I didn't even look at the circuit; all I heard was "according to this schematic you don't need all that stuff"." Someone that knows what they're doing knows what they need and why.
The fact that the circuit uses 25 volt caps and 50 volt rectifiers with a 25-0-25 transformer tells me that the designer doesn't know what they're doing. The OP would have nothing but trouble with this circuit and wouldn't know what was going on.
Thank you all for your thoughtful comments. It has been quite a lesson in electronics.
To Fast Eddie D:
Thank you for explaining to me about the workings of circuits on the Internet, compared with circuits that need to work in the real world:
“The fact is that these stripped down circuits can be made to work on the bench, and they will often work without a hitch when assembled and used in a system. The addition of these "unnecessary items" makes the operation of the completed device much more foolproof. In other words, you might hook up your newly assembled amplifier to one sound system and it's all good. But then you mix the components up (new preamp, speakers, whatever) and all of a sudden your amplifier isn't performing the same. And since you built the thing, it's going to be up to you to figure out why.”
I will be adding, what I unfortunately called “unnecessary items”, to my amplifier as I develop it. Thanks.
To stuhuber:
Thank you for your comments on the Foreplay III. My plan is to now add the potentiometers in the amp so that I can use it, should the Foreplay make my system sound bad. I now have some modifications to try on my Foreplay should I want to attempt to fix it later. Thanks.
Also, you made a comment:
“if all the missing pieces were not enough to worry you, note also that the instructions call for a 25-0-25 transformer, which will push the PSU caps roughly 40% over their absolute maximum 25 volt rating and will also push the suggested 50 volt rectifiers to roughly 40% over their absolute maximum ratings.”
This may be a stupid question. If I used a 15-0-15 transformer instead of the 25-0-25, would I be able to still use the amp, and avoid this problem? The reason is because I have a 15-0-15 toroidal transformer, and would like to avoid spending the extra $40.00 to acquire the bigger transformer if the small one would work.
Again, I am a newbie, and don’t understand all the implications of changing a component from the one in the specifications.
To Bare:
The only reason that I choose the eBay gainclone is cost. The eBay gainclone at $19.95, plus the two LM3875 chips at $6.50/each was less than half of the cost of the comparable chipamp. In retrospect, maybe I was being “penny wise and pound foolish”. I am limited financially, and would be out less money should the amp blow up in my face (a real possibility with my limited experience).
Thanks again for all your comments. This has been quite a learning experience already.
To Fast Eddie D:
Thank you for explaining to me about the workings of circuits on the Internet, compared with circuits that need to work in the real world:
“The fact is that these stripped down circuits can be made to work on the bench, and they will often work without a hitch when assembled and used in a system. The addition of these "unnecessary items" makes the operation of the completed device much more foolproof. In other words, you might hook up your newly assembled amplifier to one sound system and it's all good. But then you mix the components up (new preamp, speakers, whatever) and all of a sudden your amplifier isn't performing the same. And since you built the thing, it's going to be up to you to figure out why.”
I will be adding, what I unfortunately called “unnecessary items”, to my amplifier as I develop it. Thanks.
To stuhuber:
Thank you for your comments on the Foreplay III. My plan is to now add the potentiometers in the amp so that I can use it, should the Foreplay make my system sound bad. I now have some modifications to try on my Foreplay should I want to attempt to fix it later. Thanks.
Also, you made a comment:
“if all the missing pieces were not enough to worry you, note also that the instructions call for a 25-0-25 transformer, which will push the PSU caps roughly 40% over their absolute maximum 25 volt rating and will also push the suggested 50 volt rectifiers to roughly 40% over their absolute maximum ratings.”
This may be a stupid question. If I used a 15-0-15 transformer instead of the 25-0-25, would I be able to still use the amp, and avoid this problem? The reason is because I have a 15-0-15 toroidal transformer, and would like to avoid spending the extra $40.00 to acquire the bigger transformer if the small one would work.
Again, I am a newbie, and don’t understand all the implications of changing a component from the one in the specifications.
To Bare:
The only reason that I choose the eBay gainclone is cost. The eBay gainclone at $19.95, plus the two LM3875 chips at $6.50/each was less than half of the cost of the comparable chipamp. In retrospect, maybe I was being “penny wise and pound foolish”. I am limited financially, and would be out less money should the amp blow up in my face (a real possibility with my limited experience).
Thanks again for all your comments. This has been quite a learning experience already.
Fast Eddie D, instead of scaring people perhaps you could explain what is wrong with this amp and why.
I am getting +-23.7Vdc on the rails supplying two chipamps using a 230:15-0-15Vac transformer on 240Vac.
For the same reasons that have been posted dozens of times previously.
It is not a duty of any Member to do the research of another Member's project.
At least get the facts correct.
It does have feedback capacitors.
It does have a Zobel network.
It has an additional DC output detection, not included with most other AMP kits.
Input capacitors can easily be added.
Two problems most first time builders have is getting the PSU and grounding right. This kit goes a long way in solving these problems.
People seem to have forgotten that it is the minimalistic approach adopted by 47 Labs that made these chips so popular. More traditional designs with all the additional components did not.
It does have feedback capacitors.
It does have a Zobel network.
It has an additional DC output detection, not included with most other AMP kits.
Input capacitors can easily be added.
Two problems most first time builders have is getting the PSU and grounding right. This kit goes a long way in solving these problems.
People seem to have forgotten that it is the minimalistic approach adopted by 47 Labs that made these chips so popular. More traditional designs with all the additional components did not.
part of the confusion here (at least on my part) is that there is more than one schematic among thread and the builders' site.
the schematic containing the elements to which you refer also has 50v PSU caps, which covers one of the concerns i raised. that schematic is silent on the ratings for the PSU bridge rectifier, however. it also fails to reflect any distinction between signal and voltage ground.
i suppose it would be more precise to say that the "PG" everywhere implies that SG and PG are one, which strikes me as suboptimal.
PG and SG are not one but they do need to be connected. Some PCB designs connect the feedback and other returns separately to PG. If you look at the rear of the PCB you can see a star ground with a single connection to PG.
Some information printed on the PCB including bridge rectifier current.
There are plenty of things I would do differently but that could be said about most of the kits. If you are not designing your own PCB and want to build a kit your choice is limited to what others have designed.
Maybe somebody could recommend a better amp in the same price range?
Some information printed on the PCB including bridge rectifier current.
There are plenty of things I would do differently but that could be said about most of the kits. If you are not designing your own PCB and want to build a kit your choice is limited to what others have designed.
Maybe somebody could recommend a better amp in the same price range?
Thanks for the discussion. It has been helpful.
Sorry about the confusion w.r.t. the schematics.
The first schematic was the one supplied by the vendor on eBay. I didn’t know then, but I do know now, that it was a simplified schematic.
The second schematic is the actual one of the kit that I purchased.
The third schematic was one that I thought was similar (but for a LM3886 chip) to the one I purchased, but without the protections suggested by Fast Eddie D.
Hope this helps.
I will now ask a few questions that will probably demonstrate my ignorance.
Per Mike Whitney:
“Input capacitors can easily be added.”
Does this mean I should add a high pass filter between the transformer and PCB in order to filter out the 60 HZ mains noise?
And if so, will I have an amp that will “work” (not as good as Fast Eddie D’s proposal) with a reasonable amount of reliability?
Now for a question about using a less powerful transformer. I know this is simple, but please help this newbie.
P = V2 * I; going from 25 volts to 15 volts is 60% of the power. Squared is 36%. 10 log(0.36) = -4.4db. Halving of perceived volume is between -6db and -10db. The decrease in perceived volume is much less than half, regardless of the definition. Is this analysis correct (BTW, I enjoy listening at low volumes)?
Thanks again for all your input.
Best regards, Bill
Sorry about the confusion w.r.t. the schematics.
The first schematic was the one supplied by the vendor on eBay. I didn’t know then, but I do know now, that it was a simplified schematic.
The second schematic is the actual one of the kit that I purchased.
The third schematic was one that I thought was similar (but for a LM3886 chip) to the one I purchased, but without the protections suggested by Fast Eddie D.
Hope this helps.
I will now ask a few questions that will probably demonstrate my ignorance.
Per Mike Whitney:
“Input capacitors can easily be added.”
Does this mean I should add a high pass filter between the transformer and PCB in order to filter out the 60 HZ mains noise?
And if so, will I have an amp that will “work” (not as good as Fast Eddie D’s proposal) with a reasonable amount of reliability?
Now for a question about using a less powerful transformer. I know this is simple, but please help this newbie.
P = V2 * I; going from 25 volts to 15 volts is 60% of the power. Squared is 36%. 10 log(0.36) = -4.4db. Halving of perceived volume is between -6db and -10db. The decrease in perceived volume is much less than half, regardless of the definition. Is this analysis correct (BTW, I enjoy listening at low volumes)?
Thanks again for all your input.
Best regards, Bill
Input capacitor, DC blocking capacitor or AC coupling capacitor is placed between the source and amp, it prevents DC entering the amp.
Check the LM3875 data sheet for correct implementation of the external Components.
http://www.ti.com/lit/ds/symlink/lm3875.pdf
This kit is designed to be supplied by a 24-0-24 V AC transformer.
The only thing you need to do is decide on the current rating of the transformer.
Check the LM3875 data sheet for correct implementation of the external Components.
http://www.ti.com/lit/ds/symlink/lm3875.pdf
This kit is designed to be supplied by a 24-0-24 V AC transformer.
The only thing you need to do is decide on the current rating of the transformer.
are you using post1 .doc sch?
or
are you using post15, step3 sch?
Both are bad examples of circuits that "might" work, but may have problems that require expertise in debugging.
Don't use either without much modification.
But they should be capable of modification and thus capable of working properly in most domestic situations.
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Thanks for all your input!
The items that were brought out will help point me in specific areas of study. It is difficult to study and learn electronics at my age and background (nearly 62; my profession is presently semi-retired accountant) without a focus and project in the real world from which I can learn. This gainclone seems to be such a project. Especially since the result will realize my dream of a fine stereo system at a cost that I can afford.
I will refer to this thread for things that are beyond me now, but will not be in the future. Thanks to all, especially Mark Whitney whose comments didn’t go over my head.
Maybe in a year or two (once I have move beyond the material in “Electronics for Dummies”), I hope to be able to make a real contribution to this forum.
May God bless you as you get to know Him.
Very best regards, Bill
The items that were brought out will help point me in specific areas of study. It is difficult to study and learn electronics at my age and background (nearly 62; my profession is presently semi-retired accountant) without a focus and project in the real world from which I can learn. This gainclone seems to be such a project. Especially since the result will realize my dream of a fine stereo system at a cost that I can afford.
I will refer to this thread for things that are beyond me now, but will not be in the future. Thanks to all, especially Mark Whitney whose comments didn’t go over my head.
Maybe in a year or two (once I have move beyond the material in “Electronics for Dummies”), I hope to be able to make a real contribution to this forum.
May God bless you as you get to know Him.
Very best regards, Bill
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