[sdiy] OT: TL07x Friend or Foe?

[Harry Bissell]

another caveat... phase reversal !!!

Some opamps clip nicely, some will change direction if driven into the stops.
This is bad in an audio circuit, sure death in a servo amplifier...

H^) harry



----- Original Message -----
From: Tim Ressel <madhun2001 at yahoo.com>
To: Synth DIY <synth-diy at dropmix.xs4all.nl>
Sent: Tue, 28 Sep 2010 01:32:48 -0400 (EDT)
Subject: Re: [sdiy] OT: TL07x Friend or Foe?

The TL074 is a design from 1978. It is not surprising that the TLE2144 (1997) 
performs better. I would say replacing any vintage opamp with one generations 
newer should yield better performance. I am currently in love with the LME49710. 
600 ohm drive capability and distortion too low to measure. Nice.

Beware swapping amps. Sometimes it will cause trouble. Possible scenarios: 

An amp is driving a large capacitance and can handle it inherently. The new amp 
may not be as forgiving.
The output of the amp sees a large current spike (sawtooth discharge; I've seen 
this one) and the new amp wigs out.

Long story short (too late): Don't hesitate to replace an opamp, but be prepared 
to put the old one back.

--Tim (been there, done that) Ressel



----- Original Message ----
From: mike ruberto <somnium7 at gmail.com>
To: Synth DIY <synth-diy at dropmix.xs4all.nl>
Sent: Mon, September 27, 2010 5:18:44 PM
Subject: [sdiy] OT: TL07x Friend or Foe?

Hi All,

I hope I don't spark a fistfight here and I don't want to come across
opinionated ;-) but I am rooting these things out of every piece of
gear I own now. How have I come to this?

It all began with a compressor. A nice compressor - JBL/Urei 7110. I
thought it would be neat to have two of them for stereo processing of
my stereo output synths such as the Kawai K3 and the Casio CZ-1 as
well as my Akai sampler. As luck would have it I detected a pronounced
difference in the sound of the two compressors. They sounded like two
totally different machines. Upon investigation I discovered one of the
two has an output transformer and the other doesn't. Case closed?
Nope.

I quickly found that the output transformer option is unobtainium at
any price. The world supply of them is most likely depleted to my
disappointment. But I liked the sound of the transformer toting unit
better than the other with the direct output.

Soooo through some research I discovered another JBL/Urei product
(mind you this took years to track down) the Model 5330 Microphone
Mixer has identical transformers despite them having a different part
number. Eventually I found one cheap on Ebay and sure enough I had a
perfect electrical match. Not that it would have mattered because the
5330 has two output transformers with the same footprint as the 7110's
transformer. I could if necessary use both 5330 transformers had there
been a significant difference between transformers of the two devices.

While I was installing the transformer I noticed that the input buffer
stage of the compressor used a TL074. So on a whim I desoldered it and
installed a nice IC socket then put the 074 back in. Months have
passed and I am just now testing that work on the compressor and
making comparisons between them. Happily both units sound almost
identical enough for me to be happy with all the effort. And they both
have the nice sound resulting from the transformer output stage.

Then I got ambitious and popped out the TL074 and stuck a TLE2144 in
the socket. I have tons of these because I am using them to upgrade a
mixing console with 22V rails. To my surprise the compressor was
cleaner and quieter. I won't get too into subjective adjectives but I
really liked what I heard. Soooo begins the trials....

Test results between 7110 A with TL074 and 7110 B with other quad
opamp ICs. Test material was various synths, beats and music.
Compression was set fairly high (6:1 at -20dB) in order to bring up
noise levels so I could hear the hiss clearly without straining my
ears.

7110 A:

Hiss objectionably loud. Sounds bad.

7110B:

TLE2144  - Hiss very low. Sounds good.
LT1359    - Hiss very low. Sounds very good.
TLE074   - Hiss very low. Sounds good.
OPA4131 - Hiss low. Sounds OK.
OPA404  - Hiss very low. Sounds good.
New TL074 - Hiss loud. Sounds poor.

Surprisingly the brand new TL074 was a noticeable improvement over the
late 70s vintage counterpart.

The TLE074 was a pleasant surprise for me. Not a bad device in the
least. Overall sound was similar to a TL074 but with more depth and
cleaner highs with lower noise.

The OPA4131 was disappointing and not that much better than the TL074
sound-wise but noise was considerably lower.

However, there was one part of the test where the old original TL074
shined. Electronic drum sounds for some reason sound remarkably fatter
coming through the old-timer. Perhaps it is an increase of distortion
in a certain bandwidth or something to that effect but I certainly
won't be chucking these older opamps in the garbage. I have found a
use for them.

Which one will stay in the 7110s? Hmmmmmm...... I will leave that to
your imagination. ;-)

So considering the plethora of vintage and newer synths, mixers,
effects and other gear that have TL074s I just don't see any reason
not to get rid of the noisy, bad sounding 07x opamps. I am not some
audiophile snobberino but I have this thing against objectionable hiss
levels and flat, muddy audio where the treble is all grainy and
fatiguing. I am on a mission to eradicate the TLs from all audio
pathways and I hope others will join me. This is a fight we can win to
the benefit of generations to come.

This has been a public service announcement.

Note: No TL07x devices were harmed in the performing of this experiment.

Ummmm, well maybe one..... MUHAHAHAHAHAHAHA!

Mike
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-- 
Harry Bissell & Nora Abdullah 4eva