Re: SC ULD2
Yes, I see that now. I'm going to add a switch over the trimpot for the current mirror as you suggested, once I've got decent speakers and Transporter set up, and done some extended listening tests.sandyK said:
Jeremy,
Not quite the full story - I also suggested that a third order filter between the DAC and the analog output stage would reduce noise, as long as it was an eight times oversampling DAC.
This would be tricky to fit on your existing DAC, as it's tightly packed.
Cheers,
Hugh
Sorry Hugh - I was trying to be funny; I hope it didn't come across the wrong way.
What I really should have said was that "sit further away" was the one suggested fix that is currently within my limited technical capabilities! 🙂
What I really should have said was that "sit further away" was the one suggested fix that is currently within my limited technical capabilities! 🙂
After a fair few hours listening with the Transporter, I can't say I can hear a difference, other than the removal of the slight hiss (which was only audible from within 3ft of the speaker, and only if no music is playing). It seems like the external DAC I was using was pretty good - it's just that it has some minor HF hiss (only audible when using this high-gain amp).
I've replaced a couple of albums in my listening test - I'm now using some recordings from Mercury's "Living Presence" series for some of my classical albums. They're absolutely stunning recordings - just about the best classical recordings I've heard, I think. Not bad when you consider they're 40-50 years old!
I've replaced a couple of albums in my listening test - I'm now using some recordings from Mercury's "Living Presence" series for some of my classical albums. They're absolutely stunning recordings - just about the best classical recordings I've heard, I think. Not bad when you consider they're 40-50 years old!
Well, interesting developments with this 'hiss' issue... I heard back from Lawrence Chan, who makes the DAC, and he said in his two years of selling it this is the 1st he's heard of any HF hiss. I've tried the DAC with 2 other amps, and I don't hear any hiss at all.
So even although the hiss isn't being produced by this amp, it does seem that it's particularly sensitive to it. I've also testing my Duet's internal DAC with a couple of other amps, and although some hiss is audible in all of them, it's far worse with the SCULD than with the other two.
So I'd say that, at least in the standard spec (and with the tweaks suggested so far), the SCULD is only a good choice if you've got a very low-noise source, or if you're not too sensitive to HF noise.
BTW, I've tried increasing both the 820pf cap and 100R, but couldn't get rid of the hiss without destroying the SQ.
So even although the hiss isn't being produced by this amp, it does seem that it's particularly sensitive to it. I've also testing my Duet's internal DAC with a couple of other amps, and although some hiss is audible in all of them, it's far worse with the SCULD than with the other two.
So I'd say that, at least in the standard spec (and with the tweaks suggested so far), the SCULD is only a good choice if you've got a very low-noise source, or if you're not too sensitive to HF noise.
BTW, I've tried increasing both the 820pf cap and 100R, but couldn't get rid of the hiss without destroying the SQ.
SC ULD2
Jeremy
If you are only able to use a low volume setting on your source to achieve a decent listening level, perhaps the gain of the amplifier could be reduced a little ? This could be achieved by increasing the value of the 510 ohm resistor up to as high 1 K ohm. Any other suggestions from other members?
Alex
Jeremy
If you are only able to use a low volume setting on your source to achieve a decent listening level, perhaps the gain of the amplifier could be reduced a little ? This could be achieved by increasing the value of the 510 ohm resistor up to as high 1 K ohm. Any other suggestions from other members?
Alex
Hehe - Alex I just sent you an email asking about just that idea; what a coincidence! Unfortunately, when listening to high dynamic range classical music, I have to set the volume to ~75% to hear the quiet passages clearly.
Still, I may as well use the full volume range all the way up to 100% - so I guess I can change the gain a bit... I'll try it and report back.
Still, I may as well use the full volume range all the way up to 100% - so I guess I can change the gain a bit... I'll try it and report back.
Hi,
remind me, what is the gain of the LD?
What is the sensitivity of the speakers you're using?
remind me, what is the gain of the LD?
What is the sensitivity of the speakers you're using?
Andrew,
Gain is (12000 + 510)/510 = 24.53, which is 27.8dB.
The 510R can be replaced with 1K, reducing gain by 5.3db to 22.28dB. This is just about half the subjective loudness.
Cheers,
Hugh
Gain is (12000 + 510)/510 = 24.53, which is 27.8dB.
The 510R can be replaced with 1K, reducing gain by 5.3db to 22.28dB. This is just about half the subjective loudness.
Cheers,
Hugh
I would class ~+28dB as a low gain amplifier.
In my book +30dB to +35dB is medium gain and >=+36dB is high gain.
In my book +30dB to +35dB is medium gain and >=+36dB is high gain.
Yes, I do agree with that. My Lifeforce and Soraya have gains of 31dB. Reducing the gain of the ULD200 could have its problems as with conventional CD sources it may have difficulty reaching full output, certainly into 8R.
Cheers,
Hugh
AndrewT said:
I'm afraid I don't know that, and I don't have the equipment to test. They are Interdyn P2 speakers, made in Melbourne in the 80's and 90's - but I can't find any info about them now.
I'm checking out some Plutos tomorrow - I'll bring my DAC and amp around and see what that sounds like.
If you reduce the closed loop gain you increase the unity loop gain frequency proportionally.
This should not be recommended unless the emitter degeneration of the LTP and/or Cdom is increased to maintain the same unity loop gain frequency, otherwise the amplifiers stability will be compromised.
This should not be recommended unless the emitter degeneration of the LTP and/or Cdom is increased to maintain the same unity loop gain frequency, otherwise the amplifiers stability will be compromised.
hi jp_howard,
I was just wondering if the issue was caused or exagerated by the relative low input impedance of the amp. Are you using a preamp or buffer between your Transporter and SCULD 200?
Can you borow an amp from Hugh? I think all Hugh's amp have an input impedance 4 times greater. My AKSAs work well directly connected to my Transporter.
Can anyone compare the SCULD 200 to the other Silicon Chip amps? awpagan ?
BTW: I am bit a a Perl hacker (not programmer) myself and was able fix a bug in SlimServer. The open source server and streaming concept seduced me 2 or 3 years ago.
TIP: Don't waste to much time on the chipamps.
I think Andrew might have to migrate to Australia to be fair dinkum participant of this thread.
regards
I was just wondering if the issue was caused or exagerated by the relative low input impedance of the amp. Are you using a preamp or buffer between your Transporter and SCULD 200?
Can you borow an amp from Hugh? I think all Hugh's amp have an input impedance 4 times greater. My AKSAs work well directly connected to my Transporter.
Can anyone compare the SCULD 200 to the other Silicon Chip amps? awpagan ?
BTW: I am bit a a Perl hacker (not programmer) myself and was able fix a bug in SlimServer. The open source server and streaming concept seduced me 2 or 3 years ago.
TIP: Don't waste to much time on the chipamps.
I think Andrew might have to migrate to Australia to be fair dinkum participant of this thread.
regards
Greg, just to clarify: I'm getting no hiss at all when connecting to the Transporter directly. I'm only getting hiss when connecting to the Duet directly (lots of hiss, audible from my listening position if room is very quiet), or connecting to my external DAC (slight hiss, just audible 3 ft from tweeter). The external DAC has the same slight hiss regardless of whether it's connected to the Transporter or the Duet.
By comparison, with Hugh's amp even the Duet connected directly only had a small amount of hiss - I could hear it at 4 ft from the tweeter. So either the SCULD or my speakers are very sensitive to HF noise.
I've tried to use my oscilloscope (PoScope) to measure the noise, but didn't find anything useful. The signal of the amp picked up by the oscilloscope, connected to the external DAC, was exactly the same regardless of whether the amp was on or off! So whatever is causing the hiss is beneath the level that can be detected by my oscilloscope, I guess. Here's a pic of the signal I got:
x-axis is in ms. y-axis is volts. Could an audible signal be smaller than this size (20mV)?
By comparison, with Hugh's amp even the Duet connected directly only had a small amount of hiss - I could hear it at 4 ft from the tweeter. So either the SCULD or my speakers are very sensitive to HF noise.
I've tried to use my oscilloscope (PoScope) to measure the noise, but didn't find anything useful. The signal of the amp picked up by the oscilloscope, connected to the external DAC, was exactly the same regardless of whether the amp was on or off! So whatever is causing the hiss is beneath the level that can be detected by my oscilloscope, I guess. Here's a pic of the signal I got:
x-axis is in ms. y-axis is volts. Could an audible signal be smaller than this size (20mV)?
Even building and testing poorer equipment seems to be useful for the education - it's good to see the pros and cons of different approaches.Greg Erskine said:
Jeremy
Greg has plenty of experience building Chip amps.
Just pretend that the SC HA was a chip amp, and progress from there. (It did have a chip in it !)
Alex
P.S. I sent you those 2 links.
Greg has plenty of experience building Chip amps.
Just pretend that the SC HA was a chip amp, and progress from there. (It did have a chip in it !)
Alex
P.S. I sent you those 2 links.
sandyK said:
Hi Alex,
I can't see any comparison between "a basic chipamp kit" and a HA with an IC, sure they both use opamps.
regards
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