Basic capacitor theory question

Loquah · 5146

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Offline Loquah

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on: April 07, 2014, 06:54:34 PM
I have a portable amp which is designed for owner DIY modifications and was supplied with some alternate capacitors. The stock capacitors are a Wima 2.2uF and the provided alternates are Elna Tonerex 10uF.

My question is very basic so please forgive my lack of knowledge in this area. In theory, disregarding the different natures of the 2 capacitors, what would be the impact of changing decoupling capacitors from a 2.2uF capacitor to a 10uF capacitor?

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Offline Paul Birkeland

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Reply #1 on: April 07, 2014, 06:56:16 PM
What is this cap doing?  Is the amp a headphone amp? Power amp? Preamp? 

Is the cap at the output? Input? In the middle?

(Or is it a power supply cap?)

Paul "PB" Birkeland

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Offline Loquah

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Reply #2 on: April 07, 2014, 08:35:52 PM
What is this cap doing?  Is the amp a headphone amp? Power amp? Preamp? 

Is the cap at the output? Input? In the middle?

(Or is it a power supply cap?)

Sorry - should have stated all of that:

It's a portable headphone amp (Fiio E12DIY) and as far as I can tell from other people's comments, the caps in question are decoupling caps and are apparently used on the input.

I'm using this as a practical example to help me better understand the role of capacitors in an audio circuit so thanks for your patience and assistance.

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Offline Loquah

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Reply #3 on: April 07, 2014, 08:36:50 PM
Just clarifying the above: the caps are definitely coupling caps and apparently on the input.

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Offline Grainger49

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Reply #4 on: April 08, 2014, 02:01:38 AM
Coupling caps are used to block DC from one stage to another.  In the case of an input coupling cap it blocks DC from a source to the input stage. 

The voltage rating has to be high enough not to be damaged by incoming voltage.  This applies to the input stage and all other stages. 

The value, the number of microfarads, determines the lowest frequency that will be passed with out some roll off.

Of course, the different methods of making a coupling cap determines the flavoring of the cap, the tonal balance it imparts to the device it is used in.



Offline mcandmar

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Reply #5 on: April 08, 2014, 03:32:13 AM
In my limited knowledge and experience building opamp based amps 2.2uf is pretty much the norm for input or output DC filtering, however 4.7uf can sometimes bring a little more low end extension.  Anything above that is largely irrelevant, though it does seem the case where your better with a 10uf electrolytic than a 5uf, the reason i am not entirely sure.   And in extreme cases with hybrid tube/opamp circuits those caps can be 220-1000uf due to the high dc voltages you have to block, i believe the larger the cap the less DC leakage.

From a purely sonic point of view, WIMA or Roederstein poly caps would be my choice, looking at the physical size of that amp they will have to be the Polyester (MKS series)  rather than the Polypropylene (MKP Series).  Where space isnt a concern i would use real Poly film caps like you would use in a speaker crossover, or in the case of my Grado RA1 clone i used huge Russian PIO's at one stage before switching to Mundorfs.

For electrolytics Elna Silmic II would be my choice, though i have never tried the Tonex range.  2nd choice would be a tie between Panasonic FM or Nichicon Gold Tune.  Personally i try to avoid lytics in the signal path at all costs, the WIMA's are a better solution IMO.

M.McCandless


Offline Loquah

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Reply #6 on: April 08, 2014, 11:48:18 AM
 Thanks Grainger and Mark. Very helpful!!

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Offline mcandmar

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Reply #7 on: April 18, 2014, 04:21:01 AM
I'm curious, how are you getting on with this?

All this talk got me thinking about my own portable rig and how i should really treat it to a pair of nice output caps so i replaced the Panasonic FM's with Elna Silmic II.  I always preferred Elnas but having made the change last night and listened to the amp all day it has only reinforced that opinion, i'm actually surprised how much more transparent they are, this little amp has never sounded so good :D

If only i could squeeze a few poly caps in there, unfortunately in this application they have to block ~9v DC so i dont think a few uF is going to cut it.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fcdn.head-fi.org%2F3%2F38%2F900x900px-LL-380ae3d5_IMG_6857.jpeg&hash=7fb42e8997c8877759fd08d9dcc274cb91d19675)

M.McCandless


Offline Loquah

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Reply #8 on: April 19, 2014, 02:27:52 AM
I'm curious, how are you getting on with this?

All this talk got me thinking about my own portable rig and how i should really treat it to a pair of nice output caps so i replaced the Panasonic FM's with Elna Silmic II.  I always preferred Elnas but having made the change last night and listened to the amp all day it has only reinforced that opinion, i'm actually surprised how much more transparent they are, this little amp has never sounded so good :D

If only i could squeeze a few poly caps in there, unfortunately in this application they have to block ~9v DC so i dont think a few uF is going to cut it.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fcdn.head-fi.org%2F3%2F38%2F900x900px-LL-380ae3d5_IMG_6857.jpeg&hash=7fb42e8997c8877759fd08d9dcc274cb91d19675)

Nice pic!

I've not done anything with mine yet because it's a small space and already has some good Wima caps installed. I may yet get brave / inspired after I upgrade the caps in my SEX once they get here...

Which op amp are you running there? Is it a tube pre and SS output or vice versa?

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Offline mcandmar

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Reply #9 on: April 19, 2014, 10:10:24 AM
Yes exactly, tube amp then opamp output. Currently i'm using a 6021wa mil spec GE tube with an LM4562 opamp. Its precise and detailed but with a magic mid range only a tube can give, i think it sounds absolutely wonderful, and it cost peanuts.

M.McCandless


Offline Loquah

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Reply #10 on: April 20, 2014, 04:13:13 PM
Yes exactly, tube amp then opamp output. Currently i'm using a 6021wa mil spec GE tube with an LM4562 opamp. Its precise and detailed but with a magic mid range only a tube can give, i think it sounds absolutely wonderful, and it cost peanuts.

Beautiful!

Ever tried the NJM5532 op amp? I had it recommended recently and it's a real bargain at about $1 - $1.50 a pop! I haven't directly compared it to my LM4562 yet, but would say it's on par with the LM4562. Probably slightly less dynamic, but more transparent and neutral sounding - really nice!

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Offline mcandmar

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Reply #11 on: April 20, 2014, 04:52:00 PM
Yes and no. The Texas Instruments NE5532 was used in just about everything since the 1980s as it was THE standard for low noise audio opamps, the NJM is a JRC copy.  JRC make a lot of good quality opamps, for example the Objective2 amplifier uses JRC opamps exclusively, x2 NJM4456, x1 NJM2068 and a NJM2903, reason being they are decent quality and cost less than $1 each.

I would take a genuine NE5532 over an NJM any day, and oddly the TI is $1.10 vs $1.28 for the JRC on Mouser, go figure.

Having said that i always bin the 5532's and replace them with the LM4562 lol.   The 4562 was the first opamp to dethrone the 5532 as the gold standard and outperforms it in many areas, specifically being a much faster opamp.  It is a direct replacement in 90% of cases unless the amp PCB is lacking decoupling capacitors, and it is perfectly happy working in unity gain (i.e. 1x). This tube amp was originally a 5532 based unit which i swapped out for the 4562, and note the two bypass caps i had to add as the original amp didn't have any ::)  Only catch is its more expensive, $3.48 on Mouser.

Sonically i find the 5532 a little brittle, where as the 4562 has a little more meat to the bones if you like. Being a faster opamp i find tends to show up with better clarity and resolution. The 5532 is leaner sounding, and a little too metallic for my tastes.  Interestingly thats the exact same problem i have with the stock Objective2, despite what all the fanboys say it just sounds dull and lifeless to me. It may appear as more transparent at first but i would be curious to see what you think given time, i'm going to wager you will go back to the 4562 :P

The only other opamps in the same league are the Burr Brown OPA range but personally i find them a little too warm and artificial.  Commonly people rave about them and say "the bass is amazing!" which says it all to me, ideally you shouldnt be listening to the opamp at all.  I prefer to let the tubes do the talking :)
« Last Edit: April 20, 2014, 04:54:43 PM by mcandmar »

M.McCandless


Offline Loquah

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Reply #12 on: April 20, 2014, 05:07:45 PM
Interesting. Now I'm really keen to compare the 4562, 5532 and OPA2107 that I have.

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Offline Loquah

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Reply #13 on: April 20, 2014, 05:13:21 PM
PS I think OPA1611/1612 is my current, reasonable cost favourite, but they're SMD, not DIP-8

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Offline mcandmar

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Reply #14 on: April 20, 2014, 05:17:11 PM
Yeah the SMD is a faff alright. I have a bunch of converters on order to try the LME49990's in the O2, and OPA827's in a DIY DAC project i'm tinkering with but i may try them in this amp too out of curiosity.

M.McCandless