12AT7 Linestage design

sorenj07 · 19th October 2006, 09:07 PM

I was fooling around in TubeCAD and was wondering about the following linestage. It has nice bandwidth and a comfortable gain of just under 3. What do you think?

SY · 19th October 2006, 09:15 PM

Quote:

It has nice bandwidth and a comfortable gain of just under 3.

And that nice vertical load line should manage to get the distortion below 15%.

Zen Mod · 19th October 2006, 09:27 PM

>curseword<load of feedback

that reminds me on AR line of preamps........ tons of feedback without actual need ;hehe-they sound exactly the same- sound without actual cause

12AT7 have mi in range of 70 ,academically speaking.....and wasting that to 10 db is blasphemy; at least for me.

Ra for first stage is too small
same for second stage
(this is explanation of Sy's post)

sorenj07 · 19th October 2006, 09:36 PM

ouch. ok then, back to the drawing board

SY · 19th October 2006, 09:40 PM

Rule of thumb: when you decide what gain you want from the line stage, look for a tube with a mu 1.5-2 times higher.

Wavebourn · 19th October 2006, 09:46 PM

Quote:

Originally posted by sorenj07
I was fooling around in TubeCAD and was wondering about the following linestage. It has nice bandwidth and a comfortable gain of just under 3. What do you think?

Positive feedback to the cathode, it decreases stability.

woody · 20th October 2006, 01:00 AM

One of the primary reasons to use a cathode bypass cap
is to keep the gain high if you arn`t after a lot of gain leave
the cap out. Eleminating this cap gives you a little local feed
backand removes the distortion from a cap. You also want your plate resistor to be a lot larger than your plate resistance. I seem to rember a good line stage using this tube (30 years ago so I might be wrong) using 47k for the plate resistor and about 20k for the cathode follower.

Wavebourn · 20th October 2006, 01:51 AM

Quote:

Originally posted by woody
One of the primary reasons to use a cathode bypass cap
is to keep the gain high if you arn`t after a lot of gain leave
the cap out. Eleminating this cap gives you a little local feed
backand removes the distortion from a cap. You also want your plate resistor to be a lot larger than your plate resistance. I seem to rember a good line stage using this tube (30 years ago so I might be wrong) using 47k for the plate resistor and about 20k for the cathode follower.

Do you describe how to turn this multivibrator into the Shmitt's trigger?

sorenj07 · 20th October 2006, 01:59 AM

well, here's another crack at a linestage, using the lower-gain 12BH7 tube. I've heard it's more linear than the 12AU7, which was my natural next recourse. I had the plate curves in front of me when fiddling with bias and stuff so hopefully this one turned out better.

SY · 20th October 2006, 02:19 AM

The grid of the second stage appears to be floating. DC to the plate of the first stage?

19th October 2006, 09:07 PM	#1
sorenj07 diyAudio Member Join Date: May 2006	12AT7 Linestage design I was fooling around in TubeCAD and was wondering about the following linestage. It has nice bandwidth and a comfortable gain of just under 3. What do you think?

19th October 2006, 09:27 PM	#3
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	>curseword<load of feedback that reminds me on AR line of preamps........ tons of feedback without actual need ;hehe-they sound exactly the same- sound without actual cause 12AT7 have mi in range of 70 ,academically speaking.....and wasting that to 10 db is blasphemy; at least for me. Ra for first stage is too small same for second stage (this is explanation of Sy's post) __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery;I'm dumb

19th October 2006, 09:40 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Rule of thumb: when you decide what gain you want from the line stage, look for a tube with a mu 1.5-2 times higher. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

20th October 2006, 02:19 AM	#10
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	The grid of the second stage appears to be floating. DC to the plate of the first stage? __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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19th October 2006, 09:36 PM	#4
sorenj07 diyAudio Member Join Date: May 2006	ouch. ok then, back to the drawing board

20th October 2006, 01:00 AM	#7
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	One of the primary reasons to use a cathode bypass cap is to keep the gain high if you arn`t after a lot of gain leave the cap out. Eleminating this cap gives you a little local feed backand removes the distortion from a cap. You also want your plate resistor to be a lot larger than your plate resistance. I seem to rember a good line stage using this tube (30 years ago so I might be wrong) using 47k for the plate resistor and about 20k for the cathode follower.

20th October 2006, 01:59 AM	#9
sorenj07 diyAudio Member Join Date: May 2006	well, here's another crack at a linestage, using the lower-gain 12BH7 tube. I've heard it's more linear than the 12AU7, which was my natural next recourse. I had the plate curves in front of me when fiddling with bias and stuff so hopefully this one turned out better.

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