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PostPosted: 31 Aug 2011, 04:56 
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Joined: 30 Aug 2011, 02:32
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Location: Italy
Hi guys!
I'm new to this websiste (and to tube amp) but i would like to build the Poddwatt Tube Amp!
I've seen that many of you realize the links using wire connections instead of a PCB, there's a particular reason?


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PostPosted: 31 Aug 2011, 07:07 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
Hi, welcome! :D

Here are a couple of reasons that are my belief for this:

1) Tradition
2) Heat. Unless you're using the latest NASA/JPL PCB technology, the heat from tubes will kill PCB's in short order. I have yet to see any but teflon PCB's (which are fabricated completely different) where the traces didn't lift.
3) Flexibility. We love to tinker. Kinda hard to change topologies on the fly with a PCB ;)

Cheers!

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PostPosted: 31 Aug 2011, 07:25 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
neborkia wrote:
Hi guys!
I'm new to this websiste (and to tube amp) but i would like to build the Poddwatt Tube Amp!
I've seen that many of you realize the links using wire connections instead of a PCB, there's a particular reason?

Not everyone will agree with me but I think printed circuit boards (PCB) dull the sound. If you think that when joining two resistors on a PCB there are two soldered connections and six dissimilar interfaces. Component wire-lead/tin solder-copper strip-lead/tin solder-component wire. At each junction the electrons speed up and slow down (different propagation delays). Then multiply this mess by dozens of components???

In point-2-point wiring the components are often soldered to a tag strip then “hook-up” wire is use to link components, sockets etc. Not a lot different from PCBs is it. Just messier and even longer signal paths.

Now heat-up your iron for component-2-component wiring. In this method each component is wired directly to the next component with only the connecting leads that component was manufactured with. Now if I link to resistors I have ONE joint. Each component lead is rapped or wired around the next then soldered. One connection not six junctions. Yes there is solder in there but the leads are hard wired to each other. This produces a fast cct. and an extremely short signal path. The big disadvantage is if there is a fault it can be hard to fix. Luckily for me this is very rare.

So move beyond point-2-point and go straight to component-2-component wiring. It will take you a lot more thought and time to assemble your high-speed short signal path creation put you will get much more out of it, over and over again.

OK you can throw the stones now.
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PostPosted: 31 Aug 2011, 10:53 
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Hi, Generally I agree. A goodly number of PCBs are not all that good or durable. But to say all are inferior does not do justice to many companies and high end products that use quality materials. I (through the commercial side) have some experience with PCBs. They are used in the kit versions of the various projects. These are premium double sided, boards with 4 ounce copper traces. Areas not carrying signals are plated as part of the ground system. Boards are used partly because it is much easier to have someone build the amps and the success rate of having it work right the first time is greatly improved. Heat has not been a problem as the boards, attachments and chassis are designed with the potential in mind. In my entire experience, I have had only two boards fail (not ours) and both were perf boards that had heat generating components too close together and it cooked the board. To be fair, I have seen boards from other sources (I'll be polite and not mention the companies or sources) that have failed. They have always been of cheap manufacture. I would be ashamed to put out stuff like that.

The largest problem with good PCBs relates to the fact that there are indeed two connections for each part. The increase in number of connections increases the possibility of a bad solder joint. I have found that to be the single most frequent issue with the projects. On the flip side I could argue that the number of wires reduced by the PCB reduces the likelihood of errors. Not wishing to start a row, I feel that both methods have a place in audio and both can be quite excellent and both can be quite poor. I have the luxury of having both the wired prototypes of the posted projects and the actual commercial kits (with PCBs). In extensive testing and listening the differences are so small as to be below the thresholds of the measurements. They actually tend to lean toward the PCB versions being a little better. I find considerably more differences in the choice of tubes used than in the stuff they are plugged into. In the Poddwatt in particular I can demonstrate a change in low frequency (100HZ or less) distortion of over 2% (goes from under 1% to over 3%) by just changing the brand of tubes.

Much of this is academic concerning the Poddwatt as the only way you can get the PCBs is to get the kit (not a sales pitch here, just how it goes). As a diy project I would certainly use point to point with quality wire, quality components (especially sockets and capacitors), good resistors from a known good source, and likewise for tubes. Careful layout and attention to grounding is also important (there are guidelines for this elsewhere on the site). The Poddwatt is rather nice small amplifier and will surprise many folks with the quality of the sound. Sorry for the soapbox, :soapbox: a lot of good thought went into the various posts and the subject like many others in audio is really open ended. :)

Good listening
Bruce

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PostPosted: 31 Aug 2011, 13:28 
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Location: Canada
Hi.
gofar99 wrote:
PCBs ... all are inferior does not do justice to many companies and high end products that use quality
gofar99 wrote:
Boards are used partly because it is much easier to have someone build the amps and the success rate of having it work right the first time is greatly improved.
gofar99 wrote:
I feel that both methods have a place in audio and both can be quite excellent and both can be quite poor

Yep, I agree.

From viewpoints of the manufacturers & DIYers, particularly newbies, PCBs do reduce
the chance of going wrong, otherwise resulting claims & pains.

Let me take an excellent example of a high-end phono-preamp from Vacuum State Electronics, retailed for USD24,900.00. Its latest producions are built on PCBs. Also supplied in kit form. One of the very best sounding phono-preamps now available in the marketplace - a 25-year brainchild of Allen Wright, late founder of Vacuum State.

It can sound very good if built right even on PCBs. Building preamp on PCBs, heat should not be an issue.

Here I have to salute Allen Wright whom I communicated even last fall. He passed away so shortly last February. A hugh hugh loss to the tube audio world. :bawling:

c-J

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PostPosted: 31 Aug 2011, 17:23 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Bruce: I was not discussing quality of PCBs and as we all know this can vary wildly, but just PCBs themselves. BUT if we didn't have PCBs there would not be thousands of easy to assemble kits out there and a lot of newbies may never get onto electronics and audio. So the PCB is a real hand-holder for the beginer and when it comes to SS intergrated cct. etc, and absolute must. No argument there.

And I guess this is where tube amps shine as often there is a low component count so assemble the whole amp section on the socket of the tube means no PCB and ultra short sig. path. All my tube amps, apart from the early two stage tube preamps I was building, have been assembled by placing the passives directly on the socket of that tube. BUT as I have said, make a mistake in assembly or try to change a single component, Cursing becomes your first language.

Getting back to SS builds my Boz on a cap (BoZoaC) is an example of no hook-up wire in the amp section with a simple SS device. I guess that is what I am striving for, short sig. path, no hook-up wire in the amp section and few solder joints.
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PostPosted: 31 Aug 2011, 23:00 
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Location: Arizona, USA
Hi Mark, Amen. :)

Good listening
Bruce

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PostPosted: 01 Sep 2011, 02:48 
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Joined: 30 Aug 2011, 02:32
Posts: 3
Location: Italy
Hi guys,
Thanks for the answers!
In my DIY project (most of them are low voltage) i'm used to build a PCB, it helps a lot in finding errors in the component assembly.


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PostPosted: 18 Sep 2011, 21:22 
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Joined: 19 Nov 2010, 01:09
Posts: 2
Hi there,

Would it be OK to use a 50ohm 5W pot instead of the 25ohm 3W? This is what I can get locally.

Also is there a guide to bias the output tubes correctly? What should I be looking for when I probe the 2 check points? Would it be easier if I put in another 1ohm resistor with another set of check points so that I can plug in 2 sets of multimeter?

This is my 2nd tube amp attempt and my first was a kit SET with a fixed resistor, so no experience with balancing the output tubes.

Thanks!

Edwin


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PostPosted: 19 Sep 2011, 07:46 
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Location: Australia
southernoise:

work through this to learn all you need to know about bias, mystical spells and the Dream Time:

http://www.diyaudioprojects.com/Forum/v ... f=9&t=2699

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