Dear All,
I am a beginner trying to diy a sun audio sv-2a3 amp. But i have some questions about the transformers. I do not intend to make a purchase of the originals, they would cost me a bomb =/ any advice? My plan now is to get the ratings and look for cheaper alternatives!
SPT150 power/main transformer: what is the VA rating?
SCH515 choke: I understand the significance of the choke, but how do i select one?? i can't seem to find any information on this choke =/
output transformers i have found. Not top notch, but i believe will do the job =)
My output transformers:
http://singapore.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2106475
The schematics for SV-2A3:
http://www.ys-audio.com/wce/sunaudiosv2a3.JPG
What are the items within the dotted lines? There is one labeled N.L. a RC filter. but without ratings...and the capacitors tied to the choke, are they implied to be optional? why the dotted line huh?
I look forward to receiving the enlightenment from anyone in this esteemed forum on this subject.
Best regards,
Ming Yang
I am a beginner trying to diy a sun audio sv-2a3 amp. But i have some questions about the transformers. I do not intend to make a purchase of the originals, they would cost me a bomb =/ any advice? My plan now is to get the ratings and look for cheaper alternatives!
SPT150 power/main transformer: what is the VA rating?
SCH515 choke: I understand the significance of the choke, but how do i select one?? i can't seem to find any information on this choke =/
output transformers i have found. Not top notch, but i believe will do the job =)
My output transformers:
http://singapore.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2106475
The schematics for SV-2A3:
http://www.ys-audio.com/wce/sunaudiosv2a3.JPG
What are the items within the dotted lines? There is one labeled N.L. a RC filter. but without ratings...and the capacitors tied to the choke, are they implied to be optional? why the dotted line huh?
I look forward to receiving the enlightenment from anyone in this esteemed forum on this subject.
Best regards,
Ming Yang
Hello Ming Yang,
This will depend on whether you power 2 channels or only 1. Since a 2A3 can run at 60mA maxium, you will want at least a 75mA current rating for one channel. Twice that for two channels on the same transformer. This is figuring 10mA more for the 6SN7.
Use the above current figures as a guide. Inductance value will be somewhat of a guess with 5 to 10 Henrys being typical with about 150 ohms DC resistance.
The N.L. capacitor across the line is a Noise Limiting cap which has an internal resistor. They are available from makers like ERO and Wima. But you can make one with typical values of .1ufd/600V and perhaps 500 ohms. These are not critical and it can even be left out.
The dashed lines around the two capacitors indicate a dual electrolytic can type filter capacitor. Single capacitors will work just as well. They are needed and are not optional.
For maxium power transfer, a 2A3 wants to see a 2.5/3K plate load. The transformer you chose will work but you will suffer a reduction of output power with it's 4 to 5K impedance. Also, it's maxium rating is a little low with only 40mA and 3½ watts. Some people like the sound of a lightly loaded DHT, so you might too. But you will not be able to get the maxium performance power with it. I would choose a little higher rated output transformer myself of perhaps 5 watts or more to prevent saturation on loud passages.
BTW, your English is very good. Better then some locals that grew up with it.
Victor
This will depend on whether you power 2 channels or only 1. Since a 2A3 can run at 60mA maxium, you will want at least a 75mA current rating for one channel. Twice that for two channels on the same transformer. This is figuring 10mA more for the 6SN7.
Use the above current figures as a guide. Inductance value will be somewhat of a guess with 5 to 10 Henrys being typical with about 150 ohms DC resistance.
The N.L. capacitor across the line is a Noise Limiting cap which has an internal resistor. They are available from makers like ERO and Wima. But you can make one with typical values of .1ufd/600V and perhaps 500 ohms. These are not critical and it can even be left out.
The dashed lines around the two capacitors indicate a dual electrolytic can type filter capacitor. Single capacitors will work just as well. They are needed and are not optional.
For maxium power transfer, a 2A3 wants to see a 2.5/3K plate load. The transformer you chose will work but you will suffer a reduction of output power with it's 4 to 5K impedance. Also, it's maxium rating is a little low with only 40mA and 3½ watts. Some people like the sound of a lightly loaded DHT, so you might too. But you will not be able to get the maxium performance power with it. I would choose a little higher rated output transformer myself of perhaps 5 watts or more to prevent saturation on loud passages.
BTW, your English is very good. Better then some locals that grew up with it.
Victor
Excellent, your explaination was crystal clear! Now i have a very good picture of what to look for in future projects. Thanks! 
HAHA my english is so so only lah, yours is very commendable too. I haven reveal my true powers (singlish) to you yet; a local slang unique only to singaporeans
Ming Yang
HAHA my english is so so only lah, yours is very commendable too. I haven reveal my true powers (singlish) to you yet; a local slang unique only to singaporeans
Ming Yang
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