Well I have just about finished my first express build (which is my first tube amp build) and I have a question about the gain/volume. I knew going into this project that it would be a beast but I was very supprised at the SPL this thing puts out at the lowest gain setting. I can't put the volume past 1 without needing hearing protection. In fact, even with the volume/gain all the way down I still get signal getting through. Is this normal with this design? I aso get a tremendous amount of Hiss. I have checked all wiring and pot values, I even replaced my volume pot. With that said, is does sound great!
WilliamDouglas wrote:I knew going into this project that it would be a beast but I was very supprised at the SPL this thing puts out at the lowest gain setting.
Yup yup. That's why I like master volumes on my TWs. You can try a PPIMV (LarMar) master, or power scaling like the Hall VVR. Both will reduce hiss as you reduce the master, making bedroom/home playing much more reasonable.
I build and repair tube amps. http://amps.monkeymatic.com
xtian wrote:You can try a PPIMV (LarMar) master, or power scaling like the Hall VVR.
I was looking at th LarMar and I have a question. The schematics show the 220k resistors removed and the MV pot connected directly to the tubes. So the 2.2M Pot takes the place of the 1.5k's and they also get removed? Should there be a fixed resistor to limit the minimum resistance?
Hi,
the LarMar has no 2m2 Pot. But is a stereo pot with 2 2M2 resistor on each mid to out lug.
Usualy from 250k to 1M. Depends of the max. grid value of the powertubes.
Only the 2x 220k have to be removed, nothing else. Because the pot make now the job of the 2x220k.
Haven't built an express yet, but if everything is working 100% then sounds like you need to play with different flavors of V1 and maybe V2 - Good NOS. Maybe you have one of those extra high gain Sinos in V1? This won't help with the quick gain of the Vol pot, from what I've read here you might want to try diff makes of pots too, something with a different taper. Might have to go to ebay for an oldie but goody or ask Apex Jr.
Different pots won't really make the amp quieter once it is up enough to clip, but it sure helps in dailing in your settings. I should mention on my original '85 Express the volume pot comes up so slowly that 1/4 up is barely playing, and 1/3 up is just starting to break up. Point is, Ken's choices in pots really made the amp more user friendly and made it so that all the knobs on 1/2 wasn't all that gainy. Good luck finding pots with as gradual taper as what Ken used, as his favorite pots were even becoming made of unobtanium when he used them. That said, find the most gradual taper pot you can find, like a 1 meg pot that is only ramped up to about 100k when on 1/2.
For newer type pots,the CTS are usually about 80k at mid point. And slower value changes after mid point. The Bourns are fairly close at about 85k give or take a bit. The Alphas about 130k at mid point.
The after mid point values---between straight up noon to 2 oclock--> CTS much slower increase in value change.Next would be the Alpha, then Bourns has a much larger or faster value increase from noon to 2 ocklock.
These will definitly effect how the amp sounds or reacts to the control position. You could even hand pick some to how you might want the amp to react. And as geetarpicker mentioned, compairing the taper to the older type too. Kind of similar to the guitar pot taper thread.
