I'm using this: Minimalist Discrete Hi-Fi Preamp
for my Dx Precision. Read the article to find how to reduce the gain a bit, and add a potentiometer.
Or, if you wanted, you can find other preamps on his site using several opamps and including tone controls.
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humming
bro. try check mo yung input connector na ginamit mo .dapat hindi sya directly naka ground sa chassis iderecho mo sa board ng amplifier.alisin mo muna sa chassis yung connector at i connect mo yung input connector mo sa source.wala rmuna potentiometer.
bro. try check mo yung input connector na ginamit mo .dapat hindi sya directly naka ground sa chassis iderecho mo sa board ng amplifier.alisin mo muna sa chassis yung connector at i connect mo yung input connector mo sa source.wala rmuna potentiometer.
You have a L - R ground "loop' . It can't be a source loop since you used a portable device and still have the "hum". Try running (powering) BOTH amps from just one PS (cap's + bridge), hum will most likely cease. The fact that you have 2 PS's would lend itself to having 2 trafo's , as well (true dual mono).
You DO have the space in the case !
PS- in short ... 1 trafo = 1 BIG power supply (35A bridge + all that capacitance) grounds star at that single point. Or 2 supplies like yours = 2 trafos , Left totally independent from right. (I encountered this issue on my first build)
OS
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I love the curvy traces. It has more than a hint of the hand drawn style of the old days.
Heatsink is needed to driver transistor, the VAS transistor too
and you have two more units hot..the ones send current to drivers..these transistor needs heatsinks.
regards,
Carlos
and you have two more units hot..the ones send current to drivers..these transistor needs heatsinks.
regards,
Carlos
Pre-drivers (the devices that send current to the drivers) rarely need heatsinks.
Similarly VAS & it's CCS rarely need heatsinks in a well designed amplifier.
Could performance over a very wide range of operating temperature be improved by fitting heatsinks? Possibly, in that the devices would run cooler. But, how much cooler?
Similarly VAS & it's CCS rarely need heatsinks in a well designed amplifier.
Could performance over a very wide range of operating temperature be improved by fitting heatsinks? Possibly, in that the devices would run cooler. But, how much cooler?
I started using a bigger heatsink for the VAS than what is pictured in most pictures of the Precision I. I found the heatsink did get hot. Not hot enough for failure obviously but to the point of becoming uncomfortable (not necessarily painful) to touch for more than ~10-15 seconds.
After switching to a bigger heatsink for it, the sound quality has improved.
Also, not sure if this was a good move or not, but I learn from mistakes. I changed the VAS transistor from the 2SC4793:
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7846.pdf
to the 2SC5171:
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7870.pdf
The differences being a lower Cob, a higher base current capability, a higher collector current, twice the Ft, and I had hand selected them (with multimeter) to have highest hFE.
I perceived a subtle increase in sound quality but not enough to use adjectives for.
I had read a long time ago in this thread concerns that the base current of the 4793 could be exceeded in large transients if the BC547C wasn't included. I may have misunderstood, but if that is true, than this shouldn't be a worry anymore with the 5171, right? I took the BC547C out when I originally put it together.
After switching to a bigger heatsink for it, the sound quality has improved.
Also, not sure if this was a good move or not, but I learn from mistakes. I changed the VAS transistor from the 2SC4793:
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7846.pdf
to the 2SC5171:
http://www.toshiba.com/taec/components2/Datasheet_Sync//66/7870.pdf
The differences being a lower Cob, a higher base current capability, a higher collector current, twice the Ft, and I had hand selected them (with multimeter) to have highest hFE.
I perceived a subtle increase in sound quality but not enough to use adjectives for.
I had read a long time ago in this thread concerns that the base current of the 4793 could be exceeded in large transients if the BC547C wasn't included. I may have misunderstood, but if that is true, than this shouldn't be a worry anymore with the 5171, right? I took the BC547C out when I originally put it together.
Skilled designers knows that we must try to keep transistors
cool.... room temperature is the idea...or to keep them at 25 degrées celsius.... to do that, in some designs, where the designer decided to increase current above the traditional calculated levels you must use heatsinks to avoid transistors to get hot or highly warm.
Transistors specifications are made at this temperature..so..we must try to keep them cool to preserve their main characteristics.
These decisions are taken by the ones makes the design..of course people can make it different if they have courage to make design and offer to the community...it is very easy to suggest the amplifier was not perfectly designed when we have not exposed our own work to be evaluated...very easy this way...also shows a big lack of courage.
You gonna learn a lot tweaking this way...go ahead and enjoy this nice amplifier that deserves that attention, love and care... sound is excellent and hundreds have built in Brasil and they said they are happy with this amplifier.
Amplifier was built, was tested and approved by many guys.... circuit is old and works fine..will not be changed...no suggestions of changes will be accepted or implemented.... good performance is without that small transistor..this was the biggest mistake i have made to include that awfull thing there..i regret a lot to listen evil suggestions..people trying to kill my amplifiers.
Temperature here is high.... so, they use heatsinks as i use to suggest them to use.
regards,
Carlos
cool.... room temperature is the idea...or to keep them at 25 degrées celsius.... to do that, in some designs, where the designer decided to increase current above the traditional calculated levels you must use heatsinks to avoid transistors to get hot or highly warm.
Transistors specifications are made at this temperature..so..we must try to keep them cool to preserve their main characteristics.
These decisions are taken by the ones makes the design..of course people can make it different if they have courage to make design and offer to the community...it is very easy to suggest the amplifier was not perfectly designed when we have not exposed our own work to be evaluated...very easy this way...also shows a big lack of courage.
You gonna learn a lot tweaking this way...go ahead and enjoy this nice amplifier that deserves that attention, love and care... sound is excellent and hundreds have built in Brasil and they said they are happy with this amplifier.
Amplifier was built, was tested and approved by many guys.... circuit is old and works fine..will not be changed...no suggestions of changes will be accepted or implemented.... good performance is without that small transistor..this was the biggest mistake i have made to include that awfull thing there..i regret a lot to listen evil suggestions..people trying to kill my amplifiers.
Temperature here is high.... so, they use heatsinks as i use to suggest them to use.
regards,
Carlos
Thanks Os, for sure that's a good explanation.
Let me dig on some surplus shop in here for additional trafo
Carlos:
This is a technical forum and several people with different experience or persuasion will give suggestions, make predictions, etc. Its up to the designer to test, include, ignore, whatever. And there are builders who had made circuits from the designer, experienced his results, have full trust, less trust, no trust, whatever. Saying that some other members are evil, trying to kill someone's project is crossing the line. This is not a blog, its open discussion, and all should be contributing. Its the membership's basic right. Learn to stomach that, or there is an ignore list function you may add members you don't feel well with their postings. But painting other members openly as evil even in general, is insult and carries penalties you have had before for the same reason. I will not repeat.
This is a technical forum and several people with different experience or persuasion will give suggestions, make predictions, etc. Its up to the designer to test, include, ignore, whatever. And there are builders who had made circuits from the designer, experienced his results, have full trust, less trust, no trust, whatever. Saying that some other members are evil, trying to kill someone's project is crossing the line. This is not a blog, its open discussion, and all should be contributing. Its the membership's basic right. Learn to stomach that, or there is an ignore list function you may add members you don't feel well with their postings. But painting other members openly as evil even in general, is insult and carries penalties you have had before for the same reason. I will not repeat.
Hey joel, yes bro the RCA is not grounded to chassis it has a plastic insulator in between..sorry Pre I need to type it in English. we should exchange views in English it's a forum rules 😛
people trying to kill my amplifiers ??
Quite to the contrary. I want DX amps to be cool , quiet , (and humfree).
Me and (andrew) have only tried to help any fellow DIY'er do better to achieve this.
"extra transistor" (evil suggestion) I tried it ... it was a folly. YOU were right. OK 😱
"kill my amp's" No , I am glad you finally embraced the LIN (blameless) topology. Even as you said they had crappy sound 2 years ago when I was building them (frugalamp) and I should not bother with them. 😕
In this case you were incorrect (they DO sound nice ,right 🙂 )
And the suggestions on grounding/layout WILL make for quieter amps , alex's new layouts are the best yet for any of these amps.
You have much fame , even as chinese bootleggers are selling "DX's" , is this not enough?
You are funny , and are an asset to DIYA (helping other DIY'ers - 😎 video's) ,I have not seen evidence of any obvious "ill will" toward you , a suggestion is just that ... not a personal attack. Nuff' said. 😛
OS
Quite to the contrary. I want DX amps to be cool , quiet , (and humfree).
Me and (andrew) have only tried to help any fellow DIY'er do better to achieve this.
"extra transistor" (evil suggestion) I tried it ... it was a folly. YOU were right. OK 😱
"kill my amp's" No , I am glad you finally embraced the LIN (blameless) topology. Even as you said they had crappy sound 2 years ago when I was building them (frugalamp) and I should not bother with them. 😕
In this case you were incorrect (they DO sound nice ,right 🙂 )
And the suggestions on grounding/layout WILL make for quieter amps , alex's new layouts are the best yet for any of these amps.
You have much fame , even as chinese bootleggers are selling "DX's" , is this not enough?
You are funny , and are an asset to DIYA (helping other DIY'ers - 😎 video's) ,I have not seen evidence of any obvious "ill will" toward you , a suggestion is just that ... not a personal attack. Nuff' said. 😛
OS
Does someone know if you run the DX off +/-45V if the VAS and other driver
transistors need heatsinks anymore.
transistors need heatsinks anymore.
Where you will use this 45 volts dear Benproiii?
In the precision we have voltage regulator in the power rail lines...so..modifications have to change zeners too.
Really man.... why not to install heatsinks?...they can be made with aluminium blade if you do not have them ... for a while can be this way..then in the future you search for nice heatsinks.
45 volts as main supply will demand modifications in the rail voltage regulator..if i remember...we have voltage regulator there...maybe i am confused...i will check that.
regards,
Carlos
In the precision we have voltage regulator in the power rail lines...so..modifications have to change zeners too.
Really man.... why not to install heatsinks?...they can be made with aluminium blade if you do not have them ... for a while can be this way..then in the future you search for nice heatsinks.
45 volts as main supply will demand modifications in the rail voltage regulator..if i remember...we have voltage regulator there...maybe i am confused...i will check that.
regards,
Carlos
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