I always perceive this way too.... a complicated circuit sounding good!
I always feel this as an exception... a very good amplifier, with a very clear sonics, wonderfull dinamics....very nice bass and trebles...and using a lot of transistors...when in my mind 7 is more than enougth.
regards,
Carlos
I always feel this as an exception... a very good amplifier, with a very clear sonics, wonderfull dinamics....very nice bass and trebles...and using a lot of transistors...when in my mind 7 is more than enougth.
regards,
Carlos
MikeB said:
Maybe jfets are THE devices for input diffamp ?
Mike
Hi Mike,
jfets are said to be more linear and produce a different (nicer) distortion spectrum. You have to carefully select the operation region for each device (or matched pair) seperatly to gain the most of performance. You need to know (and match for) the Idss and the Vp (gate pinch off voltage), so you can calculate (or actually measure) the transconductance curve. You then set the operating piont so, that you operate the fet in the most linear region. With very hot devices (V-grade) you may even manage to operate them at zero tempco (=Vp+0.6V). Bear in mind that Vp is negative for npn-devices.
This is how I understand using jfets.
What's the rating of your fets and at what Id and Vgs do you run them?
thanks,
Rüdiger
Fired up my Syasym today, and its working perfectly!
Hello,
I fired up my stereo Symasym today. Both are running from the same PSU with +-40,5V sek.
Q1 and Q2 are 2sc2240, all others as recommended.
As suggested the input-pairs and the 2N5xxx types were matched for Ube.
The DC-Offset is below 3mV on both channels.
Still I have to make some corrections on my enclosure, then I#ll post some pics.
Thanks to MikeB for this perfect AMP-design-
Greetings
Black
PS: It would have been better to use 470R pots for the bias, 1k are difficult to adjust and very sensitive. Luckily you have to adjust the bias current only once.
Hello,
I fired up my stereo Symasym today. Both are running from the same PSU with +-40,5V sek.
Q1 and Q2 are 2sc2240, all others as recommended.
As suggested the input-pairs and the 2N5xxx types were matched for Ube.
The DC-Offset is below 3mV on both channels.
Still I have to make some corrections on my enclosure, then I#ll post some pics.
Thanks to MikeB for this perfect AMP-design-
Greetings
Black
PS: It would have been better to use 470R pots for the bias, 1k are difficult to adjust and very sensitive. Luckily you have to adjust the bias current only once.
Before I forget it....
Many thanks to MikeB, Anatech and all others who encouraged me to nuild this AMP with higher Railvoltage, and the suggestion to use the 2sc2240 types in the Input!
Greetings
Many thanks to MikeB, Anatech and all others who encouraged me to nuild this AMP with higher Railvoltage, and the suggestion to use the 2sc2240 types in the Input!
Greetings
Hi BlacK_Chicken,
The suggestion of a 500R bias control was made earlier in the thread. That's what I used.
The Symasym sounds pretty good, doesn't it? 😀
-Chris
The suggestion of a 500R bias control was made earlier in the thread. That's what I used.
The Symasym sounds pretty good, doesn't it? 😀
-Chris
Pls let me say a word about the sound, yes this amp sounds good, colorful, solid, detailed, but over the time i loose any impression, this amp gets out of the way... and I think that's what an amp should do!
Maybe some call it transparency or naturalness, but maybe one could say it just works very well...
Maybe some call it transparency or naturalness, but maybe one could say it just works very well...
Yes, sounds nice on my bench, with low quality speakers. Better than my gainclone (I just had build it for fun, i dont take it seriously😀 )
My faceplate is drying at the moment, after 3 more layers, I'll mount everything together, adjust the bias once again, then I'm finished.
MikeB suggests using the 470R pot on his HP, I ordered both values, but now I am too lazy to change them. On top my 1k trimpots are higher quality than the 470R.
Hope get some pics up soon.
Greetings
Black
My faceplate is drying at the moment, after 3 more layers, I'll mount everything together, adjust the bias once again, then I'm finished.
MikeB suggests using the 470R pot on his HP, I ordered both values, but now I am too lazy to change them. On top my 1k trimpots are higher quality than the 470R.
Hope get some pics up soon.
Greetings
Black
too lazy to change them
Suggestion, place a 1k resistor in parallel with the 1k pot and it will be fixed.
My 2 cts.
Loek
Suggestion, place a 1k resistor in parallel with the 1k pot and it will be fixed.
My 2 cts.
Loek
Hi loek,
I got the impression that BlacK_Chicken didn't want to readjust his bias, although it may have to be done once the case is finished.
-Chris
Yup.
I got the impression that BlacK_Chicken didn't want to readjust his bias, although it may have to be done once the case is finished.
-Chris
Well.....yes.
I am too lazy to demount my heatsinks, to work on the copper-side of the boards. 🙄 ,was quite hard work to get them in there properly.
1k works fine, but I would recommend everyone, whos planning a symasym to start with the 470R value🙂
Update: The second layer of paint should be dry by now. Time to finish my case.
Greetings
black
I am too lazy to demount my heatsinks, to work on the copper-side of the boards. 🙄 ,was quite hard work to get them in there properly.
1k works fine, but I would recommend everyone, whos planning a symasym to start with the 470R value🙂
Update: The second layer of paint should be dry by now. Time to finish my case.
Greetings
black
no bias adjust
Indeed he told us that but also that 1k is difficult to adjust and very sensitive, so it is a decision he has to make and not we.
But if you want stability over a long period......
Anyway it is good to be informed through the forum.
Greetings, and waiting for the pictures now.
Loek
Indeed he told us that but also that 1k is difficult to adjust and very sensitive, so it is a decision he has to make and not we.
But if you want stability over a long period......
Anyway it is good to be informed through the forum.
Greetings, and waiting for the pictures now.
Loek
Symassym is ALL good !
I still very happy with mine ! 😀
Listen to Jane Monheit !
Anybody here knows Francis Hime ?
I still very happy with mine ! 😀
Listen to Jane Monheit !
Anybody here knows Francis Hime ?
I dindn't adjust the bias of my amps...
I forgot to do it, and I could remember when it was playing in my house, COLD. It don't get more than warm, no pop noise when I turn it on, no Hum or hiss at all.
So, why should I open the case and adjust the bias? 😕
I forgot to do it, and I could remember when it was playing in my house, COLD. It don't get more than warm, no pop noise when I turn it on, no Hum or hiss at all.
So, why should I open the case and adjust the bias? 😕
pictures of my finished symasym...
Hello again,
Here are some (many) pictures.
I think they speak for themselves. Good to see is the added Speaker Protection (and turn-on-delay) board, and the heatshrinked 2sc2240 input transistors.
The Faceplate is only screwed, maby I'll change to wood or something else some day.
The whole AMP is built on the basis of an old Nordmende PA1400 Amplifier. The aim was to keep as much of the old chassis as possible. The main problem was the small amount of space inside, and that alle big parts (i.e. heatsink, transform) were already screwed down. The Internal Layout is far from perfect, but a good compromise.
The pictures:
Thanks alot for your support!
Black🙂
Hello again,
Here are some (many) pictures.
I think they speak for themselves. Good to see is the added Speaker Protection (and turn-on-delay) board, and the heatshrinked 2sc2240 input transistors.
The Faceplate is only screwed, maby I'll change to wood or something else some day.
The whole AMP is built on the basis of an old Nordmende PA1400 Amplifier. The aim was to keep as much of the old chassis as possible. The main problem was the small amount of space inside, and that alle big parts (i.e. heatsink, transform) were already screwed down. The Internal Layout is far from perfect, but a good compromise.
The pictures:
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An externally hosted image should be here but it was not working when we last tested it.
Thanks alot for your support!
Black🙂
Black chicken, great work!
Looking at the parts, you were obviously also shopping at Reichelt... 😀
Nando, you really should check the bias, symasym sounds much better with properly adjusted bias, or in other words, it sounds quite bad with too low bias. With bias below 20ma the crossover distortion becomes audible.
Mike
Looking at the parts, you were obviously also shopping at Reichelt... 😀
Nando, you really should check the bias, symasym sounds much better with properly adjusted bias, or in other words, it sounds quite bad with too low bias. With bias below 20ma the crossover distortion becomes audible.
Mike