JCX,
the capacitor tests for distortion applied a heavy filtering action to the capacitors. They needed a high AC voltage across the capacitor to be able to measure the distortions when in filtering mode.
If there is no AC voltage across the capacitor, then there can be no added distortion to that zero signal.
the capacitor tests for distortion applied a heavy filtering action to the capacitors. They needed a high AC voltage across the capacitor to be able to measure the distortions when in filtering mode.
If there is no AC voltage across the capacitor, then there can be no added distortion to that zero signal.
As long as the capacitor has an impedance and an AC current flowing through it, there'll be a voltage across it. Ohm's law and that...
You're right, though, that if the cap has very little voltage across it relative to the signal voltage, it would follow that any THD contribution from the cap would also be small.
Tom
You're right, though, that if the cap has very little voltage across it relative to the signal voltage, it would follow that any THD contribution from the cap would also be small.
Tom
So I followed the advice of some of the very active members of this board and finally bought all the components to build a lm3886dr stereo amp with a smps86 power supply. I have to thank Tom who has already been very helpful with some of the newbie questions I had.
This being my first project of this kind I have tons of other question so I'd be happy if you could share your knowledge with me.
Currently I am thinking of which heat sink and which case to use. I'd like to use one of the smaller cases from modushop / hifi 2000 .... just because I like the looks of the smaller enclosures I guess really .... so that's the one I'd like to get:
https://www.modushop.biz/site/index.php?route=product/product&path=67_194_190&product_id=562
Now it seems it will be a bit of a challenge to fit everything in there. I'm thinking of mounting both LM3886 chips to one heat sink that is rated at 0.5 k/w. I'm attaching a sketch of the setup I have in mind and I'd greatly appreciate to hear feedback from the more experienced builders.
of course I'd also have to fit all the cables and an alps pot in there as well .... but thats for the next post ....
so what do other people think ... would this setup make sense?
This being my first project of this kind I have tons of other question so I'd be happy if you could share your knowledge with me.
Currently I am thinking of which heat sink and which case to use. I'd like to use one of the smaller cases from modushop / hifi 2000 .... just because I like the looks of the smaller enclosures I guess really .... so that's the one I'd like to get:
https://www.modushop.biz/site/index.php?route=product/product&path=67_194_190&product_id=562
Now it seems it will be a bit of a challenge to fit everything in there. I'm thinking of mounting both LM3886 chips to one heat sink that is rated at 0.5 k/w. I'm attaching a sketch of the setup I have in mind and I'd greatly appreciate to hear feedback from the more experienced builders.
of course I'd also have to fit all the cables and an alps pot in there as well .... but thats for the next post ....
so what do other people think ... would this setup make sense?
What will be dimensions of heat sink? It's been a while since I've shopped them, but my instinct says 0.5 k/w might be too tall (long) to fit in the chassis.
Think about how (where) you will route wires. Where will input and speaker terminals be, and where will you mount volume pot.
You're in the right track drawing this out in advance. You'll be able to have a nice and clean layout.
Think about how (where) you will route wires. Where will input and speaker terminals be, and where will you mount volume pot.
You're in the right track drawing this out in advance. You'll be able to have a nice and clean layout.
I've built three amps using the LM3886. One is a stereo amp connected to the TV and separate speakers. Another an amp with microphone input (sort of a PA system).
My grandson and I built a 50 Watt guitar amp using a kit preamp and LM power amp.
Specs on this chip are terrific. And it's easy to use.
My grandson and I built a 50 Watt guitar amp using a kit preamp and LM power amp.
Specs on this chip are terrific. And it's easy to use.
I'd like to order some cables for the internal wiring of the amp. I need cables to run from the RCA Input to the pot and from there to the LM3886DR. The manual recommends to use shielded cable but I really have no idea which ones to get. I don't even know whether to look for balanced or unbalanced..... can anyone point me in the right direction?
since you recommend a balanced cable i guess that's the answer regarding my question of balanced vs. unbalanced. 
for some reason i thought RCA inputs would always use unbalanced cables ....
thanks for recommending the cables and for suggesting which are easiest to source in the EU.
the cable you recommended has 3 leads ... i guess thats left / right / ground. i believe i would need a shielded cable with only two leads (signal / ground) as i am using one lm3886dr amp for each channel. which cable would be the right one in this case?
for some reason i thought RCA inputs would always use unbalanced cables ....
thanks for recommending the cables and for suggesting which are easiest to source in the EU.
the cable you recommended has 3 leads ... i guess thats left / right / ground. i believe i would need a shielded cable with only two leads (signal / ground) as i am using one lm3886dr amp for each channel. which cable would be the right one in this case?
Would it not also make sense to use a cable like this:
Mogami W2319 | Redco Audio
Use the center lead for signal and the shield for ground? ...and have the benefit of having fewer leads to twist and braid and less cluttered space around the pot?
Thanks!
Michi
Mogami W2319 | Redco Audio
Use the center lead for signal and the shield for ground? ...and have the benefit of having fewer leads to twist and braid and less cluttered space around the pot?
Thanks!
Michi
That would work. You could also use microphone cable. Use one conductor for the centre conductor, the other for the shield. Terminate the cable shield at one end (the transmitting end). That would be your standard "audiophile" interconnect cable setup. Just add directional arrows...
You'll probably get better performance if you use one conductor for the shield connection and connect the shield at both ends as that reduces the ground impedance. Of course then the cable won't be audiophile approved as it won't have the directional arrow.
The W2319 you link to above would make sense for the wiring inside the chassis. Use the centre conductor to carry the signal and the shield to carry the ground.
Tom
You'll probably get better performance if you use one conductor for the shield connection and connect the shield at both ends as that reduces the ground impedance. Of course then the cable won't be audiophile approved as it won't have the directional arrow.
The W2319 you link to above would make sense for the wiring inside the chassis. Use the centre conductor to carry the signal and the shield to carry the ground.
Tom
Last edited:
You'll probably get better performance if you use one conductor for the shield connection and connect the shield at both ends as that reduces the ground impedance. Of course then the cable won't be audiophile approved as it won't have the directional arrow.
That's what I'm using with my Modulus-86... but oh, forgot to paint the directional arrows!
I once bought the "Mystery Box" (I think it's called) from Redco.
I ended up with a nice variety of microphone cable to put XLR ends on. They throw in the ends of rolls of expensive cable too. The short pieces are perfect for wiring inside the amp chassis.
I always "liked to believe" the amp sounded better, because I was using expensive cable,... but darn it, I just realized that I forgot to draw arrows. No worry, I can make a nice template of an arrow with a stencil, I'll cut an arrow shape out of a piece of heat-shrink-tube. Once I put those arrows on, I know I'll get that improved sound quality!
I ended up with a nice variety of microphone cable to put XLR ends on. They throw in the ends of rolls of expensive cable too. The short pieces are perfect for wiring inside the amp chassis.
I always "liked to believe" the amp sounded better, because I was using expensive cable,... but darn it, I just realized that I forgot to draw arrows. No worry, I can make a nice template of an arrow with a stencil, I'll cut an arrow shape out of a piece of heat-shrink-tube. Once I put those arrows on, I know I'll get that improved sound quality!