Just a quick thought from my ears here at the BI Test Kitchen ...
Not as mid forward as my gar2520 Not as clean as my gar918 Not quite as warm/thick as my gar1731
garAM10BC... A MUCH more polished lower mid range than any of my other offerings. Should help with mud buildup In a mix. These have a very nice vintage sound about them that will work on lots of sources. It's just yet another audio colour and besides working on 16V rails, its a nice 24v option as well for 51x.
Great, Test kitchen was able to do more testing with comments. I plugged the AM10 into a Litz Wire CAPI VP 25 & 26 Doing a Voiceover on a vintage Walley Heider Neumann U87. Nice solid deep bass and low mids. Not mid forward. Smooth almost slightly compressed. Changed the sound of the CAPIs. A great flavor to an opamp collection.
Last Edit: May 9, 2018 17:09:58 GMT -6 by winetree
Post by hugostiglitz on Jul 10, 2018 2:34:58 GMT -6
I am very interested in Gary's DOA too. 2520 and 1731 seem the most common. But what can you guys report about the garAM10 and gar918. Highly interested in those. How do they compare and especially: how do they compare to the 2520/1731
This was buried in another thread. Just for fun I did a quick comparison between op amps. The files are labeled, but I sent a mono stem of drums, guitars, and bass out through a BTA, into the summing amp, and out of the line amp in the box. Each position has an op amp, so each iteration changed all three of the op amps in the signal path. This was all done at low gain, and bipolar 20V (the QE can go up to 28V and the Neumann to 22V). I did retest the QE at 28V and the two files played out of phase nulled completely, so at these gain levels there's not much difference in the voltage.
There’s no summing going on, it’s all mono from end to end. This is like sending a single line input to your console and listening back through the stereo bus.
Q is a Quad Eight style N is a Neumann style G is a GAR2520 (the control)
Post by hugostiglitz on Jul 11, 2018 15:47:42 GMT -6
I have listened to your OpAmp test you just posted. Definitely good samples and very well recorded. But frankly, I couldn't hear any big differences. I never thought that differences were so subtle - it's almost not audible. Crazy.. I am having second thoughts if there really is a need to make use of different DOAs.
The Red dot was for years my favorite, the difference between a well built far equivalent is very very small the biggest thing That Scott’s brings to the table is your eyesight and sanity of not having to build the thing, but building som GARs sure will improve your DIY chops.
More or less you don’t need to match transistors on most of the designs floating out there. Easiest is to buy transistors on a reel and use two adjacent ones for the input pair. That’ll be good enough.
The issue with testing is depending on what you're matching hfe may not be all that critical. For an op amp input pair usually hfe in a batch close 'nuff, though some circuits supposedly need minimums even from within gain-specified transistors (B,C etc). hfe changes with current (it is zero at zero and zero at infinite), so to test "properly" you need to test the transistors at the current they're going to be used at. But hfe matching only matters if the external DC resistance is matched.
Vbe matching is much more important than beta for a long tailed pair. Vbe is important for DC offset because Vbe mismatch is multiplied by DC gain. If you have emitter resistors in your design this forces the input pair operate closer, so matching is less sensitive. Negative feedback wrapped around the entire op amp reduces nearly all of the problems except for DC offset from Vbe mismatch on the input pair.
Both are very temperature sensitive so you need to make sure you match that - even the heat from your fingers will make the readings vary, so you need to use insulating gloves or pliers with insulating jaws. Or tape them down to something, let them normalize, and use probes to test without touching them. And you have to be consistent, because self-heating can also skew the readings. I attached a way to make a test jig to test Vbe.
On the other hand, most circuits are capacitor coupled so DC offset doesn't really matter a ton, and most op amp applications don't use a ton of DC gain (mic pres excluded). Unless you have something that is sensitive to DC, it's basically audio-transparent (we hear the AC wave, not the DC offset). AND the truth is that even if you perfectly match the input pair, you can still have DC offset due to circuit topology and component mismatch.
In my 312 preamps I use the GAR AM10 as my go-to vocal mic channel. It's sort of middle of the road on guitars for some reason but I love it on vocals. I find it to have a bit of a zippy top end and a girthy lower/middle end. Just sounds kind of exciting. Puts vocals where I want them to sit. A bit saturated automatically also.
The OA10, the Neumann style one, I love in my Five Fish NK72DI that I primarily use for recording amplifiers. I guess for the 312s I kind of stick to the 2520s for that. But the OA10 is special in its own way. Has a lot of detail. No mid hump. Perfect balance to the big Carnhills in the FiveFish. That preamp is a little picky about op amps but this one is perfect.
The only op amp Gary makes that I haven't found a permanent home for yet is the 1731. It sounds good but I don't choose it for the circuits I have here. Actually I need to try it in the Five Fish, haven't heard that combination. The OA10 sort of takes over where the 918 used to sit in my kit, but both are good sounds.
Last Edit: Sept 30, 2019 20:56:53 GMT -6 by monkeyxx