Hi all
This may seem like a very infantile question but hey I'm no electronics engineer.
I'm currently looking to mod my system to suit my room/preferences.
The area I'm currently looking at is the Cambridge Audio DAC and Rotel RC03 preamp.
My aim is to open up the soundstage and clean up the midrange during busy sections of tracks.
The two items listed don't have a huge modding background s but I found a couple.
The one I'm focussing on here is short the DC blocking caps in the DAC.
Simple enough however they state to check the DC offset. Truth is I don't know what that actually means and how to measure it.
Do I need to pop the hood or can it be measured at the RCA/XLR terminals?
Is it simply checking for DC at the pins to ground?
It goes on to say if the preamp has dc blocking there is no need to concern yourself with any offset present.
I cannot find a service manual. I've emailed Rotel tonight. I believe they will send one at a cost.
Is there a way to determine if the preamp has dc blocking caps without a schematic?
Thanks in advance if anyone can assist with this question.
Ian
This may seem like a very infantile question but hey I'm no electronics engineer.
I'm currently looking to mod my system to suit my room/preferences.
The area I'm currently looking at is the Cambridge Audio DAC and Rotel RC03 preamp.
My aim is to open up the soundstage and clean up the midrange during busy sections of tracks.
The two items listed don't have a huge modding background s but I found a couple.
The one I'm focussing on here is short the DC blocking caps in the DAC.
Simple enough however they state to check the DC offset. Truth is I don't know what that actually means and how to measure it.
Do I need to pop the hood or can it be measured at the RCA/XLR terminals?
Is it simply checking for DC at the pins to ground?
It goes on to say if the preamp has dc blocking there is no need to concern yourself with any offset present.
I cannot find a service manual. I've emailed Rotel tonight. I believe they will send one at a cost.
Is there a way to determine if the preamp has dc blocking caps without a schematic?
Thanks in advance if anyone can assist with this question.
Ian
It's not such a good idea to remove DC blocking output capacitors in a source component.
With some preamps it is safe to remove the DC blocking input capacitors as they
are there only to block a DC input. Not in all preamps, though.
Since your preamp has a bipolar input stage, you should not remove those caps either.
https://elektrotanya.com/rotel_rb_03.pdf/download.html
With some preamps it is safe to remove the DC blocking input capacitors as they
are there only to block a DC input. Not in all preamps, though.
Since your preamp has a bipolar input stage, you should not remove those caps either.
https://elektrotanya.com/rotel_rb_03.pdf/download.html
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Thanks Rayma
So you're saying its best to not touch the caps in the dac?
I'm guessing the idea was to remove caps not required from the signal path. He stated they were blocking almost nothing and his preamp has dc blocking on the input.
I suppose the overall layout with blocking on both output and input is overkill and not required?
If you don't mind could you explain how to measure offset? and what it actually means?
So you're saying its best to not touch the caps in the dac?
I'm guessing the idea was to remove caps not required from the signal path. He stated they were blocking almost nothing and his preamp has dc blocking on the input.
I suppose the overall layout with blocking on both output and input is overkill and not required?
If you don't mind could you explain how to measure offset? and what it actually means?
Without knowing more about the DAC, doing this could cause problems.
There is a good reason that the capacitor is there in the first place.
Even if the normal DC voltage before the DAC output coupling capacitor
is say under 100mV , this still could cause noise in a preamp's
switching, balance control, and volume control, or worse. It depends on the
signal flow in the preamp. Some DACs do have much more DC voltage there
because of the topology of the circuit. Electronic circuits in audio normally have
both AC and DC voltages at many circuit nodes. This is how they can function properly.
But the DC is not intended to be amplified along with the AC signal.
To measure it, just locate the output capacitor and measure the DC voltage wrt ground
on the input side of the capacitor. The output side will always be at 0VDC.
There is a good reason that the capacitor is there in the first place.
Even if the normal DC voltage before the DAC output coupling capacitor
is say under 100mV , this still could cause noise in a preamp's
switching, balance control, and volume control, or worse. It depends on the
signal flow in the preamp. Some DACs do have much more DC voltage there
because of the topology of the circuit. Electronic circuits in audio normally have
both AC and DC voltages at many circuit nodes. This is how they can function properly.
But the DC is not intended to be amplified along with the AC signal.
To measure it, just locate the output capacitor and measure the DC voltage wrt ground
on the input side of the capacitor. The output side will always be at 0VDC.
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DC blocking caps have nothing to do with your perceived sound shortcomings. What makes you think they would? You most likely have some EQ work to do by the description.
You have pretty decent equipment, but source, amp and speakers are all in the chain.
Those of us who mod everything we can get our hands on usually have degrees in electronics or at least started breaking things when we were small.
There is a reason those units are not mod favorites. They don't need it. I would pay attention to the "no user serviceable parts inside" sticker.
You have pretty decent equipment, but source, amp and speakers are all in the chain.
Those of us who mod everything we can get our hands on usually have degrees in electronics or at least started breaking things when we were small.
There is a reason those units are not mod favorites. They don't need it. I would pay attention to the "no user serviceable parts inside" sticker.
Once you do something like that, you’re placed into a realm where you will have to question and carefully consider every move you make regarding unplugging and plugging in cables. Hot plugging without some isolation will often blow things up. Also there may be inordinate loads placed on certain parts of the circuit without that component.
There’s a common understanding that you should first know the design fairly well prior to altering it. So that’s not to say that there may be something to be gained, but it will be at a price/risk. This hobby works better when you analyze everything, do extensive research before the soldering. And then it’s always better to have some decent practice in that area as well if working on something with actual replacement value…
There’s a common understanding that you should first know the design fairly well prior to altering it. So that’s not to say that there may be something to be gained, but it will be at a price/risk. This hobby works better when you analyze everything, do extensive research before the soldering. And then it’s always better to have some decent practice in that area as well if working on something with actual replacement value…
Thanks for the replies guys.
I've already modded the speakers to tame an overly bright presentation.
This seems to have revealed another area where I feel improvements can be made.
I'm only going off what other people have described as worthwhile tweaks.
The Dacmagic tweaks I've found are the coupling caps and utilising the XLR outputs both are simple mods that can easily be reversed if not desirable.
From what I've seen on here power supplies seem to offer the most bang for buck.
I was considering op-amp replacement but that's quite a lot of hassle.
I can't change the room of move the kit so the only thing left is live with it, playing with internals or full replacement.
I'm not ready to live with it yet, happy to make minor tweaks and can't afford to replace.
I've already modded the speakers to tame an overly bright presentation.
This seems to have revealed another area where I feel improvements can be made.
I'm only going off what other people have described as worthwhile tweaks.
The Dacmagic tweaks I've found are the coupling caps and utilising the XLR outputs both are simple mods that can easily be reversed if not desirable.
From what I've seen on here power supplies seem to offer the most bang for buck.
I was considering op-amp replacement but that's quite a lot of hassle.
I can't change the room of move the kit so the only thing left is live with it, playing with internals or full replacement.
I'm not ready to live with it yet, happy to make minor tweaks and can't afford to replace.
Have you tried near field listening?
From the DAC manual it seems very risky to bypass the DAC output coupling capacitors.
The rest of the circuit is direct coupled, and could be damaged under certain conditions.
There also could be substantial startup/power down voltage transients that the capacitors block.
https://elektrotanya.com/cambridge-audio_ap25144-1_dacmagic_2008_sm.pdf/download.html#dl
From the DAC manual it seems very risky to bypass the DAC output coupling capacitors.
The rest of the circuit is direct coupled, and could be damaged under certain conditions.
There also could be substantial startup/power down voltage transients that the capacitors block.
https://elektrotanya.com/cambridge-audio_ap25144-1_dacmagic_2008_sm.pdf/download.html#dl
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“can’t afford to replace”
I can understand that, and when in that situation, I leave well alone, and use as a reference, or backup while
Kind of like my late model car; not as likely to have the cylinder head on the workbench with the die grinder hanging out of one of the ports anytime soon.
Have you looked at any kits or assembled project boards to play around with? They can be rewarding and fairly low cost.
I can understand that, and when in that situation, I leave well alone, and use as a reference, or backup while
Kind of like my late model car; not as likely to have the cylinder head on the workbench with the die grinder hanging out of one of the ports anytime soon.
Have you looked at any kits or assembled project boards to play around with? They can be rewarding and fairly low cost.
Thank you all for your contributions.
I'll leave well alone and just play around with damping/positioning etc.
Out of interest I just sat on the floor the changes are not subtle!
Trouble is I have a very heavy ceramic table right in my way!
Maybe I should focus on a diy rack to reduce airborne vibration and allow the right hand speaker to move 30mm closer to equilibrium Maybe a plinth to raise the speakers a bit sitting on the floor certainly improved the overall presentation.
I dislike the room i'm dealt with but at least I didn't pop the hood and attack with a hot iron.
Thank you again guys
Ian
I'll leave well alone and just play around with damping/positioning etc.
Out of interest I just sat on the floor the changes are not subtle!
Trouble is I have a very heavy ceramic table right in my way!
Maybe I should focus on a diy rack to reduce airborne vibration and allow the right hand speaker to move 30mm closer to equilibrium Maybe a plinth to raise the speakers a bit sitting on the floor certainly improved the overall presentation.
I dislike the room i'm dealt with but at least I didn't pop the hood and attack with a hot iron.
Thank you again guys
Ian
If there's a ceramic top table between you and the speakers, cover it with a wool rug
or throw to kill the reflections. That will make a lot of difference, for the better.
Many speakers are designed with the tweeter as the listening axis when seated.
or throw to kill the reflections. That will make a lot of difference, for the better.
Many speakers are designed with the tweeter as the listening axis when seated.
Do you mean complete amps etc or supply boards etc
I would like to try the dc filter I've seen on here for the Dacmagic but its out of stock
The shame of the whole thing is at times I know this system as is can really shine but I can't work it within the room.
I guess I was hoping to mod it to just work better within the space I have.
Maybe sometimes things just don't work out the way you want.
Sitting on the floor with the tweeters above ear height brought it to life.
You could hear the table tops reflections but overall the balance improved dramatically.
Let me go grab a throw....
Ok, then raise the speakers up on stands to compensate. The bass should become less boomy also.
Anything on the table will help, but thick wool is best.
What speakers are these?
Anything on the table will help, but thick wool is best.
What speakers are these?
Complete functional pre amp boards is what I was thinking of.
Have you tried going without the preamp?
That was a good move in my system.
covering the table is the best advice I’ve heard so far…
Have you tried going without the preamp?
That was a good move in my system.
covering the table is the best advice I’ve heard so far…
Yes, a preamp is not necessary with a DAC, if you can otherwise control the volume.
Or you can wire a 10k volume control in a box with RCA in/out instead.
Or you can wire a 10k volume control in a box with RCA in/out instead.
I'll search for some base ideas, on my smaller floor standers I used granite blocks but thats only about 20-30mm i might need more than that.
FYI speakers are PMC FB1 modded to + CA DacMagic Rotel RCD02 CD RC03 pre 2x RB03 mono blocks sitting on Sound style glass n steel rack
When th going gets tough I find the mids a little muddy highs can be a little bright a lot of symbols can be a bit crashy.
Its not on all tracks eg
The Wall sounds beautiful most of the time but at times confused and overwhelming
Is it just the recording or the room dynamics reeking havoc on a bright revealing system??
Hence the willingness to play with internals
FYI speakers are PMC FB1 modded to + CA DacMagic Rotel RCD02 CD RC03 pre 2x RB03 mono blocks sitting on Sound style glass n steel rack
When th going gets tough I find the mids a little muddy highs can be a little bright a lot of symbols can be a bit crashy.
Its not on all tracks eg
The Wall sounds beautiful most of the time but at times confused and overwhelming
Is it just the recording or the room dynamics reeking havoc on a bright revealing system??
Hence the willingness to play with internals