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Old 16th March 2012, 07:28 PM   #1
jayadev is online now jayadev  India
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Default Op-amp Guilt feel.

I guess Opa2134 is almost god of small signal audio purpose (only heard).

I used TLO84 to save space and save some bucks , .

Guess why

OPA 2134 was hard to find costed me 5 dollar for a single piece.I got 2 dozen TLO84 for 5usd

I feel kind of guilt arising in my subconsciousness .

Did I do injustice to myself ?

the preamplifier I made was for myself. it was a prototype multichannel for mid woofer ,tweetor and subwoofer.
total 32 amps plays for single channel. made two for stereo. wishing to build one more for centre channel

sonic quality:- I have no reference system to compare other than sennheiser hd448 headfones .
but it served my purpose no hissing or noise is heard so far.

how far I might have erred using TLO84 in pre amp stage?


I have Ne 5532 as well . I have earlier substituted and tested Ne 5532 vs TLO82 and difference was very much evident ,TLO82 proved noisy and bit strained .

Just for the ease of quad amp and simplicity of circuit lead me use TLO84.

But for the guilt feel.
an emotional audio enthusiast here..
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Old 16th March 2012, 10:37 PM   #2
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Hi jayadev
All is not lost, find yourself a NPN BC547, and a PNP BC556, the pin out is from the front flat part facing you Collector Base Emitter, If its OK to place these parts on your circuit or breadboard, make yourself up a capacitor multiplier for the voltage rails.... and see if that improves performance.

the image shows a NPN like BC547, you need to redraw for the PNP, so grab a piece of paper draw up the op amp, and the transistors you are going to place,
if you have a camera or scanner send it back for checking.

If you have a dual rail supply Pin 4 of the TLO84 is V+ that suits the BC547 and pin 11 is V- that suits the BC556
see the little image, and note R2 can be viewed as the op amp load itself.
The Resistor inwards to the base, make this between 2400 ohms and 4700 ohms
The capacitor marvelously multiplies by the hfe, so you only need a small cap to satisfy
the TLO84, and approx 330n would be ideal.

Cheers / Chris
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File Type: gif Cap_multiplier.gif (1.4 KB, 392 views)

Last edited by Chris Daly; 16th March 2012 at 10:41 PM.
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Old 17th March 2012, 05:39 AM   #3
jayadev is online now jayadev  India
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Chris,Thank you for the reply

From the above schematic I realize it is a voltage regulator and I am bit surprised why it should be added for TLO84. presently the voltage supply Iam is 15-0-15 regulated by 7815 and 7915 respectively.
thanks
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Old 17th March 2012, 05:55 AM   #4
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Quote:
Originally Posted by Chris Daly View Post
see the little image, and note R2 can be viewed as the op amp load itself.
The Resistor inwards to the base, make this between 2400 ohms and 4700 ohms
The capacitor marvelously multiplies by the hfe, so you only need a small cap to satisfy
the TLO84, and approx 330n would be ideal.
As shown, the transistor is likely to go into quasi/full saturation. You need a voltage divider resistive network (with one leg connected to ground), instead of R1, for biasing the transistor out of saturation.

Jayadev: There are numerous opamps that are better than the OPA2134, and even more that are better than the TL084. LME49740 is an excellent quad opamp that can replace the TL084. For duals, any of LT1057, LT1213, LT1361, LT1364, LM4562/LME49720, LME49722, LME49860, LME49880, LME49990, OPA1612, OPA1642 will comfortably beat the TL082. In singles, OPA627, OPA827, OPA1611, AD797 and AD8065 will comfortably beat the TL081 and almost everything else.
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Old 17th March 2012, 06:41 AM   #5
jayadev is online now jayadev  India
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Quote:
Originally Posted by linuxguru View Post
As shown, the transistor is likely to go into quasi/full saturation. You need a voltage divider resistive network (with one leg connected to ground), instead of R1, for biasing the transistor out of saturation.

Jayadev: There are numerous opamps that are better than the OPA2134, and even more that are better than the TL084. LME49740 is an excellent quad opamp that can replace the TL084. For duals, any of LT1057, LT1213, LT1361, LT1364, LM4562/LME49720, LME49722, LME49860, LME49880, LME49990, OPA1612, OPA1642 will comfortably beat the TL082. In singles, OPA627, OPA827, OPA1611, AD797 and AD8065 will comfortably beat the TL081 and almost everything else.
LinuxGuru,
Delighted to see you reply.

I have known most of those OPamps numbers around but the issue is avalabiltiy. and sometimes the price too. one of the AD series Opamp was available in chennai for Rs400 per piece I wonder if it is reasonable.

LME49740 sounds good here- thanks to you. never came across it and any application. can you help me with cost and other details(in India) I have downloaded the specs from NS.

LT series are more or less for instrumentation applications so using it here in my pre amp would be overdoing what say? neither I am so much familiar with their specs either.

Or could you provide me details of source to procure them at reasonable price. I do keep travelling Mumbai and Chennai often.


Ps. This is the forum where I always feel Lucky
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Old 17th March 2012, 08:44 AM   #6
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Quote:
Originally Posted by jayadev View Post
... one of the AD series Opamp was available in chennai for Rs400 per piece I wonder if it is reasonable.
It depends on the specific opamp - if it's a metal can AD797B, it's reasonable. OTOH, OP07 precision opamps are available for ~Rs.10, but they're not particularly good for audio.

Quote:
LME49740 sounds good here- thanks to you. never came across it and any application. can you help me with cost and other details(in India) I have downloaded the specs from NS.

LT series are more or less for instrumentation applications so using it here in my pre amp would be overdoing what say? neither I am so much familiar with their specs either.

Or could you provide me details of source to procure them at reasonable price. I do keep travelling Mumbai and Chennai often.
PM me or email me at siva dot chander at gmail dot com for details. I have some NatSemi, TI and Linear Technology opamps sourced from EBay. Not all LT opamps are instrumentation opamps - several are optimized for high-end audio and video use. LT1361 is a good example of a very good dual video opamp that works well in most line-level audio applications also.
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Old 17th March 2012, 09:09 AM   #7
qusp is offline qusp  Australia
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yep and some of their instrumentation opamps are superb audio opamps too, like LT1028, LT1128, LT1007
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Old 17th March 2012, 09:55 AM   #8
jayadev is online now jayadev  India
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Quote:
yep and some of their instrumentation opamps are superb audio opamps too, like LT1028, LT1128, LT1007
Hi qusp,

Agreed ,they are great. but issue is how to source them easily .
I am an amateur . it becomes too much for me to wait for 3 weeks to get something .
then comes the price .sometimes for a particular application there are cheaper alternatives which goes unnoticed .

I am bit tired of ordering via ebay and such online stores.most of the time I run out of patience.

for an amateur it is not only just building up something but his mood too contributes.

today I will be wishing to build an amp and next week I would be planning mountain hiking.

But things get messed up..!!

This time I dint wait , I just build with TLO84 the ic which was readily available in local stores now I feel weird..
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Old 17th March 2012, 10:35 AM   #9
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Quote:
Originally Posted by jayadev View Post
how far I might have erred using TLO84 in pre amp stage?
not very much! The TL07/8X series is fine. They have to be used within their limits though!
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Old 17th March 2012, 06:59 PM   #10
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Originally Posted by linuxguru View Post
As shown, the transistor is likely to go into quasi/full saturation. You need a voltage divider resistive network (with one leg connected to ground), instead of R1, for biasing the transistor out of saturation.
Quite right, Yes hfe will be much lower, however would discuss considering this is a a DC supply connecting to op amp rails, it requires a on state saturated transistor.

As jayadev points out 7815 and 7915 somewhat discount need for transistor, never the less interesting to try any sound difference, transistor vs no transistor.

Cheers / Chris

Last edited by Chris Daly; 17th March 2012 at 07:01 PM.
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