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PostPosted: 13 Jun 2018, 04:12 
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Joined: 03 Feb 2018, 00:47
Posts: 35
Location: Brisbane, Australia
I wish I could Poty, but I printed it out at work and failed to send the url to myself. The text says "Recommended changes to the power supply for large Oddwatt amplifiers (EL34 and larger) to use 300VDC on the SRPP Driver tube".
Dated November 12, 2013.

Hopefully somebody can provide the link. It regulates the 300V to the drivers and regulates the "lift voltage" for the heaters using LR8 regulators.


Edit: Found it!!!

http://diyaudioprojects.com/Forum/download/file.php?id=5995&mode=view


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PostPosted: 13 Jun 2018, 06:29 
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Joined: 24 Oct 2010, 07:05
Posts: 270
Well, it seems the schematic is one of the early experiments with the LR8 and related to the EL34 version. It's only part of the schematic and only the LR8 parts supposed to be used without modifications in all tube's versions.
I'd use unified schematic presented earlier.
Specifically:
- The resistor (its value) depends on the B+ voltage for the power stage. Different tubes have different B+ in the schematic, so there is a way to drop the voltage to appropriate level. So, the bigger the B+ voltage of the power stages - the bigger the value of the resistor.
- The capacitor: there are actually two capacitors. First - is for stability of the LR8 and it could be as low as 1u. Second - for local power supply bypass and Bruce recommends minimum 1uF (I'd use 3.3u or more). It is convenient to use an electrolytics for the first capacitor, but due to their (electrolytics) bigger ESR it is advisable to use much bigger capacitance - 47u or even 100u. The second capacitor for the sound perspective has to be film. To be short: the circuit will work with both "approaches".


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PostPosted: 13 Jun 2018, 11:55 
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Joined: 18 Jun 2016, 06:52
Posts: 28
Finished. KT77s heated AC, 6SL7s DC. The 12V PSU still needs some fine tuning (optimum dropper resistor values). The sound is positively rich. My layout requires a lot of wiring. It's probably more practical to put the balancing pots and test points on the top plate, but aesthetically less pleasing I think. Comments and criticisms are welcome.

Jan


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PostPosted: 14 Jun 2018, 18:11 
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Joined: 04 Jun 2008, 20:59
Posts: 3794
Location: Arizona, USA
Hi, Glad to hear it works well. I use that style case for some projects. Hard to beat the price.... shipping is another story though.

Good listening
Bruce

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PostPosted: 15 Jun 2018, 08:45 
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Joined: 29 Jun 2016, 15:59
Posts: 41
Hi.

Has anybody added an LED to show when the Main B+ kicks-in for the Oddblock?
May 6, 2015 unified schematic.
If so, how?

Thanks,

Danny


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PostPosted: 15 Jun 2018, 10:13 
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Joined: 24 Oct 2010, 07:05
Posts: 270
Danny, several posts earlier there were answers already, but:
1. Connect a LED+resistor to the low voltage energizing circuit of a relay which switches B+.
2. A resistor from the B+ to the LED to the ground.
3. A CCS from the B+ to the LED to the ground.
4. (if there is enough voltage) Serially connected LED || resistor in the B+ rail at any voltage dropping point.


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PostPosted: 15 Jun 2018, 12:28 
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Joined: 04 Jun 2008, 20:59
Posts: 3794
Location: Arizona, USA
Hi Everyone, The Oddwatt amps have evolved over time and I was asked recently for the latest schematics so here they are. They show the latest changes, some are very minor, but each one has what I consider some benefit. Older amps can be retrofitted with the changes fairly easily.

If you use the KT120 version the PS is like the unified version, but no recent changes have been made to the main circuit (no sense messing with something that is OK as is)

Good listening
Bruce
Attachment:
Unified Oddblock Amplifier PS June 2018.jpg
Attachment:
My Odd-Blocks Main Circuit 6-2018.jpg


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PostPosted: 27 Jun 2018, 14:28 
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Joined: 18 Jun 2016, 06:52
Posts: 28
The new schematics made an upgrade necessary, only a few days after I finished the amp. What is the purpose of the 1uF poly on the 12sl7's anode, as there already is a 1uF poly in the PSU on the other end of the anode wire? I used the same Wima for the anode as in the PSU, but I wonder if a Solen would be an improvement.

Jan


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PostPosted: 27 Jun 2018, 15:56 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi the reason for two caps is that one needs to be really close to the LR8 (under an inch is best) and the one on the tube anode is therr for extra filtering and to provide a low impedance path return path for audio. If you have the LR8 close to the tube a single cap (I would use a 2 uf) would be OK.

Good listening
Bruce

EDIT: IMO for this use a WIMA, Solen or many other brands would be OK. I have used audio grade caps there but it doesn't seem to make any sonic difference. Jantzen Audio Cross caps are OK and are small if you want to go that route.

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PostPosted: 27 Jun 2018, 16:14 
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Joined: 18 Jun 2016, 06:52
Posts: 28
Thanks Bruce. I have used Cross Caps before and I think they are great at the price. Amazing how the LR8s improve articulation. I have had them in my Oddwatt monoblocks right from the start, but I didn't realise they had such a major impact on the sound quality.


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