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Old 23rd March 2001, 04:21 AM   #1
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Well, i'm desiging my amp on CircuitMaker 2000, and working on Rod Elliot's discrete preamp... i've made some tweaks and the results are impressive (almost NO noise, completelt fast response up to 100khz, no ringings, etc), and i was wondering, are opamp preamps any better? I'm asking this because i'm having to design a regulated psu just for the preamp, which is by itself not as simple as the NE5532 based one. Is it worth it?
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Old 23rd March 2001, 04:59 AM   #2
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You're taking a vote?
Discrete, of course. Whether solid state or tubes is up to you.
Opamps score well on bench testing, but don't sound as good as discrete in the long run.
I imagine that Pixie & blmn will weigh in in favor of specs, here.
Opamps have one thing going for them. You can whomp up a circuit in no time using them as building blocks. Consider the possibility of throwing something together out of opamps to get you by while you design a more elaborate discrete circuit. I made a quick-and-dirty crossover a month or two ago with some LF353s I had on hand. Later, when I had more time, I went through and did a better job using MPSA18s and 2N5457s. That was also a quick-and-dirty, yet sounded noticably better than the opamp crossover, even without optimizing--which I still haven't done. (I've had 48 hour days on order for forever now, but they still haven't arrived...)
If it's the power supply that's slowing you down, consider using an unregulated one for the time being. Although I personally believe that regulated is the way to go, I'm also prone to getting something up and running in a hurry, but making the design modular so that I can drop in upgraded designs or components later. It suits my schedule better, There are simply some days I want to sit down and hear music, even if it's not optimal. Besides, doing it this way gives you the opportunity to learn exactly what differences opamps make vs. discrete components, or regulated vs. unregulated.

Grey
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Old 23rd March 2001, 02:42 PM   #3
mlloyd1 is offline mlloyd1  United States
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Smile re: So, what's your favourite ss preamp style?

I really like my op amp preamp. For the moment, it's a BiFET op amp with its output stage bypassed driving a high speed, high current buffer. Although op amps are easy to prototype with, I think there's subtleties that need to be taken into account for a design to most effectively utilize the op amps and make them sound their best in a particular circuit. Stuff like paying attention to supply bypassing, layout, wiring, compensation, etc. Hmmmmm, same things to worry about in a discrete design.

Fundamentally, however, I suspect that the BEST discrete is capable of better sound than the BEST op amp based design, because you have control of many more of the individual design parameters and characteristics and consequently do a better job of optimization. In general, I think discrete designs are more challenging (and therefore more rewarding to DIYers!) and those really low noise, high gain JFETS are often expensive (especially if you need matched devices) and tough to source :-) I often wish that the op amp makers would offer an 8 pin dip package of simply a pair of matched JFETs used in one of their BiFET op amps.

You'll probably find advocates in both camps though. I wonder if "op amps in high end audio" suffer from the stigma old designs that used the LM741 years ago. It is interesting to see op amps show up in Mark Levinson and Jeff Rowland products, though.

Obviously, just my opinion.

Michael

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Old 23rd March 2001, 03:51 PM   #4
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Michael,
I second the motion for a matched set of low noise FETs...
Now *that* would make life much easier, indeed. That's one useful thing about tubes--twin triodes (which includes all the usual suspects: 6DJ8, 12AX7, 12AT7, 12AU7, etc. etc. etc.) are pretty decently matched. Right out of the gate, you can plug one in and have a nice differential with fairly predictable response. You can take it a step further and match tubes...but the nice thing is that there's none of this +-25% nonsense that comes along with the choice to use silicon.

Grey
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Old 23rd March 2001, 10:14 PM   #5
blmn is offline blmn  Brazil
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Lisandro_P,

Mloyd1 is right, considering design purposes, discrete design is more flexible and allows you (in theory) the best performance. There are no problems with opamp design today (no "magic" things here too, ok?) but your design possibilities are reduced, and, over a DIY perspective, it is not "really" your own design.

Mlloyd, your assestments were very well placed, in my opinion.

Regards,

blmn

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Old 24th March 2001, 08:44 AM   #6
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Well, ofcoz the discrete design is more rewarding from the DIY side, but it's an amp i'm building afterall, and it's worth nothing if a simpler opamp design sounds better
Anyway, an opamp stage will still be there for a RIAA input (this is Rod's design, i don't want to hassle with that), but for everething else i'd like it to be discrete (main preamp and tone controls), again, if there's no noticeable improvement with opamps and it's worth it...
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Old 27th March 2001, 01:49 AM   #7
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op amps such !
There is no doubt about that.
I spent, "lost" is a better word, years with op amps. I tried all of them. From cheap lm741 to ne5534 to op637 you name it. Even strange topologies that drive the output in class A with small heatsinks on the ICīs. When I tried the balanced line stage from Pass I just couldnīt believe the difference. Clear, dynamic, deep feeling. I noticed at first at work that the simple single transistor preamplifier stages in PA mixer amps sounded better the complex circuits with op amps. So when I tried a good design like the line stage from pass I really saw the change in sound.
Descrete design in better. Opamps supress a lot of detail.
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