Calling all tube/valve gurus.

jomondz

Active Member
Why Circuit A sounds darker than Circuit B?
Which circuit will give more "triode" sound?
Are my designs wrong?
What could be improved?
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:banana::banana::banana:
 
I'm no tube expert or guru, but I'm trying to learn on my own. So take my comments from that point of view. At any rate, I stuck you circuits into a simulator, using different tubes and passives than your example. It would appear that Circuit B has WAY more even-order distortion than Circuit A. Circuit A appears to be a very clean method.

Now, to your questions,:
Why Circuit A sounds darker than Circuit B?
Without the extra harmonics of Circuit B, Circuit A will sound darker.

Which circuit will give more "triode" sound?
If "triode" sound to you means more even-order distortion, than Circuit B is the ticket.

Are my designs wrong?
Define "wrong."

What could be improved?
Is improvement necessary?
 
Hi House de Kris,
Thanks for the input.

Is it possible for you to get the frequency response graph posted as you run the computer simulation?
I want to see how does these circuit behave in terms of distortion characteristic.

Here's how:
Just inject a clean (sine) 1KHz signal at an amplitude that distort the circuit a "little" or "much" if you prefer.
 
Just to repeat, I'm to tube guru. But, hopefully my floudering about will prompt others, who are, to chime in and straighten us out.

Here are a few pictures to illustrate some of the differences between these two different configurations. As I mentioned earlier, I used a different tube, plus since you didn't specify R1 and R2, I had to guess. As well, I had to guess for the B+ value. I started with R1=R2=100k.

Hmmm, I see that we only allow six pictures per post. Oh well, this post will then focus on Circuit A. Here's a couple pictures with 100k resistors showing the AC Analysis and Transient Analysis:

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When changed to R1=R2=10k, we get this:

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  • DT1AC-100k.jpg
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  • DT1TA-100k.jpg
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Moving on to Circuit B. Again, starting with 100k for R1 and R2.

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Then changing R1=R2=10k.

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I'll do a follow up in the next post.
 

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  • DT2AC-100k.jpg
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  • DT2TA-10k.jpg
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As you can see, Circuit B has a ton more distortion than Circuit A when R1 and R2 are a high value, like 100k. With 10k, visually it doesn't appear to be too distorted. This simulator doesn't do distortion analysis.

Other things worth noting from these eight pictures:
Circuit A
10k-
gain: 14
bw: 300kHz
100k-
gain: 2
bw: 235kHz

Circuit B
10k-
gain: 36
bw: 110kHz
100k-
gain: 20 (mucho distortion)
bw: 13.5kHz

Circuit B gives a bunch more gain (all other factors equal). Circuit A has a wider bandwidth (all other factors equal).

I think a tube guru will tell us something like we need to place the tube on the load line properly in order to get satisfactory operation. This will determine R1 and R2 knowing the B+ being used. I was just grabbing values for R1 and R2 at random.

In general, I would say use Circuit A, unless a lot of gain is required. Again, I don't know tubes, so take that into consideration.
 
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