I build the T300 also but, I did not take pictures 😱 .
They do not look so neat but they sounded very good. it was from good to better!!!. My last one the M400 is a keeper. The M400 replaced my Bryston B60!😀
They do not look so neat but they sounded very good. it was from good to better!!!. My last one the M400 is a keeper. The M400 replaced my Bryston B60!😀
Very cool stuff lanchile! Thanks for sharing photos, (and advice).
Are they all integrated? Ever think of building a pre-amp? I may look to a preamp for a next project, but that probably won't be till next year. I have another project on the bench already. Some speakers i need to finish. I think they are more efficient than what i have now, so should compliment LM3875 nicely.
Signing off for the night.
Cheers!
AlexQS
There are a lot of passive integrated amplifiers like: Portal Panache, Acurus Dia-100, Adcom GCA 510 etc.. I had them and I loved the sound. I find it simple and good.😉
It works, with a little buzz
I have both channels up and running.
I used test-lightbulb cord I have, powered it up. Now that the amp is connected to power supply, the light would flash once as I turned the power switch on the amp, then no light.
I read the voltage at v+ and pg+ & v- and pg- (on the amp thistime) dropped a little to 35.8 I think (didn't write it down) but I remember yesterday I read the power supply at 37.2 before amp was connected. I'm guessing this is normal.
Next I read speaker jacks, with no load on the amp, 84 milivolts on one and 76 millivolts on the other amp (not sure why they're different)
I don't have any sinewave tools or anything, so next I connected an 8 Ohm test-speaker, and used my iPod for a source. With my ear near the speaker the amp was dead quiet, and I only listened to one channel at a time, but it sounded good.
Next I took it over to my receiver, connected the preamp out, and main speaker to each amp. Power on, and a little buzz. The buzz does not seem to get any louder when volume is increased. I turned everything off and switched back to iPod for source. Buzz continues (maybe not quite as loud)
I'm tired now, you'll have to wait till tomorrow for pictures.
I guess I should trade the cord for the one with the test light, and see if that's the condition that makes the buzz go away, if so what does that mean?
The buzz reminds me of live-band pa or guitar stuff I've heard before, not too loud though. Also either it is getting quieter, or I'm getting used to it. It seems to diss appear behind the music if I turn it up a little and distance my ear from the speaker, but it's there and will drive me crazy if I don't fix it.
I connected it back to receiver's preamp. Despite this soft buzz, i love the way it sounds!! Sound stage seems MUCH bigger, wider. I listened to some Dianna Krawl, way more detail than I had before. Things like the "k" sound at the end of word "look" when she sings or the "s" at the begening of a word comes through in a way that seems a little closer to her being in the room with me. It's truly a great sounding amp, comparing well with my memories of some very expensive highend stuff I have heard!! I am very pleased, just want to fix the buzz now.
I did notice that I also hear buzz sound in center channel, which is not driven by LM3875, but also isn't even on. I always playback 2 channel recordings in stereo. I only use 5 channel on movies or tv.
Does that mean input coupling cap? I have a 4.7uF installed, paid 9 cents for it. I couldn't get the nicer quality cap I wanted. (unavailable, so I'd need a diff vendor)
Could it be a ground loop problem? I have a 1inch 14awg solid copper wire soldered to the board on the bottom side of speaker ground. Other end of that is screwed to the Heatsink. PG +\- both have traces soldered to the middle of that wire. Chassis is earthed. Do I need the 10r resistor between star ground and chassis?
Thanks if you have any ideas, or can suggest any tests I should do. I only have a cheap multimeter though.
Also, can I listen to it as is, or could it damage amp by playing it when it buzzes? I hoped the buzz would just go away while the amp burns in, LOL -doubt it could be that easy though.
AlexQS
I have both channels up and running.
I used test-lightbulb cord I have, powered it up. Now that the amp is connected to power supply, the light would flash once as I turned the power switch on the amp, then no light.
I read the voltage at v+ and pg+ & v- and pg- (on the amp thistime) dropped a little to 35.8 I think (didn't write it down) but I remember yesterday I read the power supply at 37.2 before amp was connected. I'm guessing this is normal.
Next I read speaker jacks, with no load on the amp, 84 milivolts on one and 76 millivolts on the other amp (not sure why they're different)
I don't have any sinewave tools or anything, so next I connected an 8 Ohm test-speaker, and used my iPod for a source. With my ear near the speaker the amp was dead quiet, and I only listened to one channel at a time, but it sounded good.
Next I took it over to my receiver, connected the preamp out, and main speaker to each amp. Power on, and a little buzz. The buzz does not seem to get any louder when volume is increased. I turned everything off and switched back to iPod for source. Buzz continues (maybe not quite as loud)
I'm tired now, you'll have to wait till tomorrow for pictures.
I guess I should trade the cord for the one with the test light, and see if that's the condition that makes the buzz go away, if so what does that mean?
The buzz reminds me of live-band pa or guitar stuff I've heard before, not too loud though. Also either it is getting quieter, or I'm getting used to it. It seems to diss appear behind the music if I turn it up a little and distance my ear from the speaker, but it's there and will drive me crazy if I don't fix it.
I connected it back to receiver's preamp. Despite this soft buzz, i love the way it sounds!! Sound stage seems MUCH bigger, wider. I listened to some Dianna Krawl, way more detail than I had before. Things like the "k" sound at the end of word "look" when she sings or the "s" at the begening of a word comes through in a way that seems a little closer to her being in the room with me. It's truly a great sounding amp, comparing well with my memories of some very expensive highend stuff I have heard!! I am very pleased, just want to fix the buzz now.
I did notice that I also hear buzz sound in center channel, which is not driven by LM3875, but also isn't even on. I always playback 2 channel recordings in stereo. I only use 5 channel on movies or tv.
Does that mean input coupling cap? I have a 4.7uF installed, paid 9 cents for it. I couldn't get the nicer quality cap I wanted. (unavailable, so I'd need a diff vendor)
Could it be a ground loop problem? I have a 1inch 14awg solid copper wire soldered to the board on the bottom side of speaker ground. Other end of that is screwed to the Heatsink. PG +\- both have traces soldered to the middle of that wire. Chassis is earthed. Do I need the 10r resistor between star ground and chassis?
Thanks if you have any ideas, or can suggest any tests I should do. I only have a cheap multimeter though.
Also, can I listen to it as is, or could it damage amp by playing it when it buzzes? I hoped the buzz would just go away while the amp burns in, LOL -doubt it could be that easy though.
AlexQS
Check my logic here
Hi guys,
Tell me if this makes sense. I have a theory of why I have a slight buzz. I don't think it is a ground loop problem, but please correct me if you think I'm wrong.
The theory is that the coupling capacitor that I put at input is a peice of junk, and not doing it's job, and the buzz sound I hear is a little DC coming from my preamp.
I say this because today I discovered that the buzz sound is only present when the RCA cable connects the amp to either my pre-amp or iPod. With the cable unpluged there is no buzz sound at the speaker.
Also, the reason I didn't hear the buzz last night with my "test speaker" is because they aren't efficient enough to play it. They are some very old Sanyo 3-way with 12" woofers that were given to me.
This is the crappy cap: 4.7uF 50V Radial Mini Electrolytic Capacitor 020-1204
One more thing: I think this also explains why the volume of the buzz seems to have decreased, it's because the cap is burning in a little
Hi guys,
Tell me if this makes sense. I have a theory of why I have a slight buzz. I don't think it is a ground loop problem, but please correct me if you think I'm wrong.
The theory is that the coupling capacitor that I put at input is a peice of junk, and not doing it's job, and the buzz sound I hear is a little DC coming from my preamp.
I say this because today I discovered that the buzz sound is only present when the RCA cable connects the amp to either my pre-amp or iPod. With the cable unpluged there is no buzz sound at the speaker.
Also, the reason I didn't hear the buzz last night with my "test speaker" is because they aren't efficient enough to play it. They are some very old Sanyo 3-way with 12" woofers that were given to me.
This is the crappy cap: 4.7uF 50V Radial Mini Electrolytic Capacitor 020-1204
One more thing: I think this also explains why the volume of the buzz seems to have decreased, it's because the cap is burning in a little
Last edited:
Here's some photos
This is what I did to ground the thing. The solid copper wire is soldered to the OG of speaker on underside of board. PG+ / PG- are soldered to that. It is screwed to the chassis. Did I do it right?
You'll see my earth line that goes to chassis. I moved it from the back side of the heat sink, to screw it to the front side with the same screw that holds the end of my star ground wire. No apparent change in sound.
Thanks in advance for any comments. If you would also suggest to change out the input cap, can you tell me which one to get, and where to get it from. I had read to get electrolytic, and later read that I should use polyprop cap.
AlexQS
This is what I did to ground the thing. The solid copper wire is soldered to the OG of speaker on underside of board. PG+ / PG- are soldered to that. It is screwed to the chassis. Did I do it right?
You'll see my earth line that goes to chassis. I moved it from the back side of the heat sink, to screw it to the front side with the same screw that holds the end of my star ground wire. No apparent change in sound.
Thanks in advance for any comments. If you would also suggest to change out the input cap, can you tell me which one to get, and where to get it from. I had read to get electrolytic, and later read that I should use polyprop cap.
AlexQS
Attachments
Not burning in.
The degraded dielectric is very gradually reforming as the AC & DC voltage across the electro is applied.
Instead. remove the electro and reform it properly until it achieves an in spec leakage current. Then put it back to work.
Or, throw the electro as far as you can and use a film cap as your DC blocking capacitor.
post27
I see no twisted pairs.
For every flow current there is an identical return current. That is what defines an electrical circuit.
Twist the flow and return pair to minimise loop area.
This reduces radiated interference. It also attenuates received interference.
I see no twisted pairs.
For every flow current there is an identical return current. That is what defines an electrical circuit.
Twist the flow and return pair to minimise loop area.
This reduces radiated interference. It also attenuates received interference.
Thanks AndrewT
"For every flow current, there is an identical return current"
Does this mean for V+ there should be an identical return PG+ ?
"Twist the flow and return area pair to minimise loop area"
Did I create a loop by having PG+ & PG- connect to BOTH the wire under the board coming from OG Speaker ground on the board AND the PG+ & PG- spots on the board? Is that what a "ground loop" is, when the ground comes through the board in two different places making a circle of the current? If that's it, I feel like a finally understand.
To ID wires in post 27, Purple and Blue are V+ and V-. White and Green and PG+ and PG-. So I should un-solder the White and Green from the board, and solder them only to the copper wire under the board, bringing the ground to ONE place, making the return current more identical to the flow current????
p.s. Does the sound of DC coming in through input, and the sound of Ground Loop problem sound the same?? I would describe this sound as what a guitar amp sounds like when there is no guitar plugged into the cord. It buzzes until the guitar is pluged in... my buzz isn't that loud, but that's the sound it makes.
Also... do I need to undo my sheethed wires that run from rectifier board to amp board, and twist blue and white together, and twist green and purple, so they will be twisted pairs of wires inside the sheethe??
I feel rather imature that I have blamed my problem on a bad capacitor. I only hear the buzz when a source is connected to the amp. (Without source connected there is no buzz in the speaker, does that have anything to do with wether or not we are talking about a ground problem here?)
I just know that ground problems seem to be common especially among us first time builders. I have tried a few different ways of grounding now. Results always the same.
Any suggestions appreciated. My thought is to try to rebuild the cord between amp board and powersupply board. (Does that seem like a good place to start?)
Also I feel that there should be some sort of testing that I should do, but I don't know what. I have a multimeter, but have only learned to measure DC offset at psu, and speakers. Shouldn't I be able to "proove" if I in fact have a ground problem, bad cap, etc. Again any suggestions appreciated.
-AlexQS
I just know that ground problems seem to be common especially among us first time builders. I have tried a few different ways of grounding now. Results always the same.
Any suggestions appreciated. My thought is to try to rebuild the cord between amp board and powersupply board. (Does that seem like a good place to start?)
Also I feel that there should be some sort of testing that I should do, but I don't know what. I have a multimeter, but have only learned to measure DC offset at psu, and speakers. Shouldn't I be able to "proove" if I in fact have a ground problem, bad cap, etc. Again any suggestions appreciated.
-AlexQS
This may be way off the mark, but check your environment for big noise sources. I have a pair of BrianGt mono-blocks that are completely silent everywhere except in the room that has a dimable halogen lamp. I can hear the buzz change in both amount and frequency as I turn the rheostat. The amps have a thin metal cover and the wires between the PS and amps boards are less than an inch long. A Hafler stereo amp with a much thicker enclosure in the same location doesn't respond to the lamp - despite the fact that there are many wires as long as 8" inside the Hafler.
Last edited:
Hi there
I'm relatively new to DIY amplifiers. I have just built a pair of LM3876T based mono amps and have been trying them out.
I get a buzz, much as you describe, and have found it only occurs when both left and right source are plugged in. If I unplug either the buzz goes away.
Having checked through the forum it appears to be a 'ground loop'. My setup is not finished yet so I have no disconneting network which is a possible cure.
I have no enclosure yet either so my set up is really imperfect but for the cause of the 'buzz' it may be relevant.
regards
Foo
I'm relatively new to DIY amplifiers. I have just built a pair of LM3876T based mono amps and have been trying them out.
I get a buzz, much as you describe, and have found it only occurs when both left and right source are plugged in. If I unplug either the buzz goes away.
Having checked through the forum it appears to be a 'ground loop'. My setup is not finished yet so I have no disconneting network which is a possible cure.
I have no enclosure yet either so my set up is really imperfect but for the cause of the 'buzz' it may be relevant.
regards
Foo
First Build
Hello there and greetings from Tasmania.
I am fascinated by this ground loop situation with the amp - as I too had a problem with another type of amp just recently. I simply could not get rid of the hum so I eventually recycled the components into another project. I have vowed to never use two transformers again - unless someone can show me a pair that don't hum!
There I go again - opening up another can of worms.
Can you tell me if you are using one transformer or two?
By the way, I love those big slabs of aluminium and I want to see you get this thing up and running so that I can find out how well they dissapate the heat.
The LM3875 datasheet has some excellent information for you - albeit a little on the technical side (for me anyway). For instance it states that the absolute max dissipation inside one amp is 125W or 250W for a pair. It also states that you will get a much improved THD+N performance by running it a bit cooler than that. Watts = Heat.
I have a pair of these amps that I am going to assemble soon, so I have a vested interest in getting to the bottom of these issues. I plan to build a stereo pair of the amps on the one board, using a single 160VA
0-18+0-18 transformer. I figure that the amps will be running at may-be 75% of their potential, BUT they will be running at perhaps 100% cooler & 200% cleaner. The 160VA transformer should be adequate for this job.
Keep up the good work.
Hello there and greetings from Tasmania.
I am fascinated by this ground loop situation with the amp - as I too had a problem with another type of amp just recently. I simply could not get rid of the hum so I eventually recycled the components into another project. I have vowed to never use two transformers again - unless someone can show me a pair that don't hum!
There I go again - opening up another can of worms.
Can you tell me if you are using one transformer or two?
By the way, I love those big slabs of aluminium and I want to see you get this thing up and running so that I can find out how well they dissapate the heat.
The LM3875 datasheet has some excellent information for you - albeit a little on the technical side (for me anyway). For instance it states that the absolute max dissipation inside one amp is 125W or 250W for a pair. It also states that you will get a much improved THD+N performance by running it a bit cooler than that. Watts = Heat.
I have a pair of these amps that I am going to assemble soon, so I have a vested interest in getting to the bottom of these issues. I plan to build a stereo pair of the amps on the one board, using a single 160VA
0-18+0-18 transformer. I figure that the amps will be running at may-be 75% of their potential, BUT they will be running at perhaps 100% cooler & 200% cleaner. The 160VA transformer should be adequate for this job.
Keep up the good work.
they cannot be mono amplifiers if they have R & L inputs.
That's where you grounding problems begin.
WOW! Excellent suggestion bcmbob.
When I first started using a test-speaker and iPod there was no buzz. When I moved the amp to the front of the room by the real front speakers, I began to have problems, so used an extention cord to see if it was the wall outlet. No change.
Just now I moved the amp back to that physical location of the test speaker, plugged in with the iPod again, no buzz. OMG YAY!!!!!😛
Went and got my big speaker, dragged it over there, no buzz. Even better!!!
Apparently it is the physical location of the amp, because when it was up-front even the iPod source would make it buzz.
I think it's time to clean up the spaghetti garbage I have going on behind my entertainment center. I'll move the components 1 by one to the location where it is operating without a buzz. Hopefully I can figure out which component causes problems.
A shocking revelation to me. Perhaps a proper case would be in order (ya think?!) I truely hope the problem is not placing the amp in the vacinity of my receiver... if that's it then I have no pre-amp anymore
Thanks to all posters here. I will report back with more details. I know someone wondered about heatsinks. I have (3 x 6 x 3/4 inch) metal-supermarket $10 ea. Someone else asked about stereo / mono. I have two identicle amplifiers, each with it's own transformer and power supply. I have been refering to one of the amps as left, and the other as right. They are on seperate chassis.
If it were someone less experienced, than yourself Andrew, I would explain it. I hope I have made it clear that the figures are a first-glace estimate of the power requirements. Please bear in mind that my post is leading to an issue that will become clearer at a later date provided the details on the transformer(s) is forthcoming.
In fact you could probably explain more succintly than I. so if you would like to make a comment on the power requirements for this project, feel free.
I have browsed the entire thread and no-one has bothered to quote the LM3875 datasheet which I would imagine is a good place to start - as it explains all the equations in detail with examples of power calculations for different scenarios.
Cheers and bye for now.
I know you guys like pictures, at least I do.
With speaker and amp in the middle of the room here (away from other electronics) the amp is dead quiet with my ear right next to the speaker.
With the amp and speaker on the floor right next to my TV Stand I have the problems.
I'm getting that cleaned up now!
By the way. I know it's not to difficult to beat my old amp, but this things blows it's doors off! These speakers were built by my Dad in the 1970's. Transmission-Line speakers aren't known for being efficient, and I thought that they might be a heavy load for LM3875 to perform at it's potential. I only have 10uF on each rail of power-supply, and the bass is so solid! Not overbearing, not boomy, still nice balance with mid & trebble,.... but the floor shakes now, and I don't have to turn up the volume as much to feel it! It would vibrate a little before, but this is a SOLID VIBRATION!! Solid is the word I'll use to describe the bass performance. -So happy!!
With speaker and amp in the middle of the room here (away from other electronics) the amp is dead quiet with my ear right next to the speaker.
With the amp and speaker on the floor right next to my TV Stand I have the problems.
I'm getting that cleaned up now!
By the way. I know it's not to difficult to beat my old amp, but this things blows it's doors off! These speakers were built by my Dad in the 1970's. Transmission-Line speakers aren't known for being efficient, and I thought that they might be a heavy load for LM3875 to perform at it's potential. I only have 10uF on each rail of power-supply, and the bass is so solid! Not overbearing, not boomy, still nice balance with mid & trebble,.... but the floor shakes now, and I don't have to turn up the volume as much to feel it! It would vibrate a little before, but this is a SOLID VIBRATION!! Solid is the word I'll use to describe the bass performance. -So happy!!
Attachments
Last edited:
- Status
- Not open for further replies.