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Old 12th October 2012, 04:09 AM   #4811
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Default The second one up after 3 years

I finished another one for my second system on my bedroom. Nothing special but surprisingly found couple pairs the specs are really close. This one I go with the original design with dual 100k pot. Measure extremely good and didn't try on sound yet. Will report after serious listening.
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Old 12th October 2012, 04:13 AM   #4812
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Oh........forget the measurement photos, from 20hz to 100k. Here they come.
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Old 12th October 2012, 09:18 AM   #4813
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Hi Albert, you must have had your scope switched on AC coupling and not DC, or your source/generator is not dc coupled, as your square waves from 20hz to 100hz should have looked just like the 1khz to 20khz ones, absouletly square.
And I would say the slight rounding of the 100khz wave is most probably the scope probes capacitance.

Cheers George
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Old 14th October 2012, 02:18 PM   #4814
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Quote:
Originally Posted by georgehifi View Post
Hi Albert, you must have had your scope switched on AC coupling and not DC, or your source/generator is not dc coupled, as your square waves from 20hz to 100hz should have looked just like the 1khz to 20khz ones, absouletly square.
And I would say the slight rounding of the 100khz wave is most probably the scope probes capacitance.

Cheers George
I have my machines checked and found this is the problem of the signal generator which gives the same wave form as posted. So I presume the wave form on the lower octaves should be all square.
Time to buy another S/G, or does anyone knows how to repair the machine ??
Albert
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Old 15th October 2012, 02:22 AM   #4815
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Dear Albert,

It's the impedance of the lightsppeed attenuator is so low that the Sig Gen output impedance is a bit high to provide a perfect square waveform. The CD player or DAC output should have much lower impedance that the low frequency drive shouldn't be problem at all. Give it a try and try it in your system.

Johnny
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Old 15th October 2012, 02:27 AM   #4816
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Dear Albert,

By the way, your AN DAC is using 6DJ8 as the last buffer amp that may not able to drive this attenuator.
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Old 15th October 2012, 02:36 AM   #4817
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Quote:
Originally Posted by kmtang View Post
Dear Albert,

By the way, your AN DAC is using 6DJ8 as the last buffer amp that may not able to drive this attenuator.
Or it's (6DJ8) output series coupling cap is too small, it should be in the order of 10uf to give a -3db down point in the order of 2hz

Cheers George
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Old 15th October 2012, 03:01 AM   #4818
kmtang is offline kmtang  Canada
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Albert's DAC employs Mundorf's Silver Gold in oil caps for buffer stage output. It will get way too expensive if he replace it with 10uF one.... Albert.... you must have deep pocket.
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Old 15th October 2012, 03:18 AM   #4819
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He was using a signal generator for those LF square waves anyway and it should be fine driving into the 7k-10k load of the Lightspeed unless it's faulty or has too small coupling cap, or the scope was not switched to dc coupled, the dac is something else again.
This is why I never advocate the use of tube output dacs or cdp that have pathetic high output impedance, some are ok like the (SLCF) super linear cathode follower that's 100ohm output, but there are many that have up to 7k output impedance that have trouble driving may preamps passive or active.

Cheers George
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Old 15th October 2012, 04:03 AM   #4820
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Thanks guys for the help.
I only use my analog out with op amp from my transport. There is only 110 ohm and I thought it should be fine. What I really want to know is the capacitance of my interconnect cable to the power amp. How I can measure it with the multimeter.
Albert
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