Yeah, it is one of those things that of course makes sense once I hear it...
I had been wondering why the variable output (not digital) of my Oppo was sounding better than the digital output of my Squeezebox going through an up- sampling transformer coupled DAC. I guess in a way this is a good thing as I can make a very substantial improvement to my sound quality by simply putting a 20k pot on the input of my amp and running my digital out at maximum.
I had been wondering why the variable output (not digital) of my Oppo was sounding better than the digital output of my Squeezebox going through an up- sampling transformer coupled DAC. I guess in a way this is a good thing as I can make a very substantial improvement to my sound quality by simply putting a 20k pot on the input of my amp and running my digital out at maximum.
One way to digitally attenuate the signal without loosing the bits is done by XXHighend-player. First it adds 8 bits to a 16 bit signal and uses these resulting 24 bits to attenuate. After attenuating the first 8 bits you start loosing bits with further attenuating. But this is at a very low level so you won't hear it. Only works of course if you have a 24/32bit DAC.
Like this, two output transistors driven in anti-phase
The idea is that any distortion is cancelled because the output is the sum of the two but of course any unbalance adds even harmonics. But on the other has it's the even ones that sound best.
http://www.tpub.com/content/neets/14180/css/14180_41.htm
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Yes.
You can find very nice stepped attenuators (China, eBay) for about 20 $. Look for a 24 step ladder type.
Be aware: in digital audio headroom does not exist or has to be avoided.
Franz
This is correct. If you have a 24 bit DAC and are listing to 16-bit program material (such as a CD or digital download) you can digitally attenuate all the way back to 16 bits without any loss of quality.
This is very easy to understand. The system (all of them) scale from 16 bits to 24 by simply multiplying each sample by 256. When the audio is digitally attenuated that number "256" is reduced. As long as it is not reduced below 1 you are OK. At 1 you are still getting all 16 bits of the program source material. Below 1 and you are loosing bits
But the key here is "If you have a 24 bit DAC". Almost all of the studio grade computer audio interfaces are 24 bits but lower end "gammer" and HT interfaces might be 16-bits. If you are using 16 bit DAC then the multiplier stars at 1 and goes down from there as you move away from full volume. You do want to run the 160bit DAC at full volume
The other thing is if the program source material is something you made. Most of us will record and mix at 24 bits just because we can. In that case even with a 24 bit DAC you can't digitally attenuate without loosing bits.
But in the "normal" home hifi playback case if you have a 24Bit DAC you can digitally attenuate to about 20dB without loosing bits.
Just an explanation from another Irishman!!
"I've been bold" (in Ireland) is a confession for having been naughty!!! 😀
Thanks Franz, I have been looking at those. I don't understand the statement about headroom though😱.
Yes, thanks Brian, I should remember not to use Irish colloquialisms 🙂
BTW, guys, I don't hear any degradation in sound using my DACs digital vol control - it is a 24/192 capable DAC & I'm playing back 16/44 or 24/96 with only about 5% vol. I haven't tried any 24/192 - will do soon!
So using that layout I can use a ordinary pot on the analogue inputs to control volume instead of the digital way? I'm using it with the shigaclone -> 4398 DAC -> Lundahl LL-1517 -> T-amp
Every bit means 6db in the binary system, means times 2 or divided by 2. If you have a 24 bit dac and a 16 bit source, you have 8 "spare" bits. So you can turn the volume down to (8 times 6 db) -48 db without losing bits. With a 32 bit dac, it would be even -96 db.
With hires 24 bit material things will be different. Then you can't use a 24 bit dac without losing bits, but you can go down to -48 db with a 32 bit dac.
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Yes. Passive volume control sounds great. You won't have a remote control for volume any more , though. 😱
I got rid of a preamp with a remote and went to passive between DAC and Amp. My wife was amazed. I had to get up to change the volume.
Actually I have a Motorized ALPS with remote control so I hope I can still be seated comfortably listening at all levels, but thx. Great to know that I don't have to jump to the floating ground 2.5v t-amp thingy 🙂.
I stumbled across this thread jkeny where they also talk about the lundahl ll1517 as output with a DAC, but I'm not sure if it's for a voltage DAC?
[new design] transformer balanced DAc output buffer
[new design] transformer balanced DAc output buffer
yep, I saw that thread before - a bit confusing, I thought. For the correct schematic using LL1517s look here http://waltjung.org/PDFs/ADI_2002_Seminar_Ch6_Audio_Drivers_I.pdf
from pages 27 on 🙂. Measurements look good!
I think this might answer your request on the other thread for the LL1517 connection schematic?
from pages 27 on 🙂. Measurements look good!
I think this might answer your request on the other thread for the LL1517 connection schematic?
I'll take a look, thx jkeny. My LL1517 are actually on a calrec board with opamps (NE5532) so I thought that maybe they were already configured as driven by opamp as mentioned in my link. Unfortunately I can't find schematics or pinouts to the boards so I'm a bit lost atm 🙂.
It's a calrec LN1868 (or LN811-010-5 it says on the pcb).
It's a calrec LN1868 (or LN811-010-5 it says on the pcb).
My Sescom MI-97 transformers arrived & they look wonderfully built - I need to get some octal tube sockets for them to act as sockets into which they will plug - then I'll be able to compare them to the 80% nickel Slagle transformers I'm currently using.
I was using Dave Slagle made 80% Nickel based transformers for DAC o/p duties up to now. These are not designed for this role & are earmarked for a tube preamp.
- I bought a pair of Seccom MI-97 transformers off ebay for $50 which were recommended to me.
- Just tried them tonight & they are close to the Slagles. They might be more evenly balanced than the Slagles but it's a bit early to tell. The Slagles have a shimmering & extended HF which also seems to emphasise a background hiss coming from the laptop PS. The Sescoms don't have this shimmer (it might be a HF ringing?) but also don't have the hiss. I'll solve the PS hiss first & then some more tests & tweaking needed but I'm not disappointed with these Sescoms - for the price they're bloody great!
I don't have any resistor load on the primaries yet so this may also change things 🙂
- I bought a pair of Seccom MI-97 transformers off ebay for $50 which were recommended to me.
- Just tried them tonight & they are close to the Slagles. They might be more evenly balanced than the Slagles but it's a bit early to tell. The Slagles have a shimmering & extended HF which also seems to emphasise a background hiss coming from the laptop PS. The Sescoms don't have this shimmer (it might be a HF ringing?) but also don't have the hiss. I'll solve the PS hiss first & then some more tests & tweaking needed but I'm not disappointed with these Sescoms - for the price they're bloody great!
I don't have any resistor load on the primaries yet so this may also change things 🙂
A resistor load across the primary does present a more even impedance to the DAC. As to whether or not the DAC cares, well........
Hi John,
Did you have the opportunity to look at the responses on a scope? My Sescoms have a prominent resonance up around 200khz that does show up in the top couple of octaves of the audio band. The Jensen secondary RC filter completely eliminated it.
You might try 1kohms across the primaries. That would be in parallel with the dac chip output circuitry so the trafos would see around 500ohms depending on the series resistance you are using.
Do you think the shimmer you refer to might be an artificial modulation artifact or actually be in the source material.
Best, Bill
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