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Old 14th April 2008, 12:33 PM   #1
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Default Simple 12v gain stage

Hello

I purchased this simple kit to use as a gain stage or preamp for my digital amp. I had looked around for a long time for one, as it was hard to find anything that did not require a +/- virtual earth power supply.

I would like some opinions on the quality of this circuit. It uses a TL072 op amp.

When I googled the TL072, the info page http://focus.ti.com/docs/prod/folders/print/tl072.html states that the TLE 2072 is a high precision upgrade.

Am I likely to notice an increase in quality with the TLE2072?

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Old 14th April 2008, 12:48 PM   #2
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How good the circuit is depends what you are going to use it for. I think you can guess if the circuit is high classy or not. TL072 was cool 20 years ago. Now you have lot's of good opamps to choose from.
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Old 14th April 2008, 01:13 PM   #3
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If using on batteries remember some OpAmps are a lot more "power hungry" than the TL072. If I may beg to differ with Peranders, yes there are far better devices now but the humble TL072 is a very capable performer for high quality audio, and very docile, there are no stability issues to catch out the unwary. There are a lot of coupling caps in there (I note the frequency response as 40hz -3db) you may be able to usefully increase the value of these if you can get hold of "axial" type replacements although this will increase any switch on "thumps". You could also link out C5 and C7 as the output is AC coupled anyway to the trimpots. Just noticed the schematic has two C7,s I mean the one on the output.
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Old 14th April 2008, 01:52 PM   #4
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I have seen circuits like that which split a single power rail into 2 since the 1980's.

Its typical of guitar effects circuits that have to work off a PP3 battery.

The circuit looks pretty standard to me.
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Old 14th April 2008, 01:58 PM   #5
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Thank you for your replies.

The gain stage is to be used between a Monica TDA1545A DAC with a Rudolf Broertjes SS IV stage and a Charlize TA2020 amp. At the moment I use a passive pre in the form of a stepped attenuator, and I am missing some gain. When I tested with an active pre there was far more volume available.

What are your thoughts on using the TLE2072 instead of the TL072? Are they interchangable in this circuit?
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Old 14th April 2008, 02:00 PM   #6
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I'd replace these 1uF electrolitycs with some foil-caps (MKP, MKT, etc...).
That seven new cap would cost almost nothing, 1USD for the seven or so.

Use OPA2134 instead the TL072.

New resistors - 1%, 0.5W metal-films - would be a good idea too!
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Old 14th April 2008, 02:00 PM   #7
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I forgot to mention that this is to be powered by a regulated SMPS of 12V, or 24V dc.
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Old 14th April 2008, 02:08 PM   #8
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Thanks a gain (ha) for your replies.

Andy: I am very happy to use better components, so long as the circuit design is going to achieve what I want (just a bit of gain). I wish to maximise the quality, where possible. Can I just swap the OPA2134 with the TL072?

I suppose that I should replace the trim pots with high quality fixed resistors, once I have found the required level of gain?
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Old 14th April 2008, 02:14 PM   #9
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Quote:
Originally posted by dublin78
Thanks a gain (ha) for your replies.

Andy: I am very happy to use better components, so long as the circuit design is going to achive what I want (just a bit of gain). I wish to maximise the quality, where possible. Can I just swap the OPA2134 with the TL072?

I suppose that I should replace the trim pots with high quality fixed resistors, once I have found the required level of gain?

If you just want fixed gain I would get rid of the pots on the output and alter the resistors around the op-amp for the right gain. Thats means you can get rid of a couple of caps too.

Its always poor design to amplify then attenuate later.
Amplification tends to amplify noise as well as the wanted signal.

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Old 14th April 2008, 03:31 PM   #10
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Andy: Thanks for your reply.

I have found these caps "MKT1813 Met Polyester Cap 1uF 63V 5%" at RS: http://uk.rs-online.com/web/search/s...duct&R=1854038

Are they suitable, or what exactly would you suggest?
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