Purple Audio Discrete Opamps... KDJ 1 & KDJ 2

[Sammas]

Im not sure if this should be here, in the lab or in the brewey... but anyway.

Just wondering if anyone has had a chance to give these a try?

http://www.purpleaudio.com/Product/opamps.html

They use the 990/2520 footprint. (I spoke with Andrew and he said the KDJ-2 has been redesigned to also fit the 990 footprint and that the website should be updated soon).


I also asked him if a certian colour compressor was going to make an appearence in the 500 series format like the Purple Biz preamp.

He replied "We are working on a compressor or two"

:green: :thumb:

 

[TomWaterman]

Hey Sammas!

Are these for general sale ala Forssells or Hardy's? Any idea on pricing?

I'm looking for differing flavours of DOAs right now so these could be cool.

BTW hows that 553 coming along?

-Tom

 

[Family Hoof]

Ed will probably come along and correct me if I'm wrong, but I believe the new 990 footprint op amp w/power output stage is called KDJ-4. Also worth mentioning is that the PCB solder mask is black instead of green now. They're $45 each.

 

[TomWaterman]

Hey FH,

so is that KDJ-4 a replacement for the KDJ-2 or the same thing in a diff footprint.

I'm interested in those and especially the KDJ-1 (line receiver) any idea on the price of them (got to be less than $45)?

I emailed purple but no reply as yet. $45 for a solid output amp is more than reasonable. Even cheaper than the Hardy's.

Tom

 

[Sammas]

This is the reply I got from Andrew @ Purple Audio

"We do sell the opamps by themselves.
We just finished updating our designs and will have some new pictures
up in a couple of days.

The KDJ1 Class A type is $45

The Newer version of the KDJ2 Class AB output is $65 and is now in
the smaller footprint.


Yes we are working on a compressor or two.


thanks,
-andrew"

 

[Family Hoof]

Well I must be confused about the prices, but Andrew told me the updated KDJ-2 is called KDJ-4. The output devices were changed, the layout was changed, and this required some minor tweaking. Same circuit, yes.

 

[TomWaterman]

Thanks for the heads up guys.

I'm curious if I'll get a reply as I'm interested in the KDJ1 in a number of circuits, especially line receiver for passive eqs etc but I'm not sure it will drive a pultec-ish low impedance network. SO I'd like to find out at some point.

$65 seems more realistic for the output amp.

Cheers Tom

 

[edanderson]

the kdj1 (input opamp) really is $45 and the kdj2 (output opamp) really is $65.

andrew did design a new board, called the kdj4, and BOTH opamps are now built by stuffing this board in two different configurations. i don't think he's going to start calling the new layout version of the output opamp the kdj4, but that's up to him whenever he updates the website.

as you might guess from the preceeding statement, the input and output opamp share the same class A input stage, so you can use the "output" opamp as an input opamp with beefier drive capability. tom- i don't know what your eq network is going to look like, but if it is low impedance, then probably the "output" opamp would be a better choice for your input stage. the input opamp is really designed for lighter loads.

i'll ask andrew to update the website with new pictures and the prices, but it may take a bit.

ed

 

[TomWaterman]

Thanks for clearing it up Ed!

Would be cool to see a little more info on the website, especially if purple are looking to score a few sales to us DIY guys.

As far as my application, I have a few but I'm thinking about making stripped down pultec style eqs which I believe is a 600ohm network but I may just opt for TX in.....

Couple more ?s for you:

Do you know what voltage range these run on specifically +/-22-24V
And also if there is a price break when buying in say 20 units of KDJ1?

Cheers Tom

 

[Family Hoof]

[quote author="edanderson"]as you might guess from the preceeding statement, the input and output opamp share the same class A input stage, so you can use the "output" opamp as an input opamp with beefier drive capability.[/quote]
In other words, remove the output devices (emiter follower, push-pull pair, etc.) from a 2520, 990, or any other such device and this is what the KDJ-1 is doing. Still a functional op amp with the same amount of voltage gain, but no follower stage means the output impedance is higher and it can't pump out as much current, so driving heavy loads such as output transformer isn't advisable. It's actually a very smart idea - removing unecessary crap from the signal path - and has been done before. The N*eve class A preamp (a la 1073) which had two BA283NV input sections, the second one feeding a BA283AM output section is a good example. Another output section in between the two pre stages would've been a waste. You know what I mean?

Thanks for clearing things up, Ed! :thumb: I try to step on your turf and I crash and burn.

 

[TomWaterman]

Same with Freds DLR-1s and 992s innit?!

:thumb:
Tom

 

[Flatpicker]

[quote author="TomWaterman"]Same with Freds DLR-1s and 992s innit?![/quote]IIRC, Fred once told me not to use a 992 to drive an API type 1:2/~600ohm termination output transformer (don't know about the 993). I think a 1:1 (600:600) would be fine, though.

 

[TomWaterman]

Oh yeah its not got the drive for such a low load, but the principal of the 992 having an extra o/p stage (push/pull) I think is similar to the purple idea here.

I'm planning on experimenting with a LT1010 in-loop buffer for my 992s to drive a 150ohm trafo....LL1517 as soon as I get the whole project worked out.

-Tom

 

[Flatpicker]

[quote author="TomWaterman"]I'm planning on experimenting with a LT1010 in-loop buffer for my 992s to drive a 150ohm trafo....LL1517 as soon as I get the whole project worked out...[/quote]Sounds like a worth while experiment. Keep us posted on this. :thumb:

 

[adrianh]

I did not see Andrew at AES bummer.

 

[Family Hoof]

He decided not to have a booth this year.

 

[edanderson]

Tom:

andrew is working on an update to the site with pictures (there's some new heatsink hardware we're waiting on), pricing, recommended applications, etc. hopefully within two weeks or so the info will be up. both opamps will run great on bipolar 24vdc; no problem running them on bipolar 16vdc either.

Adrian:

andrew was really too busy working to come out to aes. he heard all about it from john klett, myself, and jens. on the plus side, we can all look forward to some more products from purple.

there are plenty of companies that have taken similar approaches to opamp design; A*PI had the high speed 2525 opamp, knocked the output stage off and called it the 2510. ton3lux also is using some kind of split configuration in their products as well.

ed

 

[TomWaterman]

Thanks again for the info Ed. Looking forward to the new webpage.

Cheers Tom

 

[edanderson]

some updated info on the purple audio discrete opamps has been posted to the site:

http://www.purpleaudio.com/Product/opamps.html

to avoid confusion, andrew has decided to call the new versions of the opamp the KDJ3 and KDJ4, and "discontinue" the original KDJ1 and KDJ2. the circuit is the same, only the output devices changed in order to accommodate the smaller footprint for the output opamp. note that as mentioned previously, both opamps are now built on the same pcb, which is labelled KDJ4.

the opamps are for sale to the public, but stocks are a bit low at the moment, as the first batches are mostly allocated for use in purple products. please contact andrew via email to order. if anyone has any questions i will try to answer them if you post to this thread.

also, a tidbit not mentioned on the webpage, the KDJ4 output opamp is designed to drive two 150 ohm loads simultaneously. so it can take just about anything you can throw at it.

ed