Input impedance of Dual Mono

markC · « **on:** 11 Nov 2003, 03:30 pm »

The input impedance of the original stereo Stratos is stated as being 10k ohms. Is the updated version of the Dual Mono, (with new Plitron trannys and updated circuit boards), the same? Klaus? Anyone? Reason I'd like to know is b/c I'm thinking of upgrading the volume pots. in my dual mono preamp and it seems that matching the impedance of stepped attenuators to the amp's input impedance is the way to go.

klaus@odyssey · « **Reply #1 on:** 12 Nov 2003, 03:08 pm »

Hi Mark,

It's the same. All Symphonic Line amps are 10 k. Which pot are you going with ???

markC · « **Reply #2 on:** 12 Nov 2003, 10:26 pm »

Thanks Klaus. I'm leaning strongly towards a pair of goldpoint ladder stepped attenuators. Whada' Ya' think? Seems to be the concensus to stick with the 50k impedance version which is what the the existing pots are, rather than 10k to match my DM's input. Klaus, your opinion on this would be much appreciated.

speedcenter · « **Reply #3 on:** 13 Nov 2003, 12:45 am »

the resistance in the attenuators will also depend on how much output your preamp has. I use a bottlehead foreplay tube preamp, and had to build attenuators running -20 to -67db to have a reasonable range of volume control. The default -20 to -50 was "trigger happy" Een at -67db, I still have a quite "loud" minimum volume setting on my 12 step attenuators, while in the range that matters most, I have several clicks separated by 2db.

The best way to pick (or build_ an attenuator is to put regular pots into the preamp, turn it to the lowest position you want for the attenuator, then measure the pot resistance, repeat the same with the loudest setting, and maybe add a few percent. If you buy the finished attenuator, you can use these numbers to order the parts. If you build them, you can use a spreadsheet to calculate the resistor values needed to give you the desired steps.

Sounds complicated, but the resources available online are good enough that even I was able to do it

Peter

markC · « **Reply #4 on:** 13 Nov 2003, 08:06 am »

Thanks Peter, I do believee that the-64db will be right for my application.

theint · « **Reply #5 on:** 13 Nov 2003, 03:52 pm »

The volume control is on the front end of your preamp. It will have no effect on the output impedence of your preamp and has no effect on your power amp. Changing the impedence of you antenuator will be seen at the front end of your preamp, ie your CD player. I would stick with the traditional 50K.

klaus@odyssey · « **Reply #6 on:** 13 Nov 2003, 06:02 pm »

Agreed

markC · « **Reply #7 on:** 13 Nov 2003, 08:22 pm »

Well, if I didn't know better, I'd believe that TheInt knew what he was talking about hehehe. Maybe I'll ask him tonight when he brings over his new "Tubelock" amplifier, (that he designed and built), for a test drive.