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PostPosted: 29 Jul 2011, 13:00 
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I was considering the fact that there was a cap. If it was possible to run the amp on bipolar supply voltages that cap could possibly be eliminated.

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PostPosted: 29 Jul 2011, 17:32 
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I have thought of putting this phono preamp and one of my single stage tube preamps in the one case. Cuts down on one set of inter-connects.

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Projects: "Precision" - 300W Class AB Holton power amp | "retro2308" - chip based headphone amp | ”Calibre 834” - tube phono MM preamp |


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PostPosted: 01 Aug 2011, 06:11 
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BLIN!!!! If I read between the lines I notice that the amp must run on 24V. Does that mean I have to scrap my electric screwdriver (where I am using another 10 1,2V-cells). However the cells I am using are fairly large (3300mAh) - maybe that's for a lifetime.
Another problem is how to charge a 24V pack, but asome intelligent wiring using a 2-way 2-pole switch solves that.

I have ordered components and will try to build something quickly - pics and story to follow.

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PostPosted: 01 Aug 2011, 07:11 
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Look forward to it.

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PostPosted: 06 Aug 2011, 11:29 
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Assembled very quickly an amp for myself. Still waiting for a bunch of NiMH cells and haven't really decided how to arrange the charging of the cells and possible an option to run on an external power source.
Anyway, here's the pics:
The board resting in the chassis:
Image

Backside. The white packing material symbolises the batteri packs, 10 cells each. Plenty of room.
Image

Looking in. Think I will have the electrolytics lying down - they aren't solder in place yet.
Image

The board. Components solder in place like on the schematic.
Image

Errr, well ...
Image

The box is approx 6" by 5 3/4" by 1 1/2". No front nor back panels came with the (surplus) box, but I will fix that on Monday (back to work).
Image

Components are standard 1/2 and 0,6W MOX and polystyrene caps. I could have kept the component cost below $15 but I had to make the purchase at a somewhat more expensive shop to get the odd resistor values and paid a 4 times higher price for the resistors. Made a mistake; missed the 1nF cap, order a 10nF :blush: . I think I have a box of odd caps but everything is stored away. Gotta make a new purchase but I need a "complicated" switch for the battery and a DC-inlet.

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PostPosted: 07 Aug 2011, 16:04 
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I have to make small alterations to the schematic to get rid of a substantial amount of distortion, especially at higher frequencies.
Change R5 to 30K
Change C1 to 82n // 8n2 and R11 to 3K6
Change C2 and C3 to 27n // 2n2 and hook them up in series with an R of 110R

But first I will run the original design and later fix according to my calculations.

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PostPosted: 12 Aug 2011, 09:25 
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Magnus, your build looks very nice.

I like the enclosure very much.

I would also like to give a try on this preamp.

But i´d like to go with PCB, so before I start messing around with software, I wonder if anybody has the PCB print?

I have already all components.


Cheers!


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PostPosted: 12 Aug 2011, 09:46 
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HT: with a little effort you do not need a PCB. Try a long tag strip. It may even sound better.

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PostPosted: 12 Aug 2011, 10:20 
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I swapped some old PC stuff for the box with other stuff and I feared it would never come to use as I never will stuff a 10W SE-amp into it ...
When deciding for the experimental board I was considering using other components then Boozhound's and I got it that the pCB wasn't available separately. Now I am soldering all the batteries together and thinking how to secrure them in the box.

I found this thred on DIYAudio: http://www.diyaudio.com/forums/analogue-source/129126-simplistic-njfet-riaa.html

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PostPosted: 13 Aug 2011, 04:15 
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Thanks for the replies!

I´m going to give it a try on a universal board :)

Another thing... How much current does the pre-amp draw?


Cheers!


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