Anyone with Manley Chinook use a custom Power Cord?

JB, On the subject of changing capacitors, the basis for choosing the value of the output coupling capacitors is to provide for the best possible extreme low frequency response, first of all.  (f = 1/2*pi*R*C, where R is the net impedance seen by the capacitor in Ohms, and C is the capacitance in Farads). That calculation determines the minimum value of the coupling capacitor, depending upon where you want to cut-off the LF response.  The next consideration is the overall SQ of the capacitor that you choose.  In this case, you say you switched from the OEM 30uF capacitor to 3.3uF and then to 12uF.  30uF is going to be way overkill using any imaginable amplifier, in achieving a high pass filter that goes down below ~2Hz, which is more than adequate.  But lower values of capacitance can also give you a 2Hz cut-off frequency or near enough to it in the real world.  That depends upon the parallel sum of the impedances that the capacitor works into.  Like I said above, nearly any amplifier you might own (solid state or tube) will have at least a 10K ohm input impedance.  Most will be higher.  10uF capacitance is sufficient yield a ~2 Hz high pass filter into 10K ohms. (Insert the values into the equation above, to see what I mean.)  If you are driving a tube amplifier with a more typical 100K ohm input impedance, then even a 1uF capacitor will do the job.  The next question is SQ. Yes, it is possible that your 12uF capacitor just happens to sound better than your 3.3uF capacitor; you haven't stated the types or brands that you chose.  In that case, the 12uF will sound better simply for the fact it IS better, not because a higher value is necessarily doing you any particular good for low bass response.  In the case of your Chinook and my Steelhead, the OEM coupling capacitors are 30uF in value and the brand is either REL or MIT (made by REL) metallized film type.  REL make some wonderful capacitors, but this particular type is not among them, in my opinion.  So I made my changes not only because there is no point in using such a large value capacitor in this application, but in addition because the particular 30uF capacitor they chose is not optimal with respect to SQ, in my own opinion. 


Manley were concerned with cable capacitance, when they chose to use such a high value of coupling capacitor and to insert the 47 ohm resistor in series with the output.  Their choice enables the units to drive very long runs of cable with high capacitance, without messing up the frequency response, but I just viewed their choice in that case as overkill.  I would never use such long and capacitative cables in the first place.  Many manufacturers make choices like this simply because they count on the end user abusing their product, e.g., by asking the preamp to drive 40 feet of high capacitance cable.  Then the end user comes away critical of the product when it fails to perform well under such a ridiculous stress.

etnier, My unit is a Steelhead.  I am not sure that it is configured exactly like a Chinook, so you would need to confirm that first.  I was also unable to obtain a schematic of the Steelhead.  Even my professional tech who runs a thriving repair business was unable to obtain it.  My insight comes from a verbal description of the circuit provided by Evanna Manley in the context of a review of the Steelhead published years ago in 6 Moons.  According to EM (and confirmed by my investigating the circuit with an ohmmeter), the 6922 is the only tube involved in the phono equalization and gain circuitry. 

The two 5687s are used as cathode followers (CF), as follows:  Output from the phono section goes through the first CF, which is actually a complex type called a "White Cathode Follower", requiring both halves of one 5687.  This drastically lowers output impedance and drives the volume control via a 47 ohm resistor in series with a 30uF capacitor in the original design, if you use the Steelhead as a full-function preamplifier, as I do. (If you use it only as a phono stage, bypassing the volume control and other switches, then the 47-ohm resistor/30uF cap would be driving the input of your linestage.)  According to my meter, the volume control has a 5K ohm input resistance, which is very low compared to most.  However, 30uF is very high value for a coupling cap, even one that has to drive a 5K load.  And it's way higher than needed to drive any reasonable linestage. Manley used a (mediocre in my opinion) metallized polypropylene type here.  By my calculation, all you need is 12uF into 5K, to get a hi-pass filter at 2Hz.  The closest to that value and best I had in my stash is a 10uF/200V MIT polypropylene film and tin foil type, far superior to the original cap in SQ.  (Last time I looked, Michael Percy sells the MIT caps.) So I used that in place of the 30uF cap.  (The difference between the calculated 12uF and 10uF is academic at best.) The 30uF cap and the 10uF MIT cap are about exactly the same in size, so no problem with fitting it in.  I also bypassed the 47-ohm resistor; this serves no needed function unless you are driving VERY high capacitance cables to a linestage, and I don't.  It's totally superfluous for driving the volume control.

The volume control drives another WCF using both halves of the second 5687, which drives the input of an amplifier, in the case where you use the Steelhead as a preamplifier.  Most amplifiers have an input impedance north of 10K ohms, if solid state, or north of 50K ohms, if tube type.  The Steelhead has another 47-ohm resistor in series with another 30uF capacitor at its output here.  The 30uF capacitor is once again way overkill for driving even 10K ohms. I deleted the 47-ohm resistor and replaced the 30uF capacitor with a 4uF/250V polystyrene and tin foil coupling capacitor. (I had these in my stash; you cannot buy them any more, but you would use the best possible 2 to 4uF capacitor here, if you are driving anything above 20K ohms.)

The difference is "startling".

 I didn’t have any reservations about changing the output coupling capacitors in my steelhead, because it is several years old and I am not the original owner. Thus I assume that I have no warranty in place. However, Manley seem to be very in tune with tweakers. I wonder whether they would sanction capacitor upgrades if done by a qualified tech or at their factory.

you can’t go wrong spending 69 bucks on a PC. If you don’t like it, there’s no harm.

Apologies to slaw, but I have come to think that SR is throwing sand in the public eye with $150 fuses and many (but not all) of its other tweaky products. While I also question the bang for buck value of very expensive power cords, at least there you can objectively identify desirable characteristics and aim to achieve them. 

I own a Steelhead. I’ve thought about upgrading the load resistors to nude vishay, but my prior experience with that sort of tweak on other phono stages suggests to me that there is little to be gained. I could be convinced otherwise.

Like I may have written above, the major kludge in the Chinook if the output stage is like that of the Steelhead is the choice of output coupling capacitor. The value is way higher than necessary for good bass response and the quality is mediocre at best. Upgrade those and you will be amazed.