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Old 15th July 2012, 05:05 PM   #1
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Default help needed dc coupling ,is there a better way?

I have a marantz cc4000ose that I have upgraded with a list of parts

caps
regulators
diodes
new laser
transformer sheild
mechanical dampening
ers tape

all of it is done and it works yay (not bad for a carpenter)

pics are here if you are interested

PROJECT OSE MARANTZ CC4000OSE pictures by GLENZWORLD - Photobucket

what I really want to know ...

Is there an alternative to running the signal directly through capacitors?

if you run the capacitor across the rails or I think you call it parallel, does that block dc?

right now the signal passes through or in series with 10uf from dac output then 47uf at opamp output

is there a better way to block dc without running signal through caps?

yes film is better and if it cannot be done without caps how do you calculate minimum size for that circuit?

would p spice do that for me?

thanks for any help for anyone with experience
Glen
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Old 16th July 2012, 03:42 AM   #2
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You can simply eliminate the caps on the opamp outputs, as there should be effectively zero dc offset there, assuming no faults. Can't avoid the caps on the dac outputs, so you just have to use the best combo of lytic & film you can fit.
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Old 16th July 2012, 11:45 PM   #3
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thanks again as you replied to another thread I wrote

ha and said the same

so from someone who is a layman it seem kinda silly to have dc at dac output

is that common?

if I place pos lead of voltmeter to pos side of cap and neg to neg, is that correct to test for dc before capacitor after opamp?

thinking wima poly after dac what size would you go with?

are direct coupled systems used in audio?
thanks
Glen
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Old 17th July 2012, 02:23 AM   #4
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Voltmeter neg lead to chassis ground, pos lead to the opamp-side of each cap. You should read under 100mV is there is no defect in the circuit.
The post-dac cap value I would actually double in uf value, which I would make a Nichicon FG or KW, with as fat a film cap in parallel as will fit.
I think most audio manufacturers use dc blocking caps on output lines that don't need them just to make UL happy, lest a bad opamp send out a dc voltage that won't hurt a darn thing.
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Old 17th July 2012, 06:53 AM   #5
Mooly is offline Mooly  United Kingdom
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Although nothing to do with DC coupling... have you changed those 4560 opamps ?

Looking at the circuit I can't see a problem stability wise in trying something like the OPA2134. Something like that would imo make more of a difference than all the other mods together.

The mute transistors (7839, 40, 41 and 42) might usefully be replaced with FET's such as 2SK117 and 2SK170. Think that is something Stephen often favours.
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Old 17th July 2012, 10:22 AM   #6
DF96 is offline DF96  England
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DC blocking caps are not just there to prevent fires. They also prevent damage to expensive amplifiers and speakers, and can help filter out subsonics which you can't hear anyway but may create IM distortion with signals you can hear. There is no point in sending lots of LF to a speaker which can't handle it.

Capacitors, when used correctly, are not evil!
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Old 18th July 2012, 12:19 AM   #7
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Quote:
Originally Posted by DF96 View Post
DC blocking caps are not just there to prevent fires. They also prevent damage to expensive amplifiers and speakers, and can help filter out subsonics which you can't hear anyway but may create IM distortion with signals you can hear. There is no point in sending lots of LF to a speaker which can't handle it.

is the only way to find out intermodulation with a scope?

Capacitors, when used correctly, are not evil!
just do not want to send the signal through anything I don`t have to

Quote:
Originally Posted by stephensank View Post
Voltmeter neg lead to chassis ground, pos lead to the opamp-side of each cap. You should read under 100mV is there is no defect in the circuit.
The post-dac cap value I would actually double in uf value, which I would make a Nichicon FG or KW, with as fat a film cap in parallel as will fit.
I think most audio manufacturers use dc blocking caps on output lines that don't need them just to make UL happy, lest a bad opamp send out a dc voltage that won't hurt a darn thing.
except maybe my amp or pre or god forbid my dynes

so you say go from 10uf to 20uf is that to lower esr and ripple?

right now every cap has been replaced with muse and silmic II, schottky diodes into belleson regulator and silmic II polar on dac out muse es bipolar on opamp out, h/p is unplugged and kill transistors are gone on analog L R out

would like to put smaller polypropylene on dac out and put 250 ohm wirewound strait out from opamp to rca

would that work?

should there be something across the rails for subsonic?

will a capacitor accross + - rail block dc?

thanks again to all for help and time
Glen
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Old 18th July 2012, 12:21 AM   #8
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Quote:
Originally Posted by DF96 View Post
DC blocking caps are not just there to prevent fires. They also prevent damage to expensive amplifiers and speakers, and can help filter out subsonics which you can't hear anyway but may create IM distortion with signals you can hear. There is no point in sending lots of LF to a speaker which can't handle it.

Capacitors, when used correctly, are not evil!
is the only way to find out if there is intermodulation with a scope?
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Old 19th July 2012, 06:24 AM   #9
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Quote:
Originally Posted by GLENZWORLD View Post
just do not want to send the signal through anything I don`t have to



except maybe my amp or pre or god forbid my dynes

so you say go from 10uf to 20uf is that to lower esr and ripple?

right now every cap has been replaced with muse and silmic II, schottky diodes into belleson regulator and silmic II polar on dac out muse es bipolar on opamp out, h/p is unplugged and kill transistors are gone on analog L R out

would like to put smaller polypropylene on dac out and put 250 ohm wirewound strait out from opamp to rca

would that work?

should there be something across the rails for subsonic?

will a capacitor accross + - rail block dc?

thanks again to all for help and time
Glen
I can't even estimate the hundreds of dacs, tuners, tape decks, etc. that I have mod'd for clients & myself over the years in which I have removed unnecessary dc blocking caps. Not even one time have I ever had reports of ANY negative consequence. As I think you are, I am very much inclined to believe that anything in the signal path that doesn't need to be there should be removed. There is no cap as transparent as nothing.

You won't have any unnatural subsonics on any digital source, and any good phono stage will have a filter for warpage subsonics. And only a poor amp or preamp would be disturbed in any way by natural subsonic info, and likewise speakers. Your speakers would tell you straight away if there was subsonic intermod distortion anyway, as it would plainly modulate the upper ranges and/or cause the woofers to bottom out obviously.

The increase in cap value is just my personal philosophy of "just enough overkill to be sure", in this case for low frequency bandwidth. A pp cap by itself, especially a Wima(which I personally think suck) won't have enough LF bandwidth until it's too physically large to fit in the space, and I think Nichicon lytics do a great job on the low end, so films can do just the finesse work in the mids & highs. I'll also say that I very much believe that soft recovery epitaxials(hexfreds, etc.) are better than schottky diodes.
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Old 19th July 2012, 10:54 PM   #10
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thanks for the reply and I will test for dc on opamp

the silmic I have on dac out are large (physically) but are polar and I don`t know if that makes a difference

I have also seen tests with scope at different frequencies that show no difference when bypassing caps but there seems to be alot of people doing it and some like yourself swear by it

the only cap on my preamp (acurus RL11) is bypassed with a relcap and I dont know who built it but is also full of nichicon kz for power

I sold audio for years at A&B Sound and I found a real rift between what you could hear and what some science said.

that being said I don`t want to bottom my speakers but I do want it all.

meaning least amount of changes to the music as possible, ha you remember the music right?
what this whole thing is about

that was for some others Stephen and I appreciate ALL input
and I have to laugh because I bought epitaxial diodes in case because Mike Kerster at Parts Conection recomended but then said the TI schottkies were better
can you hear the diff?

big thanks to mike and Chris Johnson at parts con for all their help

so do you think bigger caps physically make for better low end?

thanks for everyone's time and help
Glen
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