Any interest in GC input buffer and power supply regulator pcb's?

[Sheldon]

Originally posted by Pedja

As far as I can see the voltage reference of one of its current sources is made to be supplied externally.


If I did not misunderstood you, your buffers have their own (additional) regulators hooked to the +/-24V lines(?). Connect the grounds of these regs and caps following them by some decently sized conductor to the main ground point. Keep the overall layout tight and do not make another ground connections, that is IMO about everything you can do about the buffer and grounding in this case.

If you use an additional shunt resistor at the buffer’s input, it belongs to the signal ground.

Filter in fact rather belongs to the power chip and the ground side of the filter shunt caps goes the chip’s signal ground.

Pedja

Sincere thanks Pedja,

I hope that great evening weather is keeping you up so late and that you find some time to sleep. You'll spoil us (me certainly) with your dedication.

Yes, the set up is as you describe. So I will separate the filter and signal grounds from the buffer reg grounds, and run the filter grounds to the signal ground on the power amp. The shunt resistor is already on the power amp board and does go to the signal ground on that board.

Almost there,
Sheldon

[SRMcGee]

Sheldon (& Co.):

The posts on this thread are so far over my head it isn't funny. It sounds like you're pretty far along in refining buffers for use in LM3875 Gainclones. I'm planning on buying a bunch of PCBs from Brian GT within the week. It seems that your PCBs are designed to work with Brian's (and not in substitution for his boards). When do you think your project will be available to the group?

Sorry to be so slow about this stuff.

Regards,
Scott

[Sheldon]

Originally posted by SRMcGee
Sheldon (& Co.):

The posts on this thread are so far over my head it isn't funny. It sounds like you're pretty far along in refining buffers for use in LM3875 Gainclones. I'm planning on buying a bunch of PCBs from Brian GT within the week. It seems that your PCBs are designed to work with Brian's (and not in substitution for his boards). When do you think your project will be available to the group?

Sorry to be so slow about this stuff.

Regards,
Scott

My name doesn't belong in the front of your post message. I'm not as much over your head as you think (as in just barely). The real work here in design has been done by Pejda, Carlos, and many others. I'm just taking what the've done and building one example. I'm using Brian's board and plugging Pejda's power supply and jfet buffer into it. You can see from my questions, that I don't have anywhere near the level of expertise of many contributors to this board. I'm operating on what I've learned here, reading a basic text on electronics (("The Art of Electronics" by Horowitz and Hill), plus some common sense logic about how things work (which can get one in big trouble, by the way).

I don't have the capability to really do a group design and sourcing, such as Brian has done. Actually, I was sort of hoping we could sucker Brian into doing it if enough interest could be generated. Even though a group buy of boards hasn't come out of the thread, a lot of useful information has resulted, including some board designs which could be made by individual users. Brian started his project to motivate as many people as possible to take the plunge and build an amp. I checked out the DIY site originally intending to build speakers (one done, one to start on) and here I am building a one of a kind (at least for a short time) integrated amp. The last thing like that I did was a Dynakit back in the early '70's. So Brian's subversive intentions were realized.

Sheldon

[cjd]

just a note, since I know it's been a bit since I have posted any updated layouts... I'm still working on these. I also finally got a job for a bit again, so I don't have all day every day to tweak and post. But I will soon have funds to start trying them out, so it's not at all a bad thing.

One question:

If I'm able to do a double sided board myself (probably would be toner transfer method no less), and documented it, would there be a comfort level with that? Because there are a few little things that I think double sided would help clean up that little bit extra. No vias would be required except perhaps at a through component (if even then), just solder top or bottom.

C

[Sheldon]

Well, after a few minor setbacks it's working and sounds pretty nice at first go. Haven't had time yet to listen critically, but no abvious nasty's. To recap, I'm using Brian Gt's board and resistors (premium pack), but with 47uf Cerafine caps on the board, Pedja's ultimate discreet regulated ps, and Pedja's jfet buffers. This is all stuffed (and I mean that - I'll try to post some pics later today) into one of Peter Daniels fancy chassis.

One might ask why I chose this combo. Just in case you do, here's the story. I bought Brians kit mostly on a lark. I'm in this primarily to learn, not to save money. So I figured I might as well complicate my life, and I liked the idea of building a couple of discreet circuits (have never done that before) and getting the whole thing to work. Plus, a fair number of builders have fournd the regulated and/or buffered "clones" preferable. I'm not taking sides in that debate, and I probably won't test one against the other. I'm getting out of it what I want.

As for the start-up problems. The first I had was a loose solder joint on the neg. ps j309, so no output from that side. Can you say DC offset boys and girls? I had used smd j309's to which I attached fine wire, then mounted. Those are tiny. Fiddling around, I accidently detached one of the wires. Once fixed, I discovered that I had wired the source selector switch wrong. Fixed that, and it works. By the way, I wired the selector switch so that one position grounds the buffer output, in order to eliminate the turn-on thump. That works.

I still have a little tuning to do. I'm getting about 90mv offset in one channel and some hum, about 75mv in the other but very low hum. Maybe a bad joint or grounding arrangement to chase down. Time for a break before I tackle those.

Thanks to all the DIY members who inspired me to give this a shot. It's been slow going, because I'm a complete novice, but it's been fun.

Sheldon

[Nuuk]

Congratulations Sheldon. For a novice, that's no mean achievement!

Check all the solder joints (it won't take long). I haven't used the discrete buffers or discrete regulated PSU so I can't really offer any other guidance.

[Sheldon]

If I did this right, you should see a picture of the buffer board:

[Sheldon]

And here the regulator. The half you see is the neg. side. The pos. side is below the pot shaft. I cut one of Brian's rectifier boards in half, and mounted one half one each side of the reg board:

[Sheldon]

And here the complete amp. Hard to see here, but the power amp boards are below the buffers:

[Sheldon]

Finally some Z-Horns I made for this set up, with Fostex 108's: