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Old 15th May 2014, 08:25 AM   #1
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Default DC coupled line preamp kit

Hi, i was reading a coupling capacitors shoot-out ... and i was getting mad
The prices of the good ones are unbelievably high. Like 100 USD/each
And of course the differences in sound with the cheap ones are huge.
Moreover, after reading about the high impact of different caps on sound i wonder now if an AC coupled line preamp has any chance to be truly transparent.
Therefore I am asking if anyone is aware of kits for a line preamp DC coupled.
Even op-amp based ones will be fine (no prejudices about opamps here).
Thanks a lot and kind regards, gino

Last edited by ginetto61; 15th May 2014 at 08:38 AM.
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Old 15th May 2014, 09:51 AM   #2
knutn is offline knutn  Norway
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A good 10 uF Polypropylene capacitor you can by for about 4 Euros, it is not that expensive.
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Old 15th May 2014, 10:28 AM   #3
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Originally Posted by knutn View Post
A good 10 uF Polypropylene capacitor you can by for about 4 Euros, it is not that expensive.
Hi, thanks for the reply and that is what i thought ... prior to reading the shoot-out comparison.
From what i read a minimum to get good sound is something like Mundorf Mcap Supreme, and that is not cheap.
And this was at xover level, where signal is more robust than at line level.
Therefore if there is a kit around that can do without coupling caps that would be very nice.
Maybe the writer was exaggerating the differences, but still i am umcomfortable now.
And i see that very best solid state line preamps come all dc coupled ... there must be a reason i guess.
Thanks again and kind regards, gino

P.S. i hate valves

Last edited by ginetto61; 15th May 2014 at 10:31 AM.
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Old 15th May 2014, 10:32 AM   #4
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There is a big difference in the impact of a capacitor used as a filter in the normal audio passband, to one used for AC coupling and out of the normal audio passband. You do not need crazy caps for AC coupling, don't believe the hype and often non-blind-tested claims!
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Old 15th May 2014, 11:02 AM   #5
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Originally Posted by richie00boy View Post
There is a big difference in the impact of a capacitor used as a filter in the normal audio passband, to one used for AC coupling and out of the normal audio passband.
You do not need crazy caps for AC coupling, don't believe the hype and often non-blind-tested claims!
Thanks for the reply and please let me elaborate a little.
When i see the number of comments on the Blowtorch preamp i guess that this preamp is really something of special, with a very fine sound, and provokes an immense interest about its design/construction.
Given that this is a very good preamp indeed, i see that luckily is solid state (no more tubes ever in my system) and dc coupled (i assume this; if i am wrong i would like to know which coupling caps are used).
So no signal caps is the best. That is clear.
Having to use caps the question is which are the most transparent around.
I have already an ac coupled preamp.
The former owner told me that he has replaced the original caps with better ones and with the result of a remakable improvement in the sound.
We say in Italy that appetite comes eating ...
Personally i would be much more comfortable with a Blowtorch preamp ... if it were not above my current budget.
But also a kit with a dc offset nulling circuit would be just fine ... just to try.
Thanks a lot and kind regards, gino

Last edited by ginetto61; 15th May 2014 at 11:06 AM.
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Old 15th May 2014, 01:24 PM   #6
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Also think about the fact that a huge majority of commercial amps have a cheap electrolytic at the input anyway, what is there to gain by using some wildly expensive capacitors for the preamp.
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Old 15th May 2014, 01:37 PM   #7
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Also think about the fact that a huge majority of commercial amps have a cheap electrolytic at the input anyway, what is there to gain by using some wildly expensive capacitors for the preamp.
Hi actually you are very right and i agree completely
So ANY let's say decent PP would do just fine ?
or there are some brands with a very nice quality/price ratio ?
I need four 4.7 uF nice caps ... preferably not very big
Thanks and regards, gino

P.S. i have also found something

http://www.mil-media.com/preamps.html

Quote:
Ultimately, carefully selected capacitive coupling was found most accurate for both front end and interstage coupling.
So this careful selection looks the key to satisfaction ...

Last edited by ginetto61; 15th May 2014 at 01:53 PM.
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Old 15th May 2014, 07:13 PM   #8
DF96 is offline DF96  England
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Quote:
Originally Posted by ginetto61
And of course the differences in sound with the cheap ones are huge.
Are they?
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Old 15th May 2014, 07:46 PM   #9
dmills is offline dmills  United Kingdom
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Indeed, audiability of a line level coupling cap (if it is even remotely suitable for the purpose) would be something of a surprise to me, filter caps are of course a different thing....

Lots of assertions about caps out there, very little good data (Self and Cordell have both done some work, but it is more applicable to filters then coupling IMHO).

Regards, Dan.
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Old 15th May 2014, 08:14 PM   #10
dadod is offline dadod  Croatia
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Quote:
Originally Posted by ginetto61 View Post
Hi, i was reading a coupling capacitors shoot-out ... and i was getting mad
The prices of the good ones are unbelievably high. Like 100 USD/each
And of course the differences in sound with the cheap ones are huge.
Moreover, after reading about the high impact of different caps on sound i wonder now if an AC coupled line preamp has any chance to be truly transparent.
Therefore I am asking if anyone is aware of kits for a line preamp DC coupled.
Even op-amp based ones will be fine (no prejudices about opamps here).
Thanks a lot and kind regards, gino
Maybe you can try this one? No NFB line amp (GainWire mk2)
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