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Post by jsteiger on Sept 19, 2020 9:24:05 GMT -6
I should really grab one of those... |
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Post by Mister Chase on Sept 19, 2020 9:27:12 GMT -6
I probably need them too. I hadn't built anything in a couple years and man I'm having some trouble with the eyes now.
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Post by zonkola on Sept 19, 2020 22:13:34 GMT -6
I should really grab one of those... I could have built my VP26's without magnification, but all those gar2520's? Not a chance. |
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Post by patapeter on Sept 20, 2020 15:13:57 GMT -6
I should really grab one of those... Hi Jeff, how are you doing? I'm new here so.....just saying hi.... |
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Post by jsteiger on Sept 20, 2020 19:11:05 GMT -6
I should really grab one of those... Hi Jeff, how are you doing? I'm new here so.....just saying hi.... Hey Peter! Welcome. RGO rules!! |
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Post by Darren Boling on Sept 20, 2020 22:45:29 GMT -6
These descriptions sound awesome! I'm gonna try them in my 8200A.
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Post by professorplum on Sept 20, 2020 22:47:54 GMT -6
In my opinion in most circumstances the differences between op amps is somewhere between negligible and inaudible. Exceptions are - very high gain (like a mic pre), very heavy loads, and very high output levels. Do you think the sound would be more perceptible in a dual opamp mic pre, like the JLM dual 99v? I would imagine since you're passing through it twice initially? |
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Post by matt@IAA on Sept 20, 2020 22:51:05 GMT -6
The more gain you’re asking from it, the less negative feedback you have left over, and more of the op amp’s distortion comes through. Probably the clearest way to hear differences between op amps is a 312 or similar circuit with the gain dimed and the output terminated with a low impedance load (like 600 ohms or less).
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Post by EmRR on Sept 21, 2020 11:30:16 GMT -6
In my opinion in most circumstances the differences between op amps is somewhere between negligible and inaudible. Exceptions are - very high gain (like a mic pre), very heavy loads, and very high output levels. Do you think the sound would be more perceptible in a dual opamp mic pre, like the JLM dual 99v? I would imagine since you're passing through it twice initially? Good question. Counterintuitively, 2 amps means less gain per and cleaner, so maybe not. |
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Post by Deleted on Sept 22, 2020 10:38:56 GMT -6
In terms of audible difference, one switch that sounded truly night and day to me was going from LTL Rogue 5's to GAR AM10's in a pair of CAPI 553 EQ's. It changed the way the bands respond and the overall vibe pretty significantly. I was about to sell them until I made that switch. Now I love how they sound.
Another example is in my Lola's. I have a pair w/ a set of 990s and BA512's for each. Big difference there, most notable when actively trying to drive the circuit.
I've been trying diff combos with my LC25 too. Started with a 1731, then tried a Rogue 5, now there is an OM10 in it. The differences here are pretty subtle, but enough that I know I prefer the 1731. Especially when I'm boosting in the 800hz and up range. I also haven't gotten as much satisfaction out of doing low boosts since switching it out.
The common theme seems to be, that if the Rogue 5 is really a good example of a more modern 2520 kinda vibe... that's not for me really. I've listened a lot of shootouts of GAR DOA's on gearslutz and such too, and in all of them, I preferred anything over the 2520. I know to take those with a grain of salt though, but I notice a pattern, and it seems to corroborate my dislike of the current API 3124 unit(s) that every studio I work in has. I actively try to avoid them if I have other options.
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Post by Guitar on Sept 24, 2020 8:03:16 GMT -6
I can hear the differences between op amps, apparently. It's a big part of settling on a mic pre for me, finding the best match for the rest of the circuit. The problem is finding simple western english terms to describe how they sound, so I'm not going to try too hard at the moment. They are on the warmer, fuller side of things, as far as 2520's go.
Anyway, I absolutely love the CAPI CA-0252. It's my current favorite 2520 style op amp. If this is what old API's sound like I can understand the original reputation. If I had six more 312's built up, I would buy a ten pack of CA-0252 to stuff them. Just running a stereo pair right now.
In terms of building them, buying them, it doesn't get any better than Jeff's build guides and customer service.
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Post by matt@IAA on Sept 24, 2020 8:53:37 GMT -6
Sorry if I conveyed the wrong message - a mic pre is where you'd expect to see the most difference.
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Post by dreamsambas on Sept 24, 2020 10:22:57 GMT -6
I can hear the differences between op amps, apparently. It's a big part of settling on a mic pre for me, finding the best match for the rest of the circuit. The problem is finding simple western english terms to describe how they sound, so I'm not going to try too hard at the moment. They are on the warmer, fuller side of things, as far as 2520's go. Anyway, I absolutely love the CAPI CA-0252. It's my current favorite 2520 style op amp. If this is what old API's sound like I can understand the original reputation. If I had six more 312's built up, I would buy a ten pack of CA-0252 to stuff them. Just running a stereo pair right now. In terms of building them, buying them, it doesn't get any better than Jeff's build guides and customer service. Dan, how would you compare the sound of the CA-0252 to the GAR AM10? |
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Post by Guitar on Sept 24, 2020 10:34:37 GMT -6
matt @iaa That's my only point of reference. I've never really swapped discrete op amps in anything other than a mic pre. But the differences are both noticeable and significant, there. I would assume because there's so much gain happening right there in the circuit, what is it a voltage gain ratio of a few thousand or something at full tilt. I don't remember. I have no idea what these look like on test equipment, haven't gone there yet. All I can report is an obsessive attention to audio detail with mic preamps.
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Post by Guitar on Sept 24, 2020 10:38:20 GMT -6
I can hear the differences between op amps, apparently. It's a big part of settling on a mic pre for me, finding the best match for the rest of the circuit. The problem is finding simple western english terms to describe how they sound, so I'm not going to try too hard at the moment. They are on the warmer, fuller side of things, as far as 2520's go. Anyway, I absolutely love the CAPI CA-0252. It's my current favorite 2520 style op amp. If this is what old API's sound like I can understand the original reputation. If I had six more 312's built up, I would buy a ten pack of CA-0252 to stuff them. Just running a stereo pair right now. In terms of building them, buying them, it doesn't get any better than Jeff's build guides and customer service. Dan, how would you compare the sound of the CA-0252 to the GAR AM10? The GAR AM10 in the same circuit will sound less mid forward, with a little more energy in the top end, and a little beefier bass. Very subtle stuff but I like the AM10 for vocals right now. For most other purposes I would skew to the CA-0252. This is in a 312 preamp. |
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Post by matt@IAA on Sept 24, 2020 14:04:39 GMT -6
It’s really not fair to run the poor QE op amps on +/-15. 😞
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Post by Guitar on Sept 24, 2020 14:28:03 GMT -6
It’s really not fair to run the poor QE op amps on +/-15. 😞 I wonder how or if A Designs dealt with this in their P1 preamp? It's a 500 series mic pre. The 500 version of the Pacifica. |
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ericn
Temp
Balance Engineer
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Post by ericn on Sept 24, 2020 14:34:29 GMT -6
I should really grab one of those... I hate to say it but dollar store 3+ reading glasses here are the standard . |
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Post by EmRR on Sept 24, 2020 15:45:32 GMT -6
It’s really not fair to run the poor QE op amps on +/-15. 😞 I wonder how or if A Designs dealt with this in their P1 preamp? It's a 500 series mic pre. The 500 version of the Pacifica. About 4.9dB headroom difference. Not a big deal. The console version will output about 3W into 600 ohms, +/-15 knocks that back to more than 1W, if your output transformer can even handle it, many won't. |
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Post by matt@IAA on Sept 24, 2020 16:17:19 GMT -6
It also loses about 40 dB of DC open loop gain
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Post by EmRR on Sept 24, 2020 18:27:05 GMT -6
It also loses about 40 dB of DC open loop gain Nooooo.....I find that a little hard to believe, but all my experience is with the 5 transistor AM-3 or AM-4, whichever it is. But still, out of what, 100dB? Where it'll no opamp ever runs in the first place? What does that really translate to when you restrict it to the usual range? |
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Post by matt@IAA on Sept 24, 2020 19:03:08 GMT -6
EmRR The 5 transistor job is much simpler than the AM10. Here's how it looks:  ~120 dB DC OLG at +/-20V or higher, ~70 dB at +/-15. At 20kHz it works out to around 10 dB difference. But ~35 dB difference in NFB at 1k is probably audible? Maybe? dunno.
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Post by EmRR on Sept 24, 2020 19:47:05 GMT -6
EmRR The 5 transistor job is much simpler than the AM10. Here's how it looks: ~120 dB DC OLG at +/-20V or higher, ~70 dB at +/-15. At 20kHz it works out to around 10 dB difference. But ~35 dB difference in NFB at 1k is probably audible? Maybe? dunno. Hmm, interesting. Correct me where I’m wrong, top blue is OLG and bottom blue phase? Bottom green OLG and top green phase? If so, doesn’t that mean blue is only 120dB at 20-30Hz and below, with gain dropping above that? Green is 70dB at 2-3kHz and below, with gain dropping above that? Which would be roughly 24dB NFB at 1kHz to make blue match green OLG? Appears to take 8dB NFB on green to make it flat to 20kHz, 54dB for blue. Looks like green would be flat at 40dB gain to roughly 200kHz with 28dB NFB, blue with 40dB gain to roughly 450kHz with 82dB NFB? So roughly double the NFB at the higher voltage to put gain in the normal audio op amp max operating range. Run both at 20dB gain, it’s 48dB NFB for green, 100ish dB for blue. Add the usual 312 transformer gain of 24ish dB you get 44ish dB gain with 48 or 100ish dB NFB, is that audibly different? Is 28 versus 82 dB NFB audibly different at 64dB system gain? That's 28dB and 54dB NFB at 1kHz, but only 25 and 34dB at 10kHz, 20 and 28 at 20kHz, I think. I've got some discrete instrumentation op amps that sorta do 10kHz under normal closed loop conditions, I forget how bad they are at 40dB gain, but it's comical. Clearly meant for non-audio systems. Interesting stuff. No idea what can practically be heard there. I spend a lot more of my time listening to lower amounts of NFB change in tube gear, 10-30dB total NFB range. That's pretty audible, and lacks the top end extension aspect of op amp closed loop gain. |
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Post by zonkola on Sept 24, 2020 20:22:47 GMT -6
I should really grab one of those... I hate to say it but dollar store 3+ reading glasses here are the standard . Sounds like a hot tip to me. A magnifying lamp with an articulated arm could also do the trick. Whatever works to see that glorious lack of solder bridges on a densely packed op amp build, right? |
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Post by matt@IAA on Sept 25, 2020 16:20:01 GMT -6
Yeah, solid lines are gain and dotted are phase. Me either. But if you just sit on the idea that you're reducing the amount of NFB available distortion *has* to rise. If its 6dB, THD doubles, right? Then again, I started the thread with the premise that the THD numbers in absolute sense are probably inaudible anyway so now I'm arguing against myself.  |
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