Glassman
Headphoneus Supremus
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red dots - elyt caps in way of left channel outs
green dots - probably the same for right channel
green dots - probably the same for right channel
Modding the RME PAD
- Thread starter Iron_Dreamer
- Start date
Where you made the dots are just the pads from where I removed the output coupling caps, They are shorted together on the other side of the board.
I'm anxious to hear opinions on the Class A LT1122 vs. Class A OPA627AU.. those seem to be the "winners" here.
Darn you two and your Wayward Modding Adventures.. I think you're making it so i'll have to send my gear back to I_D once again.
Curse you Head-Fiiiiii!!! *shakes fists in Epic fashion*
Darn you two and your Wayward Modding Adventures.. I think you're making it so i'll have to send my gear back to I_D once again.
Curse you Head-Fiiiiii!!! *shakes fists in Epic fashion*
dip16amp
100+ Head-Fier
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I'm currently using the digi96/8 pad into my headphone amp which has the opa627 opamp and buf634 buffer and I like what I hear now but I haven't tryed the sterophile editor's choice cd yet to see what that's all about.
Is there any reason why I couldn't just bypass the opamp and caps on the digi96/8 card and go right into my amp? I can't see putting opa627 opamps on the card which will then go to the opa627s on my amp. My amp would only be a few inches from the card so it wouldn't have to drive much cabling.
Is there any reason why I couldn't just bypass the opamp and caps on the digi96/8 card and go right into my amp? I can't see putting opa627 opamps on the card which will then go to the opa627s on my amp. My amp would only be a few inches from the card so it wouldn't have to drive much cabling.
I can see what you're getting at, but you would need to massively increase the gain on your amp for that to work. Also the signal you send to the amp could be more susecptible to interference since it would be such a weak signal. Not saying you couldn't try it, but I don't think it would be the best idea in the world. Even the best CDp's and whatnot still have an analog output gain stage, the you use a seperate amp to get it to a higher level for speakers or cans.
Wodgy
Headphoneus Supremus
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Quote:
YES! You can do this. This is a mod I *highly* recommend with the AD1852. There are two ways of bypassing the output stage entirely: you can transformer-couple the outputs (see my suggestions earlier in this thread for which transformers to use), or you can actually just use a single coupling capacitor per channel and go directly to your amp.
The latter approach is how I have my DIY AD1852 DAC currently configured, after experimenting with a bunch of different output stages. It's incredibly simple but it sounds really good.
The direct capacitor coupling is possible because the AD1852 is a voltage-output DAC, rather than a current-output DAC. Note that because the output of the AD1852 is balanced, you will lose 6dB of volume by doing this. Not a problem though. Just remove the four output coupling caps from the RME, and connect V+ for each channel through a capacitor to a set of RCA jacks. I'm using Elna Silmics because I like a darker sound, but for neutrality BlackGate N/NX/NH would be a better choice.
Caveat: I don't have an RME so I can't comment on how this sounds with that card. I have my AD1852's digital filter set to a 22kHz cutoff. This pushes out of band noise down by -120dB, which is good enough for me. I'm not sure how the RME sets up the AD1852's digital filter. If it sets it to a higher cutoff, then this mod might not sound better than the current analog stage. But I'm guessing the RME designers probably use the correct digital filter for the sample rate they're using, so your results will probably be as good as mine.
| Originally posted by dip16amp Is there any reason why I couldn't just bypass the opamp and caps on the digi96/8 card and go right into my amp? I can't see putting opa627 opamps on the card which will then go to the opa627s on my amp. My amp would only be a few inches from the card so it wouldn't have to drive much cabling. |
YES! You can do this. This is a mod I *highly* recommend with the AD1852. There are two ways of bypassing the output stage entirely: you can transformer-couple the outputs (see my suggestions earlier in this thread for which transformers to use), or you can actually just use a single coupling capacitor per channel and go directly to your amp.
The latter approach is how I have my DIY AD1852 DAC currently configured, after experimenting with a bunch of different output stages. It's incredibly simple but it sounds really good.
The direct capacitor coupling is possible because the AD1852 is a voltage-output DAC, rather than a current-output DAC. Note that because the output of the AD1852 is balanced, you will lose 6dB of volume by doing this. Not a problem though. Just remove the four output coupling caps from the RME, and connect V+ for each channel through a capacitor to a set of RCA jacks. I'm using Elna Silmics because I like a darker sound, but for neutrality BlackGate N/NX/NH would be a better choice.
Caveat: I don't have an RME so I can't comment on how this sounds with that card. I have my AD1852's digital filter set to a 22kHz cutoff. This pushes out of band noise down by -120dB, which is good enough for me. I'm not sure how the RME sets up the AD1852's digital filter. If it sets it to a higher cutoff, then this mod might not sound better than the current analog stage. But I'm guessing the RME designers probably use the correct digital filter for the sample rate they're using, so your results will probably be as good as mine.
So wodgy, if you can go straight from the DAC chip to output, why isn't that done more often in products? I thought the DAC chip produced a very low level that needed to be amplified in the output stage.
Wodgy
Headphoneus Supremus
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Three main reasons:
1) Analog LPF -- It's accepted wisdom that you need to follow the output of your DAC with a low pass filter, usually using op-amps. However, there's a whole movement now for analog filterless DACs (Scott Nixon's, the Ack! dAck! etc.) because allegedly the sound is better. With the AD1852 we're compromising halfway -- the digital filter in the AD1852 is so good (-120dB stopband) that really there isn't all that much of a reason for an analog LPF. There's a project in the DIY forum right now to build a USB DAC using a chip with only a -80dB stopband, and they're leaving out the LPF. The AD1852 is a much better chip, and so it's even less of a compromise here.
2) Driving cable -- The AD1852 by itself can't drive long lengths of cable because of the capacitance. If you're only driving a couple feet, it's fine. For a professional product, of course, they couldn't leave this out. Also, you'll need an analog output stage if you intend to drive amps with an input impedance less than 2k. All of the DIY amps around here are fine.
3) Performance -- By not summing the balanced outputs of the DAC, you lower the device's measured performance in most categories (noise floor, etc.) by 6dB. However, the AD1852's measurements are good enough that it's a worthwhile tradeoff, since you're getting rid of all the op-amp grunge. I'd imagine that this would make an even bigger difference in a computer, because you'd be bypassing the analog output stage and its power supply (which could be suboptimal) completely. For me, even outside of a computer, I felt the audible improvement was worthwhile.
Try it! It's an easy mod, especially since you've already removed the output coupling caps (it's almost trivially easy for you). There's nothing like getting all the op-amps out of the signal path. (Do give the caps a couple days to burn in before evaluating this mod.) I've tried a whole host of output stages with the AD1852, and this is the best. (Second best was a transformer-coupled output stage with Lundahl transformers.)
1) Analog LPF -- It's accepted wisdom that you need to follow the output of your DAC with a low pass filter, usually using op-amps. However, there's a whole movement now for analog filterless DACs (Scott Nixon's, the Ack! dAck! etc.) because allegedly the sound is better. With the AD1852 we're compromising halfway -- the digital filter in the AD1852 is so good (-120dB stopband) that really there isn't all that much of a reason for an analog LPF. There's a project in the DIY forum right now to build a USB DAC using a chip with only a -80dB stopband, and they're leaving out the LPF. The AD1852 is a much better chip, and so it's even less of a compromise here.
2) Driving cable -- The AD1852 by itself can't drive long lengths of cable because of the capacitance. If you're only driving a couple feet, it's fine. For a professional product, of course, they couldn't leave this out. Also, you'll need an analog output stage if you intend to drive amps with an input impedance less than 2k. All of the DIY amps around here are fine.
3) Performance -- By not summing the balanced outputs of the DAC, you lower the device's measured performance in most categories (noise floor, etc.) by 6dB. However, the AD1852's measurements are good enough that it's a worthwhile tradeoff, since you're getting rid of all the op-amp grunge. I'd imagine that this would make an even bigger difference in a computer, because you'd be bypassing the analog output stage and its power supply (which could be suboptimal) completely. For me, even outside of a computer, I felt the audible improvement was worthwhile.
Try it! It's an easy mod, especially since you've already removed the output coupling caps (it's almost trivially easy for you). There's nothing like getting all the op-amps out of the signal path. (Do give the caps a couple days to burn in before evaluating this mod.) I've tried a whole host of output stages with the AD1852, and this is the best. (Second best was a transformer-coupled output stage with Lundahl transformers.)
If I were to try that mod, could I use the same rating for the output caps as was standard on the card (50V 33uF)?
Wodgy
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No problem. You can choose caps with any voltage rating greater than 5V, and I'd recommend at least 10uF of capacitance. You could get away with 3uF if you really wanted to.
I think I will give it a try, if I dis-connect the old caps legs I have used to bypass I could use the stock ouput connector.
Wodgy
Headphoneus Supremus
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If you don't want to desolder the stock output connector, you could just pick up a pair of RCA jacks at Radio Shack.
When you're done, be sure to report back on what you think. Try to give the caps a while to burn in before trying to evaluate them. (Raw caps can sound gritty and confused sometimes.)
When you're done, be sure to report back on what you think. Try to give the caps a while to burn in before trying to evaluate them. (Raw caps can sound gritty and confused sometimes.)
If Iron_Dreamer suddenly stops posting for awhile, we'll know something went horribly wrong with his computer. But I have yet to see a sound card bring down an entire computer.
Although, we are talking about a Frankenstein Sound Card now.
*Crossing fingers*
LOL, so I may very well have ordered a couple more OP amps and adapters for no reason.
I guess if we end up desoldering jacks from the RME PAD, we might as well add nice female RCA's there then.
-Ed
Although, we are talking about a Frankenstein Sound Card now.
*Crossing fingers*
LOL, so I may very well have ordered a couple more OP amps and adapters for no reason.
I guess if we end up desoldering jacks from the RME PAD, we might as well add nice female RCA's there then.
-Ed
Well, I'm back and it's working. It definitely take a few more clicks on the Gilmore to get normal volume, from 4 before now to 7 with the mod. Dare I say it sounds more direct and clean now, as if a layer of fuzz had been removed from the sound. I am using the left over Blackgate PK 50V 22UF caps BTW.
And I connected the outputs of the caps to the stock output jack, which is working fine in this configuration.
And I connected the outputs of the caps to the stock output jack, which is working fine in this configuration.
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