D1 Volume adjustments

hifimaker · 17th October 2007, 06:21 PM

Can anyone confirm if this is the correct output behavior for the D1?

With the attached SIM's see how the vertical alignment of the output voltage swings with the minimum and maximum settings of PL55. PL55 set to minimum seems right, but at maximum the signal voltage decreases slightly, and the +/- waveforms change their vertical alignment.

Somehow this cannot be correct?

-David

hifimaker · 18th October 2007, 04:32 PM

Anyone??

BTW, Here's the schematic.

-David

cviller · 19th October 2007, 02:36 PM

That PL55 circuit looks a bit odd to me, where is it discussed? Or what is it supposed to do?

I have simulated on D1 before, but I can't remember my exact voltages. I do however think the 10Vpp is quite high for this configuration.

hifimaker · 19th October 2007, 05:52 PM

PL55 is straight from the D1 Service manual as a volume control.

I believe a lot of DIYer's have not included this in their own implementations.

Attached is the PL55 diagram.

Thank you for any help!

-David

hifimaker · 19th October 2007, 06:01 PM

I'd really like to know why PassLabs placed the 4.7u cap C1 on the wiper of PL55!

Running a sim with the cap removed I get the correct vertical phase output with PL 55 set to 90%.

What is the purpose of C1?

-David

cviller · 19th October 2007, 06:04 PM

Oh, I see!

I'm not sure, but it kinda looks like it is implemented differently on your schem compared to the service manual.
In the service manual, I supose the "volume+" of PL55 is connected to "vol+" of the IV diagram, and if this is correct, the capacitor C1 is just left dangling in parallel with the resistors until the wiper. In this way, unlike your schem, the capacitor is not placed between the active nodes.

It does however seem a bit odd to me, but it might be worth a try in the simulator.

cviller · 19th October 2007, 06:06 PM

Great - you tried my suggestion even before I posted it!!

cviller · 19th October 2007, 06:07 PM

I think C1 is there to suppress noise picked up on the floating resistors.

hifimaker · 19th October 2007, 06:25 PM

Thanks cviller for helping catch the schematic error!!

I fixed the connection to PL55 and the circuit now seems to sim correctly with the C1 cap in place.

-David

cviller · 19th October 2007, 06:28 PM

Cool. Then you just have to replace the irf610 with jfets as papa always suggests...

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19th October 2007, 02:36 PM	#3
cviller diyAudio Member Join Date: Dec 2005 Location: Copenhagen Blog Entries: 2	That PL55 circuit looks a bit odd to me, where is it discussed? Or what is it supposed to do? I have simulated on D1 before, but I can't remember my exact voltages. I do however think the 10Vpp is quite high for this configuration.

19th October 2007, 06:04 PM	#6
cviller diyAudio Member Join Date: Dec 2005 Location: Copenhagen Blog Entries: 2	Oh, I see! I'm not sure, but it kinda looks like it is implemented differently on your schem compared to the service manual. In the service manual, I supose the "volume+" of PL55 is connected to "vol+" of the IV diagram, and if this is correct, the capacitor C1 is just left dangling in parallel with the resistors until the wiper. In this way, unlike your schem, the capacitor is not placed between the active nodes. It does however seem a bit odd to me, but it might be worth a try in the simulator.

19th October 2007, 06:06 PM	#7
cviller diyAudio Member Join Date: Dec 2005 Location: Copenhagen Blog Entries: 2	Great - you tried my suggestion even before I posted it!!

19th October 2007, 06:07 PM	#8
cviller diyAudio Member Join Date: Dec 2005 Location: Copenhagen Blog Entries: 2	I think C1 is there to suppress noise picked up on the floating resistors.

19th October 2007, 06:28 PM	#10
cviller diyAudio Member Join Date: Dec 2005 Location: Copenhagen Blog Entries: 2	Cool. Then you just have to replace the irf610 with jfets as papa always suggests...

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