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uA726 - a word of advice
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LeBon



Joined: Mar 23, 2015
Posts: 18
Location: USA

PostPosted: Mon Jul 06, 2015 12:55 pm    Post subject:  uA726 - a word of advice Reply with quote  Mark this post and the followings unread

Hi,

For those planning to build or repair a minimoog or vintage Roland, the uA726HC integrated circuit is needed.
This part was manufactured by Fairchild and discontinued in the early 80's.

There has been around a recently reissue by an unknown manufacturer from Korea, very close to the original and carrying the "F" logo. The original had golden legs, the clone has silver legs.
The new IC is available from certain sellers on eBay and AliExpress.

To my surprise, the clone not only works, but works very well, as I could test some of them in a custom built minimoog VCO. There is another guy out there who made some tests and published it on his site.

So, this is not about if the clones are fakes or not (and they're not), but how to put your hands on them. It's not that simple as it may seem.
I got mine from hkutsource for 13 USD each, but he's no longer selling it.

An eBay seller from UK, little_diode, sold them in the past for 90 USD. There were no picture in the listing, but he sent me one and it was the Korean clone, not the original.

Polida, an eBay seller from China, sells it for 90 USD.

Glenn Nichols (webmaster@icelectdata1.com) from ICEC sells the original golden-legged 1979 uA726 for about 50 USD each.
Seems that he has many left. Rush and buy all if you can.

Aliexpress has the lowest prices, maybe as low as 5 USD per piece. However it's not a good idea to trust all those sellers. I recently bought 10 pieces for 62 USD from an AliExpress seller called global Super Electronic market, via this auction. When I opened the box, there were some capacitors instead.

So here's my advice: think twice before spending a lot of money on these ICs. Buy one first, and be sure the seller will actually ship a uA726 and not some junk. Then order more. Shipping from China/HK is usually cheap.

You can post here your own experience/advice about the matter.
You can also post here your approaches to substitute this part in a VCO.

Hope this article is helpful.
Robin


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sduck



Joined: Dec 16, 2007
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PostPosted: Thu Jul 30, 2015 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

O course the question that comes to mind is... why the picture of some caps?

edit: oh I see - another more careful reading would have answered my question

Last edited by sduck on Thu Jul 30, 2015 1:51 pm; edited 1 time in total
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LeBon



Joined: Mar 23, 2015
Posts: 18
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PostPosted: Thu Jul 30, 2015 10:53 am    Post subject: Reply with quote  Mark this post and the followings unread

sduck wrote:
O course the question that comes to mind is... why the picture of some caps?


This is only to show that "global Super Electronic market" sent junk instead of uA726, and to be careful about dishonest sellers.
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dingebre



Joined: Aug 10, 2008
Posts: 270
Location: Salt Lake City, UT USA

PostPosted: Wed Nov 11, 2015 12:54 am    Post subject: Reply with quote  Mark this post and the followings unread

For what it's worth, UTSource.net has the uA726HC for about $15.00 USD each. They can't test their stock, but I've had good luck with them in the past. The one time I got counterfeit parts, they found a new source, and sent me new ones that were real. Others may have different opinions, but I have purchased a lot of hard to find items from them and have always come away happy.

I've ordered some, but don't have them yet.

David

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DaveFormantOwner



Joined: Apr 06, 2016
Posts: 2
Location: Chester

PostPosted: Sun Apr 10, 2016 1:39 pm    Post subject: A word of CAUTION
Subject description: uA726 clones
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Despite reading this thread, I decided to order some 'clone' 726s via AliExpress. I wasn't bothered about the colour of the leads, as long as they worked like the original Fairchild 726. Well I got scammed. I tested several of them and although there was an NPN transistor connected to leads/pins 9, 10 and 1; there wasn't one connected to leads/pins 2, 3 and 4. My transistor tester just showed the latter as being two diodes. I repeated the test with a genuine 726 (which I've had in my Elektor Formant since I build it around 1982). The test showed two transistors matched in gain to 2.4%.

I am attempting to return the part and gain a refund, but the seller is being difficult. Fortunately, I didn't spend more than I can afford to lose - something I considered from the outset.


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dingebre



Joined: Aug 10, 2008
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PostPosted: Sun Apr 10, 2016 9:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's very aggravating. I received my order from UTSource and they test fine. See photos below. Vbe 0.894 and 0.896 although I wasn't being very careful how I handled the device while I was testing it.

David


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Collision Forensics & Enginering, Inc.

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LFLab



Joined: Dec 17, 2009
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Location: Rosmalen, Netherlands

PostPosted: Mon Apr 11, 2016 1:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Using UA726 is sketchy business, there are other matched transistor pairs available, which aren't faked.
Unless you really really really need them, don't use UA726.

David, how do you like the DCA75? I have a DCA55 (as do you Very Happy ), but the added accuracy is very welcome.
Have you used it as a curvetracer on the PC already?
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dingebre



Joined: Aug 10, 2008
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PostPosted: Mon Apr 11, 2016 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

I like it a lot. Yes I have used the PC interface and have analyzed some parts, mostly for fun. The PC interface is very easy to use and very interesting as you can overlay two parts and can see very clearly if they behave in the same way.

I also have an old Heathkit IT-1121 for nostalgia and a Saelig/Syscomp CTR-101 if I need more accuracy or need to test at higher power.

http://www.radiomuseum.org/r/heath_curve_tracer_it_1121_it11.html
http://www.syscompdesign.com/CTR-101_ep_60-1.html

David

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DaveFormantOwner



Joined: Apr 06, 2016
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PostPosted: Mon May 09, 2016 2:36 pm    Post subject: Re: A word of CAUTION
Subject description: uA726 clones
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Just an update on my 10 April post re counterfeit uA726s. Only last week, after a long battle, I have received a full refund from AliExpress for the 10 items I bought from a company claiming to be the reputable 'Mouser Electronics'. I didn't get any joy resolving the dispute with the seller, so it was eventually escalated to AliExpress. My evidence in the form of transistor tester displays seemed to convince them of my claim. Anyway it was a difficult and time-consuming fight, not least because all message attachments had to be in the form of PNG graphics! I would advise others to be extremely cautious when dealing with Chinese sellers who offer goods at surprisingly reasonable prices.
As others have said, there are now alternatives to the 726, so no reason to be hell-bent of buying them!
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LeBon



Joined: Mar 23, 2015
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PostPosted: Tue Jan 31, 2017 5:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
Using UA726 is sketchy business, there are other matched transistor pairs available, which aren't faked.


Besides being a matched pair, they have to be in an "oven" to get proper tracking.
Maybe this post helps: http://lec.ebraz.co/tempco.php
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LeBon



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PostPosted: Wed Feb 01, 2017 12:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

dingebre wrote:
I received my order from UTSource and they test fine.


There's one more thing, currently in fashion among Chinese and HK sellers: the "out of stock" trick.
One day I stumped on an AliExpress listing offering a bag of 50 SSM2056 for $10. The seller was UTSource. I ordered two bags (100 ICs). Now guess what. He just probably realized that his supplier was now charging $50+ for a piece and offered me a refund instead of shipping it. Days later he relisted the SSM2056 for $60 each.
Sometimes it can be difficult to understand Chinglish, but they'll usually try to tell you that the part is "out of stock", "bad quality", etc, and offer you a refund. Since there is no way of leaving a negative feedback in this case, their reputation stays untouched.
Just try to find and buy some CEM or SSM chip for less than $5 and see what happens next. I don't believe UTSource and many others are dishonest (some are), they just don't know what they're selling.
There is currently a new listing in AE offering 10 uA726 for $62.14, probably from the same seller that shipped capacitors, but now named "Shenzhen Longsheng Electronics". A guy from Philippines ordered one lot four days ago. Let's wait for his feedback.
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nuipb



Joined: Oct 06, 2009
Posts: 49
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PostPosted: Sun Jan 02, 2022 9:07 am    Post subject: Reply with quote  Mark this post and the followings unread

LeBon wrote:
There is currently a new listing in AE offering 10 uA726 for $62.14, probably from the same seller that shipped capacitors, but now named "Shenzhen Longsheng Electronics". A guy from Philippines ordered one lot four days ago. Let's wait for his feedback.

Any news about that guy from Philippines' feedback ?
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analogmonster



Joined: May 30, 2011
Posts: 58
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PostPosted: Mon Jan 03, 2022 2:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Use a heated 3046 solution instead.
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nuipb



Joined: Oct 06, 2009
Posts: 49
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PostPosted: Tue Jan 04, 2022 3:52 am    Post subject: Reply with quote  Mark this post and the followings unread

OK, and where do you get your 3046s from ?
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analogmonster



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PostPosted: Tue Jan 04, 2022 5:26 am    Post subject: Reply with quote  Mark this post and the followings unread

nuipb wrote:
OK, and where do you get your 3046s from ?


Ebay.

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LeBon



Joined: Mar 23, 2015
Posts: 18
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PostPosted: Tue Jan 04, 2022 5:51 am    Post subject: Reply with quote  Mark this post and the followings unread

nuipb wrote:
Any news about that guy from Philippines' feedback ?


The same seller is now selling 10 pcs for $135.
https://www.aliexpress.com/item/32789581800.html
There is one order placed but no feedback at all.
I wouldn't buy it. Smells like scam.

analogmonster wrote:
Use a heated 3046 solution instead.


That's true. I would never bother using a uA726 again. I developed the circuit below from the original datasheet, made some mods and it works very well. It does not require a trimpot to adjust the temperature, but uses precision resistors instead. For better results, I used a CA3045F3 because the ceramic package might improve stability even more.


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nuipb



Joined: Oct 06, 2009
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PostPosted: Tue Jan 04, 2022 6:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice development. And did you design a proper PCB ?
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LeBon



Joined: Mar 23, 2015
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PostPosted: Tue Jan 04, 2022 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

nuipb wrote:
Nice development. And did you design a proper PCB ?

Thanks, but no, I did not design a PCB yet beacause I don't repair or make minimoog clones. I build my own synthesizers from scratch, so this circuit is incorporated (or integrated) in the VCO board. But I can design a PCB that fits directly onto a 10-pin socket and post it here if someone is interested.
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nuipb



Joined: Oct 06, 2009
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PostPosted: Tue Jan 04, 2022 6:49 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd be for sure. The smaller the better of course...
And would you have any confirmed reliable eBay sellers for CA3045s or 3046 to indicate ?
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LeBon



Joined: Mar 23, 2015
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PostPosted: Tue Jan 04, 2022 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

nuipb wrote:
I'd be for sure. The smaller the better of course...
And would you have any confirmed reliable eBay sellers for CA3045s or 3046 to indicate ?

Most ICs come from China and are being sold on Ebay by US and European sellers for a higher price. Ebay forces the sellers to use Paypal, which is a nightmare to deal with. So if I wanted to buy something from China, I would go to Aliexpress. Here's a CA3045:
https://www.aliexpress.com/item/4001039089567.html

Apart from that, the most reliable source for synth ICs is Syntaxis.
https://syntaxis.com.pl/en/3_syntaxis
They have a large selection of ICs from AlfaRPar and other manufacturers.
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nuipb



Joined: Oct 06, 2009
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PostPosted: Tue Jan 04, 2022 8:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. Any rough idea of how long it would take to design that 726->3045-PCB ?
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LeBon



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PostPosted: Wed Jan 05, 2022 6:13 am    Post subject: Reply with quote  Mark this post and the followings unread

nuipb wrote:
Thanks. Any rough idea of how long it would take to design that 726->3045-PCB ?

Here you go, a direct replacement PCB for the uA726. This PCB is plug'n'play, no adjustment is required. Calibrate your VCO as usual (or as per manual). Open the file with Sprint Layout 6.0.

The 49k9 resistor and the 10n capacitor were omitted, because they are part of the VCO board. The resistor is for temperature control and must be kept at 49k9 ± 1% for the minimoog. It may vary for other models. The current between the resistor and the rest of the circuit must be kept at 40 uA (microamperes) ± 1% for all applications requiring 1V/octave.

The 200R resistor is the current limiter for the heating transistor and must be kept at 200R ± 1% for all applications. All other resistors are ± 5%.

The funny thing about it is that the solution for the 726 problem was already there all the time, but for some reason nobody had noticed it. This trick can also be used on the Jupiter 8, VCS3, ARP Odyssey, ARP 2600, etc. For the ARP VCO, a CA3096 is used.


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nuipb



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PostPosted: Wed Jan 05, 2022 7:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, and thanks a lot for the speedy delivery !
A few questions from the noob I am :
- the 10-pins location where it says "726" should remain empty right ? I should simply insert 10 pins in each hole that will be soldered in the 10 holes of the original PCB below where the original UA726 was right ?
- not sure what you mean by "49k9 resistor and 10n capacitor were omitted, because they are part of the VCO board". Which VCO board you mean ? this PCB of yours is a total/fully autonomous/fully compatible replacement for a UA726 to be used in any UA726-synth as it is right ?
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LeBon



Joined: Mar 23, 2015
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PostPosted: Wed Jan 05, 2022 7:29 am    Post subject: Reply with quote  Mark this post and the followings unread

nuipb wrote:
the 10-pins location where it says "726" should remain empty right ? I should simply insert 10 pins in each hole that will be soldered in the 10 holes of the original PCB below where the original UA726 was right ?

Yes, that's right. You can either solder it onto the VCO board or use a 10-pin socket. Remove the original/damaged uA726 first.

Quote:
not sure what you mean by "49k9 resistor and 10n capacitor were omitted, because they are part of the VCO board". Which VCO board you mean ? this PCB of yours is a total/fully autonomous/fully compatible replacement for a UA726 to be used in any UA726-synth as it is right ?

The resistor and capacitor are not part of the uA726 chip. The designer must place them on the VCO board. This is valid for all boards which originally use a uA726. What synthesizer are you trying to repair/build. Is it your own design?
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nuipb



Joined: Oct 06, 2009
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PostPosted: Wed Jan 05, 2022 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

LeBon wrote:
You can either solder it onto the VCO board or use a 10-pin socket.
You mean a rectangular socket would fit ? or there are round sockets available ? (never seen any)

Quote:
What synthesizer are you trying to repair/build. Is it your own design?
I'm not a designer, I try to maintain and service my collection. In this case it would be a replacement for a UA726 in a RSF Expander and a Roland System-100. So should these 49k9 resistor and 10n capacitor be added ? If yes, where or how ? Wouldn't it be better to add them to your compact PCB if they are needed in all cases ?
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