Steve -- Something surely seems amiss with the phase reverse switch/wiring. It shouldn't do anything but basically reverse the speaker connections to the right speaker. If the switch allows the right channel speaker to operate in the normal position, but the sound all but disappears when the switch is set to reverse, then either the switch or its connections must be at fault, as the wiring between the switch and the rear connections is always used regardless of which position the switch is in. Be sure to get that resolved before turning the volume up high with a source playing but the right speaker not sounding due to the phase switch being in the reverse position. That scenario effectively amounts to no load being placed on the amplifier, which under high volume conditions is not healthy for any one of a number of components.
OK. Some discussion on the minimum volume signal bleed issue in the X-202: As a basic statement, it is the result of the physical design of the unit, in conjunction with the use of modern high output digital sources.
The X-202 is not the only product to suffer from the "won't turn down" issue. For example, I have a Scott LC21 preamp, that was meticulously built, that would exhibit the same symptoms that Steve is describing with his X-202. There are others as well. At the heart of the issue is (typically) modern CD players, that rather routinely output 2 volts of signal, which is 4 times the rated input voltage for the Scott, and at least 8 times that for the Fisher. Some units, like Heath's AA-141 preamplifier simply roll over and give up -- not displaying any bleed-over issues -- but producing gross amounts of overload distortion at any setting of the volume control. To make that unit really behave and operate properly with modern sources requires nothing less that a complete redesign of the unit. In the X-202, such extremes are not required, but correcting the possibility of minimum volume bleeding does require some deliberate corrective action.
The high source levels can also produce other problems in vintage equipment as well, causing volume controls to operate down "in the weeds", where channel tracking is usually anything but good. A number of folks use external attenuator pieces that cause the volume control to operate up higher in its range of rotation, simply to address the channel inequity that can occur at lower settings. But the attenuators are also helpful in subduing signal bleed issues as well, because they reduce the signal level floating around inside the chassis, and therefore, the tendency to produce bleeding from one circuit, to another. So, one approach to the signal bleed issue is to use external attenuators for all the benefits they can offer, and call it a day.
In my own listening room, my Denon CD player has a variable output, whose setting has been set at 50% of its 2 volt rated output for so long that I forget about the fact that its output is reduced. In the case of my own equipment, the reduced setting is not used to address any potential signal bleed, channel imbalance, or gross distortion issues but rather, to simply obtain a smoother volume control "action", versus one that would be rather touchy by comparison. With the client's X-202 that I have here, along with my own X-202, this reduced output doesn't present any observed operational problems, as in, problems that draw your attention as is the case with Steve's unit of this thread. However, with an intentional scrutiny of the volume control's minimum volume action in both my own and my client's unit, I too observed that technically, the right channel does not reach the same minimum volume level that the left channel does. Then, remembering the reduced output that I use, I ran the Denon's output up to maximum (2 volt) output. This definitely made the minimum volume level more pronounced, and more unbalanced between the channels as well -- not to the extreme that Steve is indicating -- but enough that with three units now all displaying the same tendency to one degree or another, it meant that likely, something in the original design or build of these units was contributing to the effect, and therefore not only for my own clients, but the good of the Fisher community as a whole, should be investigated.
In a nutshell then, what's happening is that because of the much higher than ever expected input levels, coupled with the high sensitivity of the X-202 design -- and where the volume control appears in the circuit, it means that there is plenty of opportunity for circuit interaction, where the signal at one point, can jump to other areas it was never intended to be at -- at least, not from that circuit point anyway. This is all aided by the high input impedance levels that vacuum tube amplifier stages typically represent, in close quarters with the two Cathode Follower stages that the X-202 employs. These stages act like blow torch transmitters of the highest signal level that appears within the chassis for other stages and points in the circuit to pick up. At normal listening levels, this bleeding is inconsequential as the actual level of signal that bleeds to other areas is really quite small and very frequency dependent -- unless the input signal level is much high than specification and the volume control is turned to minimum: then you hear the effects of this scenario rather easily, which is only made worse by a small quiet room and high sensitivity speakers. Packing a lot of performance into a relatively small chassis is always a recipe for potential concerns (which is what the X-202 represents), and is exactly the reason that the highest performance systems always include separate pieces to handle small and large signal amplification. The build of the X-202 was certainly good enough for the source levels of the day, but in the audio environment of this day, some examples of it can become challenged.
The answer to the problem is simple: just add some shielding to prevent the signal interaction. That's true, but the trick is to find out where and how much. As is usually the case, the real answer lies in a combination of shielding the components that can be shielded, while relocating those that can't be otherwise shielded to a less sensitive location -- and doing it all in a neat, orderly fashion, so as not to make the modification draw attention to itself. After a couple of rather intense days of going after this issue, I've developed a series of four modifications that when implemented in the X-202, will make any signal bleed between circuits a nonissue. More specifically, they allow a three volt rms signal (overload point) to be applied to any of the high level selector switch or Tape Monitor inputs, and require your ear to be within 1 ft of 101 db efficient speakers to hear any source material from either speaker. Standing in front of these (Cornwall) speakers in a small dead quiet room, the minimum volume signal with this input level applied is inaudible at even a close field listening position. The reduction is significant in units that suffer excessively from this issue.
I will start a new thread to outline the actual procedures of the modifications, but suffice to say, there a few rules that need to be observed when restoring an X-202:
1. Around the tone control amplifier stage of the X-202 (Sams V4), neat, tight work is a must. Long leads are an antenna just asking for bleed type problems to occur.
2. Ditto for using large, oversized boutique or otherwise replacement components in this area. They too act as giant antennas to pick up unwanted signals.
3. The bottom plate is also part of the shielding relative to this issue. Not only does its installation minimize hum and noise in the X-202, but signal bleed as well.
Finally, the X-202B is the continuation of the X-202 line, and it's interesting to note just how compartmentalized the build of that amplifier is -- almost surely to address potential issues of bleeding that would otherwise exist from one unit to the next in a hand wired, mass produced piece of equipment. In that way then, the X-202B is an improved build over that of the X-202. I should have a thread on the modifications that provide the proper shielding posted soon.
Dave
