samsagaz said:
Never tried those as they were not generally available from the usual distributors, when I was developing minimized GC circuit.
From spec sheet, they look basically the same as MK132, just smaller. Could be a difference in sound, but if any, it will be rather subtle.
BTW, in a GC input shunt and feedback position MK132 were the best resistors I could find, better than Caddock TF020 or Vishays S102.
Just to show you the possibilities with implementation of those kits, here's a custom 4 channel amp that will be used in an active system.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Peter,
I've looked through this thread and can't quite answer my own question. I have my rectifier board wired to my transformer as you instructed me earlier. I'm getting 37.8 VDC between V+ and PG+ and the same on the negative side. Is that OK?
Secondly, since I'm only using one rectifier board do I just run the two amp boards off the rectifier board in parallel?
Thanks again for all your guidance.
Mike
I've looked through this thread and can't quite answer my own question. I have my rectifier board wired to my transformer as you instructed me earlier. I'm getting 37.8 VDC between V+ and PG+ and the same on the negative side. Is that OK?
Secondly, since I'm only using one rectifier board do I just run the two amp boards off the rectifier board in parallel?
Thanks again for all your guidance.
Mike
If you measure between V- and PG- you should be getting -37.8V. Everything else is correct.
An example for your second question can be found here: http://www.diyaudio.com/forums/attachment.php?s=&postid=1539936&stamp=1213593687
An example for your second question can be found here: http://www.diyaudio.com/forums/attachment.php?s=&postid=1539936&stamp=1213593687
Wood or metal case?
I'm finishing up my first Audiosector chipamp. Does it make a difference if I use a metal case or a wood case, other than obvious safety issues
? It seems I read somewhere that these kits should be put in a metal case.
I have a Velleman kit I built and have it in a wood (cigar box) case and it woorks fine.
Any ideas or suggestions or greatly appreciated!
Mike
I'm finishing up my first Audiosector chipamp. Does it make a difference if I use a metal case or a wood case, other than obvious safety issues
? It seems I read somewhere that these kits should be put in a metal case.I have a Velleman kit I built and have it in a wood (cigar box) case and it woorks fine.
Any ideas or suggestions or greatly appreciated!
Mike
A metal case provides shielding and heat dissipation. In many locations shielding is not critical and heat dissipation can be taken care by heatsinks. So a wooden case is certainly possible, here couple examples:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=19816&highlight=
http://www.mother-of-tone.com/index.htm
http://www.diyaudio.com/forums/showthread.php?s=&threadid=19816&highlight=
http://www.mother-of-tone.com/index.htm
Rarely I do see smoke when testing newly built equipment but today it was not a case. The amp pictured few posts earlier had a series connection problem where each secondary was powering both positive and negative rail bridges, which obviously couldn't work, even though making for a very elegant layout. Now you know why I promote single rectifier boards when using single transformer In this case though, I wanted to separate multiple filter caps with bridges.
Here how it should be wired correctly
In this case though, I wanted to separate multiple filter caps with bridges. Here how it should be wired correctly An externally hosted image should be here but it was not working when we last tested it.
Finished my First 3875!!!
I just finished my first AudioSector chip-amp. It's playing music as I type this. Sounds great so far.
One question...with no music playing and the volume up a little I get a very slight background noise, almost a hum. It goes up and down with the volume. I did the star ground as Peter advised. When I touch the RCA connectors, one or both, the noise goes away. I don't have the RCA's mounted yet, as I only have everything on a 12" X 12" board since I just finished assembling it. Any ideas?
I'm looking forward to getting this kit in a box/cabinet. I'll post some pics once I have it mounted.
Thanks for your quick answers on all my questions Peter. This is a great thread, project, hobby!
Mike
I just finished my first AudioSector chip-amp. It's playing music as I type this. Sounds great so far.
One question...with no music playing and the volume up a little I get a very slight background noise, almost a hum. It goes up and down with the volume. I did the star ground as Peter advised. When I touch the RCA connectors, one or both, the noise goes away. I don't have the RCA's mounted yet, as I only have everything on a 12" X 12" board since I just finished assembling it. Any ideas?
I'm looking forward to getting this kit in a box/cabinet. I'll post some pics once I have it mounted.
Thanks for your quick answers on all my questions Peter. This is a great thread, project, hobby!
Mike
Hi All
I'm in the final stages and have a couple of questions:
RLED/R3 - According to Ohms Law, if I figure the supply voltage to be 25v, my green LED to have a voltage of 2.1v (a guess) and I want to supply it with 15ma, then a suitable value for RLED would be 1.5K ohm?
CHG and the earth from the mains IEC get connected together at a star ground, for instance one of the bolts holding the IEC to the chassis plate?
Many thanks in advance
Matt
I'm in the final stages and have a couple of questions:
RLED/R3 - According to Ohms Law, if I figure the supply voltage to be 25v, my green LED to have a voltage of 2.1v (a guess) and I want to supply it with 15ma, then a suitable value for RLED would be 1.5K ohm?
CHG and the earth from the mains IEC get connected together at a star ground, for instance one of the bolts holding the IEC to the chassis plate?
Many thanks in advance
Matt
Re: Finished my First 3875!!!
I usually prefer the LED to be less bright, and adjust it for brigtness in a circuit. Although your calculations look OK, 1k5 seem to be a bit on a low side. I would start with 20K or so and then adjust.
IEC ground connects directly to the chassis. CHG connects to chassis as well, but the star ground is not there: it's at the amp boards: http://www.diyaudio.com/forums/showthread.php?postid=1518369#post1518369
When the hum goes up and down with volume it could indicate that it's generated by a source. Even without chassis, touching RCAs should not be affecting anything. Check the link above, it shows proven way to connect grounds.
I usually prefer the LED to be less bright, and adjust it for brigtness in a circuit. Although your calculations look OK, 1k5 seem to be a bit on a low side. I would start with 20K or so and then adjust.
IEC ground connects directly to the chassis. CHG connects to chassis as well, but the star ground is not there: it's at the amp boards: http://www.diyaudio.com/forums/showthread.php?postid=1518369#post1518369
mikje said:
When the hum goes up and down with volume it could indicate that it's generated by a source. Even without chassis, touching RCAs should not be affecting anything. Check the link above, it shows proven way to connect grounds.
Hi Peter
Thanks for your reply. I have built the amps up as dual mono - connecting PG+ and - and V+ and - exactly as shown in post #31. Other than to ground the earth from the IEC to the chassis, there seems no need for any further connections.
CHG is connected to the chassis via the pcb to SG to the ground side of the input jack, so no need for separate connection.
Please could you confirm this as I'm going to try powering them up
Cheers
Matt
Thanks for your reply. I have built the amps up as dual mono - connecting PG+ and - and V+ and - exactly as shown in post #31. Other than to ground the earth from the IEC to the chassis, there seems no need for any further connections.
CHG is connected to the chassis via the pcb to SG to the ground side of the input jack, so no need for separate connection.
Please could you confirm this as I'm going to try powering them up
Cheers
Matt
Hi Peter
I've tested one mono block. The voltage at v- and v+ is approx 29v and 33v. DC offset is around 6mv.
This seems quite a bit different from your measurements. The heatsink gets hot quickly with no load attached. The transformer is a nuvotem 230v - 2x 25v.
Would the bigger trafo account for the readings I get, or do I need to look at my soldering? I'm thinking with a load attached, I won't get anywhere near the heat in the chip?
Thanks
Matt
I've tested one mono block. The voltage at v- and v+ is approx 29v and 33v. DC offset is around 6mv.
This seems quite a bit different from your measurements. The heatsink gets hot quickly with no load attached. The transformer is a nuvotem 230v - 2x 25v.
Would the bigger trafo account for the readings I get, or do I need to look at my soldering? I'm thinking with a load attached, I won't get anywhere near the heat in the chip?
Thanks
Matt
Hi,
This is my first soldering experience and finally, after purchasing some months ago an lm3875 kit from audiosector for my "reference" amp and an lm1875 kit from chipamp for my computer amp, I am now ready for the first test (the lm1875 amp, it is cheaper, so let's destroy it first).
The lm1875 is in stereo version.
The amp is now placed on a plywood panel for testing. The heatsink is a piece of copper 1cm thick. A first question: should I connect the power supply ground to the main AC earth?
The power supply seems to work fine: I measure 25VDC as should be with a transformer of 18VAC and the lightbulb tester lights up just for a while when I switch on.
I only connected the amps and I measured between out and ground out 20mV in one channel and 30mV in the other one.
Then I added a 50K pot and the RCA inputs and now I measure at amp outs -10mV and -15mV when volume is at minimum and +10mV and +15mV when volume is at maximum.
Can I connect the testing loudspeakers and a source?
Thank you for your help
Renato
This is my first soldering experience and finally, after purchasing some months ago an lm3875 kit from audiosector for my "reference" amp and an lm1875 kit from chipamp for my computer amp, I am now ready for the first test (the lm1875 amp, it is cheaper, so let's destroy it first).
The lm1875 is in stereo version.
The amp is now placed on a plywood panel for testing. The heatsink is a piece of copper 1cm thick. A first question: should I connect the power supply ground to the main AC earth?
The power supply seems to work fine: I measure 25VDC as should be with a transformer of 18VAC and the lightbulb tester lights up just for a while when I switch on.
I only connected the amps and I measured between out and ground out 20mV in one channel and 30mV in the other one.
Then I added a 50K pot and the RCA inputs and now I measure at amp outs -10mV and -15mV when volume is at minimum and +10mV and +15mV when volume is at maximum.
Can I connect the testing loudspeakers and a source?
Thank you for your help
Renato