Happy and Sad
Happy to see the venerable OPA627 is still holding it's own. Sad to see it potentially being made out of unobtanium, along with questionable sources.
This is quite similar to what I heard in an opamp comparison. The 627 was just was more alive. More of that relaxed ease, a sense of involvement, solidity, PRAT. In configs where the 637 worked, even more so. Others at the time either sounded fuzzy, constricted; or if they sounded clean, it was a boring, homogenized, lifeless kind of clean.
Anyone compared it with the current 827?
I don't prefer CCS biasing the output stage to class A , but for those that do, try a 2n5486 as the "top" cascode fet. It is a high Idss 2n5484, so to speak.
From the internal schematic of the 627/637, it appears that the input stage, unlike other monolithic designs, has the potential to be in a constant power mode. This helps with low offset drift, but more importantly, allows the input stage to have less "memory distortion" or thermal tails. That is likely a key to good sonics.
I haven't checked lately, but peufeu had a very clear explanation of this phenomena on his website a while back.
Cheers,
WMS
Happy to see the venerable OPA627 is still holding it's own. Sad to see it potentially being made out of unobtanium, along with questionable sources.
This is quite similar to what I heard in an opamp comparison. The 627 was just was more alive. More of that relaxed ease, a sense of involvement, solidity, PRAT. In configs where the 637 worked, even more so. Others at the time either sounded fuzzy, constricted; or if they sounded clean, it was a boring, homogenized, lifeless kind of clean.
Anyone compared it with the current 827?
I don't prefer CCS biasing the output stage to class A , but for those that do, try a 2n5486 as the "top" cascode fet. It is a high Idss 2n5484, so to speak.
From the internal schematic of the 627/637, it appears that the input stage, unlike other monolithic designs, has the potential to be in a constant power mode. This helps with low offset drift, but more importantly, allows the input stage to have less "memory distortion" or thermal tails. That is likely a key to good sonics.
I haven't checked lately, but peufeu had a very clear explanation of this phenomena on his website a while back.
Cheers,
WMS
WMS,
Here is something I put together with two 2N5484 JFETs. I just had to measure the Idss to make sure the higher Idss transistor was Q2. However, as you suggest, you can use the 2N5486 as Q2 instead. But you still need to know the Idss. When you make a pair of these, the exact amount of mA biasing isn't that important, just that both cascodes have the exact amount of biasing (mA) or is real close.
Let me also say that above 1mA and below 3mA is ideal with a cascode for the 627. Some people push it past that but I don't know what the results of that are.
The pair I made with only 2N5484s has mA values of 1.209 mA and 1.269 mA. I should have tested the Idss before assembling these for a closer match but the learning experoence was invaluable. So I am going to order a bunch at 12 cents each, measure them and pair them off to enhance my creation (FrankenCD Player). I should say that two guys in the forum really helped me to understand this. Thanks guys!
Attached is the layout for my cascodes.
I hope some will give it a try, the lone resistor is not the way to go, especially under load.
Regards//Keith
Here is something I put together with two 2N5484 JFETs. I just had to measure the Idss to make sure the higher Idss transistor was Q2. However, as you suggest, you can use the 2N5486 as Q2 instead. But you still need to know the Idss. When you make a pair of these, the exact amount of mA biasing isn't that important, just that both cascodes have the exact amount of biasing (mA) or is real close.
Let me also say that above 1mA and below 3mA is ideal with a cascode for the 627. Some people push it past that but I don't know what the results of that are.
The pair I made with only 2N5484s has mA values of 1.209 mA and 1.269 mA. I should have tested the Idss before assembling these for a closer match but the learning experoence was invaluable. So I am going to order a bunch at 12 cents each, measure them and pair them off to enhance my creation (FrankenCD Player). I should say that two guys in the forum really helped me to understand this. Thanks guys!
Attached is the layout for my cascodes.
I hope some will give it a try, the lone resistor is not the way to go, especially under load.
Regards//Keith
Attachments
=[ OMG I've just build a preamp using the OPA4134 for ADC in and a DAC out, no gain just single to push pull and visa versa. Is there an alternative that has the quaility of the OPA627 but with 4 built in amps that run on prefrably +/-15V? Is the OPA4134 really that bad? Is there ways to improve it?
For Ridin '24'z
Like the Addams Family, it's all relative...
We all have our preferences, what matters is does it sound good to you, are your endorphins happy? Regaradless of other preferences and references, including mine.
The 132 and 134 series does at least have a fet cascode input stage, among desirable characteristics. Low input bias and offset current and reasonably tight DC drift is good. The quad version is great for tight layouts, the cost/value is certainly easier to take than chasing down 627s. With the higher input bias and offset currents of the 4562, I would lean towards not using the 4562 for A/D input signal conditioning, but would consider it for D/A I/V and filtering.
One factor that is essential is clean, tight power and grounding. If using stock 78xx/79xx regulators for simplicity, try pre-regulating them with one of slightly higher voltage, ie a 7818 feeding a 7815 for positive and a 7918 feeding a 7915 for negative. Use big bypass caps, like 1000uF right at the regulators, and use smaller ones, like 0.1uF at the opamps. This dumps less supply noise into the grounds at the opamps.
Cheers,
WMS
Like the Addams Family, it's all relative...
We all have our preferences, what matters is does it sound good to you, are your endorphins happy? Regaradless of other preferences and references, including mine.
The 132 and 134 series does at least have a fet cascode input stage, among desirable characteristics. Low input bias and offset current and reasonably tight DC drift is good. The quad version is great for tight layouts, the cost/value is certainly easier to take than chasing down 627s. With the higher input bias and offset currents of the 4562, I would lean towards not using the 4562 for A/D input signal conditioning, but would consider it for D/A I/V and filtering.
One factor that is essential is clean, tight power and grounding. If using stock 78xx/79xx regulators for simplicity, try pre-regulating them with one of slightly higher voltage, ie a 7818 feeding a 7815 for positive and a 7918 feeding a 7915 for negative. Use big bypass caps, like 1000uF right at the regulators, and use smaller ones, like 0.1uF at the opamps. This dumps less supply noise into the grounds at the opamps.
Cheers,
WMS
The LME49740 will do nicely. My final design using these amps will, be of 8 channels in and out, and with about 3 amps per channel per stage will add up to 48 amps in total :S but if its worth the quality I may look into duals in he future.
I plan to use the system as a home theatre DSP for DVD audio and general music too.
In fact I'm listening to the OPA4134 now and it seems to be running very well. It's currently going through from single line to push pull then back again.
I'm using a +/- 15V supply with 4700uf on + and - supply and decoupled with 1uf tantalum caps.
I plan to use the system as a home theatre DSP for DVD audio and general music too.
In fact I'm listening to the OPA4134 now and it seems to be running very well. It's currently going through from single line to push pull then back again.
I'm using a +/- 15V supply with 4700uf on + and - supply and decoupled with 1uf tantalum caps.
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