Capacitor questions

I’m building a small cmoy amp and my goal is to reduce it to SMD parts only, now I have a friend who repairs various electronic equipment and I asked if I could replace it with a lower voltage. He said yes along at its higher than the highest voltage on the power rail, anything above plus 20% would be a waste.
So here’s my question in your opinion could I replace 1.0 µF 100V metallized polyester capacitor with EEE-FC1V1R0AR . Also why would he choose a 100v Cap on an 18v max rail?

All info I have tried to put in the attached picture including the circuit

Attachment 9283

From the creator of the amp at Tangentsoft :

C1 (film)
To understand the issues involved in deciding whether to add C1 or to put a jumper across this position, read my article Input Capacitors for Headphone Amps.
Many types of capacitors will fit here, up to 0.4" pin pitch. You will probably have to go with metallized polypropylene or polyester to fit a usefully high value cap here.
Optional? Yes, jumper across it.
Largest Part Size: 13mm × 6mm. Lead spacing 10mm.

I read the article but there was nothing about voltage

I don't think you can replace that capacitor with an electrolytic.
The original one is a pass through and will need to see currents in both directions.
I would tend to go with the designers schematic as I would assume he has done some form of testing.
Electrolytes are used to smooth dc.

Peter

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Originally Posted by ptjw7uk

I don't think you can replace that capacitor with an electrolytic.
The original one is a pass through and will need to see currents in both directions.
I would tend to go with the designers schematic as I would assume he has done some form of testing.
Electrolytes are used to smooth dc.

Peter

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Hi , thanks for the answer , do they do a pass through SMD replacement for the cap ? How would I search for the part, bit new to this sorry :)

Actuall I might just replace all the resistors with SMD and leave the rest as through hole I think I will have enough room in the end.

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.

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

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

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!

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.

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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!

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

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.

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Originally Posted by 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.



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

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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

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Originally Posted by Fivetide

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

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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

Post deleted - I made an error!

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Originally Posted by HankMcSpank

Post deleted - I made an error!

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

actually, no I'm still a little puzzled.

The schem shows two 9V batteries in series (connected back to back) then uses a rail splitter to provide a virtual ground (the mid point of the battery voltage) ....I'm curious why bother, why not just use signal ground which will always be pretty close to mid voltage anyway (yeah, sure the batteries might not fade with the same 'profile' but there won't be much in it to warrant the extra expense & component count of the virtual ground IC)

Edit: Actually the schem just shows a single 18V single battery! (but I'm assuming that will be implemented by 2 x 9V batteries?)

Yes that's basically what I say above!

Boscoe I did look at the "The Wire" ages ago , I never saw a schematic for it so never considered making one ,as for the TI headphone amp that looks amazing ! Link did you mean this one ? Because quite frankly TI have done all the hard work on the data sheet , might even buy the evaluation board ? Looking for schematic now :) thanks for the answer.

I mean really how simple does that look ? and 2 x 9v batteries to boot .. you are a star mate :)

Attachment 9302

I bought the board .. 1 left at Mouser so I got it .. hey i can always convert it to a headphone amp and for £48 quid ..not bad :)

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Originally Posted by Boscoe

Yes that's basically what I say above!

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I must have been typing when you posted that one - great minds think alike eh?! lol.....

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Originally Posted by Fivetide

Boscoe I did look at the "The Wire" ages ago , I never saw a schematic for it so never considered making one ,as for the TI headphone amp that looks amazing ! Link did you mean this one ? Because quite frankly TI have done all the hard work on the data sheet , might even buy the evaluation board ? Looking for schematic now :) thanks for the answer.

I mean really how simple does that look ? and 2 x 9v batteries to boot .. you are a star mate :)

Attachment 9302

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Don't worry about it! Happy to help.

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Originally Posted by Boscoe

Don't worry about it! Happy to help.

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No I mean it I lost hope at one point , but this is awesome, when I've got a working one I'll PM u and send one to you :)

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Originally Posted by Fivetide

No I mean it I lost hope at one point , but this is awesome, when I've got a working one I'll PM u and send one to you :)

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Fantastic thank you!

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Originally Posted by Fivetide

No I mean it I lost hope at one point , but this is awesome, when I've got a working one I'll PM u and send one to you :)

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If you need help on the layout or questions for anything else don't hesitate. I assume you will be doing your own PCBs, if so use eurocircuits or goldphoenix in china I've found they are the cheapest!

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Originally Posted by Boscoe

If you need help on the layout or questions for anything else don't hesitate. I assume you will be doing your own PCBs, if so use eurocircuits or goldphoenix in china I've found they are the cheapest!

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That’s really generous of you Boscoe, I won’t bug u about the tedious stuff but if I’m really stuck I will take you up on the offer. The electronics are not my first goal, but I want to know what I’m doing. I want to make mega cases for them out of wood plastic and metal (hence why this is a CNC forum and not DIY audio), I want people to be proud to own one of my amps or it’s for nothing. That’s why I want a good amp as the basis of the project then built some nice enclosures around it. I have the skills and the equipment to build some outlandish enclosures but I lack electronic skills to make the amp sadly ..

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Originally Posted by Fivetide

That’s really generous of you Boscoe, I won’t bug u about the tedious stuff but if I’m really stuck I will take you up on the offer. The electronics are not my first goal, but I want to know what I’m doing. I want to make mega cases for them out of wood plastic and metal (hence why this is a CNC forum and not DIY audio), I want people to be proud to own one of my amps or it’s for nothing. That’s why I want a good amp as the basis of the project then built some nice enclosures around it. I have the skills and the equipment to build some outlandish enclosures but I lack electronic skills to make the amp sadly ..

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That's some very good ethics for selling a product - ethics I share and wished a lot of companies would too. See I am the complete opposite! I have electronics knowledge to design and build products but nothing to build them with!

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Originally Posted by Boscoe

That's some very good ethics for selling a product - ethics I share and wished a lot of companies would too. See I am the complete opposite! I have electronics knowledge to design and build products but nothing to build them with!

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Then its good to meet you Boscoe :)

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Originally Posted by Fivetide

Then its good to meet you Boscoe :)

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Likewise!!