I cant figure out why the output is so low on a pair of p2p wired lm3875's. The wiring seems correct and the lightbulb does not even flicker on the tester. The PS is 300vac 25. I checked the VDC on the rectifier and its a solid 27v on each line. there is sound but it is very low and has trouble driving a 40w 8 ohm load.
Here are some pictures. Any help would be great.
Thanks
Here are some pictures. Any help would be great.
Thanks
Attachments
Well, first what is the value of the potentiometerthere!
and someone correct me if I am wrong here but if you have 25vac on the secondaries you should get over 30 vdc after rectifiers.
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25k or 50k are fine but 100k is too high! Get a cd player and try.also make sure all those wires hanging out do not get shorted.
OK so I hooked up a source with a volume control (Ipod). With this source there is more power than I would have ever thought. With this being the case is it my pot or my source? I was oping to mod the PS1 and use it as the permanent audio source in this system, but if the problem is not the pot than I will need to build a preamp to go with it.
Thanks again for the help!
Thanks again for the help!
Ok, if you are using you Ipod as the source with the ipod volume all the way up and you are getting enough power. the problem is not your integrated amp! the problem is with the source you connected before.if I were you I would leave the amp as integrated (with the 25k or 50k pot).leave the volume of your Ipod all the way up and you adjust the volume in your amp only.Good luck buddy!
PS: leave the volume of your Ipod all the way up and then adjust the volume from your amp....up and down and if everything is fine.............your integrated amp is fine!!!
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The schmatic is the one right off the nationals website. the parts are from Peter Daniels commercial gainclone site.
# Part Name/Description Digikey Part Number
2 LM3875TF LM3875TF-ND
4 1500uF 50v Panasonic FC Capacitor P10334-ND
4 22.1k ohm resistor (min quantity = 5) PPC22.1KXCT-ND
2 680 ohm resistor (min quantity = 10) P680BBCT-ND
2 220 ohm resistor (min quantity = 5) PPC20.0KXCT-ND
8 On Semiconductor MUR860 fast diodes MUR860OS-ND
2 4.7uF 50v Panasonic FC Capacitor P10315-ND
# Part Name/Description Digikey Part Number
2 LM3875TF LM3875TF-ND
4 1500uF 50v Panasonic FC Capacitor P10334-ND
4 22.1k ohm resistor (min quantity = 5) PPC22.1KXCT-ND
2 680 ohm resistor (min quantity = 10) P680BBCT-ND
2 220 ohm resistor (min quantity = 5) PPC20.0KXCT-ND
8 On Semiconductor MUR860 fast diodes MUR860OS-ND
2 4.7uF 50v Panasonic FC Capacitor P10315-ND
I believe it is the source. I asked him to do use his Ipod with the volume all the way up and adjust the volume of the inte-amp.that is a fast and easy way to know if the problem is with the pot or the source.
I have a couple of sources like that. OH, and the new Sony digital radio that does make enough output but it strains (schematic shows a bum AF secion) and when it strains, the output is horrible.
These share in common a quick fix with a headphone amp/preamp--sort of like a CMOY, but give it whatever gain is needed to get the job done.
This can provide an output not remarkably different from the Ipod, except that you can fine tune your preamp however you like.
Edit:
Like this: Buffer. . . with gain.
Edit2: Decibel Dungeon
http://myweb.tiscali.co.uk/nuukspot/decdun/gainclone2.html#gcbuffer
These share in common a quick fix with a headphone amp/preamp--sort of like a CMOY, but give it whatever gain is needed to get the job done.
This can provide an output not remarkably different from the Ipod, except that you can fine tune your preamp however you like.Edit:
Like this: Buffer. . . with gain.
Edit2: Decibel Dungeon
http://myweb.tiscali.co.uk/nuukspot/decdun/gainclone2.html#gcbuffer
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I have a couple of sources like that. OH, and the new Sony digital radio that does make enough output but it strains (schematic shows a bum AF secion) and when it strains, the output is horrible.
These share in common a quick fix with a headphone amp/preamp--sort of like a CMOY, but give it whatever gain is needed to get the job done.
Edit:
Like this: Buffer. . . with gain.
Edit2: Decibel Dungeon
Building a buffered Gainclone chip amp.
Daniel I have try many sources mp3 players, cd player, netbooks, pc, satellite receivers etc but I have never had a problem with any of these sources.I guess there are some sources that are trouble makers for the chipamps eh. Wait....I just remember that once I had some back noise when I connected a cable box to it.But that is another story. it was with the ground of the cable box. I guess there was a "loop" with the antenna of the cable box.since I lift the ground of antenna the back noise disappeared. Maybe I have to use a filter in the input( but I rather not do it).I never measured if I had serious dc voltage of the output of the cable box.
OH! Yes. Well, if the source does have a DC output and its cable/rca jack happened to be inverted, it would be crippled. I don't know who would make a source like that, but it is possible. It should be easy to measure for this problem--see if the source has dc voltage from any part of its own output to its own ground. If it was made somewhat backwards, that would be a "very quiet" source indeed because it would short itself. You can just give it an output cap (interrupt the dc so that it doesn't go to the rca jack) if its design is that bad.
Well, its possible.
Actually, it isn't unlikely. lol!
Some sources are designed to drive headphones, and if given an insufficient load, sometimes there's no power--like its pushing really hard onto nothing. Some sources, like my Sony, can't handle a load tougher than 1M! and practically faint at line level--like trying to pull an Airstream travel trailer with a riding lawnmower.
You wouldn't believe the blunder that Sony made with their top of the line radios--lots of extra effort for a terrible audio section, when all it really needed was an op amp.
These extremes are why my best guess is to just whip up a quickie op amp based preamp and see if there is a rather obvious improvement for that one "too quiet" source.
Its very cheap, its kind of fun, and it will probably work.
This is how I have it set up. I was really trying to avoid adding anything between the source and the amp, but I don't really want to use the ipod as my source full time either. I feel that there is just too much variation in source quality with mp3's.
I guess I may remove the pots and add a preamp like you suggest.
On the upside this has been a very fun project for me. I learned a lot. I had never even really soldered before. The sound from this amp is simply astonishing. It is so clear and clean at any volume compared to the Harmon kardon that i have been using.
My next step is creating a cozy home case for each mono channel. I have some interesting ideas.
Thanks for all the input and help guys.
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Are you saying that there should be a 4.7uf cap between the RCA and the pot? The only 4.7 cap i have seen in the design is the smoothing caps on the rectifier.
My wiring goes RCA to POT then pot center pin to input, pot 3rd pin to signal ground. is this wrong?
You have no dc protection for the input of your amplifier.
If a source outputs dc, speakers will fry.
For safety "dc blocker," usually the manufacturer will recommend a Blackgate "N" 4.7uF between the RCA Jack and the Potentiometer.
If you have complete control of all known sources, of course its possible to put the DC block cap on only the sources that output dc. This would involve checking all sources with a sensitive voltmeter before using them, and any failure to do so could cook speakers.
Its simply easier to install the dc block cap/ input filter cap. AudioSector and other places may stock the recommended model of capacitor for that particular amplifier. Other caps can work too.
I believe that Audiosector also has a transformer option as an interesting substitute for the DC block capacitor.
The buffer project at Decibel dungeon also incorporates dc block capacitors.
If a source outputs dc, speakers will fry.
For safety "dc blocker," usually the manufacturer will recommend a Blackgate "N" 4.7uF between the RCA Jack and the Potentiometer.
If you have complete control of all known sources, of course its possible to put the DC block cap on only the sources that output dc. This would involve checking all sources with a sensitive voltmeter before using them, and any failure to do so could cook speakers.
Its simply easier to install the dc block cap/ input filter cap. AudioSector and other places may stock the recommended model of capacitor for that particular amplifier. Other caps can work too.
I believe that Audiosector also has a transformer option as an interesting substitute for the DC block capacitor.
The buffer project at Decibel dungeon also incorporates dc block capacitors.
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Of course.
It either adds or subtracts.
Check with Audiosector for the exact model that is recommended for your amplifier, if you wish to avoid the expensive trial and error input filter cap sport.
I believe that Audiosector recommends a BlackGate "N" 4.7uF, I cannot remember the other details, and so check with Audiosector.
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