1. My preference is for Gewa's BUF634 DIP-8 version. Those are much easier to use in many different amps - Millett, PIMETA, etc. Not able to afford dozens of BUF634's, I regularly transfer one stack to the other during multiple build-ups. It works great, but that would obviously be difficult (impossible) with the TO-220 version.

2. A Brown Dog adpater to utilize two single opamps for the dual opamp socket will fit right over a pair of stacked BUF634's. That is the same method used in a PIMETA for OPA627's and stacked BUF634's. Even so, stacking an extra DIP-8 socket underneath the Brown Dog should take care of any concern with clearance. We should probably not implement a two-single opamp layout, since the Brown Dogs are so readily available.

3. Gewa is partly right about the bandwidth resistors. However, the ratio is inversely proportional to 200ohms/BUF634. Here is what Tangent says:

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[Quoting Tangent]

"According to tests by KurtW and others, distortion drops as bandwidth goes up, though once R11 falls below about 200 Ω, distortion starts rising again.

If you're stacking your buffers, R11's value needs to be halved every time you double the number of buffers in order to maintain the same bandwidth setting. This means that the minimum R11 value should be 100 Ω with two stacked buffers, not 200 Ω."

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So, one buffer - 200 ohms, 2 stacked buffers - 100 ohm (per channel, of course). Too much resistance, and the current is reduced. Lesser resistance will not increase the current after that, but will introduce distortion. BUF634's without bandwidth resistors are not optimum. That is the important conclusion.

Greg:
It has been stated in Steinchen's thread and hinted in others: not only should the 12V Regulators be TO-220 case style, but they should probably have heat sinks, too. A double BUF634 stack arrangement may approach the current demand of a discrete buffer. Personally, I would use the TO-220 Regulators, period. Then if unusual heat develops, add the heat sinks.

[Edited by tomb on 10-19-2006 at 06:34 AM.]

Stacking BUF634s improves the sound. The quiescent current will increase somewhat, and the current thrown into the headphone drivers will stay mostly the same. The maximum current that the BUFs can output will increase by a larger factor. If I'm not mistaken, one BUF634 can put out 250mA of current. Double-stacked stereo BUFs could then use a whole amper into a short, theoretically. Implementing the regulators to handle that kind of current - the maximum theoretical output of BUF634s - would surely be overkill.

Tomb, I assume that you mean "real-world" current drain (into headphones) when you think of the current demand vs. regulator packaging and heatsinking options. Did you have a ballpark figure in mind?

Does anyone have any idea about realistic current demands of hungry headphones, like Grados?

Edit: This discussion makes me recall someone's insightful comment that the SOHA thread had entered discrete buffer mode. Indeed! Buffers are just so much fun!

[Edited by kristleifur on 10-19-2006 at 08:58 AM.]

I have a request as you all are drawing and working on dip8 buffers: My neutrik Locking will come inside the pcb very hard, and so I really would like the buffer board the smallest possible, and if possible, decentered toward the power caps. I know, this will be difficult. I'll go Eagle tonight!

All the best,

GregVDS

Regards

Gewa - those boards look great - let's get Digi moving on them! (I still prefer the bottom one that uses the DIP-8's.)

So, yesterday evening, I went in the garden, with some tobacco, my pipe, a glass of Talisker, a Laptop, and listening to some music through my Millett, I draw this after some attempts:

I'm not sure if the Right - Left position is correct, maybe it's the other way.
I checked as far as I could, but feel free to double check it, for twice is better than once. The board achieves to pack 2 OPA627, two BUF634, each with its own Bandwidth resistor, and if one feels the need, a cap (around 200pF) can be put between the loopback and the output of OPA - input of BUF. This cap would come backside under the BUF634. I saw this as schematic suggestion in the BUF634 or OPA627 pdf, but am not sure if mandatory at all. It could be useful to try other opamp more prone to instability (if I understand well the usefulness of this cap)

Let me know what you think.

The board should be 21.5 by 24.7 mm, so less than a square Inch, and would come straight upside the current OPA2134 and to its right, SOHA board seen from upside, the volume shaft pointing up.

Digi01, I would be sooo happy this one was in production, let me know if you have some board surface to fill. I made this into Eagle, but don't know still how to make masks and stuff like that.

All the very best,

GregVDS

[Edited by GregVDS on 10-20-2006 at 02:44 AM.]

to gewa,
have you consider make a ha3-5002 boost unit?I find a big source of 5002 chips at beijing.

Zang

if you want, I can send you the brd file,

Let me know,

All the best,

GregVDS

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[Quoting digi01]

GregVDS,
it looks niceI will check out the layout weekend.

to gewa,
have you consider make a ha3-5002 boost unit?I find a big source of 5002 chips at beijing.

Zang

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I hadn't mentioned it because that chip is dismissed so often on account of its reported tendency to fry at the slightlest short. (They have no output current protection.) One should definitely include the SOHA output resistors if using these. Reportedly, the slight shorting that occurs in plugging/unplugging the headphones could be enough to kill them.

No doubt, that's why they sound so good.

I have a quick question about parts, the bridge rectifiers 1&2 are supposed to be rated at 100v 1A, I can only find 200v 1.5A in a WOG package - pinout and spacing looks ok to me. Uprated specs is a little overkill right? but will it have any act on performance of the AC rectification and or filtering?

I hope you can help ease me in - I may need some guidance (a quick smack normally works) throughout, is this the place to ask?

Cheers

James

It doesn't seem this should be a problem to have this part overrated. Maybe still, wait untill specialists come and answer you, for I only know what I learned building amps.

All the best,

GregVDS

[Edited by GregVDS on 10-20-2006 at 10:03 AM.]

Regards

[Edited by gewa on 10-20-2006 at 12:58 PM.]

Keep the comments and suggestions comming.

digi01

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[Quote]

have you consider make a ha3-5002 boost unit?

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Regards

[Edited by gewa on 10-20-2006 at 07:04 PM.]

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[Quoting gewa]

Attached all the various PCB designs. A few boards were missing a V+ connection on the Op-Amp

Keep the comments and suggestions comming.

digi01

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[Quote]

have you consider make a ha3-5002 boost unit?

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What the hell is that? Is it a direct replacement of a BUF? If you can give me a schematic I will give it a go.

Regards

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Gewa,

Please refer to my Post #92 up there. The HA3-5002 is an Intersil buffer that is very similar to a BUF634. It can be stacked and seems to perform quite well in that configuration in my Milletts. Unfortunately, the pinouts do not match.

Intersil is a major semi-conductor manufacturer. Here is the primary reference web page:
www.intersil.co...%2D5002,00.html
The data sheet on the HA-5002 is here:
www.intersil.com/data/fn/fn2921.pdf

Should look something like this. No PS decoupling cap's yet.
Sugestions, comments any one?

Regards