UREI 1178 fet distortion

[AudioIngenia]

I have replaced all electrolytic capacitors following Jim Willians recommendation.
https://gearspace.com/board/so-much...1178-jim-williams-mod-highly-recommended.htmlEverything seems to work correctly.
But I have discovered, that with the NPD5566 double fet inserted some harmonics appear. If I remove the double fet, the distortion disappears.
Is there something abnormal here?

 

[gyraf]

..the FET introduces some distortion if there's more than a few milivolts of signal across it. This is "the sound of FET-compressrs", I think

 

[jensenmann]

It´s not a bug, it´s a feature ;-)

 

[Bo Deadly]

I wouldn't change all of the things suggested on that page. Do you want an 1178 or do you want something else? I also question their judgement when they suggest changing a 5532 for something "better".

As for the distortion, that's over 60 dB down which is going to be completely inaudible. And consider that when the limiter kicks in, distortion is going to go waaay up anyway. When pushed hard, it adds character to vocals and on fast settings it's good for recording drums. If you're using a FET limiter, you're probably not terribly concerned with fidelity.

 

[JohnRoberts]

There are techniques for reducing distortion in JFET shunts (effectively adding some drain signal back into the gate). But this will result in a different sound signature.

JR

 

[Bo Deadly]

There are techniques for reducing distortion in JFET shunts (effectively adding some drain signal back into the gate). But this will result in a different sound signature.

From what I can tell the 1178 (and 1176) already do this. Both also "bootstrap" the JFET source to reduce Vds (and thus distortion). It could probably be trimmed to reduce distortion slightly but I wouldn't bother.

 

[Whoops]

I have replaced all electrolytic capacitors following Jim Willians recommendation.
https://gearspace.com/board/so-much...1178-jim-williams-mod-highly-recommended.html

I wouldn't do the mods described in that thread it will ruin the original sound of the unit

But I have discovered, that with the NPD5566 double fet inserted some harmonics appear.
Is there something abnormal here?

Very nice that distortion and harmonics, there's nothing abnormal, everything's normal thats the sound of the Urei 1178/1176 embrace it

 

[karloff70]

If someone made a subtIe saturation kit for onIy the fet harmonic signature of a reaI 1178 I wouId buiId it in a hurry......

 

[gswan]

FETs work like triodes and give you 2nd harmonic distortion. The amount will depend on how they are biased and where on the gain transfer curve they are operating (and the type of circuit).

 

[AudioIngenia]

Great. Thanks to all for the contributions.
I'm going to play a bit in the studio with the 1178. Then I'll decide whether to keep the mod. or return to the original design.

 

[Matt Syson]

Putting a 'new' FET in means relatively little as FETS are notorious for their wildly different characteristics. Manufacturers of FET based compressor/limiters would typically buy a big bag of FETs and a lowly paid employee would have to sit and test them all in a jig to find the ones suitable for the job that allows the product to meet specifications. The 'reject' FETS can often be uses either in the meter drive circuit (if it has one) or for other jobs entirely. Similarly for 'Vari Mu' valve compressors, buy a load of valves and select the ones that are well enough 'matched' for the job. The rest get used elsewhere.

 

[Mr. Moscode]

Well, considering the Teletronix LA2 uses a cadmium sulfide photocell and a fluorescent light on the the cell, driven by a low power pentode. . . . it was loved the world over. How linear is a CDS cell and light combo.

Variable Mu tube compressors were workhorse comp/limiters in the 40s and 50s. A lot of black metal octal tubes in there. And iron.

Probably the majority of the results in this project come from cap & IC swaps, both being in the signal path. And I'm interested in seeing/hearing about the result.

And I agree that distortion at -60db should not be an issue. It's most likely the worst when it is in hard limiting, which is a distortion all its own.

 

[Mr. Moscode]

Here's the mod:
"
If it ain't broke, break it then fix it! Unless you want to dwell in the world of mediocrity.

This is NOT an 1176, it's an opamp based knock-off like a Distressor, ripe for improvement unless you like the sound of 1975 5532

opamps, you know, the one's that drove up the prices for discrete English consoles... but I digress.

Replace IC 1 with a >>>National LM6172 or a LM4562. Add a >>>22 pf cap across pins 1 and 2. Replace C3 with >>>22 pf. Replace C6

with a >>>Panasonic FM 47 uf 25 v. Bypass with a >>>Wima MKP-2 .1 uf 250 v. Replace C7 with another >>>47 uf FM with the >>>.1

bypass. Replace C9 with a >>>220 uf FM with the >>>.1 uf bypass. Place a >>>47 pf cap across R6. Replace C10 with a >>>470 uf 25v

FM with the >>>.1 uf bypass cap.

Next, replace C21 with a >>>Panasonic FM 100 uf/50v with the >>>.1 uf bypass cap. Replace C22 with a >>>220 uf FM with the

>>>bypass cap. Change C23 to >>>10 pf. Use either a >>>Linear Tech LT1358 or a National LM4562 for IC2. Replace C25 and 27 with a

>>>470 uf 25 v FM cap. Change C60 and C61 to >>>3300 or 4700 uf 35 volt FC or FM. Change C62 and C63 to >>>1000 uf 25 v FM.

Now, that's a compressor! Save your old parts, install quality machine sockets for the IC's, a return to "stock" condition requires just

dropping in the 5532's and removing the bypass caps, no worries, mate! As if these things have any "vintage" value in the first place?

Jim Williams
Audio Upgrades "

Just as I thought. Caps and IC's.

 

[abbey road d enfer]

"If it ain't broke, break it then fix it! Unless you want to dwell in the world of mediocrity.

This is NOT an 1176, it's an opamp based knock-off like a Distressor, ripe for improvement unless you like the sound of 1975 5532

opamps,

So what's wrong with the sound of 5532?

you know, the one's that drove up the prices for discrete English consoles... but I digress.

Stupid comment. The availability of good, cost-effective audio IC's resulted in mixers available at a price that could not be achieved before with discrete circuits (Neve, Helios, Trident...)

Replace IC 1 with a >>>National LM6172 or a LM4562. Add a >>>22 pf cap across pins 1 and 2. Replace C3 with >>>22 pf. Replace C6

with a >>>Panasonic FM 47 uf 25 v. Bypass with a >>>Wima MKP-2 .1 uf 250 v. Replace C7 with another >>>47 uf FM with the >>>.1

bypass. Replace C9 with a >>>220 uf FM with the >>>.1 uf bypass. Place a >>>47 pf cap across R6. Replace C10 with a >>>470 uf 25v

FM with the >>>.1 uf bypass cap.

Next, replace C21 with a >>>Panasonic FM 100 uf/50v with the >>>.1 uf bypass cap. Replace C22 with a >>>220 uf FM with the

>>>bypass cap. Change C23 to >>>10 pf. Use either a >>>Linear Tech LT1358 or a National LM4562 for IC2. Replace C25 and 27 with a

>>>470 uf 25 v FM cap. Change C60 and C61 to >>>3300 or 4700 uf 35 volt FC or FM. Change C62 and C63 to >>>1000 uf 25 v FM."

That's the worst part. Rolling opamps and caps eventually shows that the circuit's topology and the implementation in the comples structure of a mixer dominate over component types.
Of course when one has spent significant money and hours of work, cognitive bias plays its role in inducing the illusion of betterment.

 

[Mr. Moscode]

@Abby Road- You may have missed the quotation marks "' around the Jim Williams mod instructions, You're not attacking me, your comments are aimed at Jim Williams. I posted it because it is pertinent to this thread.

Everything's a filter, and microphonic, too: caps, op amps , resistors, wire, PC boards, transistor, fets,tubes transformers , connectors, mics, speakers, etc.

you are correct - the IC made big desks affordable. But there are good ICs and mediocre ones. Just like mics and speakers, cars, houses, horses, singers, men and women.

Hey, we're all after the same thing: great sound.

The high end has spent millions trying to fix the cd, sold as the perfect recording.

Keep at it.

Finding the right mics,
MM

 

[abbey road d enfer]

@Abby Road- You may have missed the quotation marks "' around the Jim Williams mod instructions, You're not attacking me, your comments are aimed at Jim Williams.

And that's exactly how I intended. I had not missed the quotation marks; I was not attacking you, rather the nefarious JW.

I posted it because it is pertinent to this thread.

Sure it is. However, you may have made the quotation a little more obvious, by presenting it from the start as JW's assertions.

you are correct - the IC made big desks affordable. But there are good ICs and mediocre ones.

Indeed, but nicknaming the 5532 as "the sound of 1975" in a derisory way is just stupid.

Again, I'm not addressing these criticisms to you, but at JW.
I must admit, citations of JW usually trigger some kind of epidermic reaction in me.

 

[gyraf]

..here I was, thinking I was the only one with such allergies..

 

[Mr. Moscode]

I've made a living doing hi end upgrade mods and designs on the consumer side of the phonograph needle/DAC. I also designed the recording chain for Chesky Records make transformerless AKC C12, 24, tube mixers and ADC.

That said, professional audio has to be reliable and work each time or you don't make any money. Semipro audio has to meet a price point. That's what I see here. Every one wants the sound of $10K mic for $85 and some sweat and thank the universe for it. It moves the art form along. Going to 24/96 cleaned up the sound of everything and is cheap and plentiful.

The high end is a bit different in the tube world. While every one wants everything to be reliable folks are willing to put up with some issues of reliability for better sound. They are also willing to spend $ on it for a sound that makes them feel great when they listen. Great bass, realistic mids and hi frequencies, a big open sound stage, great imaging. That's what I do on my side of the needle and do I it reliably.

 

[abbey road d enfer]

Great bass, realistic mids and hi frequencies, a big open sound stage, great imaging. That's what I do on my side of the needle and do I it reliably.

I have no idea what a "big open sound stage" is?
I suspect it has to do with the placement of speakers and acoustic treatment of the room...

 

[Whoops]

The high end has spent millions trying to fix the cd, sold as the perfect recording.

Nothing wrong to me with the sound of the CD, actually no influence in sound on it's own, or better nothing wrong to me with the sound (in a final master) of a WAV 16bits 44.1khz.

It sounds better than tape to me, less hiss, no degradation at all every time you listen to it, and it sounds miles better than a Vinyl which has very high noise, distortion, limited frequency response (much limited than what we can actually hear), limited bass energy and stereo placement and it was always a compromise for the artist that had to see their Tape mixes and artistic decisions adapted (destroyed) to a very limited format. Vinyl was never used or chosen because it sounded great (it was always worse than tape), but because it was very cheap and easy to manufacture in an assembly line.

Most of the bad rep of CD's comes actually from the Loudness wars, where audio files where overly digitally limited to have more volume than the neighbour and then transferred to a CD, it has nothing to do with the CD format but to what was put into it. That's something that less knowledge people forget, as also forgetting that Loudness War started a long time ago, in Vinyl and tape eras, every artist, label, Producer and AR wanted their record louder than the competitors,

This is just a side note here, I don't want to hijack this thread at all.

CD was a fine format, and when it appeared in the 80s it became popular because it solved the issues and complaints people had about Cassette tapes and Vinyl, and it solved that very well.