Re: Re: This is what I did to the P3A
They replaced C+ C1- and those MKT went under the PCB. This works if the boards are not mounted over the output devices (option 1 in the buyers instructions) but I'm sure MKT's would fit under there if laid flat.
The price for the 100uF is some turn off thump.
You'd have to put the OPA627's on a Browndog adaptor as they are single opamps and not duals like the OPA2134. Another option is the single AD825 (Browndog as well) but I'm sure there are heaps of alternatives like the new LM4??? (can't remember) that's been mentioned on this forum.
billybob66 said:
They replaced C+ C1- and those MKT went under the PCB. This works if the boards are not mounted over the output devices (option 1 in the buyers instructions) but I'm sure MKT's would fit under there if laid flat.
The price for the 100uF is some turn off thump.
You'd have to put the OPA627's on a Browndog adaptor as they are single opamps and not duals like the OPA2134. Another option is the single AD825 (Browndog as well) but I'm sure there are heaps of alternatives like the new LM4??? (can't remember) that's been mentioned on this forum.
i forgot to mention
that the capacitor in the vas stage may be possible to kill sonics ...but also make the amp go unstable if not used at all ....
have seen amps working even without it ....as about stability though can not really tell.....
the best results i got with 68pf styroflex smd located down under the pcb very next to VAS ....
scopes and ears agree to that ......
will try a version to compair next days ..... one made with standard 2SC3281 2SA 1302 TOSHIBAS i use and also an other one with mjl 3281 A and mjl 1302A ... to see i f there is any difference .... these mjl are original motorolas ....not on semi and i have also plenty of them since ZECK (amplifier company in belgioum ) provided these as spairs ....
( some times i feel so lucky and proud for my stock ) ha ha ha ha
that the capacitor in the vas stage may be possible to kill sonics ...but also make the amp go unstable if not used at all ....
have seen amps working even without it ....as about stability though can not really tell.....
the best results i got with 68pf styroflex smd located down under the pcb very next to VAS ....
scopes and ears agree to that ......
will try a version to compair next days ..... one made with standard 2SC3281 2SA 1302 TOSHIBAS i use and also an other one with mjl 3281 A and mjl 1302A ... to see i f there is any difference .... these mjl are original motorolas ....not on semi and i have also plenty of them since ZECK (amplifier company in belgioum ) provided these as spairs ....
( some times i feel so lucky and proud for my stock ) ha ha ha ha
Re: Re: This is what I did to the P3A
Keep the 100nF caps as they are by-pass caps for the new electrolytics. You should be able to fit them under the PCB even if you have the PCB mounted against the heatsink.
That's right.... C- is for the -ve rail so the +ve side of the cap goes to ground and the -ve side of the cap goes to -ve rail side. For C+ the -ve side of the cap goes to ground. Get it wrong and the caps can pop.
Have a look at the schematic of the power supply and you can see how caps go in relation to +ve and -ve rails. Then trace the amp PCB to be sure.
billybob66 said:
Keep the 100nF caps as they are by-pass caps for the new electrolytics. You should be able to fit them under the PCB even if you have the PCB mounted against the heatsink.
That's right.... C- is for the -ve rail so the +ve side of the cap goes to ground and the -ve side of the cap goes to -ve rail side. For C+ the -ve side of the cap goes to ground. Get it wrong and the caps can pop.
Have a look at the schematic of the power supply and you can see how caps go in relation to +ve and -ve rails. Then trace the amp PCB to be sure.
HI everybody
Just my 2 cents.........
The best way of making big improvements to the sound of this amp is to mod the compensation.
Sakis is on the right track regarding his compensation scheme, go a bit further and get even better results.
Experiment with different values and use a combination of phase lead and the miller compensation here, this amp can sound extordinary indeed from such a simple circuit.
The bd140 is a bad choice for vas transistor the mje15035 even worse, look at something like 2sa1209 and get huge improvements. Best comes with trannies like 2sa1406 but they are hard to get. Its also very important to use best possible caps in the compensation scheme, polistyrene *styroflex* is one of the best.
There are other mods to the differential stage you could do in particular to improve the soundstage but these would require you to alter the pcb which i dont think youd be up for.
Alex
Alex
Just my 2 cents.........
The best way of making big improvements to the sound of this amp is to mod the compensation.
Sakis is on the right track regarding his compensation scheme, go a bit further and get even better results.
Experiment with different values and use a combination of phase lead and the miller compensation here, this amp can sound extordinary indeed from such a simple circuit.
The bd140 is a bad choice for vas transistor the mje15035 even worse, look at something like 2sa1209 and get huge improvements. Best comes with trannies like 2sa1406 but they are hard to get. Its also very important to use best possible caps in the compensation scheme, polistyrene *styroflex* is one of the best.
There are other mods to the differential stage you could do in particular to improve the soundstage but these would require you to alter the pcb which i dont think youd be up for.
Alex
Alex
homemodder said:
You are completely right and and I'm sure the larger values were chosen for stability over sonics. A reduction would certainly gain sonic benefits.
Has any one reduced these values and found the optimum before the amp went nuts? I'm not an amp guy, but don't you need a scope when reducing these values to make sure it doesn't go unstable?
not really
to define values like that you will for sure need a scope
some more input about this :
pcb for this amp ( others also ) is very critical ....meaning : proximity between traces creates capacitance also ground and feedback rooting changes the overall performance (beyond by pass caps electrolytics and other improovments )
i made my own pcb. rods pcb might be perfect but i didnt like it since its not symetrical just a question of looks ..... so while design pcb and perform the same testings ( ive made 2 versions ) but between identical componets used ,the one pcb requierd 47pf miller styroflex cap and the other required 68pf cap .....
straight conclusion is that the pcb had diferent behaviour.
as about vas transistor and bd139, the amplifiers i ve made performed like hell didnt feel like playing arround there but i will take a look at this and let you know
i will follow homemodder's advice though and look at that since i have 77 pcs of 2sa1406....will test and let you know
to define values like that you will for sure need a scope
some more input about this :
pcb for this amp ( others also ) is very critical ....meaning : proximity between traces creates capacitance also ground and feedback rooting changes the overall performance (beyond by pass caps electrolytics and other improovments )
i made my own pcb. rods pcb might be perfect but i didnt like it since its not symetrical just a question of looks ..... so while design pcb and perform the same testings ( ive made 2 versions ) but between identical componets used ,the one pcb requierd 47pf miller styroflex cap and the other required 68pf cap .....
straight conclusion is that the pcb had diferent behaviour.
as about vas transistor and bd139, the amplifiers i ve made performed like hell didnt feel like playing arround there but i will take a look at this and let you know
i will follow homemodder's advice though and look at that since i have 77 pcs of 2sa1406....will test and let you know
Just one simple question ... why is there a miller cap in the negative rail driver transistor ?? 
About VAS, styroflex and other types of miller caps - if I find a scope I'll check it out how it's doing.
Another thing - I made my PCB design already, and these days when I have some spare time I'll try the P3A with a current mirror in the diff. stage and a CCS in VAS.
About VAS, styroflex and other types of miller caps - if I find a scope I'll check it out how it's doing.
Another thing - I made my PCB design already, and these days when I have some spare time I'll try the P3A with a current mirror in the diff. stage and a CCS in VAS.
TO SEE .....
what exactly does, and how much miller cap you will use you will see applying square wave of more than 10khz -20khz .....
current mirror and ccs on vas is a very nice idea will improove stability but will reduce sonics ..... check that and let us now please kalmara ....
thank you very much
what exactly does, and how much miller cap you will use you will see applying square wave of more than 10khz -20khz .....
current mirror and ccs on vas is a very nice idea will improove stability but will reduce sonics ..... check that and let us now please kalmara ....
thank you very much
A good way to start experimenting is to start with about a 10pf smaller miller cap as required and connect a 5 to 10 pf cap from the vas collector to the base of the ltp feebback node. Whether you want to call it, phase lead, feedforward comp doesnt matter, the importance is the sound.
In most cases this will imediately bring about a wider soundstage, take some harshness away and your amp will be even more stable to reactive loads. Sakis is absolutely right with his statement about layout, different boards will most often require different value compensation.
From experiments i did some years ago i found that in many instances when phase lead is used that the hig
In most cases this will imediately bring about a wider soundstage, take some harshness away and your amp will be even more stable to reactive loads. Sakis is absolutely right with his statement about layout, different boards will most often require different value compensation.
From experiments i did some years ago i found that in many instances when phase lead is used that the hig
Re: TO SEE .....
Ãåéá óïõ Óáêç
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Åãù åäù óôç Äñáìá å÷ù ôçí ðïëõôåëåéá íá áðïëáìâáíù ôçí ðáãùìåíç ìðéñá ìïõ ôåôïéá ùñá (óïõ óõíéóôù íá äïêéìáóåéò ôéò íååò ×åíéíãêåñ, áëëá óå ìðïõêáëé ôùí 0,5lt, åéíáé åîáéñåôéêåò êáé êïóôéæïõí ìïíï 0,55 åõñù. Ïôáí åõêáéñåé åíá öéëáñáêé ìïõ áðï Èåóóáëïíéêç, ìïõ áãïñáæåé åíá ôåëáñï áðï êáðïéï ôïðéêï óïõðåñ ãéá 0,48 åõñù ôï ìðïõêáëé êáé ìïõ ôï óôåëíåé ìå ôï ÊÔÅË).
Åóåéò óôçí Áèçíá ðñåðåé íá åñãáæåóôå ôïõëá÷éóôïí ìå÷ñé ôéò 6ìì. Áíôå, äïõëåéá!
Ãñáøå ìïõ íåá óïõ.
Öùôçò
sakis said:
Ãåéá óïõ Óáêç
Ôé êáíåéò åêåé ñå, áíôé íá äïõëåõåéò êáèåóáé êáé áëëùíéæåéò ôï öïñïõì?
Åãù åäù óôç Äñáìá å÷ù ôçí ðïëõôåëåéá íá áðïëáìâáíù ôçí ðáãùìåíç ìðéñá ìïõ ôåôïéá ùñá (óïõ óõíéóôù íá äïêéìáóåéò ôéò íååò ×åíéíãêåñ, áëëá óå ìðïõêáëé ôùí 0,5lt, åéíáé åîáéñåôéêåò êáé êïóôéæïõí ìïíï 0,55 åõñù. Ïôáí åõêáéñåé åíá öéëáñáêé ìïõ áðï Èåóóáëïíéêç, ìïõ áãïñáæåé åíá ôåëáñï áðï êáðïéï ôïðéêï óïõðåñ ãéá 0,48 åõñù ôï ìðïõêáëé êáé ìïõ ôï óôåëíåé ìå ôï ÊÔÅË).
Åóåéò óôçí Áèçíá ðñåðåé íá åñãáæåóôå ôïõëá÷éóôïí ìå÷ñé ôéò 6ìì. Áíôå, äïõëåéá!
Ãñáøå ìïõ íåá óïõ.
Öùôçò
A good way to start experimenting is to start with about a 10pf smaller miller cap as required and connect a 5 to 10 pf cap from the vas collector to the base of the ltp feebback node. Whether you want to call it, phase lead, feedforward comp doesnt matter, the importance is the sound.
In most cases this will imediately bring about a wider soundstage, take some harshness away and your amp will be even more stable to reactive loads. Sakis is absolutely right with his statement about layout, different boards will most often require different value compensation.
From experiments i did some years ago i found that in many instances when phase lead is used that the higher uneven distortions tend to be lower, eg 5,7,9 harmonics and this may also be an important factor in the change noted in the sound using phase lead . John Curl, regarding amps it should be Dr Curl, has mentioned these harmonics as the source of metallic and harsh sound.
Sakis if you use a scope and use a transistor as good as 2sa1406 you will notice quite a fair drop in all harmonic distortions compared to other transistors especially in the mold of the bd140. You could even sim this on simulators. I have found that when this mod is done youll also have to tweak the compensation and sometimes requires a larger miller cap although i have encountered cases on Rotel amps where i could decrease the miller substancially. The smaller value miller cap the better the sound. The 2sa1406 transistors are exceptionally fast with very low cob and very linear. Check out the datasheet.
Looks like i have a trip to make to Greece as i stated in another thread. Im in dire need of 2sa1406 and its compliment 2sc3600. I must have wiped the entire stock here in my country, the 2sc1540 and the Toshiba 2sa1306 are also very good choices. Sakis i would appreciate if you could check on availible stocks there. Also the other transistors i mentioned in that thread. Please make sure they are original Sanyos, Sanyo has a distinct way of marking and its very easy to distinguish from fakes although these are not often faked. Just check the datasheet for details. I will see if i can take a pick of some of my originals.
I have come to the conclusion that the vas and the compensation used in amps is about the most important factor for good sound. Ive modded even some of the nastiest sounding amps, super high slew rate japanese like pioneer jvcs and the like from the slew rate races and got some very good results. High slew rate is no bad thing, these amps tend to sound very accurate and require good input sources to match.
Happy modding
Alex
In most cases this will imediately bring about a wider soundstage, take some harshness away and your amp will be even more stable to reactive loads. Sakis is absolutely right with his statement about layout, different boards will most often require different value compensation.
From experiments i did some years ago i found that in many instances when phase lead is used that the higher uneven distortions tend to be lower, eg 5,7,9 harmonics and this may also be an important factor in the change noted in the sound using phase lead . John Curl, regarding amps it should be Dr Curl, has mentioned these harmonics as the source of metallic and harsh sound.
Sakis if you use a scope and use a transistor as good as 2sa1406 you will notice quite a fair drop in all harmonic distortions compared to other transistors especially in the mold of the bd140. You could even sim this on simulators. I have found that when this mod is done youll also have to tweak the compensation and sometimes requires a larger miller cap although i have encountered cases on Rotel amps where i could decrease the miller substancially. The smaller value miller cap the better the sound. The 2sa1406 transistors are exceptionally fast with very low cob and very linear. Check out the datasheet.
Looks like i have a trip to make to Greece as i stated in another thread. Im in dire need of 2sa1406 and its compliment 2sc3600. I must have wiped the entire stock here in my country, the 2sc1540 and the Toshiba 2sa1306 are also very good choices. Sakis i would appreciate if you could check on availible stocks there. Also the other transistors i mentioned in that thread. Please make sure they are original Sanyos, Sanyo has a distinct way of marking and its very easy to distinguish from fakes although these are not often faked. Just check the datasheet for details. I will see if i can take a pick of some of my originals.
I have come to the conclusion that the vas and the compensation used in amps is about the most important factor for good sound. Ive modded even some of the nastiest sounding amps, super high slew rate japanese like pioneer jvcs and the like from the slew rate races and got some very good results. High slew rate is no bad thing, these amps tend to sound very accurate and require good input sources to match.
Happy modding
Alex
ALEX ....
thanks for all the usefull input .....
i am very busy now days with my pa and rendals but on the side i am procecing all this information and also my conquest about original stock of japanese transistors in greece ...
there is plenty dont worrie ...i am going to finish this search and upload the list in my site to anyone that may be interested to buy
thanks for your input so far ....
thanks for all the usefull input .....
i am very busy now days with my pa and rendals but on the side i am procecing all this information and also my conquest about original stock of japanese transistors in greece ...
there is plenty dont worrie ...i am going to finish this search and upload the list in my site to anyone that may be interested to buy
thanks for your input so far ....
rabbitz said:That's all Greek to me.
Hey, rabbitz
To not misunderstand me - i'm not so good in English like Sakis - i made a joke to he. Because Sakis is living in the capital of Greece Athens, instead me i'm living in a small town in north Greece. As you know in big cities the people works continuously from 9am to 6pm. Instead all of us where are living in small towns, we have the benefit of the midday work interval from 2pm to 6pm.
Well, that i said to Sakis was that i am drinking my midday beer before lunch and he must be worked at this time instead to browse the forum; and i suggested to he a nice and cheap (0,55euros the 0,5lt bottle) beer brand Henninger. Poverty knows no laws.
Fotios
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