How about Fred Forssell? Didn't he have something to do with the Millennia?

Fred designed the MM-99 (originally designated MM-990) while he was still w/ them. His own "990" is the evolution of that design. I believe he has the original design on his website in the schematics. These designs are roughly equivalent in function to the Deane Jensen 990 design, but with a very different topology at work, IIRC using FET's instead of bipolar transistors. Check Fred's website for lots of info.

Peter is a brave soul in taking on the fabrication of these discrete opamp designs, but he doesn't have the easy availability we have in the US of so many different ready-made units. Takes a hell of a tech to pull this stuff off, so I'll wimp out and buy someone else's product.

Bear

Hi Bear

It's a combination of inquisitiveness & a bad exchange rate. An Avedis 2520 will cost over 600-00 South African rands which is a good part of my take home.

I'm learning a lot at the same time which is one of the reasons I do it.

It's a good opportunity to over engineer the parts so there is no compromise in the sound quality - a DIY plus.

Regards
Peter

I got this in an email from Avedis at Brent Averill:

quote:

---

I've got something to send to you related to the opamps you've been testing.
It's a small circuit board which connects to the same footprint but has a 8
pin socket on top to connect some high performance IC opamps like the
Burr-Browns which I will also provide. Although they would need to be
optimized for a particular application with source and load impedance, it
will however give you some idea. And on paper you can see that they perform
well in specifications like DC off set and slew rate have difficulty pushing
current through an output transformer which is why some of us choose to
build them using discrete components. Anyway it'll be a good thing to play
with.

I think in the picture of the 3124, the third channel looks like an older
Melville 2520, not a new one, but it's hard to see. One way to tell old/new
is that the newer ones (from about '90 onward) are a little shorter versus
the old ones.

Call or email me your address again and I'll send it off this week.

Avedis

---

Dan Richards
Digital Pro Sound
The Listening Sessions

Hey, Peter, did you ever get around to thermal coupling the diodes to the output transistors on that 990? Also, the Jensen paper recommends using the Motorola 77-03 package as opposed to the TO-5 for improved thermal and secondary breakdown performance with the MJE-181 and MJE-171. I can’t remember if you had tried these or not.

Dan,
While we’re waiting on Mr. Hardy regarding your M-1 questions, I'll throw this in: keep in mind is that it's supply voltage is + and - 24 volts and that the transformers are 1:2 in and 1:1 out. It also uses a dc servo circuit to keep the op-amp’s output dc at 0V and a special ‘bias’ circuit (to keep form using that big electrolytic cap in the feedback?) that the API circuit doesn’t have. A Forssell 992 or Millennia MM-99 may work fine here, but I’m wondering if the servo circuit will react differently with these. Also, the API 2520 is only rated to +/- 20V, so it’d probably smoke (literally) in the M-1. On the other hand, a +/-15V version of the JH990 might work in the API circuit, although I’m guessing the noise will not be nearly as low due to the high input transformer ratio of the API which is 1:8, I think.

quote:

---

Originally posted by Dot:
I got this in an email from Avedis at Brent Averill:

[QUOTE]
I've got something to send to you related to the opamps you've been testing...

---

Hey Dan. Did you ever get this?

Yes, flatpicker - it's a 2520 footprint "frame" adapter that allows plugging in of different IC's. Avedis included 2 IC's. I'll post some pics when I get a sec.

Dan Richards
Digital Pro Sound
The Listening Sessions

quote:

---

Originally posted by Dot:
Yes, flatpicker - it's a 2520 footprint "frame" adapter that allows plugging in of different IC's. Avedis included 2 IC's. I'll post some pics when I get a sec.

---

Cool!
Also, post the names/numbers on the IC's and other included info, if you have time.
Thanks!

quote:

---

Originally posted by Dot:
Yes, flatpicker - it's a 2520 footprint "frame" adapter that allows plugging in of different IC's.

---

Soooo, have you tried any other ICs yet?

quote:

---

Originally posted by Flatpicker:Soooo, have you tried any other ICs yet?

---

Guess not...

Another question - Have you (or anyone else) ever tried the Avedis version of the 2520? If so, does it sound anything like the newer API version in Session #2?

Flatpicker, I just got back from being out of town. I'll dig up the IC's and post the model #.

I've tried a lot of 2520's and they all sound different. The Avedis 1122 opamp is pretty damn good. I can't say that it sounds like any of the 2520's we have, but that's not to say it doesn't sound like other 2520's.

We'll be doing some more playing around with opamps soon, and could probably give you better info then.

Dan Richards
Digital Pro Sound
The Listening Sessions

Thanks Dan.
I found out you were at Jazzoo’s right after I made my last post. Hope I’m not ragging you about too much about this (I see the ol’ Gallagher guitar all over this thread ). I’m in the process of designing a mic preamp ‘testing’ platform for 990 type op-amps where I can swap out the op-amps and input transformers, and the curiosity is getting the best of me right now as I wish to explore every practical possibility. When I get something off the bench and in the studio, I’ll start posting clips and gathering opinions.

Hey Dot,

I have an older API 312 preamp but the 2520 is soldered to the board. How are you swapping the opamps?

Did you add the sockets yourself? Or is newer API gear already socketed??

Kato

Kato, the 3124 has sockets. None of the opamps are soldered.

Dan Richards
Digital Pro Sound
The Listening Sessions

Designing with Opamps - Douglas Self
http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm

Dan Richards
The Listening Sessions
The Project Studio Handbook

Stirring again a bit with this whole swappable opamp topic. I had a hand in the new ADK AP-1 preamp. I finally got my own production AP-1 today. So, we'll be playing with different opamps and transformers on this unit for an upcoming review. And also just kind of revisiting the whole opamp thing again.

http://www.adkmic.com/AP-1/index.html

Actually now that I have a unit that is set up for swapping I would like to see some reviews. Dot if you can get Some 992's from Fred Forssell that would be so cool. A lot more of my focus will be
in this area as I will be constructing my owm

quote:

Dot if you can get Some 992's from Fred Forssell that would be so cool.

Yes and the 993 as well. I'm currently using 992s in my home-built pre (with LL1538XL input transformer) and would like to hear your opinion of them.

TLS has WAV sound files of various opamps and transformers in an ADK AP-1.
http://www.thelisteningsessions.com/session9.htm