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Old 23rd September 2010, 02:55 PM   #1
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Default adding volume control to my chip amp

Hi - I just finished a TDA 2050 stereo amplifier - my first project. Now I'd like to add a volume control. I think I need a "passive attenuator". I need less volume from the CD player, basically. Can someone point me to a simple schematic or something? I assume I just need to solder a potentiometer into the input path, but I guess I need to somehow mechanically gear them so that both channels are adjusted with one knob? I'm in the UK, so 'll probably be ordering parts from Farnell.co.uk.

I would love to add bass/treble control, but I'm going to save that for later, unless it's very simple, cheap and quick.

I did some searching on here before I posted this, but I couldn't find what I need. If the answer is somewhere obvious, can you please hook me up?

thanks
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Old 23rd September 2010, 03:23 PM   #2
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Search on this forum, or google "dual gang pot". Once your understand the function go to your parts distributer and see what's out there. Do you know the input impeadance of the TDA 2050 amp? as this will be important information in selecting a pot value. Also the output impeadance of teh CD player. (perhaps low like <1K).
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Old 23rd September 2010, 06:31 PM   #3
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Here what ive learnt so far from recent question I've posted. For one choose a decent pot if you going the Pot route. Nobel have been recomened to me as well as Alps
potentiometers - Hifi Collective see here for UK supplier.

You'd use a pots that has is stereo compatibility from the get go. no need for connectors and such.

Also look at using a shunt resistor.

Also take a look at stepped attenuators
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Old 23rd September 2010, 09:47 PM   #4
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Here's the basic idea. You need a dual-gang logarithmic potentiometer. Dual-gang means 2 pots linked on a common spindle

Click the image to open in full size.

The 100k pot shown is from a valve amplifier, 10k is probably more appropriate for a CD player and chip amp. You might conceivably need to go as low as 1k, but I doubt it. The value should ideally be higher than the CD player output impedance and lower than the chipamp input impedance. You connect the input signal to one side of the pot, signal ground to the other, and take the signal from the wiper (centre connector) to the amp. If the volume control is not clockwise for UP then swap the input signal and ground connections.

w

Last edited by wakibaki; 23rd September 2010 at 09:49 PM.
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Old 23rd September 2010, 10:36 PM   #5
dmx2020 is offline dmx2020  New Zealand
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Here's some (bass mid treb vol). (found on google)

Adam's Amplifiers: Tone Stacks

Tone Control circuit diagrams using IC TL082 | ELECTRONIC CIRCUIT

Portable Mixer - RED - Page53
Attached Images
File Type: gif ToneControl.gif (3.7 KB, 534 views)
File Type: gif active-Tone-controll-that-Boosts.gif (5.5 KB, 535 views)
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Old 24th September 2010, 08:36 AM   #6
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Thanks all! This is great stuff. I'm going to research my impedances and order a dual gang pot.

I'll probably be switching between the CD player and my ipod, so I guess I'll just pick a potentiometer that seems like it will work for both.
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Old 24th September 2010, 09:06 PM   #7
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Hi

Not sure about tone controls in th context of your question but what I did was
type ' Stepped Attenuator ' in E bay and choose a value to suit.
You can spend a lot or spend very little and still get good results.
There are plenty of values to choose from once you decide or find out the best impedance match for your kit - as already mentioned.

Andrew
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Old 24th September 2010, 10:04 PM   #8
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darkczar,
The 23 step resistor type attenuators on ebay work pretty darn good for less than 20.00 each. You will notice at times that the switch does not fully engage the slot and may need to be touched. Once set they are almost invisible in the circuit. You could search long and hard and spend serious money but these chinese units are really good.
Please ask for a wiring schematic from the seller. It sometimes speeds things up. There is also a seller for the full monty, source selector step attenuator and all which comes with a nice aluminum housing and all. You may have to search for it. A complete passive in one housing. It is important to order the input impedance your amp design requires or your volume settings may be too low or too high.

Good luck on this project you are now addicted to diy Tad
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Old 25th September 2010, 12:00 AM   #9
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HI - I couldn't resist walking over to Maplin this morning and buying a 10K dual gang pot for 2 pounds and 53 pence. It's made in the UK. It seems to work fine. I had to solder a few different times before I got it set up correctly, but it works OK. I plugged my TV's audio output into the amplifier, and it's wicked loud, but I was able to turn the volume almost all the way down, and it was OK.

I'm definitely going to add some bass and treble next. The TV puts out very bass heavy sound through my amp and speakers. It sounds tinny through the TV speakers. It would be a nice blend, except that there's a few millisecond delay between them, so everyone sounds like Darth Vader.
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Old 26th September 2010, 08:32 AM   #10
inVain is offline inVain  Indonesia
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Hello,

it's nice that you already bought your dual-gang pot....

but during my past experience, I found out that stepped attenuators has better sonics performance than the log pots....
even if they were made of cheap resistors and rotary switch (in similiar price range)

so my suggestion,
you should try one compared to your pot

regards
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