Has anyone tried the composite op amp OPA 627 to OPA 603 given in the app bulletin of BURR-BROWN curious of what kind of results
joensd said:
Mmmmh, never tried...
Maybe the OPA604 will do it then...
And more important I can use the OPA627 for the new preamp.
Only got 3 of those damn expensive things
thanks for the hint!
Some of the OA need feedback capacitor between pins 2 and 6 when the buffer is inside global feedback loop. The value of the capacitor is best find by means of oscilloscope when measuring step response of the preamp.
In case of using this capacitor a small resistor of 51 Ohm - 100 Ohm value should be inserted between output of the OA and input of the buffer.
jhead said:
Not yet but I am thinking of testing it. As the CFB OA I will probably not use OPA603 but AD844.
The OPA627 MUST have capacitance on the PSU pins, not just 100nf. From 22 to 100uf is what I recommend.
If you don't have the space now, put them under the PCB.
Lack of bass? No way!
Lack of highs? No way!
Just do it as I say, you'll be surprized.
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No matter what you decouple the 627 with, I don't like the sound. Bass is there, treble is there, but sound is hifi, very clean, detailed plus all the adjectives. Just not musical.
I think it may be because the 627 doesn't settle and drive capacitance well compared to AD opamps.
If you don't have the space now, put them under the PCB.
Lack of bass? No way!
Lack of highs? No way!
Just do it as I say, you'll be surprized.
------------------------------------------------------------------------------------
No matter what you decouple the 627 with, I don't like the sound. Bass is there, treble is there, but sound is hifi, very clean, detailed plus all the adjectives. Just not musical.
I think it may be because the 627 doesn't settle and drive capacitance well compared to AD opamps.
fmak said:
Which one you prefer over OPA627 then?
Recently I did some comparisons and tested AD823 against OPA2604 and I had similar findings: AD chip had everything right, for some reason it didn't sound as musical as OPA2604 (in that particular application, which was I/V stage after a DAC working as volume control).
carlos, have you tried the 8620's yet?
i've recently been busy testing some opamps for use with my new preamp. It's based on a pimeta head amp and is very much "under construction". i'm using a gain of 2 for my pre.
I've tried 2 ad8610's on a browndog 2x single -> 1xdual opamp convertor board and to me they sound better than the opa627's on a self made convertor, much more musical and open. live music (especially eva ciassidy's live@blues alley) sounds really *live*.
in my pre i've tried ad823, op275, op2134, 2132, 2107, tle2082, opa227 and a number of others too but didn't like the overall sound of them. If you're using them in unity gain stages differences might be smaller. My personal preference (only for use in my preamp, that is!): 1: ad8620 2:ad826 3:627
prob is that i'm looking for an all-round best opamp for use in my pre.
in my cdp i prefer (shoot me!) the ad823 over anything i've tested so far (haven't tested the ad8610's yet though); in my project phono preamp i happen to like the ad826 best. with my simple diy usb dac i can;t really hear any difference (it's a buffering, unity gain output stage only) between opamps.
i've recently been busy testing some opamps for use with my new preamp. It's based on a pimeta head amp and is very much "under construction". i'm using a gain of 2 for my pre.
I've tried 2 ad8610's on a browndog 2x single -> 1xdual opamp convertor board and to me they sound better than the opa627's on a self made convertor, much more musical and open. live music (especially eva ciassidy's live@blues alley) sounds really *live*.
in my pre i've tried ad823, op275, op2134, 2132, 2107, tle2082, opa227 and a number of others too but didn't like the overall sound of them. If you're using them in unity gain stages differences might be smaller. My personal preference (only for use in my preamp, that is!): 1: ad8620 2:ad826 3:627
prob is that i'm looking for an all-round best opamp for use in my pre.
in my cdp i prefer (shoot me!) the ad823 over anything i've tested so far (haven't tested the ad8610's yet though); in my project phono preamp i happen to like the ad826 best. with my simple diy usb dac i can;t really hear any difference (it's a buffering, unity gain output stage only) between opamps.
matjans, fiddling with adapters with most OPAs, specially the OPA627, 132/2132, 134/2134... can be very misleading.
They will sond murky if not correctly bypassed.
When everything's right, OPAs sound better to me than the ADs I tested.
I only have first impressions of the AD8620, a quick and not ideal test I made, and I didn't like it.
The same goes for the AD8066.
I tested some ADs more extensively, like the AD825 and the AD826 and they are not bad, but I just don't like them.
But you can get good results with them, even on a bad circuit, or with adapters.
I understand why LC-Audio sells AD op-amps on adapters.
The ADs have a common characteristic to me, a recessed midband.
It may go well with some systems.
But when everything's right, the best, the most neutral, the real thing for me is still the OPAs and also the LM6171/2.
And I don't limit my tests to my systems.
BTW my pre has a gain of around 3.5.
They will sond murky if not correctly bypassed.
When everything's right, OPAs sound better to me than the ADs I tested.
I only have first impressions of the AD8620, a quick and not ideal test I made, and I didn't like it.
The same goes for the AD8066.
I tested some ADs more extensively, like the AD825 and the AD826 and they are not bad, but I just don't like them.
But you can get good results with them, even on a bad circuit, or with adapters.
I understand why LC-Audio sells AD op-amps on adapters.
The ADs have a common characteristic to me, a recessed midband.
It may go well with some systems.
But when everything's right, the best, the most neutral, the real thing for me is still the OPAs and also the LM6171/2.
And I don't limit my tests to my systems.
BTW my pre has a gain of around 3.5.
We seem to share the same perceptions.
I was also suspicious of the adapters. Eventually i moved the entire design from strip-board to teflon, got rid of sockets and adaptors and expected a miracle but the improvement was rather gentle. Certainly better, only not night and day.
matjans, if you made a layout similar to this one:
http://tangentsoft.net/audio/pimeta/bitmaps/pimeta-1.0a-hires.png
forget the OPA627.
You'll have better results with AD chips here.
Also, you get better results with the TO220 version of the BUF634, heatsinked.
http://tangentsoft.net/audio/pimeta/bitmaps/pimeta-1.0a-hires.png
forget the OPA627.
You'll have better results with AD chips here.
Also, you get better results with the TO220 version of the BUF634, heatsinked.
Yup. Grounding and decoupling sucks big time. Makes you wonder why people waste double sided pcbs.
Carlos
Have you compared dil to to220 buf634? How would you describe the difference?
Carlos
Have you compared dil to to220 buf634? How would you describe the difference?
i was planning on using those pcb's with some added decoupling caps, (soldered to the bottom side of the pcb), cutting some ground traces and making a nice star ground. That and a regulated supply should take care of it.
ad8610/20's for channels, buf634 for buffering. (how much of a difference is there between the to-x and the dil-package?) i do plan on using alu/tiny copper heatsinks on the bufs.
i won't use an alps or standard pot here as i can get my hands on pretty cheeap (4 eur) 19 step 4-deck rotary switches with which i will build a stepped ladder attenuator.
ad8610/20's for channels, buf634 for buffering. (how much of a difference is there between the to-x and the dil-package?) i do plan on using alu/tiny copper heatsinks on the bufs.
i won't use an alps or standard pot here as i can get my hands on pretty cheeap (4 eur) 19 step 4-deck rotary switches with which i will build a stepped ladder attenuator.
An externally hosted image should be here but it was not working when we last tested it.
analog_sa said:
I haven't but I have tried dip and sot packaged opas and I can tell you that depending on their orientation you can clearly hear the difference between the two.
sometimes you can even hear the same chips packaged using Korean dips and Indonesian dips: the indonesian dips tend to sound positively gray.
also, time of the day of production runs also matters a lot in high-end applications.
I have some DIL versions of the BUF634 but never used them, because:
1. I can get a much tighter layout with the TO220 version (shorter feedback loop).
2. Heatsinked it has more current output (250ma against 200ma) and runs cooler (yes, this things can get hot without heatsink).
3. Some people reported me tighter bass with paralleled DIL BUF634s (one on top of the other, not ideal), while I have very good dynamics and tight bass, and I don't feel the need to parallel more buffers.
I tested several amps with my pre, and when I don't have very tight bass, the fault is not on the pre.
Also very important is to bypass each chip.
And to use a small cap (200pf is fine for me) on the feedback loop, as you can see on the datasheet, figure 4.
Oh, BW pin goes directly to V-.
1. I can get a much tighter layout with the TO220 version (shorter feedback loop).
2. Heatsinked it has more current output (250ma against 200ma) and runs cooler (yes, this things can get hot without heatsink).
3. Some people reported me tighter bass with paralleled DIL BUF634s (one on top of the other, not ideal), while I have very good dynamics and tight bass, and I don't feel the need to parallel more buffers.
I tested several amps with my pre, and when I don't have very tight bass, the fault is not on the pre.
Also very important is to bypass each chip.
And to use a small cap (200pf is fine for me) on the feedback loop, as you can see on the datasheet, figure 4.
Oh, BW pin goes directly to V-.
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