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#122
The discount on the OPA2134 is 55% of the single price at 250. The LM6172 is 53% at 250.

I plan to socket some for op amp comparisons, but will use most of mine without sockets.

Lets give it a few days to see how much interest we get. It may grow once it happens for real. Shipping may be "interesting" as standard packaging is a tube of 50. Digikey sent my last 25 in a cut tube with a rubber band around it. Whoever does the buy needs an ESD safe spot to work.

Some consider the LM6172 up there with the crazy expensive OPA 627 singles. I don't know if there is much difference but that's why the sockets on some boards. 😉

This buy started with ~150 on the wiki, and I have orders for 374 in 2 days. 300 are paid.



Only 6 Boards left before I cut off ordering to ensure a safety stock.
 
#123
The LM6172 is essentially a CFB design with an extra buffer in front of the noninverting input to make it look like a VFB op amp from the outside. Not sure that this is really the best for audio.

Downsides might be poor settling time to 0.01% and increased harmonic distortion (I believe at least one of the buffers is outside the feedback loop but it is a long time I looked at the internal schematic).
 
#124
Re: OpAmp GB

jimbo1968 said:
I am happy to run a European group buy if that is wanted/beneficial, eg if whoever volunteers to run the main GB would prefer it that way.

As long as the orders reach 250 we don't lose much discount by splitting the order.

When I looked at digikey UK the LM6172 quantity discount was hardly worth bothering with, so I am mostly interested in OPA2134 (although there is always that nagging question > why not build both and see if I can I hear the difference?)


PS. Do we want sockets as well or is soldering straight to the board preferred?
Click to expand...

Not sure if it really is better. You'd have the extra 20% or whatever the rate is in the UK for VAT, and shipping from the UK to anywhere in Europe is not necessarly cheaper than air mail from the US.

Also, incoming parcels or envelopes from the US are tax and duty exempt up to €26, but in my experience, they don't bother to charge duties up to a value of 40 to 50€, at least if it is obviously from a private person.
 
#128
Aluminum foil will work nicely. Also, even CMOS devices are not really sensitive any more. The panic was ok in the 70s, when ICs did not have protection diodes. Today, all digital and analog circuits will have these.

I am pretty lax, and I can't recall ever having fried any kind of chip through ESD.
 
#129
Wau! This is the fastest group buy I ever come across. Just put in my interest and now the offer is closed and board are been ordered.
Anyway, just complete my paypal payment. Many thanks to Bob for the email reminder and organising the GB.
 
#130
I will definitely use sockets for all the Op-amps.What is good enough in medical and test equipment is good enough for audio.
Just make sure to use the ones with the solid,goldplated pins.

For decoupling i am planning to use tantalum caps (2-10 uF)

For the other caps i am searching for a source for polystyrene caps (i think teflons are to big).

Other options would be.Vishay mkp1837 1%
Vishay mkp1839 1%
Panasonic ECQP 1%
Wima FKP2

As usual any suggestions are welcome.I am certain there are more brands/types avilable.

Kees.
 
#131
those Vishay 1% caps are available at Mouser, as long as you buy 700 to 1000 at a time.

BC Components MKP 416-420 2%

Does anyone remember where the thread was about the PC based LCR bridge? I searched a bit and couldn't find it. One dual op amp, a couple reference resistors and decoupling caps and you're in business. I built one, it gives purported accuracy <1% if you are careful calibrating. Buy a bunch of cheap 5-10% caps and pick and choose the best match.

Mouser has cheap polystyrene caps up to 10 nf. Only 10% though, so a decent bridge to match them is important.

Edit: The LMS impedance measurement article is here: http://www.arrl.org/qex/2005/Steber.pdf and the program is here: http://www.arrl.org/qexfiles/LMSProg.zip
 
#132
WOW, I didn't know this order was currently happening, I thought it was in the planning stages..D'oh!

Would I be wasting my time asking if there were 6 boards available?🙄 should I add myself to the wiki if there are?

I have a verified paypal acct but it is tapped, the payment would come from my verified acct but thru a credit card. Does that make a problem?:cannotbe:

Thanks Bob,
Marc
 
#133
I did some searching and the general consensus is that KP caps are better than the MKP caps.(foil instead of metalized film).

Prefered types are.

Vishay/Roederstein KP1830
EMZ KP72

Both are available as 1% caps.

Kees.

Ps. Bob i don't know if it is worth the extra effort and the extra ammount of caps to match 5% caps.
 
#134
THAT'S THE LAST OF THEM - THE BUY IS CLOSED

At least until everyone who has paid gets their boards.

I've heard from everyone except harryeng, so I hope that payments for the dozen orders outstanding will be along shortly.

I'll keep a waiting list for the safety stock and order cancellations. Email me if you want boards but have not already signed up. I may be able to add to the order, so contact me quickly if you want, but no guarantees.


I ordered the boards today for 4 week delivery. I expect to receive the production order the first week in April and start shipping rightaway. I'll keep you posted if there are any delays.
 
#136
Sorry Al,

You're first on the list - a virtual guarantee. Unless you are doing a bunch of 4 ways, there should be enough boards for you.

Advanced was offering a substantial discount through 2/28 that I will donate to the forum. I got them to extend the deal when there was such a rush of interest. The rush died down and I ordered a hundred more boards than were paid for at the time figuring there would be some left over.

PS - Glad you're feeling better
 
#137
That's ok Bob, I was just a little angry at the time I posted. I've calmed down now! 🙂

However, I still think you may have rushed things a little, especially as you've ordered so many. Personally, I would have built prototypes first to check operation and component placing. Though I have lots of confidence in Jan's layout skills, it is very easy to make a little error that you don't notice until you come to build something in reality. I know, I've done it...
 
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