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Old 8th October 2012, 08:23 AM   #4051
bcmbob is offline bcmbob  United States
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I believe best practice is to use inexpensive/test/junk speakers for initial testing. They don't even have to be in an enclosure at this point. I let the system run for about an hour before attaching main/real speakers.
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Old 8th October 2012, 08:44 AM   #4052
bismuth is offline bismuth  France
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Thanks bcmbob,
I did that already and it sounds OK with a martyr car speaker.
But as I was expecting a much cleaner square wave response in medium and hi range I want to be sure that I didn't miss something in my build (here is a pic of a board).
What does square wave responses look like on your working MyRef RevC amps guys ? I've searched various Myref related threads in this forum but didn't find any...
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Old 8th October 2012, 08:54 AM   #4053
bcmbob is offline bcmbob  United States
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Did you scope with something in C13?
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Old 8th October 2012, 09:18 AM   #4054
bismuth is offline bismuth  France
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Quote:
Originally Posted by bcmbob View Post
Did you scope with something in C13?
No, tested board is DC coupled, but my square wave generator has a cap on its output and send no DC. I don't think amp's response in 5Khz region will change by adding another DC blocking input cap.
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Old 8th October 2012, 02:59 PM   #4055
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Hi Bismuth,

What is the output impedance of your generator? Do you have an input potentiometer in place? What value is it / where is the viper placed?
You have 330 pF input capacitance on Myref. (Did You control?) The Tau of the input lowpass filter is ~1usec, ~130kHz. IF your generator has not more than 50 ohm output impedance!
On your picture the Tau (if that is really a 5kHz square wave, 40usec/div)) is something around 20/30usec, a lot higher than the design value.
Other possibility: Did You control the compensation cap values?

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Old 9th October 2012, 12:01 AM   #4056
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Check the input RC filter - what I included in almost every kit was 3k3 and 220 pF, though some kits may have had a 180 pF FKP2. In all cases, the input low-pass has an RC of about 0.6 to 0.7 usec.
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Old 9th October 2012, 07:31 AM   #4057
bismuth is offline bismuth  France
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Thank you very much George and Siva, I've checked the on board RC filter, it is 3K3 and 220pF.
I do not know the output impedance of the generator, I've to check that.
I guess I didn't do my homework correctly before plugin the generator directly without a pot, I now just tried to put a potential divider (3K/3K) to adapt impedance to see what happened. I do not know what I did wrong but I fried one my monoblock ! I think the LM318 is dead, no more relay clicking on startup and huge DC on LM318 output (pin 6)....
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Old 9th October 2012, 07:41 AM   #4058
soongsc is offline soongsc  Taiwan
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The MyRef design generally has a lower voltage bandwidth than a general chip amp. However, due to the different operating topology, this can be expected. I would not worry about the square wave.
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Old 9th October 2012, 04:34 PM   #4059
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what does the phase tracking look like on myref?

a local techie was telling me the other day the reason why accuphase was such an endearing listen was because of accurate phase (i already knew this, though). and I wanted to tell him that myref probably sounds better but didn't have any facts to back up my claim.

so is myref's phase response accurate?
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Old 9th October 2012, 04:40 PM   #4060
soongsc is offline soongsc  Taiwan
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I do recall I have posted some measurements a while back. Phase lag in the speaker is much more than the amplifier. If the amplifier is designed to specifically improve the phase response of the total system, that is where the improvement can be outstanding. But the MyRef is not a pure voltage source amplifier, so it needs to be considered in a different way.
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