Building a 1178 lookalike/dual 1176 replica out of a UREI 535 EQ

[pvision]

The switches are the same between 76 & 78 in the sense of what they do (with the caveat that the bottom right hand switch is a peak / average switch on the 78) and the fact that the buttons don't latch simultaneously - pressing one released any latched button. This is what I mean by non-latching

The 78 was built as a dual channel / stereo limiter rather than a dedicated stereo limiter. The distinction is a bit moot as the attack & release controls are common so I imagine the A/B / stereo switch only affects some parts of the sidechain linking

I assumed the 78 would have different switches as it has two channels. However, I had a quick a look at the differences between the sidechains of the 76 and 78. The 76 has two-pole switches for ratio, and switches signal & sidechain. The schematic suggests the 78 uses a different setup with the same switches as the 76 but switching L & R. The schematic I have doesn't show the RH channel so I can't be sure. A photo of the inside of a 78 should give the answer

Looks like UREI did some clever work adapting the 1176 into the 1178

Nick Froome

 

[PRR]

> seems like a legit store to me

You can find the address in Google Maps Streetview. Not a "store" but a large house in the Belgian woods a few minutes away from the Dutch border. Very large garage.

This makes sense. When a chip is new sales may be good. (And maybe not.) Distributors order a whole box. 5 or 10 years later the box is part-empty and sales have fallen-off to nearly none. A busy distributor can't keep heaps of slow/no-sellers in inventory. He'd rather sell them for pennies to buy newer chips that will sell fast. But there is a long-tail of demand. B-52s and paper-mills and other strange machines keep running long after their guts are "obsolete" and sometimes need replacement parts. And a part that sold for $2 in 1985, for $0.50 in 2001, in 2018 you may be able to jack-up to $12 for a customer who NEEDS just THAT part to keep a $1M (even $1K) machine running. It's not a big business, and customers can be anywhere, so it could be run from a house.

Is a very nice house.

 

[Zebra_PD]

assumed the 78 would have different switches as it has two channels. However, I had a quick a look at the differences between the sidechains of the 76 and 78. The 76 has two-pole switches for ratio, and switches signal & sidechain. The schematic suggests the 78 uses a different setup with the same switches as the 76 but switching L & R. The schematic I have doesn't show the RH channel so I can't be sure. A photo of the inside of a 78 should give the answer

Looks like UREI did some clever work adapting the 1176 into the 1178

Nick Froome

Here is some pics of the inside of an 1178

https://www.proaudioeurope.com/info/wp-content/uploads/2016/08/Urei-1178-Inside.png

https://www.proaudioeurope.com/info/wp-content/uploads/2016/08/Urei-1178-Inside-2.png

 

[pvision]

From the photo it's clear that the 1178 has a wider chassis than the 1176 which is why the 1178 front panel doesn't line up with the bolt holes on other Urei chassis

Looks like the switches are the same on 76 & 78 models

Just in front of the output transformer for channel B you'll see a nicely-symetrical layout of an IC, two trimpots and two electrolytics. I think those are the dual FET, the Q bias controls and the audio caps feeding into the FET

Nick Froome

 

[trashcanman]

Perfect! I'll prob make an order within the next month or so. Just need to plan the rest of my BOM to see if there is anything else I might need to order from the same site that I cant find on Mouser or similar. Send me an email to pierre(a)zebrastudios.se and we can take it from there

Well seems like a legit store to me, feels more safe then ordering from China/Hong Kong. Send me an email at the same mail as above if u would like to order some too.

Also curious about your 1176 stereo version build. Is it based on the 1178 or a custom design of your own based on one of the 1176 REVs?

Well it looks like the picture on their website is the same as the one on the ebay listing so I'm guessing they selling the same thing, in which case it would be cheaper to get them straight from china. This is a long obsolete part so most of them around will be fakes I think so I might just go with some well matched fets.

I'm basically just sticking two rev d 1176s in a case for my stereo version. I made my own boards but their essentially the same as the original.

 

[Zebra_PD]

Well it looks like the picture on their website is the same as the one on the ebay listing so I'm guessing they selling the same thing, in which case it would be cheaper to get them straight from china. This is a long obsolete part so most of them around will be fakes I think so I might just go with some well matched fets.

I'm basically just sticking two rev d 1176s in a case for my stereo version. I made my own boards but their essentially the same as the original.

Well that is an valid point but I´ll think I will send him an email and ask if they are original national semiconducters or chinese made copies...

But I have perhaps tracked down som NOS stereo JFETs in the state. If so I let you guys know if will be able to get a hold of more then the two I need. Will prob be a little higher cost but hopefully overly expensive.

Cool! Are building it using original transformers or modern replacements? Have you design your own stereo link?

 

[Zebra_PD]

An update on my progress.

Im perhaps half way in designing the custom PCB for this build. I have put the different layers of the board of Gustavs old design in different layers in Illustrator. Next step will be to incorporate the original UREI output transformers and power transformers and perhaps some other of the 353 components in the design.

Also replace the holder parts for the rotary pots to use switch buttons instead.

Then scale the hole design up from A4 to A3 to get a more vintage look of the PCB that takes up more of the inside of the UREI case. Might also modify the design to be only one copper layer instead of two for a more "original" look.

Will post some sketches soon.

Still undecided if I should incorporate the Jim Williams mod in the design or not though. 

 

[pvision]

What mod does Jim Williams recommend for the 1178?

Nick Froome

 

[Zebra_PD]

What mod does Jim Williams recommend for the 1178?

Nick Froome

replace:
IC 1 National LM6172 / LM4562
bypass pin 1/2 22 pf
C3 22 pf
C6 Panasonic FM 47 uf 25 v
bypass C6 Wima MKP-2 .1 uf 250 v
C7 Panasonic FM 47 uf
bypass C7 wima .1 uf
C9 Panasonic FM 220 uf
bypass C9 wima .1 uf
bypass R6 47 pf
C10 Panasonic FM 470 uf 25v
bypass C10 wima .1 uf
C21 Panasonic FM 100 uf/50v
bypass C21 wima .1 uf
C22 Panasonic FM 220 uf
bypass C22 wima .1 uf
C23 10 pf
IC 2 Linear Tech LT1358 or a National LM4562
C25 and C27 2 Panasonic FC/FM 470 uf 25 VOLT
C60 and C61 2 Panasonic FC/FM 3300 or 4700 uf 25 VOLT
C62 and C63 Panasonic FM 1000 uf 25 v

 

[trashcanman]

Well that is an valid point but I´ll think I will send him an email and ask if they are original national semiconducters or chinese made copies...

But I have perhaps tracked down som NOS stereo JFETs in the state. If so I let you guys know if will be able to get a hold of more then the two I need. Will prob be a little higher cost but hopefully overly expensive.

Cool! Are building it using original transformers or modern replacements? Have you design your own stereo link?

There is a company called Interfet who have remade a bunch of obsolete dual JFETs which are available at mouser so I may get mine from them. Looking at datasheets the INF411 should be a good sub for a dual 2n5457, don't know if it will work as a sub for NPD5566 though should be pretty similar. They actually make a NPD5566 too but it has a long lead time.
On my unit I'm using Luhndal 1540 for input and the Ed Anderson copy of the original output, basically the same as the Hairball version. I was using BF547 for the fets but they were messing with the gain reduction so I thought I'd just go all out and get some matched units.

 

[Gustav]

I have a few 5566 I could sell, but Id have to check what they are going for now first.

[email protected]

Gustav

 

[pvision]

At first glance the Jim Williams mods look like the kind of thing you'd be  tempted to do anyway - increase the size of the audio coupling caps and bypass them

Nick Froome

 

[Zebra_PD]

I have a few 5566 I could sell, but Id have to check what they are going for now first.

[email protected]

Gustav

Perfect. I'll send u an email Gustav!

 

[Zebra_PD]

At first glance the Jim Williams mods look like the kind of thing you'd be  tempted to do anyway - increase the size of the audio coupling caps and bypass them

Nick Froome

Ah ok, sorry for the newbie question but the reason for that is what exactly? To get less noice and/or to alter the sound of the compressor?

 

[scott2000]

Ah ok, sorry for the newbie question but the reason for that is what exactly? To get less noice and/or to alter the sound of the compressor?

If nothing else, because he said so...... ;D

Here's what I found regarding JW mods to the 1178

 

[Zebra_PD]

If nothing else, because he said so...... ;D

Here's what I found regarding JW mods to the 1178

Ohh thanks for the info.

Haha well just because he said so is a valid point regarding JW

 

[Zebra_PD]

Been quiet here a while since the family had had both fever and then the flu the last weeks and just been busy taking care of my daughter

Well so Im still in the process of tracking some key parts down. Been really hard to find a dual gang 5 mohm pot for the release. But I think a has find one that might work. Its a one from Allen Bradley with these stats:

minimum resistance: 0.0 ohm
maximum resistance: 5000000.0 ohm
resistance tolerance: 10%
number of turns: 1
power rating: 2.000 w
voltage rating: 500.000 v
taper: linear

Do you guys think it will be worth the hazel to order this NOS pot from the states?

In Gustav design the release pot is a more common dual 4M7 Lin POT pot, same value as in the Gyraf /Mnat 1176 designs right? The schematics of the original 1176 its also a 5 mohm release pot but are the two interchangeable? or is there some other design changes that I'm missing to be able to use this 4M7 instead of 5 mohm?

----

Im also still trying to figure if I want to go with the JM mod or not. But would it be possible to just add a switch to switch between the original 5566 Jfet and the LT1358/ LM4562 suggested by JW? Or would the possible resistans in the cables and the switch mess up the sound?

Do you guys think to increase the audio coupling caps and bypass them as in the JW mod would change a lot of the original character of the sound or just improve on it?

 

[scott2000]

Have you reached out to Studio Electronics? Maybe they have one .....

http://studioelectronics.biz/


LOL....I just saw the million links already....

 

[gyraf]

4M7 is the same as 5M for pots, as they are 20% tolerance anyway.

About modding, the whole idea seems problematic to me - why would you alter a design that you like for what it is? Sometimes I simply dont get this whole "upgrade everything" credo - even from people who should know better..

Jakob E.

 

[Zebra_PD]

4M7 is the same as 5M for pots, as they are 20% tolerance anyway.

About modding, the whole idea seems problematic to me - why would you alter a design that you like for what it is? Sometimes I simply dont get this whole "upgrade everything" credo - even from people who should know better..

Jakob E.

Thank you Jacob!!

When I'm sticking with the original design for the first prototyp/build but using 47M pots! Prob easier for a newbie like my self to just follow a established and known to work design/schematics.

If I'm successfull with this build and decide to create a group buy for kits or something in the future might be an idea to make an alternative pcb  as well inspired by JW redesign just to be able to make a mauser BOM for all components. Mainly because of the lack of 5566 jfets. Perhaps even include TM019 or
TM022 output transformers in that BOM since Luny Tune was successfull to use them in the LA4 clone that originally use the same output transformer as the 1178. But that is for the future