|
Post by matt@IAA on Jun 8, 2019 0:05:45 GMT -6
Has anyone actually used a W276 preamp? It really is a novel / weird design. It looks like they had an input transformer (probably 1:5) and designed the stage around it.
The input gain stage is a quasi op amp that has about 90 dB of open loop gain, starting to roll off around 1kHz...it has about 60 dB of open loop gain at 20kHz. In the highest gain setting you’re getting ~40 dB from it. That’s a lot to ask, and is certainly going to lead to a good amount of distortion.
If someone has used these, I’m kind of curious if you use it at high gain settings often? Because I’m very inclined to change the input transformer to a modern design (~1:8) and change the output stage to 1:2. This gives me 20 dB of gain over the original, at the cost of maybe a half or one dB noise figure. That by itself should result in lower distortion at all gains. Combined with the Jensen input and changing a few cap values, the low end should open up a ton. But I’ve never used one, so I don’t know if that distortion and filtering it has built in is the reason you might reach for it?
Also, just got an email that the pcb for the EQ prototype shipped.
|
|
|
Post by Bob Olhsson on Jun 8, 2019 11:17:10 GMT -6
The consoles were designed to be fed only by condenser microphones and run at operating levels of around -13, if I remember right. They are not compatible with ribbon or dynamic mikes or U.S. +4/+8 line levels. EMI Abbey Road ran everything at these line levels and modified American gear to be optimized for European line levels.
|
|
|
Post by jacobamerritt on Jun 8, 2019 11:34:57 GMT -6
Has anyone actually used a W276 preamp? It really is a novel / weird design. It looks like they had an input transformer (probably 1:5) and designed the stage around it. I haven't, but I have on of these and love it. Also was only like 34 dB of gain until he revised to get it up. Kept a choke plate and transformer for the character. www.locomotiveaudio.com/wt-72
|
|
|
Post by matt@IAA on Jun 8, 2019 11:51:20 GMT -6
The consoles were designed to be fed only by condenser microphones and run at operating levels of around -13, if I remember right. They are not compatible with ribbon or dynamic mikes or U.S. +4/+8 line levels. EMI Abbey Road ran everything at these line levels and modified American gear to be optimized for European line levels. Thanks Bob. The spec sheets on the W276 and W295 say nominal +6dB outputs into 300 ohms and maximum +21 dB. The input impedance could be an issue for sure, it says >950. If the original was 1:5 going to 1:8 would make the minimum ~350. But those numbers are at the high gain points when there’s a lot of NFB. So maybe another reason to use a 1:8 input and 1:2 output, and using less feedback.
|
|
|
Post by jeromemason on Jun 8, 2019 13:00:32 GMT -6
Will spice let you simulate and measure the impedance on each gain point?? 350z seems kinda low on input, but I have no information behind that so maybe it's not that big a deal?
|
|
|
Post by matt@IAA on Jun 8, 2019 13:17:17 GMT -6
Will spice let you simulate and measure the impedance on each gain point?? 350z seems kinda low on input, but I have no information behind that so maybe it's not that big a deal? Yeah. At the max gain point spice gives me like 1k. Significantly less than the 950 specified by Siemens when considering the transformer ratio by the transformer so I’m not sure I trust it. At min gain it’s around 50k. But that’s a vote for the different transformers - more transformer gain means you don’t need the higher gain from the amp, so input impedance stays higher.
|
|
|
Post by jeromemason on Jun 8, 2019 14:06:26 GMT -6
Yeah, I'd step it up if it were me.
|
|
|
Post by matt@IAA on Jun 9, 2019 10:36:11 GMT -6
Here's the 500 series layout of the W276 preamp. Not sure anyone wants one, but it was entertainment on my flight..
|
|
|
Post by matt@IAA on Jun 12, 2019 18:13:57 GMT -6
|
|
ericn
Temp
Balance Engineer
Posts: 14,809
|
Post by ericn on Jun 12, 2019 20:42:55 GMT -6
Very Clean layout my friend!
|
|
|
Post by peterhess on Jun 12, 2019 22:01:39 GMT -6
Exciting!
|
|
|
Post by matt@IAA on Jun 24, 2019 17:37:31 GMT -6
I’m a dummy and didn’t consider the output transistors need heat sinks. A quick glance at some photos of vintage modules confirmed. They get pretty hot!! I’ll fab something up for these and rev the PCB to give enough room for proper ones...
|
|
|
Post by audioscape on Jul 2, 2019 20:53:41 GMT -6
This is SO KILLER! Dying to hear what it sounds like... No experience with these particular units. Ridiculously great work as always man!
|
|
|
Post by levon on Jul 6, 2019 5:52:06 GMT -6
Reviving this thread for those who are still interested in the Sie-Q. Eric Valentine did a nice shoot-out video comparing the Soundtoys plugin to the original:
Interesting...
|
|
|
Post by jamiesego on Jul 7, 2019 13:03:42 GMT -6
That's a great clip! Glad to know Eric Valentine is in the same boat as the rest of us.
|
|
|
Post by Mister Chase on Jul 19, 2019 14:29:38 GMT -6
Need this in my life.
|
|
|
Post by matt@IAA on Aug 2, 2019 19:54:06 GMT -6
Transformers for the prototype shipped!
|
|
|
Post by Mister Chase on Aug 2, 2019 20:24:56 GMT -6
I'm ready.
|
|
|
Post by gouge on Aug 2, 2019 21:55:03 GMT -6
im interested too. is the idea it's a kit?
is the pre also on the cards?
|
|
|
Post by Blackdawg on Aug 2, 2019 23:02:53 GMT -6
Watching this with interest!
|
|
|
Post by matt@IAA on Aug 3, 2019 8:03:58 GMT -6
im interested too. is the idea it's a kit? is the pre also on the cards? Maybe to a kit. Pre is not on the card, that would be a separate module.
|
|
|
Post by matt@IAA on Aug 14, 2019 8:05:14 GMT -6
Inductors shipped... inching toward the finish line...
|
|
|
Post by matt@IAA on Aug 16, 2019 17:50:02 GMT -6
Usual cinemag shipment.. With something special inside...!
|
|
|
Post by Mister Chase on Aug 16, 2019 18:20:35 GMT -6
Oh man. You can't do this to me.
|
|
|
Post by woofhead on Aug 16, 2019 21:58:33 GMT -6
now THATS schexy!
|
|