[briantf27]

So I thought I'd make another simple mod to my MG Head with 47k pot input->wiper shunt resistors as recommended by Videoshielded.... Yeah Right!!! In the process of simply soldering the Caddocks to the stock Alps pot I lost the right channel. Input to wiper is now open. So off to angela.com I went and ordered up the economical Alps blue velvet. (http://www.angela.com/catalog/potent...Alps_Pots.html) In a timely manner, it arrived but low and behold the b!tch didn't fit!!! Looking back at the original pot, the shaft was not positioned dead center which allowed for enough clearance between it and the PCB in the MG Head!

So out came the dremel... I managed to reshape the top side of the circular hole (now eliptical) in order to provide enough clearance between the bottom of the pot and the PCB. Of course, a few kickback incidents renderred the front panel permanently scarred, but what are you going to do.

I also had to shave off the ancor stud on the Blue Velvet, because it was too large and not oriented correctly for the MG Head. The stud isn't needed anyhow, because once screwed in the thing has nowhere to go since it is resting on the PCB below it. The dremel easily performed the task of removing the stud as well as shortening the shaft length.

Well now that's all in the past... on to listening.... One word: WOW ! Of course now I've got a different pot in addition to the Caddock shunts, so it isn't a direct comparison.... Nevertheless, this is a completely different amp today. It is really astounding, and has catapaulted to the top of my list of bang for the buck MG Head improvments one can "easily" make.

HIGHLY HIGHLY recommended. The detail is so vastly improved that I can't believe I actually enjoyed this amp prior to this mod!! I am hearing things in every track of every CD that I haven't heard before. Literally. Its really unbelievable how homogenous the overall sound was before, and how distinct each component of the sound is now. This beats the improvement you get from tube rolling from the stock tubes to cream of the crop NOS tubes by at least an order of magnitude.

Do yourself a favor if you own the MG Head and make this mod. And after you do, tell your friends! One FYI: the Alps Blue Velvet doesn't seem to attenuate evenly once volume gets fairly low. And there is not much room between comfortable listening volume and zero volume. Therefore I'm considering getting a 250K pot and slapping that in. It should move the comfortable listening postion from where it is currently (1/8 of a turn) to somewhere between 1/4 and 1/2 turn depending on the taper. Perhaps, then, the shunt should be on the order of 100k. Hmm. Not sure....

Brian.

 

[Videoshielded]

Yipee, congrats! Yeah, it's a heck of a mod. The only two other things I know of that will kick it up a similar notch are (a) replacing the coupling caps and all the resistors or (b) putting constant current source boards on the plates of the driver tube. I've done both and continue to enjoy them a boat-load.

Sorry the install turned out to be like marine maintenance. The stock pot on my MG Head has always been a touch flaky and I've been thinking about replacing it. Now I know what NOT to get.

 

[briantf27]

Quote:

Originally posted by Videoshielded Yipee, congrats! Yeah, it's a heck of a mod. The only two other things I know of that will kick it up a similar notch are (a) replacing the coupling caps and all the resistors or (b) putting constant current source boards on the plates of the driver tube. I've done both and continue to enjoy them a boat-load. Sorry the install turned out to be like marine maintenance. The stock pot on my MG Head has always been a touch flaky and I've been thinking about replacing it. Now I know what NOT to get.

Hey long time no see, VS!

The pot itself, I would think, is in part responsible for the improved sound. I just have a hard time believing the shunt did *this* much. And if you have a steadier hand than I do, perhaps you could avoid the dremel kickback when enlarging the opening for the new pot.

One question I was going to throw at you was about increasing the sweep range on the pot. Right now I go from 0 to approx 1/6 of turn before the volume is too loud. I'd like that to be about 1/2 a turn or so. My thought was to put a couple 100k resistors in front of the pot at the inputs to create a voltage divider. What do you think? Also, if I do this, do you think 47K is still an appropriate shunt value?

Thanks!

Brian.

 

[Videoshielded]

Based on my experience, the improvement could well all be attributable to the shunt. Pots really, really crud up an input signal.

I don't think additional input padding is going to give you significant extra control. You won't likely move the volume down that much. But it might work if you only need a little wiggle room. You might put the padding resistors in-line in your RCA plugs if that's easier than mucking around in the amp.

More likely you need to t-pad the shunt. I've proven through trial and error that I have no instinct for selecting the resistor values. Best you consult here: http://www.siteswithstyle.com/VoltSe...ure_Shunt.html

 

[briantf27]

Quote:

Originally posted by Videoshielded Based on my experience, the improvement could well all be attributable to the shunt. Pots really, really crud up an input signal. I don't think additional input padding is going to give you significant extra control. You won't likely move the volume down that much. But it might work if you only need a little wiggle room. You might put the padding resistors in-line in your RCA plugs if that's easier than mucking around in the amp. More likely you need to t-pad the shunt. I've proven through trial and error that I have no instinct for selecting the resistor values. Best you consult here: http://www.siteswithstyle.com/VoltSe...ure_Shunt.html

Wow, great link. I love the java script that calculates your resistor values. I'll give it a shot. Not sure that the output impedance of the T matters, so for the sake of just being able to use the same resistors I'll have it match the input impedance.... Will let you know how it all works.

Brian.