[sdiy] OT: TL07x Friend or Foe?

mike ruberto somnium7 at gmail.com
Tue Sep 28 03:12:06 CEST 2010

I wasn't being scientific and even if I wanted to make changes like
that it would be almost impossible since all the resistors in the
input stage are monolithic arrays and no compensations caps at all.
The input impedance is 47K and the impedance of the following VCA
stage is set at 27K. A typical balanced input buffer with a gain of 1.
I only checked to make sure the parts I used were unity-gain stable.
Honestly, I'm not even sure if the LT1359 is. I should pop it back in
and check for RF oscillations.

On Mon, Sep 27, 2010 at 8:49 PM,  <tu at alphalink.com.au> wrote:
> Did you modify the feedback compensation, input and load impedances of the circuit to match the
> characteristics and limitations of each opamp you tried? Or was this just an exercise in random chip
> swapping?
> /Tristan
> On Tue, Sep 28th, 2010 at 10:18 AM, mike ruberto <somnium7 at gmail.com> wrote:
>> 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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