Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jerrydyer on July 13, 2011, 02:42:58 pm
-
I have two similar preamps but one has .022 all throughout and the other uses .047.. it has 4 gain stages and I also changed the entrance to the PI cap to .047. the one with .047 sounds constipated and just does not have the sustain and singing quality the one with .022 's throughout. I know im lowering the bass cutoff but I didnt realize how BIG of a difference this would make. I used them out of convenience. this make sense or am I high? ( I dont get high anymore. At least not on pot.. Margarita every now and then)
-
It makes sense to me . You have twice the capacitence so with the .047 you are allowing more lows to pass cutting highs. I know when I made my fender build I used the .1uf values of the 5E3 in the preamp coupling cap and replaced it with a .022 . Now I had a heavy duty speaker in the amp at the time which brought out more lows , I changed the cap to the .022 , I can't say to contradict myself that I heard much difference , I changed the speaker and that made the difference but left the .022 cap in place..never did put the .1 cap back in. My main issue was the tone control had to be on full treb to get highs.
I suppose it depends on the amp and all else as well
-
"constipated" is another one of those subjective words that mean any number of things to different people but...you are right in that there's more bass thoughout the entire preamp which can have detrimental negative effects to tone, sustain, oscillations, etc. Bass is the primary frequency range responsible for blocking distortion. Even in minimal amounts it can have an effect of muddying up your tone very quickly and when muddiness is compounded and reamplified it can get even uglier in a hurry. As Merlin & Aiken suggest, each gain stage can be manipulated to increase hi & low frequencies from what the input signal contained just as you can reduce these frequencies too. The trick or better to say 'task' on designing multiple gain stages is to find the right balance through each gain stage to the other and amplify the 'right' frequencies AND in the correct way too. Simply changing coupling caps or tone stack values isn't really enough because knowing how to utilize your load line w/ voltage, load resistors, cathode resistors, bypass caps, smoothing caps, feedback loops, etc. all come into play here along with the coupling caps. This being said, subbing a .02mF w/ a .002mF early in the first one or two gain stages can make a very nice improvement w/out making things overly complicated. For me it's got to where my first gain stage (or two) can easily use a 2k2 w/ 2.2uF for the cathode to also go along w/ the .002uF coupling cap afterwards where it works and sounds beautifully going forward.
-
exactly, like walking a tight rope. Im having great results with the .047 in the first gain stage. these two circuits are almost identical except for that switch noted above. thanks guys for the help )confirmation)_