Stepped Attenuator to replace Potentiometer.

Hello Mr. Porter:

It is good hearing from you. I spoke with you some time ago from up here in New Hampshire. We are using the original CA-250 monos from 1972 -- pretty much renovated throughout -- that was listed as MR-250 (for Marine Research). As for the controls on the front of the monos, they are gain controls. We have a Threshold Stasis R5 controlling the main volume. I was just wondering if it be worth an upgrade on the MR-250s to upgrade the gain controls to something like DACT attenuators, known for their precise management of signal levels; however, given the 25 meg ohm impedance on the gain control pots, I am at a loss as to how to get around this without having a tech do some surgery on the innards. Any ideas? Thanks and hope all's well in TX.

Thanks for the responses. I have not contacted Henry Wolcott as of yet; he and Mr. Lomax are quite busy (great, knowledgeable gentlemen by the way!), so I might first try the technician who knows these amps well enough to wrestle with their intricacies and quirks. Eldartford, I went to the DACT website and they offer the reknown CT-2 Attenuator, with the greatest resistance rating at 500kOhm. Given the gain pot on these monos indicates 25 meg Ohm -- and if my calculations are on track -- do you mean I would need to increase resistance by 50 Ohm were I to get the 500kOhm Attenuator? I'm not an engineer, so I just want to clarify.

I called Shallco and await response on an attenuator with a closer if not equal impedance match. You guys sure seem to know your stuff: Thank you for your informative suggestions, and long live audio engineering in advancing the Arts & Sciences.

Good evening to all. Pardon the misperception: I just zoomed in on the gain pot of each monoblock and I saw a faint "." stamp followed by a space in "OHMITE TYPE-AB 0. 25 MEG OHM." Apparently, this means I could substitute a 250kOhm resistance attenuator. Please correct me if I'm wrong, as I was with the previous calculation above. Thanks gentlemen.

The amps are not single-ended; they are push-pull at about 225W per side, each side using eight 6CA7's.

Ngjockey: that's a pretty technical question, which will take me a day or so to research: for now, all I know is that the input on the amps are the two pronged banana plug type (I plug the the male RCA connector coming from the preamp. into a banana plug adapter, which then gets plugged into the banana inputs on the monoblock).

By the way, I contacted Marchand Electronics and they are making up a set of Elma attenuators. I briefed through IAG's attenuators -- they appear to make some cutting-edge Shallco attenuators; however, given the depth measurement on a Shallco attenuator, it would not fit inside these monoblocks without some surgery to the chassis and wiring infrastructure. Thanks again.