I found this diagram on an old electronics book.
Briefly it has presets such as:
-bass
-loudness
-hiss
-rumble
The problem which I see is that audio signal is going on T2 base, but for bass, the author says that while "B" is closed, the group of R6-C3 is lead to the ground. How? If the collector of T1 is not coupled at V+ (via a resistor)? Any idea?
Briefly it has presets such as:
-bass
-loudness
-hiss
-rumble
The problem which I see is that audio signal is going on T2 base, but for bass, the author says that while "B" is closed, the group of R6-C3 is lead to the ground. How? If the collector of T1 is not coupled at V+ (via a resistor)? Any idea?
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1) that circuit is improperly called "tone control".
It is actually one set of filters, which were once very common in Home Hi Fi amps, later were dropped because IF they were actually needed, you had GROSS problems which you´d better address first.
They fell out of favour because they actually "solved" nothing, only partially obscured the problems, and that by MURDERING sound quality.
* "Hiss" (include far worse "Scratch" there): if you were listening to a very hissy tape (even worse with cassettes) or had a very worn dirty scratchy Vinyl disk, it murders anything above 5 kHz, and quite a chunk under that, because it´s a crude 6dB/oct filter, which is "slow".
* Rumble: same thing but killing anything below 100 Hz , also attenuating something from 200Hz down for the same reason (6dB/oct)
What is it for?: old cheap turntables were *everywhere* (Vinyl and Radio were the only sources for normal people) and most were a DISASTER, cheap edge drive motors were basically a home fan or hairdryer quality motor directly driving turntable platter edge using a rubber wheel, and transmitting all kinds of odd vibrations, also records were easily warped by leaving them in the Sun or inside a hot car trunk, sometimes very cheap records had the center hole off center, etc. , all generating tons of low frequency noise ("rumble")
* Loudness: since human ear response worsens at low volumes (that´s why we love to listen to LOUD Music), low and high ends get lost first, and mids become prominent, Music becomes nasal or "like cardboard"; this filter attenuates frequencies between 200 Hz and 5 kHz.
Keep track of the frequencies attenuated so far: if you switch all "on" .... you´ve killed everything!!!! 😱
Not that deep of course, because these are all very poor filters, but you get the idea.
* now to your "Bass" control: it murders (now you understand the idea behind these designs) frequencies above 2800Hz (12k series + 4n7 to ground).
To avoid turning everything into mud, R6 7k5 limits the attenuation.
By killing highs you apparently have "more Bass" 🙄
About T1
It is not "amplifying" but it´s used as an electronic switch.
Normally open, so C3 and R6 are out of the circuit, when you apply positive bias to its base through R2 and R3 it turns ON, and connects bottom of R6 to ground.
In a nutshell: this kind of "corrective filters" had *some* usefulness when turntables or records were in HORRIBLE condition, obvious solution is to take care of records, keep them clean and unscratched, using at lest basic quality turntables, etc. , but for decades horrible ones were present everywhere.
Personally, I would not waste time building that Filter unit, just study it out of curiosity.
PS:loved reading Rumanian text.
Never studied it but speaking various Latin languages (Spanish, Portuguese, French, Italian), it was not hard to decipher 🙂
It is actually one set of filters, which were once very common in Home Hi Fi amps, later were dropped because IF they were actually needed, you had GROSS problems which you´d better address first.
They fell out of favour because they actually "solved" nothing, only partially obscured the problems, and that by MURDERING sound quality.
* "Hiss" (include far worse "Scratch" there): if you were listening to a very hissy tape (even worse with cassettes) or had a very worn dirty scratchy Vinyl disk, it murders anything above 5 kHz, and quite a chunk under that, because it´s a crude 6dB/oct filter, which is "slow".
* Rumble: same thing but killing anything below 100 Hz , also attenuating something from 200Hz down for the same reason (6dB/oct)
What is it for?: old cheap turntables were *everywhere* (Vinyl and Radio were the only sources for normal people) and most were a DISASTER, cheap edge drive motors were basically a home fan or hairdryer quality motor directly driving turntable platter edge using a rubber wheel, and transmitting all kinds of odd vibrations, also records were easily warped by leaving them in the Sun or inside a hot car trunk, sometimes very cheap records had the center hole off center, etc. , all generating tons of low frequency noise ("rumble")
* Loudness: since human ear response worsens at low volumes (that´s why we love to listen to LOUD Music), low and high ends get lost first, and mids become prominent, Music becomes nasal or "like cardboard"; this filter attenuates frequencies between 200 Hz and 5 kHz.
Keep track of the frequencies attenuated so far: if you switch all "on" .... you´ve killed everything!!!! 😱
Not that deep of course, because these are all very poor filters, but you get the idea.
* now to your "Bass" control: it murders (now you understand the idea behind these designs) frequencies above 2800Hz (12k series + 4n7 to ground).
To avoid turning everything into mud, R6 7k5 limits the attenuation.
By killing highs you apparently have "more Bass" 🙄
About T1
It is not "amplifying" but it´s used as an electronic switch.
Normally open, so C3 and R6 are out of the circuit, when you apply positive bias to its base through R2 and R3 it turns ON, and connects bottom of R6 to ground.
In a nutshell: this kind of "corrective filters" had *some* usefulness when turntables or records were in HORRIBLE condition, obvious solution is to take care of records, keep them clean and unscratched, using at lest basic quality turntables, etc. , but for decades horrible ones were present everywhere.
Personally, I would not waste time building that Filter unit, just study it out of curiosity.
PS:loved reading Rumanian text.
Never studied it but speaking various Latin languages (Spanish, Portuguese, French, Italian), it was not hard to decipher 🙂
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Regarding T1, explain me step by step how does it act like a switch? Basically while measuring, the transistor is composed by two diodes B-E and B-C. This way how can be grounded that group R6-C3 if one diode B-E has a falling of voltage while conducting, and the other one B-C is operating in an opposite way?