The LA-2A's Underrated Little Sibling? Urei LA-4 Opto Compressor teardown

[@LoveExcelsAll]

My first compressor as a studio intern a million years ago. Love this thing! Thanks for the teardown.

[@Rhuggins]

Dude, I adore these types of videos. I wish y'all would make more of them. A little 2 minutes "compressor workout" section tacked on at the end (so we can hear the unit on some drums or a mix) would be the icing on the cake. In fact I would pay for such content. Thanks for all you do!!

[@artysanmobile]

The yellow ‘IC’ is actually a package of 8 matched resistors for general use in the circuit. The matching benefits the transformerless input topology so it is common to see in this vintage.

[@SoumaMondal]

Our boy geeking out over yellow ICs and I am HERE FOR THIS! So informative, loved this ❤️

[@petercornell2002]

The LA4 is my favourite all round comp. It has a big fat squishy compression that sounds absolutely wonderful. As my mentor said to me, "It just works!" Mighty machine.

[@delusionwalker8852]

I don't know how can you "hope" that we enjoyed that one.... I love it! I really enjoy to see and hear how you break down the topolgy the real estate the parts the comments you are saving me years of frustrations and wasted money and you ignite my gas and fascination with electronics. I must say I have bigger humble lace in my brat for the diy community and people like you than any other well knowen brand I simply enjoy this stuff. So thank you for doing all this and doing this videos

[@freaksarise]

I've been self educating and obsessing for several yrs and went from guitar pedals, to amps, and am anxiously leading into mic pres and comps now. Had no idea you were in Philly. I'm right over the bridge in woodbury. Thanks for the insight and inspiration.

[@azurplex]

Guitar pedals are a good learning ground for mic pres mixers and amps.

[@azurplex]

This piece of gear was designed for installation and studio use. Most of the time it’s hard wired into a patchbay or stationary system. So so xlr connectors would have been an extra expense and failure points. You can always add them on a pigtail or rack panel for portable use.

[@andydelle4509]

Interesting note, in the voltage divider if you make R1 the controlled variable resistor, you then have a dynamic range expander aka DBX. BTW, That yellow or mustard IC, is not really an IC. It's a resistor network. Could be 8 separate resistors or 7 with a common buss. These are found in several colors, mostly mustard and blue in that time period.

[@pierreduplan4927]

I am learning so much here!!! Thanks!

[@bodanerius]

Has anyone tried upgrading the ICs? Oughta change the sound quality significantly? It might devalue the unit but since its not superloved anyways? Why not?

[@henningriez7655]

Nothing but love for Peterson and DIYRE !!!

[@Yootjoob]

Thanks, another great video.

[@marshallbolin]

Man, your videos are so good! I'm learning a lot from them. Thanks for making them.

[@gold27b]

You are so right about the 741s. They were so popular, every audio designer wanted to use them. The 748 you could adjust the hf roll off. However it didn’t improve things much. I remember checking them out on an oscilloscope and was shocked at the slew rate!

[@peterbrandt7911]

Thanks for explaining.

[@daynaybaybe]

Today my friend brought his LA-4 with upgraded opamps. We compared it against one of mine, recapped, but unmodified. Ran a very beefy real drum track thru them and neither of us heard a dramatic difference, maybe a hair more high frequency, but not even convinced of that.

[@apollon3791]

Amazing channel, keep it up!!

[@callehellstrom]

You are great!! I would love if you would tear down a grace m101.. They to me sound so transparent and I wonder how the Grace design holds up to four instance a modern THAT 1512 design as your own preamp. Keep on rockin!

[@wither8]

Monolithic solid state op-amps (like, as we know them today, not as Harold Black at Bell Labs designed them a la Raytheon valves) were (arguably co-temporaneously) developed by first Bob Pease in literally a "brick" form (1/8th or 1/16th rack IIRC) in the early 60s, but the commercial success of op-amps and most would say the father was Widlar's oft-overlooked 702 (used in military applications mostly) and then the consumer 709 in like 66, which managed to go from $70 in the mid 60s to $2 by 1969. The slew rate was like 20us/V with 20-30MB gain-bandwidth which is more than sufficient enough to do anything audio The slew rate and GBW weren't the problems with these chips, so much as there weren't compensation caps to stabilize the networks. So you've got a real sharp knife to whittle out some wood or to slit your own throat. (You'd have to physically work out the poles/zeros as you swept through your entire operating range and do it numerically which would take a shitload of time even if you're only sweeping 20-20k up to the 5th tone; or you have to have talented nerds who read IEEE 'zines for fun and can synthetically abstract your circuit and then solve the differential equation. (That incidentally is why SPICE was so valuable. At the IC or the PCB design level, super useful) Put that LA-4 back in the casement, and see if that power switch is still flapping around. I bet it's constrained enough to be secure. For that era, that's a very standard (and reliable) hard power switch design. You even saw it on source-measure units from Keithley that cost (adjusted for inflation) 10k. But you're right about the accounting vs engineering dept wars. Those black ICs are just epoxy potting compounds. If you order a batch of anything >10k from any vendor, you can ask them to put a dye or a logo or whatever on it. Hybrids are still made out of ceramic due to their thermal properties, so pretty whiteee. RC4136 is still up at TI as active, though it says "newer version available in the TLV series". It probably went through a lot of die shrinks, so the performance won't be authentic. (Like, literally, the IC masks used will be the same, just scaled down, which is good for their profits and yield per 8", but the older technology might actually *be the actual reason why you're getting the characteristic sound you find so desirable*. Like the overshoot on the waveform, or some underdamping, that used to exist and make the shit sound muddy isn't there anymore. So, unless the part is like a 339 or whatever, if its cheap enough, I order an extra 5 and throw them into my parts bin with tons of dessicant bags In industry, an elevator controller company was going through a new batch test. As a safety company with enormous liability they were using the "Rubicon" of every part. So when they started getting failures, confusion emerged amongst the engineers. Turns out one manufacturer ran a die shrink since they last ordered. Even at the same clocking, the sensors (imagine magnetic sensors for each floor,) so your on-board elevator controller knows where he is) were latching out their data too quickly and there was bus contention. Elevator would get super confused.

[@monkeyplusplus]

Awesome video as always. I built one of your OLA5's and LOVE it. Great kit, great directions, smoooove sound. Thank you!

[@azurplex]

I’m guessing you left out the power supply transformer from the count for the sake of signal path discussion. Personally I think power supplies are the most important area of the gear for the sake of noise or lack therof, quality and reliability. They’re also the first place to look for problems right before any bypass relays if used.

[@aeiplanner]

I'd be interested in your take on a JoeMeek photo optical compressor.

[@iamelohym]

Since those where used for Cassette - Mastering and also well regarding for Classical - Mastering, would you also recommend your Replica for Stereo - Link use? I did read your FAQ's about it and am aware of both Units will do quite different Things inside, even being Stereo - Linked. So for that special purpose mentioned Above and knowing about the funkiness of those very unique little Gems.

[@benjaminjoeBF3]

awesome stuff man, thank you!

[@insidedastudio7539]

Thanks for the vdo. I have a pair of the black La4's. Love them on guitars and backing vocals.

[@azurplex]

IC’s at the time were not high end. They were for mass production of things like transistor radios etc. But careful selection and circuit design can yield good results. Slew rate is always going to color the sound especially in higher frequencies. But old stock opamps are becoming desireable for custom gear like guitar pedals for their character. New part even with the same number from the “same” manufacturers are very different from back then.

[@marthawley2206]

Does the LA-4 silverface have a light in the VU meter?

[@onteraction8294]

Hey does anyone know where to get a backlight bulb for this unit? and how to install? 😋

[@AnalogDude_]

But, shouldn't a compressor act on the threshold setting and cut everything above? How does this wave rectifier setup work in the circuit? i tried building this in the falstad simulator, but .... the scopes couldn't show me anything useful.

[@poindextertunes]

never seen one of these. pretty cool

[@christianoldewolbers7243]

chancing out to a fast op amp makes them so much better

[@lopezd-rd7wm]

Should do a distressor next! :)

[@bijouxbijouxbijoux]

Great video 🙌 may I ask what camera and what lightning system are you using to make your videos ?

[@PetersonGoodwyn]

Thanks! I use a Canon EOS M50 and 2x 20"x20" softbox lights on tripods. For the overhead shot I have a big camera stand with a heavy counterweight.

[@CharlesTsaiE]

Cool,Could you please do explanation of attack and release control in the compressor?like 1176,why is that so fast?

[@ArguZ72]

Because FETs run on electric fields, they are fast and opto elements are pretty slow , like when you look at a light bulb turning off . But both have non linear decay and also engage characteristics that are unwanted in theory but sought after in real life audio application.

[@CharlesTsaiE]

@@ArguZ72 Thank you!

[@arthurlauth1380]

Is the T4B opto cell built in a similar way as the LED/LDR shown here ? What are the real differences ? Again, thank you for your great videos :)

[@miguelpereaantonetti7576]

great video

[@wesleyleigh4063]

Great, something that costs $1500US is underrated in Pro Audio yay I'm so glad I chose this path in life!

[@caminglis53]

Awesome!!

[@Wizardofgosz]

What mic preamp you using here? Throw that SM7 away!

[@PetersonGoodwyn]

lol I mic preamp was focusrite. You don't like the SM7?

[@Wizardofgosz]

@@PetersonGoodwyn Did you change your name to Focusrite?!?!? :-) I was never a fan of that mic just because it's so low output. There are a bunch of mics I would hang before that. Back in 2005 when I was podcasting everyone thought that getting one of those would give them the "NPR Sound" which it didn't. Now I see tons of video guys using them. Next time bust out the U67. :-)

[@joeblack007forever]

@@Wizardofgosz I find the old one, not the SM7B but the Sm7, a really different beast but I will choose an EV Re20 anytime before a SM7 mic ;)

[@Wizardofgosz]

@@joeblack007forever i like the RE27s, but my go to would be the Heil PR40.

[@joeblack007forever]

@@Wizardofgosz thanks for the suggestion, I’ll try it out if I get the chance one day :)

[@darwindeeez]

my mom thinks i'm cute

[@monty4924]

every day oughta be a bad day

[@artysanmobile]

The LA-4 is a wonderful compressor with many hidden features. The 2:1 Ratio setting for example has a radically different attack-release action. I particularly like 2:1 for snare or bass drum. The ICs in the LA-4 were, at the time, of a very high grade. Analog ICs were an enormous improvement on discrete circuitry. I don’t know how you missed that memo, but describing them as ‘distorted’ ‘muddy’ ‘mushy’ ‘sounds like crap’ is a profound display of ignorance. I guess Neve, SSL, MCI, API, Trident, etc…. all don’t know what they’re doing! Perhaps you can call them and help them out. If you wish to explain circuitry, great. It’s a useful subject. But maybe put some effort into learning about sound, a subject on which you are utterly incompetent to speak.

[@tekis0]

Does this guy really know anything about UREI compressors?! There are NO input controls on LA-2, 3A, or 4. There's only make up gain.

[@PetersonGoodwyn]

On the LA-2A and LA-3A it's called "Peak Reduction." On an LA-4 it's called "Threshold."