Your microphonics might be related to the particular tube you are using, it might be cheaper to try different tubes first before modifying if that is your major concern. I've tried the Tung Sol brand with success on this pre. Also there are some tube sleeves that help with microphonics like Herbie's or Pearl's, there are others. Good luck.
Thanks Kkm, and I think that some good isolation of the preamp would also help in this area.
Will the lowering of the gain from 23dB to 14dB help with the problem of limited volume knob range. I have read that it is not a good thing to have such a limited range. Anything over 11:00 starts the lights on my amp to start going out!!
Lowering the gain should help. It sounds like you are overloading the amp.
Thanks Rwwear. The modification that I'm thinking about at Underwood is said to put this preamp in-line with those costing $4 - $5k. Here is a full detailed list of mods at Underwood...I'm thinking of going for it!!
I have done simple modifications on this preamp myself. First, change stock feet to "superspike" type or equivalent. Take a 1" by 0.25" aluminum bar and bond it with marine epoxy to the underside of the top cover in the long direction. Then buy a pair of HAL-O damping instruments from Herbie's Audio Labs and put them on a pair of Tung-Sol D-getter NOS 5687, which you can get for under $100 per dozen on Ebay. Finally, put on a VPI Magic Brick at the rear middle of the top cover.
Voila - no more microphonics. The preamp is silent up to -10db attenuation. I have installed a -60 to - 10 db switched attenuator and silver contact selector switches, which I highly recommend. Really good ones are available from www.goldpt.com. Apparently the guy will give you custom 24-step attenuator if you tell him the range you want.
The service you cite looks good and comprehensive, but should include the attenuator for best performance. I consider this Marsh preamp the best line circuit available today. It is made to a price point and can be improved with better parts.
Dimitry, thanks for your thoughts and experience with this preamp. I am not much of a DIY type of guy, so I think I will go for the Underwood mod!!
I do know that when I switched from my old Outlaw 950 pre/pro to this unit, I heard an immediate improvement in every aspect of the sound I was getting from my maggies!! Much better soundstage, more dynamic with much better low end. Then I switched from an Earthquake Cinenova amp to the Marsh A400s amp...now my system really opened up!!
Well, as a follow up, I HAVE sent my Marsh P2000t preamp in for modification at Underwood Audio. I should have it back in a few weeks and will give my reactions and results as they become available!!
I have ordered a pair of mono 100K series attenuators from Gold Point. I will report on the effect of these instead of the Marsh's balance and volume dual Alps pots.
Can you give me some input on the inverted polarity of the P2000T output. The manual says this:
"The output signal is inverted polarity to the source signal, you may need to change the polarity of both left and right speakers cables to get correct program polarity"
Do I really need to hook my speakers up + to - and - to +??
If nothing else in your system inverts polarity. In my system, my cd player and amp both invert polarity, so they cancel each other out and I hook my speakers up normally (+ to +, etc.)
Well, polarity is a complex issue. Some people are sensitive to it, some are not. In a well recorded material, where relative polarity of all tracks is maintained, inverted polarity at playback is heard as lack of ambiance and pace in the mid-bass.
However, most material is not recorded in such a fashion. Often different tracks have different polarity and final polarity of the master is either "in-phase" or "out-of-phase" with the original event.
Therefore, since polarity is essentially random on most recorded material, it is not really necessary to maintain it on playback.
However, for those rare records and CDs that are recorded in constant and correct polarity it is nice to have it right on playback.
So, I do hook my speakers backwards, as per Marsh's manual. Since their manual is the first manual for a tube product that never mentions the word "tube" it is remarkable that they decided to include the relatively exotic topic of polarity into it.
I wrote to Marsh, that since their manual excludes instructions on how to change the tubes entirely, they should expect customers to start returning them in about a year, complaining of lack of air and drive.
I can report good results from bypassing the main coupling caps with REL TFT 0.1uf 400v units. The sound has gain more air and presence and improved in the areas of pace and drive.
However, the soldering required is a bit tricky, as the leads from the bypass cap can't touch the ground plane of the PWB and the main caps leads are only about 1/8" above it. Can be done - just need to be careful.
That, my friend, is why I am paying a pro to do this!! I am not a DIY type of guy when it comes to electronics.
My preamp will be delivered today...I can't wait to hear it. BTW, I also bought an Onyx XCD-88 HDCD player from Underwood HiFi with a level 1+ modification. It is the same machine as a Music Hall CD-25 which I have read many good reviews on!! Both ar made by Shanling.
Well, how does the darned thing sound after the upgrade ? I am installing Gold Point attenuators shortly and plan to add at least some of the commercial mods via homemade tinkering...
It is still breaking in, but I can report very good sound so far. I am also breaking in an Onyx XCD-88 mod unit that I bought from Underwood.
I'll send you a couple pics Dimitry!!
After about 200 hours of burn-in and some new sub cables, everything about the sound of my system is BETTER!! I can now turn to listening to the music instead of the system!!
Here are a few pics if you are interested...