Dared SL2000a Preamp Block Distortion?
zingo
AudiophilePosts: 11,837
in Electronics
I was listening to music last night and the new Dared SL2000a tube preamp it had a fantastic sound stage and warm detail. However, when I was listening to an a cappella song that hit a big transient (they were stomping), the preamp would distort (almost sounded like clipping) during those points. I tried a pop song with similar transients and it did the same thing, but the distortion disappeared when I ran the source direct to the amp; and the sound quality decreased too.
My first thought was clipping or major microphonics? Since the Hafler amp had volume pots, I tried running it full with low volume on the pre, and low with full volume on the pre with the same results. The music was a bit loud but a reasonable volume that I use for dedicated listening.
I swapped the input tubes this morning, but also tried lowering the output on my source (iPhone which I was using last night as well) and the distortion went away. I found a discussion on "block distortion" online and it seems to be the issue I was hearing. I tried running my Squeezebox as the source and also didn't hear the problem, so I might have been overdriving the preamp, but I'll play around with it more as it doesn't seem like there is an issue with unit.
"Blocking occurs when the output tube grids are driven to the point of conduction. Since the previous stage is a relatively high impedance source, and, to make matters worse, is AC-coupled, it cannot maintain enough drive to the output tube grids to maintain the signal once the output tube goes into grid conduction."
Does anyone have experience with something similar?
My first thought was clipping or major microphonics? Since the Hafler amp had volume pots, I tried running it full with low volume on the pre, and low with full volume on the pre with the same results. The music was a bit loud but a reasonable volume that I use for dedicated listening.
I swapped the input tubes this morning, but also tried lowering the output on my source (iPhone which I was using last night as well) and the distortion went away. I found a discussion on "block distortion" online and it seems to be the issue I was hearing. I tried running my Squeezebox as the source and also didn't hear the problem, so I might have been overdriving the preamp, but I'll play around with it more as it doesn't seem like there is an issue with unit.
"Blocking occurs when the output tube grids are driven to the point of conduction. Since the previous stage is a relatively high impedance source, and, to make matters worse, is AC-coupled, it cannot maintain enough drive to the output tube grids to maintain the signal once the output tube goes into grid conduction."
Does anyone have experience with something similar?
Comments
Input signal was too hot for the preamp to handle at that particular musical transient.
Even if you turn it down, you can't get serious sound from an iPhone. I know we all have different types of rigs for different purposes and the convenience is nice, but don't use a device like that if you expect great sound, IMHO, of course.
H9
Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
More than likely the issue was the signal being too hot for the iPhone to process and probably overloading the output signal. I doubt it's the pre's fault. A device like an iPhone is not in any way shape or form designed to be a stellar hi-fi unit.
H9
Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
I agree, Brock. Unless you are somehow bypassing the internal DAC/3.5mm headphone output.
I guess the point of my post was that the issue lies with the source.
I was mostly using my Squeezebox Touch, but wanting to do some testing with tracks on my phone, but had never had that result on any tube equipment before.
You can bypass it with a DAC that has a USB input and the lightning cable, or you can buy Apple’s lightning to HDMI adapter. Both of these bypass the internal DAC. I’m sure there are more ways to do it as well.
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I guess the Dared is a little more revealing? Maybe you should try it in your main rig?
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I like my NAD integrated, and for fun disconnected the power section and connected this Dared and the preamp, and WOW! It bested the NAD preamp section in every way for musical playback. That's not to say a modern NAD integrated is a bad piece of equipment, but I'm frequently impressed by this simple preamp.
When integrated properly into a system it's a real sleeper, even with mediocre tubes. Roll in some classic tubes and the tone, soundstage and timbre is most excellent.
H9
Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
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