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Old 11th June 2015, 03:49 PM   #1
prasi is offline prasi  India
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Default Tone control TL074

Dear all,
I made a schematic for tone control (stereo) using TL074 based on TI application circuit. Need your comments on the same for improvements.
regards
prasi
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Old 11th June 2015, 06:41 PM   #2
Mooly is offline Mooly  United Kingdom
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I think the volume/balance arrangement needs looking at. As it stands you can short out either input at max volume.

Look at figs 7 and 9 here,
Potentiometers (Beginners' Guide to Pots)
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Old 11th June 2015, 07:42 PM   #3
rayma is offline rayma  United States
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Quote:
Originally Posted by Mooly View Post
I think the volume/balance arrangement needs looking at. As it stands you can short out either
input at max volume. Look at figs 7 and 9 here, Potentiometers (Beginners' Guide to Pots)
Yes, a resistor (1k-5k) on each input before the volume control should fix it.
There are no coupling capacitors at the outputs, so there could be loud noises (or worse)
when turning the power on/off, or when a supply fails. The amplifier could be damaged
from output DC if it has no input capacitor.

Last edited by rayma; 11th June 2015 at 07:46 PM.
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Old 12th June 2015, 02:48 AM   #4
prasi is offline prasi  India
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Quote:
Originally Posted by rayma View Post
Yes, a resistor (1k-5k) on each input before the volume control should fix it.
There are no coupling capacitors at the outputs, so there could be loud noises (or worse)
when turning the power on/off, or when a supply fails. The amplifier could be damaged
from output DC if it has no input capacitor.
Hi all,
Here is the modified schematic as per your suggetions. Hope its all right this time. I have used a 1k resistor at input before vol control and 1uF coupling cap at output.
regards
prasi
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Old 12th June 2015, 03:09 AM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by prasi View Post
Hi all,
Here is the modified schematic as per your suggetions. Hope its all right this time. I have used a 1k resistor at input before vol control
and 1uF coupling cap at output.
Seems ok, but it depends. What are your source components and their impedances, and what is the output component and its input impedance?
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Old 12th June 2015, 04:53 AM   #6
prasi is offline prasi  India
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Hi Rayma,
I am planning to use a general purpose DVD/Blueray player as the source. on the output side planning to use the DIYAUDIO honey badger amp / APEX kelvin amp.
reg
prasi
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Old 12th June 2015, 01:05 PM   #7
rayma is offline rayma  United States
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Quote:
Originally Posted by prasi View Post
Hi Rayma,
I am planning to use a general purpose DVD/Blueray player as the source. on the output side planning to use the DIYAUDIO
honey badger amp / APEX kelvin amp.reg
The source should be ok. The honey badger has around 25k input, so you'll want at least 1uF for the output cap.
If the other amp is also fed by the circuit, the cap would need to be larger, maybe twice as large.
I would increase the value of R10 to 100k or more, as it needlessly loads the output cap.
Remember to use small decoupling caps near each op amp's supply pin, around 0.1uF.

Last edited by rayma; 12th June 2015 at 01:10 PM.
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Old 12th June 2015, 03:08 PM   #8
prasi is offline prasi  India
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here are answers to the points that you mentioned.
1. by output cap do you mean C15/C16? They are already 1uF 63V. For the other amp ( APEX amp), I will try to use 2.2uF.
2. I will increase the R10 to 100k.
3. Decoupling caps are used (right of schematic -C6, C7: 104)
apart from the above any other construction/ layout tips.
I am trying to layout the PCB but its quite a job!.
reg
prasi
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Old 12th June 2015, 05:57 PM   #9
rayma is offline rayma  United States
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Originally Posted by prasi View Post
any other construction/ layout tips.
I am trying to layout the PCB but its quite a job!.i
You can post your layout here, I'm sure there will be a few suggestions.
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Old 14th June 2015, 06:04 AM   #10
prasi is offline prasi  India
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Originally Posted by rayma View Post
You can post your layout here, I'm sure there will be a few suggestions.
Hi Rayma and others,
Finally I was able to layout the PCB. I am attaching the layout (and the final schematic for convenience).
Appreciate very much if you can suggest improvements/corrections.

some design values and considerations that went into the layout.
1. pots to be pcb mounted with adequate spaces between adjacent pots for operation of knobs(of reasonable sizes).
2. width of the traces is kept as 0.6096mm (24 mils). Hope this is sufficient for current levels.

regards
prasi
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File Type: jpg layout123.jpg (902.7 KB, 163 views)
File Type: jpg schematic123.jpg (562.3 KB, 156 views)

Last edited by prasi; 14th June 2015 at 06:12 AM. Reason: oops! forgot to attach schematic !
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