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PostPosted: 02 Sep 2012, 20:06 
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Well, here's the initial information. First is the schematic showing the power supply.
Attachment:
schematic.jpg

At low current, tube rectified supplies can be extremely quiet with only simple filtering. Design point on this one is -110dBv ripple at 258v and 1.8 mA. We'll have to see how close it comes in the build. You'll also notice a ground lift switch. This is necessary because I have the metal chassis grounded to the mains safety ground. When using the preamp with a grounded amp, I'll lift the ground and let the preamp signal ground reference to the amp inputs. This eliminates the mains panel ground loop.

And here is how it looks.
Attachment:
Assembled.jpg
Attachment:
top_view.jpg

No fancy wood chassis this time. It's the purely industrial look for this one. I brought everything out through the top plate to simplify wiring. And here is the underside showing the interior layout and tie points.
Attachment:
Underside.jpg

No wiring yet but the build should go quickly. I do have to fabricate one metal plate that will slide into the slots in the Pomona case between the PS section and the amp section. The final filter cap is just on the amp side of the divider. This is to protect the final HV filtering from HV AC fields in this small chassis.

One other note. Pomona uses the absolute worst aluminum alloy for the top plate with which I have ever worked. It is soft and gummy and doesn't machine worth squat. I almost made an entirely new top plate out of 6061 T6. I will probably never buy a Pomona case again. At the prices they charge, they really should be much better quality.

When she's wired and tested I'll post more.


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PostPosted: 02 Sep 2012, 21:45 
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Talk about compact. My only layout concern (too late now Houston) is the RCA at the from will hide the volume control. BUT if you install gold plated right-angle RCA adapters the inter-connects will lay flat to allow easy access to volume. If you like the idea I'm happy to send you 4. I get them at staff cost so very cheap and they look schmick.

In the PS for mine I had two CRC stages. 100uf-150ohms-100uf-150ohms-100uf. But with the large choke you shouldn't have problems. If you do add a CRC stage.

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PostPosted: 03 Sep 2012, 12:06 
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Mark;
So by gold plated right angles do you mean something like one of these?
Attachment:
gold.JPG
Attachment:
black.jpg

I have to admit, I thought of that but the space was cramped and really didn't want to have to bring them out the side of the case. The right angle adapters may be a good way to go. What do you think?

Matt


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PostPosted: 03 Sep 2012, 16:51 
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Matt: Yes that's them. The ones we sell are solid metal. I have used them before when I ran out of space at the back of a CD player. Unfortunately it is another connection in the signal path but it may just be more practical.

How about you set the preamp side on so the RCAs come in from the left. That way you will get clear access to the knob!

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PostPosted: 04 Sep 2012, 08:43 
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There are also 90° power cables too.
Image

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PostPosted: 04 Sep 2012, 08:48 
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It is.

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PostPosted: 09 Sep 2012, 16:30 
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Well, it's half wired. :(

So anyone who has been following my various builds over the last few years knows that I have the tendency to repeat layout mistakes from project to project. For whatever reason, this seems to be one set of lessons which I have trouble learning. Enter this build... Once again I have tried to put a project into a container that is at least 50% too small. Take a look at this photo.
Attachment:
Half Wired.jpg
The final filter cap (100µf) will go on the terminal strip to the left of the divider. The power supply turned out to be a pain PITA to wire. I know that I should have had a larger enclosure so that I could isolate the AC from the filtered DC in a better manner. As it is, I am concerned about the proximity of all that AC to my main filter choke. Hopefully the grounded iron on the inductor will give it some added noise immunity. Also, the very low levels of current being drawn should help as well. I guess I'll have to wait and see.


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PostPosted: 09 Sep 2012, 18:00 
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Matt: I think you should be right. In my builds I have DC on the filament. I was using 12V regs. but in the end just a big RC network did the job.

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PostPosted: 11 Sep 2012, 19:45 
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After running around the threads on this forum for a week or so and asking several questions regarding conversion of a guitar amp to RIAA and 12AX7/6SR7/12AQ5, I've decided that at first I want to try something a little simpler. I have therefore ordered all the parts for the ps and and the SSSS preamp. Hopefully, bits will arrive in the next couple of days and I'll start laying out the PS.


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PostPosted: 11 Sep 2012, 22:00 
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nodz wrote:
After running around the threads on this forum for a week or so and asking several questions regarding conversion of a guitar amp to RIAA and 12AX7/6SR7/12AQ5, I've decided that at first I want to try something a little simpler. I have therefore ordered all the parts for the ps and and the SSSS preamp. Hopefully, bits will arrive in the next couple of days and I'll start laying out the PS.

Which of the 4S preamp are you to build?

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