Content of the material
- Samples in periodicals archive:
- Video
- Dial-Normal Transmission Signal
- Output Transformer Saturation
- Line Busy Tone
- Intentional Phase Inverter Mismatch
- The Baxandall Tone Control Circuit
- 5# Classic Low noise Pre Tone control circuit using 3 transistors
- How to build
- Call States
- v.21
- Tone Options
- CNG Calling Tone
- Active Baxandall Circuit
- 7# High-quality Tone Control Mono using 5 Transistors C945
- Making this project
- Download This
- Alternate Of C945 and A561 Transistor
- 18V Regulator circuit
Samples in periodicals archive:
Share "U.S. SIT (Special Information Tones) signal: Vacant Circuit"; View: Mobile | Desktop © 2009-2015 YouMail. All rights reserved. Sign In. (These…
Readbag users suggest that Special Information Tones is worth reading. The file contains 3 page(s) and is free to view, download or print.
Dial tone; Ringtone; Ringback tone; Busy signal; Reorder tone; Disconnect tone; Special information tones; Off-hook tone; Dual-tone multi-frequency; 2600 Hz
Special information tones; Off-hook tone; Dual-tone multi-frequency; 2600 Hz; Read in another language. Last edited on 4 November 2015, at 19:10…
Check out some special information tones. LifeHacker cited the "Vacant Circuit" tone as causing a disconnect for auto-dialers. Putting that at the…
Automated phone bots keep interrupting your dinner with their pre-recorded marketing messages? Play the U.S. Special Information Tone signal for "vacant…
In telephony, a special information tone (SIT) is an international standard three beep signal indicating a call did not go through and usually precedes a recorded…
Definitions of Special information tones, synonyms, antonyms, derivatives of Special information tones, analogical dictionary of Special information tones (English)
special information tone In Short Description : special information tone In Long Description: Full DVD Ripper Pro 9.3 Adjust the image brightness/ contrast…
Special Information Tones IC – Intercept – Number changed or number disconnected, FTC Robocall Challenge: Consumer Tips & Tricks, A special frequency, a mini "cure…
Using Special Information Tones to Foil Telemarketers!; used by most.telemarketers will take you off their list after hearing these tones.
In telephony, a special information tone is an in-band international standard signal consisting of three rising tones indicating a call has failed.
Special Information Tones and Telemarketing Predictive Dialers are machines used by telemarketing firms to place many telephone calls at a rapid rate.
Concerning S.I.T. (Special Information Tones), disconnected telephone lines, predictive dialers and the Telezapper…
Special information tones; Off-hook tone; Dual-tone multi-frequency; 2600 Hz; Read in another language. Last edited on 23 August 2015, at 03:09…
Spanish Translation, Synonyms, Definitions and Usage Examples of English Word 'send special information tones'
LINESPECIALINFO_ Constants; Special information tones are defined for advisory messages and are not normally used for billing or supervisory purpose. Requirements.
U.S. SIT (Special Information Tones) signal: Vacant Circuit. out of service or nonexistent phone number. Added: 11/30/08 From…
GR 674 CORE:2000 Lssgr: Special Information Tones Describes generic requirements for Special Information Tones (SITs). SITs are used to identify network-provided…
Special Information Tones (SIT) [link to www.yourhomenow.com] Record these three musical notes (play this WAV file) as the very first part of your telephone answering…
SIT (Special Information Tones) SIT's are the three sequential tones usually followed by a recording like "We're sorry, your call did not go through as…
The high-order 16 bits can be assigned for device-specific extensions. The low-order 16 bits are reserved. Special information tones are defined for advisory messages…
A method and apparatus (10) for returning a false signal substantially similar to at least a first portion of a special information tone (SIT) after a device…
Precise Call Progress and Special Information Tone Generator 1 Features; detector for call progress and special information tones (SIT), as defined by CCITT.
The Telezapper can emit a 'disconnect' tone when your phone line goes off-hook; You can get a set of all three Special Information Tones from Private Citizen.
CMX882 – Baseband Processor IC with GPS Data Signalling for FRS, MURS, PMR446 and; to handle FSK, DTMF, Call Progress and Special Information Tones…
System and method for privacy screening with special information tones Abstract. A system and method delivers an audible tone to an unidentified caller who places a…
MX643P datasheet, MX643P pdf, MX643P data sheet, datasheet, data sheet, pdf, MXCOM, Call progress tone detector with special information tones (SIT)
System and method for privacy screening with special information tones. United States Patent 7079638. Abstract: A system and method…
SIT tones are the "Special Information Tones" that are used in the telecommunications industry to facilitate the communication of a message to a computer or similar…
Video
Dial-Normal Transmission Signal
The Dial-Normal Transmission Signal is a second dial tone returned to an operator between digits indicating that he/she may dial the remainder of the number. For example, when an operator reaches a link-type Community Dial Office via a step-by-step office after dialing a routing code, he/she must pause until an idle link at the Community Dial Office returns dial tone. This method of operation is not recommended or considered standard.
Dial-Normal Transmission Signal is a steady Low Tone.
Output Transformer Saturation
An undersized output transformer can be saturated (maxed out) by the guitar signal coming off the power tube plates. When this happens the loudest passages will be capped causing compression. This dynamic compression can add to the character of an amp by adding note bloom and sustain. This tends to make an amp sound more round and tubey and less sterile. A smaller output transformer can help a modern amp sound more vintage. Most high gain amps do not use undersized transformers.
A "right sized" or oversized output transformer will let you get the maximum volume out of your amp and enhance dynamics, especially the low end.
Line Busy Tone
The Line Busy Tone indicates that the called customer’s line has been reached but that it is busy, being rung, or on permanent signal. When an operator applies a line busy signal, it is sometimes called a busy-back tone.
Line Busy Tone is a Low Tone that is on and off every .5 seconds.
Intentional Phase Inverter Mismatch
Howard Dumble added a phase inverter balance control to his Tweedle Dee tweed Deluxe amplifier. The control allows intentional mismatch between the two phase inverter output signals which generates sweet sounding even order harmonic distortion and intermodulation distortion to fatten up the amp’s tone. Anytime harmonic distortion is created intermodulation is also created. The phase inverter balance control lets you thicken your clean tone but also maintain control when pushing the amp hard into overdrive.
The Baxandall Tone Control Circuit

The circuit discussed here is an example of the Baxandall tone control circuit, illustrated in Fig. 4.2.2, which is an analogue circuit providing independent control of bass and treble frequencies; both bass and treble can be boosted or cut and with both controls at their mid positions, provides a relatively flat frequency response, as illustrated by the blue ‘Level response’ graph line in Fig. 4.2.5. The original design, proposed by P. J. Baxandall in 1952, used a valve (tube) amplifier and feedback as part of the circuit to reduce the considerable attenuation (about −20dB) introduced by the passive network, and to provide true bass and treble boost. There are still many variants of the circuit in use, both as active circuits (with amplification as originally proposed), and as passive networks without an incorporated amplifier. In passive variants of the Baxandall circuit, extra stages of amplification may be used to make up for the approximately −20bB attenuation caused by the circuit.
Read the original 1952 paper “Negative-Feedback Tone Control” by P. J. Baxandall B.Sc.(Eng.) published in “Wireless World” (Now Electronics World)
5# Classic Low noise Pre Tone control circuit using 3 transistors
See image below, the preamplifier tone control circuit diagram of the home audio stereo is very well. It low noise and sound is beautiful. Because using the quality transistors.

The Schematic Diagram of Mono Classic Preamplifier Tone control using 3 transistors
It has three transistors, C945 ( Equivalents of C829 , C1815 or C458). They are old electronic components but useful now.
This circuit is the Mono form, if you want stereo system. You need to make 2 channel R+L.
The VR1 is 100kB for adjusting the treble tone sound. The VR2 is 100K for adjusting the bass tone audio as well.
The VR3 is 100Ka for control volume output. The VR4 is 100KW for control balane sound fo other channel.
The power Supply Voltage used min 12V and min than 10mA. We hope this circuit will do you are enjoying home audio. Good luck.
How to build
You may build this project on universal PCB or Perforated PCB. Or if you want to make a PCB. See below!

The PCB layout of Classic Tone control using 3 Low noise transistors

And Here is wiring and assembly guide below.

Components list
Resistors ¼ watts +5%
- R1, R8: 22K
- R2, R3: 47K
- R4: 68K
- R5, R10: 1.5K
- R6, R9: 220K
- R7: 5.6K
- R8:22K
- R11, R13, R15: 10K
- R12, R17: 330K
- R14: 4.7K
- R18: 3.3K
- R19: 5.6K
- R20: 2.7K
- R21: 100K
Potentiometers
- VR3: 100K(A) Dual Audio Potentiometer
- VR1, VR2: 100K(B) Dual Audio Potentiometer
- VR4: 100K (MN) Bal Audio Potentiometer
Capacitors
- C1: 0.22μF Ceramic or Mylar
- C2, C12: 47pF 50V Ceramic
- C3, C13: 47μF 25V Electrolytic
- C4, C10, C11: 10μF 25V Electrolytic
- C5: 470μF 25V Electrolytic
- C6: 33μF 25V Electrolytic
- C7: 0.0015μF 50V Ceramic or Mylar
- C8,C9: 0.047μF 50V Ceramic or Mylar
- C14: 3.3μF 25V Electrolytic
Semiconductor
- Q1, Q2, Q3: 2SC945 or 2SC1815, 2SC828 NPN transistors
- Other PCB, jacks RCA, jack DC, adapter, etc.
Call States
Event | Purpose | Next Event Expected: Y= Accepted, N= Not Accepted | ||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
new | ivr- conn ected | ivr- done | parked | connect | conn ected | on- hold | hold- done | consu lting | consu lt-done | confer encing | confe rence- done | ended | recor ding- started | transf erred | monit oring- reque sted | moni toring- started | moni toring- ended | wrapup -done | update -csr-attr ibutes | |
no contact | No interaction with the customer | Y | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N |
new | New interaction starts with the customers | N | Y | Y | Y | Y | N | Y | Y | N | N | N | Y | N | N | N | N | N | N | Y |
ivr- connected | ivr instance is connected | N | N | Y | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | Y |
ivr- done | ivr instance is completed | N | Y | N | Y | Y | N | N | N | N | N | N | Y | Y | N | N | N | N | N | Y |
parked | Call is kept in parked state | N | Y | Y | Y | Y | N | N | N | N | N | N | Y | Y | N | N | N | N | N | Y |
connect | New call starts with the customer | N | N | N | Y | Y | N | N | N | N | N | N | Y | Y | N | N | N | N | N | Y |
connected | Call in-progress with the customer | N | N | N | N | N | Y | N | N | N | Y | N | Y | Y | Y | Y | N | N | Y | Y |
on-hold | Call is on-hold with the customer | Y | N | N | Y | Y | N | Y | Y | N | Y | N | Y | N | Y | N | N | N | Y | Y |
hold-done | Call is put back to in-progress state from on-hold state | Y | N | N | N | N | Y | N | N | N | Y | N | Y | Y | Y | Y | N | N | Y | Y |
consulting | Call is put in consulting state | N | N | N | N | N | N | N | N | Y | Y | N | N | N | Y | N | N | N | Y | Y |
consu lt-done | Call is put back to in-progress state from consulting state | N | N | N | Y | Y | N | Y | Y | N | Y | N | Y | N | Y | N | N | N | Y | Y |
confer encing | Call is put in conference state | N | N | N | N | N | N | N | N | N | Y | Y | N | N | N | N | N | N | Y | Y |
confer ence-done | Call is put back to in-progress state from conference state | N | N | N | N | N | N | Y | N | N | N | N | Y | N | Y | N | N | N | Y | Y |
ended | Call with the customer is ended | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | Y | Y |
recor ding- started | Call reco rding started | N | N | N | Y | Y | N | N | N | N | N | N | N | N | N | N | N | N | N | Y |
transf erred | Call is trans ferred | N | N | N | N | Y | N | N | N | N | N | N | Y | N | N | N | N | N | Y | Y |
moni toring -reque sted | Call monitoring is requested | N | N | N | N | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | N | Y | N | N | Y |
moni toring- started | Call monitoring is started | N | N | N | N | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | N | N | Y | N | Y |
moni toring- done | Call monitoring is ended | N | N | N | N | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | N | Y |
wrap -up done | Wrapup done by the agent | N | N | N | N | Y | N | N | N | N | N | N | N | N | N | N | N | N | Y | Y |
update -csr-attri butes | update csr-attr ibutes | N | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y |
![]() | Flow Developer uses the Flow Designer UI to create and publish call control scripts to manage the inbound telephony contacts. The administrator maps the published flow scripts against the routing strategy. When an inbound call lands at the entry point, the flow control engine identifies the routing strategy and executes the corresponding flow script, invoking the individual flow control activities that are part of the flow script. |
v.21
- Data transmission may take place at low data signalling rates on telephone calls set up on switched telephone circuits (or on leased telephone circuits).
- The communication circuit for data transmission is a duplex circuit whereby data transmission in both directions simultaneously is possible at 300 bit/s or less. The modulation is a binary modulation obtained by frequency shift, resulting in a modulation rate being equal to the data signalling rate.
- The nominal characteristic frequencies; channel №1 (FA = 1180 Hz and Fz = 980 Hz) channel №2 (FA = 1850 Hz and Fz= 1650 Hz)
Tone Options
There is a Dialogic option for each type of tone, that the Genesys configuration environment recognizes. These tone options are as follows:
- busy-tone-1
- busy-tone-2
- disconnect-tone
- extra-dial-tone
- fax-tone-1
- fax-tone-2
- forth-tone
- intl-dial-tone
- local-dial-tone
- ring-back-tone-1
- ring-back-tone-2
- sit-tone
Tone Parameters provides more details about each of these tone options.
CNG Calling Tone
To indicate a calling non-speech terminal or that the terminal is in the transmit mode, it shall transmit a continuous 1100 Hz ± 38 Hz tone for a duration of 0.5 second ON and 3 seconds OFF ± 15%.
Active Baxandall Circuit
To overcome the substantial losses in the passive version of this circuit, which give a level response (with both controls at mid way setting) but at -20dB below the input voltage, it is common to incorporate an amplifier in the designs. Nowadays an op-amp would be a reasonable choice, with the Baxandall network forming a negative feedback loop to give the required gain figures over the necessary bandwidth. Various designs are possible with different values for resistors R1 to R4 and C1 to C4 in the network, depending to some extent on the output impedance of the previous, and input impedance of the following circuits.
With active circuits such as that shown in Fig. 4.2.6 the aim is to have the level response at 0dB so there is no gain and no loss due to the tone control circuit. The maximum amount of boost possible should not be sufficient to overload any stage following the tone control if distortion is to be avoided. The design of such control circuits is usually therefore, an integral part of the overall design of an amplifier system.

7# High-quality Tone Control Mono using 5 Transistors C945
Imagine you are listening to a very beautiful song. You hear every detail of the instrument, clear voice Softly. You can stay with it all day long.
This circuit may be the best choice for you. It is a high gain of preamplifier tone control circuit using 5 transistors.
Look at the circuit diagram.

Circuit Diagram of High-quality Tone Control Mono using 5 Transistors C945
A Designer adds a preamplifier section. It consists of transistor Q1, R1-R6, C1, and C2. It gives this circuit a higher gain, can get tiny low-level audio signals of about 1mV. While still responding to sound frequencies as well and has low distortion.
Other details Still the same as the three transistors pre tone control circuit (previous circuit).
Also, See in the circuit is mono form. If you want a stereo. You need to build other one.
We can use many number of NPN transistors like C945 or C1815 or C828. The pin configuration is the same.
Making this project
I have built this project and found that the strength and sound quality are good when compared with IC op-amp circuits.
But to build this project requires high neat. Because it uses a lot of components.
Also, you can use perforated PCB. Or make a normal PCB.

Then assemble all parts on PCB as layout below.

And see Wiring and assembly guide of this project.

Download This
All full-size images of this post are in this Ebook: Elec Circuit vol. 2 below. Please support me. 🙂

Components list
Resistors ¼ watts +5%
- R1, R13, R25: 2.2K
- R2: 220K
- R3: 56K
- R4, R8: 82K
- R5: 27Ω
- R6: 3.9K
- R7: 100K
- R9: 15K
- R10: 2K
- R11: 12K
- R12: 10K
- R14: 180Ω
- R15: 3.9K
- R16, R18, R24: 3.3K
- R17, R28: 22K
- R19, R27, R29: 220Ω
- R20, R22: 18K
- R21: 47K
- R23: 330Ω
- R26: 620Ω
Potentiometers
- VR1: 50K(A) Dual Audio Potentiometer
- VR2, VR3: 50K(B) Dual Audio Potentiometer
- VR4: 100K (MN) Bal Audio Potentiometer
Capacitors
- C1: 1μF 50V Electrolytic
- C2: 0.01μF Ceramic or Mylar
- C3, C5, C7, C15: 22μF 25V Electrolytic
- C4, C6, C13, C14, C16: 10μF 25V Electrolytic
- C8: 1000μF 25V Electrolytic
- C9, C10: 0.1μF 50V Ceramic or Mylar
- C11: 0.001μF 50V Ceramic or Mylar
- C12: 220pF 50V Ceramic
Semiconductor
- Q1, Q2, Q4, Q5: 2SC945 or 2SC1815, 2SC828 NPN transistors, or better read below.
- Q3: 2SA561 PNP transistor or better read below.
- Other PCB, jacks RCA, jack DC, adapter, etc.
Alternate Of C945 and A561 Transistor
If you cannot find the transistors. You can use alternate transistors. But Its pin configuration is different see in the diagram below before replacing in the circuits.C945: 2N3904, BC547A561: 2N3906, BC557

Its performance is similar. May be higher as well Because it has more collector current (IC) and higher frequency response.
18V Regulator circuit
These classic pre-tone control circuits (Circuit 1, 2, 5, 6, and 7) require a 12V to 24V DC power supply. Since they use low current. But it should be a DC regulator circuit only. I recommended this circuit below.

It is a series voltage regulator using Zener and transistor. So easy and cheap. However, they are enough for our pre-tone control circuits.
Here is PCB layout and components layout.

PCB layout 18V regulator

Components layout of 18V regulator
Check out these related articles, too:
- 3 (bass mid treble) Tone control circuits projects using NE5532
- Low noise pre tone control circuit using 4558 – NE55532
- Simple bass treble tone control circuit diagram