Capacitor questions

[FatFreddie]

Voltage should be pretty much irrelevant for an input capacitor unless your source has a massive DC offset. Making it a bit higher than the supply seems a reasonable start - the original may well be specified as 100v just because that's one of the more common voltage ranges for that type of capacitor - metallised polyester don't seem to go below 50v and 100v is more common than 63v which is the lowest common voltage in farnells list.

Definitely don't use an electrolytic. The article you linked to describes the choices pretty well - basically work out the value for the amount of bass attenuation you can live with and then go down the quality levels until you find something that will fit at an acceptable price.

[ptjw7uk]

I think that the reason they use the polyester type is to get a more uniform part.
The high voltage is just really an indication of the capacitors construction type in that the polyester has a high breakdown voltage.
You will have to trawl the catalogues to find the smallest physical size for that type of capacitor, if memory serves most of that type will be on the larger side!

peter

Try these quite small http://www.futurlec.com/Capacitors/C1000UPF.shtml

[Fivetide]

Thanks for the link I actually use this part on another project never thought of using it on this :) doh !

[HankMcSpank]

Slightly off topic (curiousity has got the better of me)...the schematic you posted shows a bipolar supply, so why are they using a virtual ground IC in the power supply section?

There are parts of your schematic cutoff from view so maybe that the bit of the puzzle I'm missing!

[Boscoe]

I work in one of the UKs best HiFi R&D departments so I could answer this one!

People think higher voltage elec. caps sound better as they are meant to be more linear with change in voltage on their plates. Film is the best to use in this application. Use a large ECHU capacitor perhaps use two 470nF in parallel rated at 10V or 16V is absolutely fine.

Slightly off topic (curiousity has got the better of me)...the schematic you posted shows a bipolar supply, so why are they using a virtual ground IC in the power supply section?

There are parts of your schematic cutoff from view so maybe that the bit of the puzzle I'm missing!

If you mean R3 and R4 they form the global closed loop feedback.

[Fivetide]

I work in one of the UKs best HiFi R&D departments so I could answer this one!

People think higher voltage elec. caps sound better as they are meant to be more linear with change in voltage on their plates. Film is the best to use in this application. Use a large ECHU capacitor perhaps use two 470nF in parallel rated at 10V or 16V is absolutely fine.



If you mean R3 and R4 they form the global closed loop feedback.

Thats awsome thanks for the advice Boscoe :) Do you think I can convert this to SMD ? As your the first real sound expert I've talked to. I've spent months trying to learn this stuff but i'm just scratching the surface, what i really need is a good CMoy design that I can use SMD parts on so I can get it small enough and cheap enough to shoehorn into a tabbaco tin with 2 x 9v batteries. Any ideas ? :) I wont lie, I intend to sell them, I need the money lol

[Boscoe]

Thats awsome thanks for the advice Boscoe :) Do you think I can convert this to SMD ? As your the first real sound expert I've talked to. I've spent months trying to learn this stuff but i'm just scratching the surface, what i really need is a good CMoy design that I can use SMD parts on so I can get it small enough and cheap enough to shoehorn into a tabbaco tin with 2 x 9v batteries. Any ideas ? :) I wont lie, I intend to sell them, I need the money lol

Sure it's quite easy to fit it all in with two 9V batteries. It will be a lot easier to do it all SMD just use the filters on Farnell to find your parts if the existing ones don't have an SM equivalent. But I don't understand in your first post why you would use two 9V in series then try and split them into two 9V rails again? If your worried about DC offest don't be - your op-amps will keep the output voltage to what you want irrespective of the rails (to a point). You can also use voltage regulators instead however you will loose precious voltage. Look at this guys amp he made, he uses the same technique as I mention earlier and the THD is not measurable.

"The Wire" Ultra-High Performance Headphone Amplifier - PCB's - diyAudio

[HankMcSpank]

Post deleted - I made an error!

[Boscoe]

Post deleted - I made an error!

Oh yes sorry I do mention this in my above post too.

[Boscoe]

Oh yes if you want to make an ultimate headphone amplifier use an LME49600 driven with a LME49990 with the 49600 in the 49990 feedback loop. Very simple similar to the one you post just much better.