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2011 | OriginalPaper | Buchkapitel

7. Noise in Valves (US: Tubes)

verfasst von : Dipl.-Ing. Burkhard Vogel

Erschienen in: The Sound of Silence

Verlag: Springer Berlin Heidelberg

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Abstract

Concerning electronic noise, we cannot compare the world of valves with the one of the solid-state world. Whereas the latter offers a rather narrow bandwidth of noise voltage tolerance, respectively, valves come along with a very broad tolerance noise voltage bandwidth. Sometimes the noise voltage difference between a selected low-noise type and a non-selected, “normal” one can reach up to 20 dB in the audio band. That is why the calculation of the audio band noise of a valve gain stage requires exact operating data of the chosen valve.

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Vorheriges Kapitel Noise in Field Effect Transistors

Nächstes Kapitel Noise in Operational Amplifiers

However, evolution doesn’t sleep and creativity efforts on old-time things can lead to astonishing new results: see “A new low-noise circuit approach for Pentodes”, Frank Blöhbaum, Linear Audio, Vol. 0, 2010, ISBN 9 789 490 929015.

“Telefunken Laborbuch” (Laboratory Handbook), Vol. 3, 2nd edition 1966.

See Footnote 2.

It is not only 1/f-noise (or flicker noise). Quite often, we find additional noise artefacts with a 6 dB/octave slope and a separate corner frequency that can be lower than f_c. I do not want to over-complicate things: that is why I will focus on 1/f-noise and its corner frequency only. The consideration of other and noise impacts lower than f_c will not touch the noise calculation equations of this chapter negatively.

Concerning 1/f-noise in Sect. 7.7 and in Chap. 17 I will give additional noise calculation hints.

EIN = equivalent input rms noise voltage in B_20k, referenced to 774.6 mV_rms or 1 V_rms.

On the home page of this web-site please search: “Rauschmessungen an Roehren”; The whole text is written in German; however, I guess the many measurement graphs are self-explanatory. Because of its – supposedly – insignificant contribution it is mentioned that excess and white-noise of the plate resistor was not taken into account. On the other hand the triode graphs show white-noise voltage density levels >10 kHz close to the calculated ones.

“Measurement filters” see Chap. 23.

I guess, for phono-amps there is no need treating additionally the shot noise case. The respective formulae could be studied in M/C Sect. 1.11. A bigger 1/f-noise effect (e.g. red noise with 1/f²) can simply be covered by the respective treatment of the second root of (7.7). The worksheets of Chap. 18 will cover this aspect in detail.

The “c” after rN should indicate the 1/f-noise dependency and the average rN value in a given audio bandwidth.

See also Chap. 14 of HTTG, see Appendix 6.

Details see Chap. 17.

“Valve Amplifier”, Morgan Jones, see Appendix 6.

To gain a very deep look into the triode’s gain, input and output resistances and stage transfer function mechanisms please consult HTTG, see Appendix 6.

Don’t be surprised about the strange numbering of the resistances. I’ve gone through the measurement and calculation of many different gain stages and I didn’t want changing the numbering. Hence, in every case, the same resistance in the various circuits gets the same number.

JJ Electronic, A. HLinku 4, 02201 Cadca, Slovac Republic, www.jj-electronic.com

For noise calculations only the phase relationship of a gain stage is not important and needs not to be taken into consideration.

Additional useful valve formulae for all triodes: \( {r_a}\,{g_m} = \mu. \)

Idle gain for pentodes: \( {G_p} = \left| { - {g_{m.p}}\,{R_a}} \right|\,\,\,({r_{a.p}} \,> \,> {R_a}). \)

See HTTG or the author’s “Glowing GainMaker” series, 10 short articles on triode gain-stages in EW 06-2010–03-2011.

It makes sense to “fix” the average temperature T inside a valve pre-amp case at 315 K (see also (Chap. 17); after 30 min and in a distance of 2 cm from the valve my temp-meter always showed values like this.

All details: see Chap. 12, Worksheet 12.12.

The determination of NI will be explained in Chaps. 17 and 18.

All details: see Chap. 12, Worksheet 12.12.

See respective equations in Sect. 7.13 ff.

More details on the different types of gain stages: see Chaps. 17 and 18.

CF = cathode follower.

Morgan Jones’ “Valve Amplifiers”, see Appendix 6.

See Sect. 7.16.

Nevertheless, Worksheet 12.12 shows the equations in dependency of a source resistance R0.

Worksheet 12.13 gives all details of the presented equations with a dependency of a source resistance R0.

In 2003 the third edition entered the markets.

Worksheet 12.14 offers a double triode (E88CC) example calculation for both versions. It shows the equations with a dependency of source resistance R0 and it includes the calculation of C_c1 too.

See Glowing GainMakers EW 02-2011.

The new EL84T would be a very interesting candidate for a test.

See: HTTG Chap. 4 or EW 2010-08: “Glowing GainMaker Part 3”.

Details of the equivalent noise bandwidth concept ENB see Chap. 23.

It will work with a very low 1/f-noise content only!

See Worksheet 12.13 in Chap. 12.

Mr Brüggemann, SST Brüggemann GmbH, Frankfurt, Germany, got a lot of positive practical knowledge on that issue in the past when designing and building-up many German valve driven radio station studios.

I’m a bit surprised about the many mains induced spikes in Figs. 7.15 and 7.16 because in the Quad 24P all valves got shielded.

Details see Worksheet 12.12 of Chap. 12.

See Sect. 11.16.

See Chap. 30 for further info on the Jensen Transformers JT-346-AXT.

See Chap. 10 and the respective application notes from the transformer manufacturers.

Titel: Noise in Valves (US: Tubes)
verfasst von: Dipl.-Ing. Burkhard Vogel
Verlag: Springer Berlin Heidelberg
Buch: The Sound of Silence
Print ISBN: 978-3-642-19773-4

Electronic ISBN: 978-3-642-19774-1

Copyright-Jahr: 2011
DOI: https://doi.org/10.1007/978-3-642-19774-1_7

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