|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
76.90.39.24
In Reply to: RE: A question about system and stage gain balance. posted by kyle on October 14, 2016 at 08:20:56
"if you make a 300B amp with a 6SN7 driver loaded with a CCS, you could run the driver tube at 250 V P-K from a 350V supply, 10mA and -6V on the grid. The 6SN7 has a mu of 20, most of which is available if CCS loaded, so it could easily drive the 300B grid to 80 volts with ~4 volts from the preamp. The curves still look good at these op points and there's no stress on the tubes.Is there a downside to this approach?"
IMO there is no downside at all.
In fact, I go even further.
If you can live with the reduced power, a passive preamp and a CD player with max output of 2vrms will insure that the 300b is never over driven.
There is a lot of technical benefit to that.
BTW the signal output voltage rating of a preamp (or a CD player) is RMS.
A 300b biased at 80 volts will only need 56.56 volts RMS (80*.707) to reach full power.A CD player with 2vrms output places 2.82 volts peak at the grid of the 6sn7. 2.82 * 20 = 56.4 volts peak (39.87vrms). That won't get you the full power from the 300b but is should be enough for hi eff speakers. 56 volt peak grid drive will give 4 or 5 (very clean) watts from a 300b depending on load impedance and operating point.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 10/14/16Follow Ups:
I use an active pre because I have a variety of sources with different output levels and the sound of an active pre is more to my liking as well.. If I had just one source, with a decent level, I might use a passive but not as it is now.
It's an advantage of DIY, make it the way that works best for you.
Same for me. I have six sets of input jacks on my pre, and I use them all. Much easier to balance it all out with an active pre. If all I listened to was CD's though, there would be no need for either, just go direct from the CD player out puts to amp inputs.
This doesn't address the original question which is about gain structure and not about being able to level match / adjust.
I'll side with tre' that having a preamp that puts out 20V and an amp that clips at 1V input simply means you must use at least 26dB of attenuation before you can even consider listening. Unfortunately from a commercial POV those two numbers are the norm because manufacturers need ot cover the bases for anything an end user *might* put in front of their amp or after their pre.
I routinely run into situations where 40dB of attenuation is too loud for anything but an all out session and am usually not met with a good response when I suggest they address their messed up gain structure rather than attenuating 60+dB for low level listening.
dave
"I'll side with tre' that having a preamp that puts out 20V and an amp that clips at 1V input simply means you must use at least 26dB of attenuation before you can even consider listening."
That was my original point. The question was about why even DIY types make amps that have 1V sensitivity and preamps that have overly large amounts of gain.
I try to take a more balanced approach.
"The question was about why even DIY types make amps that have 1V sensitivity and preamps that have overly large amounts of gain. "
I have a theory about that.
I think, in some cases, the user likes the sound of distortion.
If you take away his ability to over drive the system he feels a loss of "dynamics".
Harmonic distortion is the addition of a series of high frequencies that weren't in the original input signal and if the HD goes up just at the peaks of the music (ie; the system enters over drive just on the peaks of the music) the music gets brighter and louder just on the peaks of the music and the user "hears" that as "dynamics".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It's just nice to have others affirm you're not delusional.
Audio is so subjective at the end that sometimes the measurements are secondary.
It is source to eardrum/chest cavity.
Too effing bad that you tell it like it is. Get the overall gain structure correct!
Eli D.
Hang on folks. I don't know what monsters y'all are using for amps, but my 26/26/45 and my 26/845/845 (low voltage) can use all the help they can get in the gain department. Ain't no padding down involved here. The active pre (a single 26 per channel) lets me get up to a good level and gives me the leveling ability I spoke of.
Isn't your active pre essentially another gain stage on your amp?
I have made these same design choices because I like these same triodes. Unfortunately they don't have the mu to drive full power without these extra stages.
I guess you could look at any preamp that way, but I like it better than another stage on the amp it self because it can be used for several amps.
Vinnie, it seems you are getting overall gain structure right. ;> )
As for "monsters", I have (among other things) a H/K Cit. 2 and a 250 WPC AVA FET-Valve hybrid. My tiny ProAc Tablette speakers need that kind of "grunt". I am and will remain space constrained. "There's more than 1 way to skin a cat."
Eli D.
With sources yielding quite different signal levels, custom "padding" of each I/P feeding an active line stage is in order.
Still, holding the amount of "padding" used down benefits overall S/N performance. Getting overall gain structure right is quite important.
Compromises will always be with us. Phooey.
Eli D.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: