GC Preamp Suggestions

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#821
Re: Latest buffered pre design

Russ White said:
I used the LT1010 simply because I like it a lot. I find it equal in my testing to the BUF634, yet it is less expensive and easier to obtain.
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Russ, I understand that the price is more appealing, but the LT1010 is not the right buffer to use with some op-amps, including the OPA627/37.

20Mhz bandwidth, 75V/us slew rate.
These figures should be much higher (like on the BUF634) to guarantee a stable interface with fast op-amps, when used in the feedback loop.
 
#825
Russ White said:
As an example the bandwidth is lowerd well below 20hz with a 20pf cap between opa out and opa inverting input as per the buf634 data sheet.
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Notice on the datasheet what mode they recommend for the BUF634 working with the OPA627: Wide BW. Even with the 200pf cap.
Wide BW mode is 180 Mhz, instead of 30Mhz.
Now look at this table (in page 9):
 

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#826
Russ White said:
Don't get me wrong, I know the buf634 is better, I am just not sure it is that much better. 😉
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I didn't test the LT1010, so I can't comment.
I was just commenting on the technical issues, which may or may not be that important, depending on what op-amp you are going to use in the end.
If you are worried with the price of the buffer, you will probably worry about the price of the OPA627 too.😀
 
#827
Carlos, the price is of secondary concern, more important is availablility and performance.

That is why I have designed preamps that use both chips. 🙂 I believe they are both great in their own respects. I have listened to them both quite a lot.


Now tonight I desides to put GC's toner transfer method to the test! 🙂 I designed a SMD AD8620 based preamp board with the AD8620 soldered to the bottom. 🙂

It works great. I love the sound of this baby. Here are some construction photos.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


Is anyone interested in this design?
 
#828
The LT1010 should be okay with the 627, since it's GBW is only 16mhz, right? I believe TI/BB recommends using the wide bandwidth mode on the 634 since it lowers the noise and distortion figures.

Have you guys looked at any of the Intersil buffers? Or the other ones available from TI/BB? Here's a few of the ones the headphone guys use:

Intersil HA-5002 (1300V/µs slew rate, 110MHz BW, ±200mA current drive capability)
Intersil HA-5033 (1100V/µs slew rate, 250MHz BW, ±100mA current drive capability)
Burr-Brown OPA-633 (BB's replacement for the 5033, but looks like it can do 2500V/µs typical on the slew rate and has 260MHz of BW)

The Intersil buffers are harder to get ahold of (Only Newark and Arrow carry them as far as I know). The OPA633 is available from Digikey. The 5002 is the cheapest and does sound far superior to the BUF634!

From what I've read, though, the 5033 and the OPA-633 run pretty dang hot, so you'll probably want a way to attach a small heatsink to them. You also have to be careful since they don't have any output protection -- if you accidentally ground the output, poof! dead buffer...
 
#829
motherone said:
Burr-Brown OPA-633 (BB's replacement for the 5033, but looks like it can do 2500V/µs typical on the slew rate and has 260MHz of BW)
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Why bother to use a buffer when it only has 100ma output current?
For headphones it is still not needed, better use a THS4082 or THS4062 op-amps, which has around the same output current, sounds good, works alone, and is battery-friendly.😀
 
#830
carlosfm said:


Why bother to use a buffer when it only has 100ma output current?
For headphones it is still not needed, better use a THS4082 op-amp, which has 150ma output current, sounds good, works alone, and is battery-friendly.😀
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Well, they stick 4 of them on per channel (left/right/ground) and go with that. But for a preamp, shouldn't 100ma be plenty? Plus that buffer has some pretty great specs.. It's just food for thought.

I agree that the THS4082 is impressive as well. They keep putting stuff out faster than people can update/design around.. At least in the DIY community 😉
 
#831
motherone said:
Well, they stick 4 of them on per channel (left/right/ground) and go with that. But for a preamp, shouldn't 100ma be plenty? Plus that buffer has some pretty great specs.. It's just food for thought.
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I would avoid to parallel buffers.
Yes, for a pre 100ma is plenty.

motherone said:
I agree that the THS4082 is impressive as well. They keep putting stuff out faster than people can update/design around.. At least in the DIY community 😉
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I edited my post, either the 4082 and the 4062 are very good choices, sound good, and that's what I've been using to change those junk they put on the headphone outputs on CDPs, etc.
 
#832
carlosfm said:


I would avoid to parallel buffers.
Yes, for a pre 100ma is plenty.
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Yup.. At this point, the "latest" designs are basically using discrete diamond buffers or class-a output stage with an opamp for gain. At some point, it will probably return to being all-discrete designs 😀

carlosfm said:

I edited my post, either the 4082 and the 4062 are very good choices, sound good, and that's what I've been using to change those junk they put on the headphone outputs on CDPs, etc.
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Yes, but with their specs, they're probably not drop-in replacements for standard opamps without careful considerations on bypassing (gasp! 😀 ) and HF performance.

Anyhow, my suggestion was mainly so you could build a nice pre using some other IC based buffers that may offer superior performance to the BUF634. Not to say it's a bad chip, it's just that one of those Intersils might be better at this application.
 
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