The 6SN7 is not a 12AU7A on steroids, there are significant parametric differences and I'd recommend significantly boosting the operating current and taking advantage of its excellent linearity at 8 - 10mA, adjust the plate voltage supply accordingly. I would not use a plate load resistance much in excess of 33K either.
LED bias works quite well with the 6SN7 in voltage amplifier stages. (Three or four 1.7V red leds in series depending on operating point.)
I'd dump all of the RC based decoupling and use a regulated supply instead, but I am weird so... In any event you will need to scale them downwards to account for higher operating currents.
Assume you meant substituting the 6SN7 for the 12AU7A since that appears to be your intent.
LED bias works quite well with the 6SN7 in voltage amplifier stages. (Three or four 1.7V red leds in series depending on operating point.)
I'd dump all of the RC based decoupling and use a regulated supply instead, but I am weird so... In any event you will need to scale them downwards to account for higher operating currents.
Assume you meant substituting the 6SN7 for the 12AU7A since that appears to be your intent.
That is basic passive Baxandall. I have used it years ago, but later found active Baxandall better and more versatile.
Passive version uses logarithmic potentiometers while active has linear.
This is essential flaw of passive type. It is difficult to get flat frequency response when potentiometers are set to half position and this varies between different brands.
Passive version uses logarithmic potentiometers while active has linear.
This is essential flaw of passive type. It is difficult to get flat frequency response when potentiometers are set to half position and this varies between different brands.
IMO the mu of the 6SN7 is too low to permit the use of the feedback type baxandall tone control circuit, otherwise I agree 100% with your comments.
I'll second the comments about passive tone controls being hard to get flat and for that matter good channel balance but there was an interesting circuit from mullard which uses switched controls I'll see if I can remember to filch it out....
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A logarithmic stepped attenuator (say 11 steps total) with a bypass position at center might provide good channel to channel matching and flat response in the off (center position). Probably too complex as I think about it, active baxandall would be better.
Should I even consider having tone controls? I'm wanting to make adjustments to old recordings,which is why I am interested in having them. I would like to be able to bypass,and I'm not sure how to go about that.
Do it the old fashioned way - double pole, double throw switch. Out is common, one throw connects post-EQ to output, other pre-EQ signal
I am looking forward to your results because I have about a hundred 6SN7's laying around and don't know what to do with them. This could just be the project for them. Good luck and keep us updated.
Most 6sn7's are very micro-phonic, the 6CG7 would be much better for a pre-amp. { tried just about every type of 6SN7's RCA, GEC Russian, Chinese, AWA.}
I have sensitive speakers so maybe you would get away with 6SN7's if you used a very heavy box or rubber mounting. Had no trouble with 6CG7's.
Phil
I have sensitive speakers so maybe you would get away with 6SN7's if you used a very heavy box or rubber mounting. Had no trouble with 6CG7's.
Phil
These are some very good suggestions. I would need to change component values in the filter,and if I did is there a calculator I could use in order to do this. I am using a line stage now using 6SN7's, and am biasing them in the way you suggested. Thanks
I was designing a preamp with tone controls, and I believe there is merit in the option of bass and treble tailoring. It is such a shame that audiophiles have painted them with the broad black brush, as not all tone controls are equal. I actually am going to set my bass center frequency near 20-30Hz with a higher Q. I prefer this because I don't like the bass control to bloat the instruments or voices, and what I am looking for is a lift in the deepest bass. The drawback in this type of control is that as the bass is increased, the 120Hz region actually takes a dip of a couple dB, but how noticeable this is remains a point of debate. Overall, don't get too carried away with trying to get a perfectly flat response. After all, no loudspeaker is flat in a room.
If you do consider LED cathode biasing as opposed to parallel bypassing a fixed resistance with a large capacitor, you may want to additionally bias the LEDs from the B+ supply. This will reduce noise if the bias voltage is much below the intended operating voltage for that diode. Expect to invest in quality pots for the bass and treble- no carbon composition wipers here or the signal may come to contain dynamic noise, what people allude to as "hash". One thing I found funny in the schematics linked in this thread is that the Volume control is being implemented in the second half of the preamplifier, whilst I always use a divider on the input. Interesting, might be something for me to try.
If you do consider LED cathode biasing as opposed to parallel bypassing a fixed resistance with a large capacitor, you may want to additionally bias the LEDs from the B+ supply. This will reduce noise if the bias voltage is much below the intended operating voltage for that diode. Expect to invest in quality pots for the bass and treble- no carbon composition wipers here or the signal may come to contain dynamic noise, what people allude to as "hash". One thing I found funny in the schematics linked in this thread is that the Volume control is being implemented in the second half of the preamplifier, whilst I always use a divider on the input. Interesting, might be something for me to try.
It's nice to hear from someone that at least gives tone controls a chance, it will be awhile before I attack this particular project, I've been busy with other projects.
Assumption without investigation is the height of ignorance, and many base their entire belief upon one or two examples from lower quality designs. You and I know better than this. Personally, I like a little more deep bass, and treble reduction with some headphones or speakers. Tone controls make sense in this regard.
Some argue that tone controls distort the signal, but this is true of every component in the compromised nature of artificial audio reproduction, and how much is honestly audible? I don't know about them, but I don't listen to test tones nor do I gauge an Barbara Bonney and Maria Callas' performances from an audio analyzer. Those measurements are important, very important, but one cannot allow that to place limitations upon their enjoyment. Hardphile's may remain intent on locking themselves to the tonal balance that is in the recording, but it doesn't make it correct. Just remember- how many audiophiles think there is no bass in recordings under 40Hz. That's completely false, but they remain steadfast in their deeply entrenched belief systems. Let them fulfill their masochistic need for an S&M beating of blaring treble and anemic bass. I will tilt the upper and low spectrum of my audio to meet my own needs and enjoyment.
Anyway, feel free to search up schematics on Google of LED biasing, and you will eventually come across a picture or two depicting a trace from the B+ through a very high resistance value, that then makes its way to the LED. This ensures that the LED is always at it's operating potential and reduces the sandy sound of the LED that you chose (which may be green for 15mA).
Some argue that tone controls distort the signal, but this is true of every component in the compromised nature of artificial audio reproduction, and how much is honestly audible? I don't know about them, but I don't listen to test tones nor do I gauge an Barbara Bonney and Maria Callas' performances from an audio analyzer. Those measurements are important, very important, but one cannot allow that to place limitations upon their enjoyment. Hardphile's may remain intent on locking themselves to the tonal balance that is in the recording, but it doesn't make it correct. Just remember- how many audiophiles think there is no bass in recordings under 40Hz. That's completely false, but they remain steadfast in their deeply entrenched belief systems. Let them fulfill their masochistic need for an S&M beating of blaring treble and anemic bass. I will tilt the upper and low spectrum of my audio to meet my own needs and enjoyment.
Anyway, feel free to search up schematics on Google of LED biasing, and you will eventually come across a picture or two depicting a trace from the B+ through a very high resistance value, that then makes its way to the LED. This ensures that the LED is always at it's operating potential and reduces the sandy sound of the LED that you chose (which may be green for 15mA).
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I built the tone control in the article DeathRex links to early in this discussion. Information can be found here: diytube.com • View topic - Tube Tone Control Project
Kouiky,
It is not (only) a shame - it is patent ignorance. (As you say, at least presuming half-decent designs.)
In lighter vein, if I may: Under public pressure (that's a shame) I have built several amplifiers for clients with a tone controls bypass switch (my design used the Baxandall topology). At several demos I have encountered those who would swear that they heard a difference when using the switch. Some hautily defined it as obvious, congratulating me on my foresight.
Point was, that switch was not wired in ..... (I am known to be naughty on occasion...)
"Point was, that switch was not wired in ..... (I am known to be naughty on occasion...)"
How did you stop yourself from either laughing out loud or telling them they are retarded? Great stuff I love it!
How did you stop yourself from either laughing out loud or telling them they are retarded? Great stuff I love it!
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