• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

RLC serial resonance circuit

1. What is the tube amp that has a rise of impedance at 1kHz?
Please list the model number.

Perhaps you meant the impedance rise of the Loudspeaker at the crossover frequency.

2. I have many loudspeakers, about 10 or more pairs of different models.
They all sound good on my vacuum tube: Balanced PP amplifiers, SE amplifiers; and PP amplifiers.
I have many models that do not have a match to make a pair, they all sound good on my vacuum tube amplifiers too.

As far as I know, my loudspeakers do not have a Series LC, Series RC, nor Series RLC impedance correcting networks.
I measure my loudspeaker impedance variations. Most of them have widely varying impedance rises and dips.

Most of my vacuum tube amplifiers have damping factors of from 2.5 to 5.

Just my opinions and experience.
Your Mileage May Vary.

Have Fun!
  • Like
Reactions: 1 user
I sow it on this homepage from Strassacker hifi shop. They recommend this RLC and have a calculator to download on there homepage.


  • 1718103389121804148508884835537.jpg
    564.8 KB · Views: 56
All things are recommended.
Some recommendations only work in certain situations.
Many that work, have tradeoffs.

All recommendations are equal, but some recommendations are more equal than others.

One of the key words is Series Resonant. Some will resonate more than others.
Some will resonate in your ears.

Qs of 3 or less are considered by many to be non-resonant.
Qs of 4 or more are considered by many to be resonant.
Radio Days (Daze) keep coming back, and so does the old ARRL Radio Amateurs Handbook.
Thanks for the interresting and useful conversation. I think, Audio technology is very complex...
My thought was unsophisticated about this attachment i send. Is it profitable with a RCL in the crossover to compensate possible problems with the match to a valve amplifier. Do it give sense. I suppose its a question that's not easy to answer.

Your original, and re-asked question is a good one.
I wish there was a single and simple answer.
I do not know if there is, or is not.

Something to consider is which amplifier, not just which loudspeaker.

Is the amplifier single ended, or Is the amplifier push pull?
Is the amplifier damping factor low, medium, or high?

Does the amplifier use global negative feedback that is taken from the output transformer secondary?
Is there lots of global negative feedback?
Is the amplifier stable with all kinds of loads; resistive, inductive, and capacitive?

Is the loudspeaker primarily designed for solid state amplifiers, or for vacuum tube amplifiers?

Is there a specific amplifier and a specific loudspeaker that you are considering to use together?
I have build the TSE ll from the George's tubelab website with application for the type 45 tube and 6K ohm 60ma output transformer. (No catode feedback)
I want to match them with (crossover upgraded) Klipsch RP600M
Then I sow this attachment with the RCL calculator and was wondering...
I think i do not know enough about this issue.
They recommend this RLC and have a calculator to download on there homepage.
RLC = Resonance
Resonance has a Q.
Resonance with a Q has attack and decay.
High impedance tube amp has low damping ability for above Resonance.
So it will ring to some degree with slow attack and slow decay, nature of the circuit...just a question of how much it will ring and how audible it will be.
In my personal experience, a RLC cure always sounded worse than the disease it was intended to fix.
  • Like
Reactions: 1 user
Series RLC impedance correctors in the loudspeaker reminds me of a similar resonator . . .

Some full range drivers have a broad peak at perhaps 3.5kHz to 5.5kHz as an example . . .
One suggestion was to put a Parallel RLC network in series with the driver voice coil.
True, that reduces the signal to the driver at those frequencies, But now the RLC rings at those same frequencies. Just move the problem from one resonator to another resonator.

A full range driver that I mostly liked, had a whizzer cone with the expected broad resonance. I tried wool, cotton, etc. to dampen the resonance.
I very carefully cut the whizzer cone down to only 1/4 inch. Problem solved.
Generally, a small amplitude reduction of a frequency range is less objectionable than a peak in the same frequency range.

Just my experience.
Last edited:
Thanks for the input. It looks like that it is a good pointe to keep it simple, as possible... What about the quality of the components in the RCL ? I have tried to smooth a objectionable peek with a paralel RCL in serial with + on the Fostex103 EN (do it yourself kit from 2003)
The success was ok and "good", but there difference between Por or good components was Audible.
My eksperience was, that A peek especially at 4000 Hz can be very nasty for the human ear.

Conclusion for me may be to experiment and use my ears.