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[Quoting GregVDS]

Nice build rreynol!

Were did you find your different caps? What are those gold ones?

All the best,

GregVDS

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Regards

All the best,

GregVDS

[Edited by GregVDS on 10-24-2006 at 02:06 PM.]

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[Quote]

I definitely am for the squarish one (22 x 24mm) with dual single opamp and BUF634.

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I knew you where gonna say that

My order from Mouser has just arrived in Paris (love that FedEx tracking system), so maybe tomorrow I will have my LND150'

[Edited by gewa on 10-24-2006 at 02:26 PM.]

I think we are pretty safe with BUF634's. The only question whatsoever was the bandwidth resistors. If you have those, I think we're good to go. The Intersil solution will work for protecting the output transistors in the chip. If you implement SMD resistors for both of these, then great.

As for stacking, BUF634's have a proven practice in that regard. As for the Intersil's, I think my Millett exercise is encouraging, and they were stacked once upon a time in the PPA, V1. However, in the PPA, they put a 1K resistor in series with the input to the buffer. Tangent described it this way in PPA V1:

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[Quoting Tangent]

These resistors balance the current from the op-amp among the buffers, and reduce electrical ringing in the amp. R11 goes with BUF1, R12 with BUF2, etc.

There is some wiggle room on the value of this resistor, but for most purposes 1 KΩ is a good value.

Optional? You may be able to get away with jumpering these, but the amp will not perform as well as it should if you do.

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According to Amb, there is a different way to handle it, since balancing the load between buffers is the concern, and small resistances between outputs of the buffers is probably better. This puts the resistors in parallel with the buffer's outputs, and they can be of very small resistance - only enough to ensure that the outputs drive the load, not the other buffer. Amb described it this way over on DIYForums.org:

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[Quoting Amb]

tomb, what I was referring to was not the 200Ω resistor, but the pair of unlabeled resistors at the output of the BUF634. Even though HA3-5002 schematic doesn't show any such resistors, somehow the PPA gets away without using external current sharing resistors when stacking the buffers. If I was designing such an amp, though I'd probably feel better to put a resistor at each buffer output (probably no more than a couple ohms) before paralleling.

Yes, the datasheets don't say anything about paralleling these devices so we're in a bit of uncharted waters. In theory it's ok to do so with these open loop buffers with some caveats (these resistors are one such issue), and indeed many people having done it successfully.

As for the input resistor, it's less of a "requirement" when paralleling. The necessity (or not) may depend on the specific buffer chip and the previous stage. It's not quite correct to call them "current sharing" resistors because there is hardly any current flow there. What these resistors do is to provide some "padding" between the buffers so that the input transistor of one buffer doesn't become the bias source for another buffer (which could happen also from manufacturing tolerances, but the effect may or may not matter depending on the design of the buffer). The resistor also provides some isolation between the buffers' input transistors from the output of the stage before it. Here again the BUF634 has an internal 200Ω resistor which seems sufficient to do the job (although a higher value might be better but would require external resistors and complicate the stacking). The HA3-5002 has no such resistor internally and the PPA designers decided to use external 1KΩ resistors. They probably arrived at this value from testing and empirical evidence as the datasheet certainly doesn't provide any guidance.

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Amb goes on to say that these resistors can be as small as 0.22 to 0.47 ohms as used in speaker amps, where 10 times the current is involved. This makes me think there may be enough resistance in the pins and solder joints to make them work as a stack.

Digi:
I think as you see by Gewa's post, we need an idea of best cost per board size relative to Gewa's opamp/buffer boards. There is probably some optimum between board size and saw cuts. For example, if we could pack several of each of these on one Euro-size board, then cut them out ourselves, would that be the best savings?

I guess we need lowest price options, and a plan of how to get boards made. Once we know that, we could make some posts in other threads, including the marketplace, to generate interest. I would guess that many (if not a majority) of SOHA builders would be interested.

No one's lost interest on this side of the pond guys - I'm still working on Milletts (SOHA's are next) and it just feels like I need to cool it for awhile after making one of these monster posts.

MHO is that the better way to accomplish what you want is to ask Digi to make a board that is just the SOHA tube stage all the way to and including the coupling caps. This can include the integrated vol pot and input jacks if you want.

Then make separate boards for the various buffers. One board for the basic opamp output. Other boards for the monolothic buffers. Other boards for the various discrete buffers. With this modularity you can hook the SOHA front end to any buffer relatively easily.

Make the PS a separate board so that you can use different PS's with the different buffer's as needed. As you know the SOHA PS has the special voltage multiplier and the heater supply, but these are easy to include on top of any split supply that uses a 30VCT transformer. If you want you can standardize a few basic PS's with different current capacities.

If you modularize this way, then you will get more flexibility to mix and match different pieces. You will also get more flexibility to experiement with different combinations or to try new pieces as someone gets a good idea. This will also give everyone who wants to the ability to contribute boards to your collective activity and you won't have to do a complete board redesign if someone comes up with a new killer buffer.

If you want to retain a little more simplicity, you can include the basic opamp output on the tube board, but then bring out the connections from the coupling caps to some pads. This way, you can leave off the opamp and attach to another buffer. In this form the basic SOHA takes one amp board and one PS board.

If you standardize a few of the dimensions you can assure that the outputs from the tube stage board exactly match the locations of the inputs to the buffer boards. This way, you can put the boards adjacent to each other with wired connections that are very short and direct.

Trying to retrofit lots of buffers to a completely integrated board can become difficult and is limiting some of your choices. Doing a little modularization will make things much more flexible for you.

[Edited by rreynol on 10-24-2006 at 08:31 PM.]

for the buffer,my design goal is universal,alternative for standard 8pins dual pdip packaged opamp.
so there are 4 design:
1,2 single smt 8 to dual pdip 8
2,2 single pdip 8 to dual pdip 8
3,class AB solid pdip 8
4,class A solid pdip 8
the attached is my solid buffer.

to gewa,
you can group them to one big board.the board size less than 80mm x 100mm is ok,otherwise its going to costly.gerber files is okand leave 1mm dent room of each pattern.

to GregVDS,
I am still interested in your design.may I transfer the project to protel?

to tomb,
thank you for your idea,I will figure out a better way to make the photo board.

to rreynol,
I agreed with you.as a all in one design,SV3 is diy friendly.especially for beginner.

to Alex,
welcome back.as always we are friend.thanks for your ieda

all the best
Z

Sorry Gewa, your designs are nice, but because the dual opamp is shifted to left or right, it anihilates all possibility of use in my amp. OPA627 need to be stuffed in a browndog adaptor, and this one will come in conflict or with the cap or with the neutrik, the only way for me is strictly centered on the dual opamp trace, and this is only possible without the browndog, which needs to reproduce the input traces of the board.

All the best,

GregVDS

[Edited by GregVDS on 10-25-2006 at 02:25 AM.]

GregVDS

I'm confused now! The dual op-amp board isn't of center from the op-amp on the SOHA board?

Regards

Don't make my mistake, pay attention, the LND150 are the other way than the silkscreen! I enlarged the LED hole to fit the bigger 5mm ones. Be sure to have a big heatsink for the LM337, it becomes really hot.

What tube will you try?

All the best,

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[Quote]

What tube will you try?

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An ECC82 from JJ. Ordered it from Parts Connexion together with other stuff.

Regards

Regards

keep it goin fella's

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[Quote]

You could've asked for 5.

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Yes I could but first of all, 5 is an odd number and second I didn't want to push my luck

Regards

I'm wondering if anyone happens to have any extra PCBs from that group buy that I'd be able to purchase from them.

I have paypal, so I'd be able to get payment to you immediately.

Sorry for posting this here, I just thought the post might see more traffic here.

TIA for the help!!

-hartigan

A simple question: I have a 50KOhm and a 100KOhm Alps potmeter and I can't deceide which one I would use (what's the best choice)

Regards

[Edited by gewa on 10-26-2006 at 03:12 PM.]

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[Quoting gewa]

My Intersil buffers have arrived

A simple question: I have a 50KOhm and a 100KOhm Alps potmeter and I can't deceide which one I would use (what's the best choice)

Regards

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All the best,