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Dynaco PAS3 Blend Switch resistor(s) question

BuzzK

BuzzK

AK Member
Subscriber
I see there are two different sets of resistors on the blend switch used with the Dynaco PAS3.

The (presumably) older version has 560K & 270K resistors in the network between switch pins 2,3 & 4.

The PAS3X uses 68K and 33K in those positions. The ratio is essentially the same, but they are nearly an order of magnitude different.

Is one set a better choice than the other?
 
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Are the volume and balance pot values by chance different as well? All three affect input impedance, which honestly really only matters with the phono stage. Too low and it can start rolling off at the bottom.
 
The resistor change is related to Dynaco's Derived Center Channel System. The original PAS 2/3 blend configuration was intended to alleviate the "hole in the middle" effect with wider speaker spacing. The later blend configuration is more aggressive and meant to better correct crosstalk created by the third speaker implementation. The initial PAS 2/3 modification involved only the 33K resistor with the 68K change appearing with the 3X, perhaps to make the blend steps more even. You can read about the center channel system in the following Dynaco write up from way back. This particular pdf copy from the web is a bit faint but readable. The center channel scheme as it applies to the PAS begins in the second paragraph on page 2.


The following image is from my PAS Line Stage article which shows the basic blend schematic and a chart with the measured differences between the PAS 2/3 and 3X.

PAS_Blend_SW.JPG
 
Last edited:
gadget73 said:
Are the volume and balance pot values by chance different as well? All three affect input impedance, which honestly really only matters with the phono stage. Too low and it can start rolling off at the bottom.
Click to expand...
They appear to be the same in both versions.
 
audioregen said:
The resistor change is related to Dynaco's Derived Center Channel System. The original PAS 2/3 blend configuration was intended to alleviate the "hole in the middle" effect with wider speaker spacing. The later blend configuration is more aggressive and meant to emulate the additional center speaker used in the original 3 speaker stereo scheme. The initial PAS 2/3 modification involved only the 33K resistor with the 68K change appearing with the 3X, perhaps to make the blend steps more even. You can read about the center channel system in the following Dynaco write up from way back. This particular pdf copy from the web is a bit faint but readable. The center channel scheme as it applies to the PAS begins in the second paragraph on page 2.


The following image is from my line PAS Line Stage article which shows the basic blend schematic and a chart with the measured differences between the PAS 2/3 and 3X.

View attachment 3070291
Click to expand...
Terrific information. Thank you very much!!
 
I used to own a PAT-4 (kit) with the Blend feature. I think Blend can be a useful feature to help tame early stereo recordings where instruments are panned hard left and hard right. I am thinking of adding a simple blend circuit to insert between my preamp out / power amp in on my marantz integrated.
 
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