Search RFCafe.com                           
      More Than 18,000 Unique Pages
Please support me by ADVERTISING!
Serving a Pleasant Blend of Yesterday, Today, and Tomorrow™ Please Support My Advertisers!
   Formulas & Data
Electronics | RF
Mathematics
Mechanics | Physics
     AI-Generated
     Technical Data
Pioneers | Society
Companies | Parts
Principles | Groups


 About | Sitemap
Homepage Archive
        Resources
Articles, Forums Calculators, Radar
Magazines, Museum
Radio Service Data
Software, Videos
     Entertainment
Crosswords, Humor Cogitations, Podcast
Quotes, Quizzes
   Parts & Services
1000s of Listings
 Vintage Magazines
Electronics World
Popular Electronics
Radio & TV News
QST | Pop Science
Popular Mechanics
Radio-Craft
Radio-Electronics
Short Wave Craft
Electronics | OFA
Saturday Eve Post

Software: RF Cascade Workbook
RF Stencils for Visio | RF Symbols for Visio
RF Symbols for Office | Cafe Press
Espresso Engineering Workbook

Aegis Power  |  Alliance Test
Centric RF  |  Empower RF
ISOTEC  |  Reactel  |  RFCT
San Fran Circuits

Anatech Electronics RF Microwave Filters - RF Cafe



LadyBug RF Power Sensors

Please Support RF Cafe by purchasing my  ridiculously low-priced products, all of which I created.

RF Cascade Workbook for Excel

RF & Electronics Symbols for Visio

RF & Electronics Symbols for Office

RF & Electronics Stencils for Visio

RF Workbench

T-Shirts, Mugs, Cups, Ball Caps, Mouse Pads

These Are Available for Free

Espresso Engineering Workbook™

Smith Chart™ for Excel

Anritsu Test Equipment - RF Cafe

Feedback Tone Control
December 1958 Radio-Electronics

December 1958 Radio-Electronics

December 1958 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

I have to admit to not being real certain why I selected this article on feedback tone control for posting. It appeared in the December 1958 issue of Hugo Gernsback's Radio-Electronics magazine. Although it is a good write-up on some simple audio frequency filtering circuits, and the principles can be applied to any frequency, it is most likely this page was marked because it contained an electronic-themed comic on it. Oh well, Melanie already scanned and OCRed it for me, so you might as well go ahead and read it.

Feedback Tone Control

4-position feed­back tone-control circuit - RF Cafe

Fig. 1 - Circuit of the 4-position feed-back tone-control circuit.

By A. V. J. Martin

High-fidelity tone controls through feedback

Feedback circuits for each switch position - RF Cafe

Fig. 2 - Feedback circuits for each switch position of Fig. 1 and their effect on frequency response: a - treble boost; b - bass and treble boost; c - same as b, but treble boost starts at higher frequency; d - bass boost and treble cut. 

This elaborate tone control using a separate feedback chains found in some Marquett French receivers. The theoretical circuit is shown in Fig. 1. The af voltage from the anode of the preamp is applied to the grid of the power amplifier through a divider made of two 470,000-ohm resistors. The grid thus receives only half of the af voltage. However, a low-value capacitor is connected in parallel with the first 470,000-ohm resistor, effectively short-circuiting it at high frequencies and producing an important treble boost.

This arrangement is completed by a feedback chain around the power stage. A four-position switch modifies the effect of feedback. To make things clearer, the simplified diagrams Figs. 2-a, -b, -c, -d, show what is the actual circuit for positions 1 to 4 of the switch.

In position 1 (Fig. 2-a), the feedback chain is a simple 2.2-megohm resistor, giving an overall feedback ratio of the order of 10%. The high frequencies are boosted by the coupling circuit so that this is a treble-boost circuit.

In position 2 (Fig. 2-b), a series R-C combination appears in the feedback path. It reduces by approximately 50% the feedback at low frequencies, which becomes 5%. At medium frequencies, you obtain the full 10% feedback. At high frequencies, there is the boost due to the coupling circuit. This is then a bass- and treble-boost circuit.

In position 3 (Fig. 2-c), the circuit is identical with Fig. 2-b, except for the fact that the shunt capacitor in the coupling circuit now has the lower value of 250 μμf. The treble boost appears at higher frequencies. The bass and medium frequencies behave as in Fig. 2-b. This then is again a bass-and-treble-boost position, the treble boost coming into play for the higher frequencies.

In position 4 (Fig. 2-d), the circuit differs from Fig. 2-c by the connection of a 50-μμf capacitor between plate and grid of the power stage. This causes a strong feedback at high frequencies, but does not modify the behavior of the circuit for bass and medium frequencies. This is then a bass-boost-treble-cut circuit.

The simplified response curves included in the diagrams give a rough idea of the effects of this clever circuitry.

 

 

Posted June 30, 2022
(updated from original post on 1/6/2015)

Anritsu Test Equipment - RF Cafe
Temwell Filters

Innovative Power Products (IPP) RF Combiners / Dividers

withwave microwave devices - RF Cafe