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PostPosted: 14 Feb 2021, 09:29 
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Joined: 12 Dec 2018, 17:50
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Just a big thank you to Bruce and those that have contributed to this forum. After a year and half of lurking on this forum while collecting the necessary parts to build a PoddWatt I finally completed it over the Christmas holidays. First power on and no bangs, smoke or mushroom clouds rising above my house! Although not an audiophile I wanted to build a decent amp for myself and the PoddWatt seemed a good choice. I'm no expert but I was actually taken aback with how great it sounded when I first heard music playing through it. And although I don't think that I have made a very tidy build inside the chassis, there is absolutely no hum. I'm very pleased with the result.
At first power up, after setting the 200v on each side, the left channel bias was already bang on at 41mv across each resistor. Right channel adjusted easily. After a month of daily use I've checked and they are stable at 41-42mv. I'll check again in about 3 months.
Once again, thanks for those that have contributed to the forum and a big thanks to Bruce for making his great design freely available.
Regards,
Colin


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PostPosted: 15 Feb 2021, 09:11 
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Joined: 16 Feb 2016, 19:45
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Location: Boston, USA
On the contrary, that's one of the cleanest builds I've seen. I did something a bit similar with mine, using turret boards for each amp channel and the power supply. But I didn't have the patience to make it look beautiful!

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PostPosted: 16 Feb 2021, 12:31 
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You guys are so inspiring. Which is great, because since I started my project, I'm already stuck and need both the inspiration and a little help.

Working through the schematics for parts is helping me see that I don't know which schematics to use. Can you please help me figure it out? Bruce's Oct 20 post gives a Version D schematic as definitive,

Image

and mentions in a similar post from August that you should mate that audio circuit with the PSU "with the power supply with the 2 LR8s"
I think that's this one:

Image

But...a couple of things make me insecure about this.
The B+ voltages are different on the two schematics
The LR8 network shows two terminals while the audio channel only seems to have one 200v
If you were to build this, the PSU would actually have 3 LR8s

Meanwhile, Bruce's 2017 AudioXPress article ( https://audioxpress.com/article/poddwat ... -amplifier ) shows an audio channel and PSU schematic that seem to work together, but the audio channel is not the latest version...

Anyway, I would be thankful to anyone who can provide some direction for sorting this out.

Thanks in advance :)

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PostPosted: 16 Feb 2021, 16:15 
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I used the type "E" version of the PoddWatt schematic (you can find it on the post by Bruce from the 23rd June 2019 on page 68) and PoddWatt Series 2 Power Supply schematic as you have.
Got to admit, I didn't notice the B+ voltages differences. The type "E" version of the Poddwatt still indicates 235V. I guess just a typo but only a minor difference.
The second terminal you mention is ground.
It does indeed have 3 LR8s. 2 for the audio channels (adjustable with the 2K trim pots) and 1 for the heater circuit centre tap (see Bruce's post on page 71 from 11th March 2020). I built all 3 on a single board which is mounted between the audio channels. From the power supply, power is fed to the board and the 3 LR8s and from there distributed to the 2 audio channels and the heater centre tap. You can see it in the attached picture. The 2 audio channel LR8s with the trim pots are visible at the top of the board while the 3rd LR8 is hidden at the bottom of the board.
Hope that helps.
Colin


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PostPosted: 16 Feb 2021, 22:30 
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Thanks for the info and pointing me to that Bruce post. And let me join Eric in congratulating you on an heart-stoppingly beautiful build!

If I understand your post:
1) You built both channels of the monoblock "E" version onto one chassis and shared the power supply
2) The line off the bottom of the 1.0 cap that looks like it's going nowhere can be ignored, since it goes to ground and traces there anyway. It's probably vestigal in the drawing from some other version of the amp.

I've already ordered the transformers, but it looks like ther'll be plenty of time to work out the rest of the details before they arrive!

Thanks in advance

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PostPosted: 17 Feb 2021, 08:16 
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Thanks for the kind words regarding my build. Really appreciated.
You are correct on both points:
1) 2 channels of the "E" version and the power supply built into the same chassis.
2) The line off the bottom of the 1.0uF cap can be ignored as drawn. I think you may be right in that it's a hold over from a previous schematic.

I also ordered the transformers quite early which did a great job to keep me focused on getting the build done. And without any doubt the biggest time consumer of the build, by a massive margin, was the thinking how to do things bit!

Colin


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PostPosted: 17 Feb 2021, 18:29 
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...and so much fun! I can't believe the geeky joy I'm getting out of making a parts list by analyzing each element, and turning that into a shopping list.

One of the things I'm doing is working through Rozenblitt's "Tube and Circuits" and using the knowledge I gain there to do the calculations and appreciate the genius of Bruce's work.

So much fun and I haven't even started building!

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PostPosted: 17 Feb 2021, 21:05 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Thank you for the kind words. These amplifiers were designed to be diy friendly, and sound far above expectations. As you noted there are several iterations. Even the earliest ones are really nice. The later versions are IMO equal to any in the wattage range regardless of cost. The biggest issue I have with them is the machining of the chassis. Any time I don't mess up on at least one drilled hole is a great day. I use a pair of the mono block version on my Martin Logan ESLs from time to time. The only limit on the sound is that the ESLs need more power for listening at loud levels. At modest levels the sound is exquisite.

Good listening
Bruce

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PostPosted: 20 Mar 2021, 18:07 
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Just looked up those Martin Logans and am now even more intrigued.

My original plan was to use the Poddwatt to drive my Vandersteen 2Ci's and then upgrade to your OddBlocks with KT88s to use with ribbon speakers, probably Magnepans. The Martin Login electrostatics with their integrated bass drivers seem like a much better idea.

But that's a way off.

Here's my actual question....Do those exquisite Martin Logans sound even more delightful with what I would presume to be greater authority from the higher current OddBlock, or is it really just a matter of how loud you want to go?

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PostPosted: 21 Mar 2021, 21:29 
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Hi, They sound fine like I said at reasonable volumes with the Poddwatts. However, they work better with the Oddblocks. Either size is fine. My personal preference is to use the KT88 size ones with KT120s running in the lower power setting. This yields about 19 watts RMS. But IMO it has the sweetest sound of all versions (I have all to compare it with). The speakers themselves have a number of features that are different from Maggies. The most significant is they are way more efficient. I would not use any of the Oddblocks except the KT120s running at max on the Maggies. If I recall correct they have a sensitivity of about 84 db/w. The Martin Logans are 91.5 db/w. From a loudness vs power input perspective that is a huge difference. Yes the MLs have a woofer. Overall the sound is well balanced and to use an over used term...very fast. Also unforgiving of crappy source material. Being bi-polar the sound comes from the rear as well as the front. This can be an issue in some rooms. Placement is really important as it the reflectivity of the walls, floor and ceiling. Once set up well the sound is stunning. Since I also have numerous other speakers (both huge and little) I find that they do not have the pinpoint presentation that many others do. They do however have a huge sound stage that tend to wrap around the whole room. I really like that aspect. My listening room is modest in size at 12 feet wide, 9 high and 17 deep. The speakers need to be about 3 feet from either side wall and 4 feet from the wall behind them. The listening position is about 10 feet in front of them. I have foam blocks over the fireplace behind the speakers, several wall coverings, a large rug in front of them and a plush couch. I have an additional advantage as the house (now 40 years old) has a "popcorn" ceiling. It came with the radiant heat tapes embedded in it. This tends to cut down the reflections off the ceiling to a slight extent. (see photo). Some of the gear in the photo is a quad of mid sized Oddblocks (with the KT120s) two are for the MLs and two are for the subs in the corners. Electronic crossover is at 60HZ/24 db/oct. The MLs go down well to 40HZ, but I like to shake things up on occasion and huge efficient subs are just the ticket for that. On the shelves are two turntables, one a modded Empire 598 the other a diy direct drive using the motor and control assembly from a Dual 701. The preamp is under the diy one and is a modified Forewatt with a digital front end. Two phono preamps are in use, one above each of the turntables. One is a diy Groove the other a second generation prototype of the Oddwatt commercial version. There is lots of other gear around the room.

Good listening
Bruce
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