Deleted
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Post by Deleted on Oct 25, 2010 22:34:04 GMT
The 2 caps in question are the generic white caps in your photo labelled 4n7 and 683. They are unlikely to be better than 5% tolerance at best. The 68nF polyprops are fairly large physically, but the Panasonic type that I used had the leads cranked out to 5mm spacing. Would 68nF Vishay MKP1837 do the trick better than 683? What about some polystyrene instead of 4n7? That would be pretty easy fix. Valter I think the close tolerance may be more important here than the actual type. If the Vishay polyprop (MKP) is 2% tolerance, or better, it should be fine. Polystyrene are also fine provided they are close tolerance.Incidentally several RG members have verified this improvement in the SC DAC thread or via emails and PMs. The same also works well for the DIR1703E in the X-DAC V3.This has also been confirmed. Alex P.S. These 2 caps are part of a "flywheel circuit" as it used to be referred to with earlier Video decoder chips.It helps to stabilise PLL action. |
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Post by freddypipsqueek on Oct 26, 2010 17:53:32 GMT
Thanks Alex. I'll pick use an old USB cable and get the clippers out. Incidentally sent an email to Analogue Seduction as follows, Question / Comments: Are you able to supply one of the following, www.aqvox.de/usb-power_en.html A AQVOX USB Low-Noise Power Supply. Reply: Hi Adrian Thank you for your enquiry We can supply this item for 77.99 + 2.99 postage |
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jkeny
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Post by jkeny on Oct 26, 2010 18:10:19 GMT
Remember if you are DIYing this that you CANNOT cut the ground wire of the USB cable - this has to be connected between the PC & the device - you will have to splice your new PS ground into the existing USB ground.
This applies to the Aqvox device also & so their statement of " No galvanic / electrical connection of the powerlines from the computer." is incorrect (unless they are using a USB isolator which they don't make reference to!)
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Post by freddypipsqueek on Oct 26, 2010 18:38:10 GMT
John.
Thanks for your comment.
If I buy a USB 3 card and "remove" the +5 volt line from one of the sockets (leaving the data + & - and the ground) will that help (or even be worth trying).
My cable is a Wireworld thing worth a bit and I'm thinking a dedicated USB card maybe worth a try (?).
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jkeny
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Post by jkeny on Oct 26, 2010 20:08:42 GMT
Yes I would think that it will help if you are supplying an external, clean +5V but you will need to also connect your external ground into the PC/USB ground somehow, otherwise you risk possibly damaging the USB device.
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Post by freddypipsqueek on Oct 26, 2010 20:46:34 GMT
John.
I was thinking of simply breaking the 5v line and leaving the original ground (in the lead) connected. I beleive the usb device is powered within the DAC and thus the 5v line is only creating the hum. I think this is what Alex was hinting at.
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Deleted
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Post by Deleted on Oct 26, 2010 20:47:42 GMT
Remember if you are DIYing this that you CANNOT cut the ground wire of the USB cable - this has to be connected between the PC & the device - you will have to splice your new PS ground into the existing USB ground. This applies to the Aqvox device also & so their statement of " No galvanic / electrical connection of the powerlines from the computer." is incorrect (unless they are using a USB isolator which they don't make reference to!) John is correct. The USB Power Injector , for example, only breaks the pin 1 Vbus leads. The external PSU used should not have the 0 Volts side earthed. Alex |
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Post by Deleted on Oct 26, 2010 21:35:46 GMT
Earlier in the thread I made reference to the possibility of the
74HC04 oscillating at 10s of MHZ when there is no signal. '
The 74HC04 has a much higher open loop gain and phase shift between it's Input and Output than the 74HCU04.
This is because each section of this Hex Inverter is actually 3 CMOS inverters in series.
Alex
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FauDrei
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Post by FauDrei on Oct 27, 2010 1:56:27 GMT
I've been doing some reading around... I think I'd go for 74VHC04 (I can not find 74VHCU04 on my usual webshops).
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Post by Deleted on Oct 27, 2010 2:03:01 GMT
I've been doing some reading around... I think I'd go for 74VHC04 (I can not find 74VHCU04 on my usual webshops). Valter Silicon Chip uses them in the SC DAC and a new project for a SPDIF to Toslink Converter. However, they did say that the 74HC04 is easier to get. Alex P.S. In Australia,(at least) Farnell (now Element 14) stocks the 74HCU04 |
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