatively, you can use a resistor in the Emitter or Collector line of the lower NPN transistor. Use Carlos’ guidelines in his earlier post.)
12. Increase the 100E trimpot slowly and let the bias settle at around 300 mA. After about ½ hour stabilize the bias at 400mA.
13. Begin turning the 1K trimpot so as to decrease resistance between Base and Emitter of Vbe transistor. Stabilise bias at 500mA.
14. Connect either a low output impedance preamp or about a 600E resistor in the signal line if driving directly from a CD/DVD player, pot attenuated, ofcourse.
Please feel free to add to the above list, in order to help those wanting to construct the GEM amplifier. My impressions of the sonic qualities of the amp follow.
My initial impressions of the sonic qualities of the GEM amplifier:
Components used: All components are as shown in Graham’s schematic. I used insulated type 2SC3421 and uninsulated type 2SA1358 transistors along with 2SC3281 for NPNs and 2SA1943 for PNPs.
In addition I also used 48.7pF silver-mica Miller cap, ie., between Base/Collector of VAS transistor. Bypassed 10,000uF rail caps with 10uF and 0.1uF poly caps. Also bypassed 4700uF and 220uF caps with 0.1uF caps.
All ground points are tied together. I have not yet tried to separate quiet and noisy ground with 10E resistors, as I normally do. (The next time over, I will also use anti-parallel diodes in shunt with this resistor.)
Supply used was + -38Volts DC. Bias adjustments are very sensitive. However, power on surge current is nothing to speak about. Absolutely no turn on or turn off thumps. Output offset for matched input transistors was measured at less than 2mV. Massive heatsinking. Excellent interconnect. Good quality but not high capacitance output cable. (The rest is my normal test setup which is audibly superior to almost anything that I have heard as commercial hi-end gear.)
Sound:
Bass- Quite detailed. Musical and very coherent. No audible phase distortion. Very low frequency response. Negatives: Does not have the ultimate in punch, ie., attack and slam is not the best possible. Things improved drastically, after I removed the 680E resistor in the signal line. Enhancements: A low output impedance preamp with adequate voltage swing will certainly boost the performance in this area. A reasonably desirable preamp should be a Class A solid state with output impedance lesser than 10E. A very good valve preamp should also perform well.
Low Mid- Tonal characteristics are very good. Comments for Bass also apply here. Slam is found wanting when compared to the best performers in this region.
Mid and High Mid- Voices are indeed very good, they are almost fleshed out. Very wide sound stage. Quite warm but not as good as some real Class A stuff. Negatives-Lacks in ultimate low level resolution. While separation between instruments in good, layering is not very good. Depth and Height of sound stage should be improved. Enhancements: I opine that if the GEM can be made stable in a setup in which the Voltage stage operates off a higher voltage, dynamics and dynamic range will phenomenally improve and most of the negatives listed above should be dealt with. Instead of BC556, different transistors need to be tried out to improve low level resolution.
High- Before inserting 10uF bypass caps for the rails on the amplifier board, I found the highs to be a little intrusive. Silver-mica caps are very good but tend to sound a bit cold and sterile; the sound is too etched out. Styroflex should be a better bet. After the 10uF polycaps were added, the sound is very detailed. Attack is good. Negatives: The high frequency range could have a little more body. Now it is slightly thin. Enhancements: Different caps in Miller position and possibly different PCB layouts could help here. Input transistors should also make a difference.
Overall the GEM is a very satisfying experience. Heat dissipation is not like a real Class A amp. Increasing voltage for Voltage Section of the amp should put this amp in another league altogether.
Note: My reference is a Stochino Amplifier. In stock condition, it outperforms the GEM in all departments. An improvised GEM, I expect to come very close. The above comments are based on my opinion in my regular test set up. Others opinions may differ.
I hope Graham and Carlos will now join in to further take the GEM to its full potential.
It is true that Graham Maynard has generously shared with the members of this forum the result of his 30 long years of work. He was certainly not obliged to make available an official PCB layout that takes care of parasitic issues.
However, it might have helped many constructors who went ahead of me but also experienced initial output device failures, if only at the very outset a short list of guidelines could have been published.
Since Graham and Carlos have resigned from this thread, I would like to mention the following few guidelines to potential constructors; before long let me add that the GEM amp that I constructed using my own layout is working very well for the past 72 hours.
1. Remember that the GEM amp is a very high bandwidth amplifier. If properly done, it can also be used as a Video amp; hence, using RF techniques for (PCB) layout would help.
2. Keep input components and tracks about 2 inches away from output devices and tracks.
3. Tie all ground points together using star topology.
4. For a start, use 47pf capacitor between Base and Collector of VAS; if found stable, try reducing it in steps and possibly completely eliminating it. At every step of change reduce both Class A and AB bias to minimum and start all over again.
5. Bypass all large electrolytic caps with smaller caps and film caps to reduce inductance.
6. If at all necessitated by layout, use very short wires for connecting all transistors that mount on heatsink; given the nature of the GEM amp, it is wiser to use a layout wherein all transistors on heatsink also connect directly on to the PCB without the use of extra wiring.
7. In the case that direct mounting on PCB is used, as mentioned in (6) above, use separate wires to connect the leads of the Vbe multiplier transistor. Using the leads of the transistor directly on to the PCB will transfer some heat on to the PCB tracks; since most of the types to be used in this position nowadays come in insulated package, thermal tracking may be insufficient.
8. As far as possible, use non-inductive resistors for output devices and Zobel network. 1E 1Watt x 10 resistors for 0.1E and 10E 2 Watt x 4 resistors for 2.5E is one possible method if single non-inductive resistors in high wattage packages are not available. A better alternative is to use Metal Oxide Power Resistors.
9. Before powering up, check that the 100E Class A bias trimpot is set to a short and the 1K Class AB bias trimpot is set to 50% ie., 500E each between Base/Collector and Base/Emitter of Vbe multiplier.
10. Connect output leads to a Voltmeter and 22E resistors in both power rails; do not insert fuses at this time. Use + - 36 volts, adequate heatsinking and power up. Watch for any signs of fire or smoke, excessive heating of devices and output DC voltage which should be within a few millivolts.
11. If all is well, remove the 22E resistors in power rails, insert 2 Amp fast blow fuses and an Ammeter in the negative supply line. I found that the Class A bias tracking with the ammeter in the positive rail had a bit of lag, whereas in the negative rail it was spot on. (Alternatively, you can use a resistor in the Emitter or Collector line of the lower NPN transistor. Use Carlos’ guidelines in his earlier post.)
12. Increase the 100E trimpot slowly and let the bias settle at around 300 mA. After about ½ hour stabilize the bias at 400mA.
13. Begin turning the 1K trimpot so as to decrease resistance between Base and Emitter of Vbe transistor. Stabilise bias at 500mA.
14. Connect either a low output impedance preamp or about a 600E resistor in the signal line if driving directly from a CD/DVD player, pot attenuated, ofcourse.
Please feel free to add to the above list, in order to help those wanting to construct the GEM amplifier. My impressions of the sonic qualities of the amp follow.
My initial impressions of the sonic qualities of the GEM amplifier:
Components used: All components are as shown in Graham’s schematic. I used insulated type 2SC3421 and uninsulated type 2SA1358 transistors along with 2SC3281 for NPNs and 2SA1943 for PNPs.
In addition I also used 48.7pF silver-mica Miller cap, ie., between Base/Collector of VAS transistor. Bypassed 10,000uF rail caps with 10uF and 0.1uF poly caps. Also bypassed 4700uF and 220uF caps with 0.1uF caps.
All ground points are tied together. I have not yet tried to separate quiet and noisy ground with 10E resistors, as I normally do. (The next time over, I will also use anti-parallel diodes in shunt with this resistor.)
Supply used was + -38Volts DC. Bias adjustments are very sensitive. However, power on surge current is nothing to speak about. Absolutely no turn on or turn off thumps. Output offset for matched input transistors was measured at less than 2mV. Massive heatsinking. Excellent interconnect. Good quality but not high capacitance output cable. (The rest is my normal test setup which is audibly superior to almost anything that I have heard as commercial hi-end gear.)
Sound:
Bass- Quite detailed. Musical and very coherent. No audible phase distortion. Very low frequency response. Negatives: Does not have the ultimate in punch, ie., attack and slam is not the best possible. Things improved drastically, after I removed the 680E resistor in the signal line. Enhancements: A low output impedance preamp with adequate voltage swing will certainly boost the performance in this area. A reasonably desirable preamp should be a Class A solid state with output impedance lesser than 10E. A very good valve preamp should also perform well.
Low Mid- Tonal characteristics are very good. Comments for Bass also apply here. Slam is found wanting when compared to the best performers in this region.
Mid and High Mid- Voices are indeed very good, they are almost fleshed out. Very wide sound stage. Quite warm but not as good as some real Class A stuff. Negatives-Lacks in ultimate low level resolution. While separation between instruments in good, layering is not very good. Depth and Height of sound stage should be improved. Enhancements: I opine that if the GEM can be made stable in a setup in which the Voltage stage operates off a higher voltage, dynamics and dynamic range will phenomenally improve and most of the negatives listed above should be dealt with. Instead of BC556, different transistors need to be tried out to improve low level resolution.
High- Before inserting 10uF bypass caps for the rails on the amplifier board, I found the highs to be a little intrusive. Silver-mica caps are very good but tend to sound a bit cold and sterile; the sound is too etched out. Styroflex should be a better bet. After the 10uF polycaps were added, the sound is very detailed. Attack is good. Negatives: The high frequency range could have a little more body. Now it is slightly thin. Enhancements: Different caps in Miller position and possibly different PCB layouts could help here. Input transistors should also make a difference.
Overall the GEM is a very satisfying experience. Heat dissipation is not like a real Class A amp. Increasing voltage for Voltage Section of the amp should put this amp in another league altogether.
Note: My reference is a Stochino Amplifier. In stock condition, it outperforms the GEM in all departments. An improvised GEM, I expect to come very close. The above comments are based on my opinion in my regular test set up. Others opinions may differ.
I hope Graham and Carlos will now join in to further take the GEM to its full potential.
Samuel Jayaraj said:
not sure where video frequencies start but a lot of SS "audio" amps have very high bandwidth that extends into 1mhz range. While it may not be a "video" amp but certain qualifies as a "radio" amp.
In my view, extending the frequency response of an audio amp over into RF or VF range is asking for trouble, due to the potential instability issues. What do you gain in return for taking that risk? Can anyone of us hear into the Mhz ranges? how about Khz ranges?
Samuel Jayaraj said:
I think that is the key. Amps with feedback are inheriently unstable. so if you don't use some form of compensation, it will go haywire sooner or later. There is nothing special in the GEM amp that prevents that - its precedessor JLH for example can run without a miller cap at the risk of instability also.
Your approach is sound. Start safe, and try to reduce it to a point where it is reasonably stable.
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