I don't use outputcaps in my Twisted pear setup, that's fine but i've got a "thump"sound when switching on the DAC.The (Ventus) LME49600 has a short circuit protection. I want to short the output with a relay for about 5 seconds before enabling the output. I don't want to put the relay in the signalpath. Can i do that without damaging the LME, or is it saver to put a resistor in serie with it. If yes, what would be the value ? Would 1kOhm be enough ?
Thanks in advance!
Thanks in advance!
Short circuit current for LME49600 is rated around 500mA, or a minimum of 30 ohms at 15V.
But best to have at least 100 ohms in series before the shorting relay to ground, to avoid stressing it.
Even larger (500 ohms) would still not be a problem. Don't directly short its output to ground though.
But best to have at least 100 ohms in series before the shorting relay to ground, to avoid stressing it.
Even larger (500 ohms) would still not be a problem. Don't directly short its output to ground though.
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Hello duncan, it's a Twisted Pear B2 DAC > Legato i/v > Ventus. It's all DC connected, both the Legato & Ventus have potentiometers on each channel to nullify DC.
I am with your philosophy on DC connected removes the imperfect capacitor with its resistance and inductance.
I am not well up on Twisted Pear design which as you pointed out your other two units can have the DC nulled so I had a look at two of their DAC,s ,one has 22uF on its outputs and the other also has capacitor outputs .
There is also a "Buffalo" version this has servo,s to eliminate offset , into a Legato servo,s are not mentioned.
As many chips need their outputs protected its probably a pulse we are talking about and that reducing the volume makes no difference ?
I am not well up on Twisted Pear design which as you pointed out your other two units can have the DC nulled so I had a look at two of their DAC,s ,one has 22uF on its outputs and the other also has capacitor outputs .
There is also a "Buffalo" version this has servo,s to eliminate offset , into a Legato servo,s are not mentioned.
As many chips need their outputs protected its probably a pulse we are talking about and that reducing the volume makes no difference ?
Well, i haven't found out what caused the power on pulse. The (optional) balanced to single ended stage inside Legato is the Balsie and has also a relais, propably for a signal delay. I did like the conversion better with the Ventus. Volume doesn't matter, on and off thump are there.
http://www.twistedpearaudio.com/docs/community_docs/leonvb-Buffalo_II_Integration_Guide_V1.0.5.pdf
http://www.twistedpearaudio.com/docs/community_docs/leonvb-Buffalo_II_Integration_Guide_V1.0.5.pdf
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As there are several modes in the DAC - configurable switches you could try a different mode just to narrow down the pulse .
The Legato looks like it has a direct DC output from the two chips as is the two preamp chips that feed them so any DC would be amplified at switch on .
Yes I saw the relay could be used.
The Legato looks like it has a direct DC output from the two chips as is the two preamp chips that feed them so any DC would be amplified at switch on .
Yes I saw the relay could be used.
Shorting the output with 500 or 250 Ohm didn't help. I have now ordered some good Panasonic relais to switch the signal itself.
Still wondering why it made no difference.
TQ2-12VDC
TXS2-12V
AGN20012
Still wondering why it made no difference.
TQ2-12VDC
TXS2-12V
AGN20012
Because the resistance wasn't able to damp the pulse , in the Legato,s case what is the output DC connected chip ?
Because the DAC can drive a few hundred ohms with ease! Maybe a bit more distortion, but no useful reduction of thump.
Put the resistor in line with the -load-, and short the far side. If the relay has 0.1 Ohms contact resistance you get 60dB attenuation.
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Was the resistor in series, or in parallel, with the output?
Of course it should be in series with the output, and before the relay to ground.
See post #3.
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EDIT
Just looked at Legato 3.1. 22R output resistor will make a pitiful attenuator with 500R to ground. I would just short the output as is, without adding an additional resistor, or change the 22R for a 100R if feeling paranoid.
Just looked at Legato 3.1. 22R output resistor will make a pitiful attenuator with 500R to ground. I would just short the output as is, without adding an additional resistor, or change the 22R for a 100R if feeling paranoid.
"....best to have at least 100 ohms in series before the shorting relay to ground, to avoid stressing it.
Ambiguous. Which "it" is being stressed?
Long-term circuit shorters (I was putting thumbtacks in line-cord when I was 4) will understand where a short may be applied without flame or strain. People with a less interesting upbringing may need a picture.
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