ADA4637-1 - any experience? - diyAudio
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Old 1st June 2011, 08:48 AM   #1
GLooP is offline GLooP  Bulgaria
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Join Date: May 2011
Default ADA4637-1 - any experience?

Hello, everyone!

I have a pair of ADA4637-1BRz. Doing some OpAmp rolling on my sound card (which drives LM47910, AD8620, AD797, OPA637 flawlessly), I noticed that using the ADA4637-s produces some distortion, noticeable in the low-freq register.

First thing to do was opening the datasheet and reading through it and couple of thing just do not appeal much to me:
- The DS is very "scarce" on application circuits, compared to AD797 for example.
- There is no frequency compensation pin
- The chip seems very picky on application. There are some very strange recommendations about the traces and PCB design around the chip.

Since the OpAmp is not cheap and I cannot use it the way I intended, I consider building some preamp/input buffer for say LM1875 gainclone or some headamp.

I would be very grateful is you can share your experience with this OpAmp, especially if you have designed something around it.

Thank you!
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Old 1st June 2011, 10:15 AM   #2
madwolf is offline madwolf  Singapore
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ADA4637 is only stable with a Gain of 5 or move.
Check the Gain of your sound card or the gain of that part of the circuit.
if not you have to use 4627 version, it is de compensated version

I believe LM1875 need to have some gain as well
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Old 1st June 2011, 11:26 AM   #3
GLooP is offline GLooP  Bulgaria
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Gain main not be the reason since OPA637 is running smooth and it is also not compensated.

Running the OpAmp on the sound card is not the issue anymore, it's just does not do the job there.

The issue now is making a preamp or input with this chip. Gain of 6 or so will be default by design. The more I'm interested in is has anyone encountered something specific in putting this chip in work? The datasheet suggests minimul leakage current and "guarding" the traces around the chip. My impression is that this chip requires its own design, not just putting it in a general OpAmp design and expect it to work. My goal is to take most of it.

Also- noise figures are not best, I guess I'll have troubles using it as input either...
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Old 26th August 2011, 03:27 AM   #4
fjc is offline fjc  Taiwan
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Unhappy 4637-1 first experience

I have met similar situation on my OP pre-amp.
It has a buffer stage in front, then follows with dual step resistor volume control, then comes this main stage, before buffer and DC servor. I am using standard 9k:1k in the negative feed back for the amplification rate,10 fold.
I have no problem with this pre-amp by using OPA 637, untill trying out the replacement of AD 4637-1 (Arz). It can sing, but gives out occasional pop out low level noise. Even noise comes out from the moment turn on volumes. (Those case never happens with the 637 in.)
I will do a OSC check to the wave forms, first thing to check output DCV....
I suspect the fast speed wide band OP easily gives oscillation (ringing)that needs 10-20pF capacitor compensition to cure.
As you said, the first impression on this OP is not good, more to come of the progress over the weekend.
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Old 7th September 2011, 05:09 AM   #5
fjc is offline fjc  Taiwan
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Quote:
Originally Posted by fjc View Post
I have met similar situation on my OP pre-amp.
It has a buffer stage in front, then follows with dual step resistor volume control, then comes this main stage, before buffer and DC servor. I am using standard 9k:1k in the negative feed back for the amplification rate,10 fold.
I have no problem with this pre-amp by using OPA 637, untill trying out the replacement of AD 4637-1 (Arz). It can sing, but gives out occasional pop out low level noise. Even noise comes out from the moment turn on volumes. (Those case never happens with the 637 in.)
I will do a OSC check to the wave forms, first thing to check output DCV....
I suspect the fast speed wide band OP easily gives oscillation (ringing)that needs 10-20pF capacitor compensition to cure.
As you said, the first impression on this OP is not good, more to come of the progress over the weekend.
Since I failed with a pair of 4637, and not to put into scope chk yet. But, I have tried with 4627 and it works fine. The problem may relate to soldering-over heat the tiny SOIC. I will try to solder quick to a second pair of 4637 ( expensive lessons ), then, compare the sonic difference btw 27 and 37 before jump into conclusion.
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Old 10th September 2011, 06:01 PM   #6
fjc is offline fjc  Taiwan
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I have tried to do a new pair of 4637, with careful soldering, it works fine.
My problem may really comes from over-heating the first pair. But while run a long period, the pop sound disappears of the trouble pair. I wonder it can do a self-healing. May be you could do the same. By the way, in between I did worked on the 4627-1. Sonic effect is similar or less than the 4637, I have to give a good try.
This tiny SOIC OP (SMD version in OP) really gives challenge to us, beware of the solder type and gun power.
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Old 13th September 2011, 03:56 AM   #7
fjc is offline fjc  Taiwan
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One last thing, I have given the leads short heat up treatment ( prevention of cold spot) and a good rinse of alcohol. The board is much clean to be examined from the mag glass, this final step is important, at least it solved my problem of soldering a pair of 4627-1, wish you can do this. This is my final reply, no futher thing I can give.
My conclusion is: if we do not burn the tiny Op, do not give up easily, try short heat up (1-2 second with fine tip ceramic heater -constant temp servo, solder gun), and rinse it, then give the OP a couple hours run. I have solved my problems that never faced like those regular size (plug in) OPs.
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Old 21st November 2011, 09:26 AM   #8
GLooP is offline GLooP  Bulgaria
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Hello again.

An interesting observation I made is that it is not the OpAmp to cause any troubles. Actually, ADA4637-1BR seems so good and detailed that it revealed how flawed my headphone amplifier is. Since the RMAA tests showed no sign of actual degradation using this particular OpAmp, I just decided to plug the headphones directly instead of using an amplifier and I was amazed of the sound. Using other good OpAmps (LME 49710HA, AD797 BR) couldn't reveal the amplifier's flaws at such extent (so I'm building a new one for this reason).
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