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Old 20th October 2009, 07:57 PM   #1
adamus is offline adamus  United Kingdom
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Default first go at design - pp

Hi,

I have built other peoples designs, but want a go myself. I have a basic understanding of the theory, but a lot of it is pieced together.

Basically, will the following design work?

Click the image to open in full size.

The css would be borrowed from morgan jones, the output valves could be css biased ala baby huey.

no feedback shown, but i could work it in.

I am new at this, so constructive criticism is very very welcome. my valve choices are what i have in my box.
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Old 20th October 2009, 08:11 PM   #2
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Go to SY's website and read through his desription of the Heretical pre-amp. Sure, its not at all what you are aiming to build, but it is a grerat insight into a detailed design process. I was just blown away by the new to me yet oh-so-obvious considerations that are set out there. It has completely changed how I think about designing ANYTHING...
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Old 20th October 2009, 08:15 PM   #3
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will do mate, cheers.
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Old 21st October 2009, 12:42 PM   #4
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any glaring errors?

Any tips for bias points of the input and splitter?
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Old 21st October 2009, 12:55 PM   #5
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It would help if you could number the components so that the design could be discussed. Some stuff on there looks not-quite-right, but I don't have you here to point at the screen.
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Old 21st October 2009, 02:14 PM   #6
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I don't understand the use of CCS in the cathode of the power valves...?
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Old 21st October 2009, 02:56 PM   #7
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sy. thanks forthe advice. I will number the components tonight.

the css is just a better auto bias.
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Old 21st October 2009, 06:24 PM   #8
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Here is the number schematic

Click the image to open in full size.
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Old 21st October 2009, 06:32 PM   #9
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Brilliant! Let's start with R11. What's it doing in there? You've got a CCS keeping the two sides of the phase splitter balanced- why not return the grid of the bottom side to the upper grid through a large resistor, then bypass that lower grid to ground? This will give you balance limited only by how well you can match R5 and R6. That also allows you to eliminate C2.

Do you have any philosophical objections to getting rid of R2/C1 and replacing with a diode or LED?

Will the rather high source impedance of the output stage without feedback be a problem with your speakers?

I will not be popular for saying this, but an output stage CCS is not generally a good idea, especially if you're going to clip the amp every once in a while (as we all do, at least all of us who don't have 102dB/1W speakers).
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Old 21st October 2009, 06:48 PM   #10
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Sy, how is this looking. Re led bias for the first stage, i like it and will have a play when buiilding.

Click the image to open in full size.

As for the CSS in the output, I have some bias perfboards that i can take from my baby huey and try. I did try the huey without, and it lost something.

clipping.... not in my flat with my neighbours unfortunately!

Feedback, i will apply some and i have shown how, but just to the first stage. I'll have to keep an eye on oscillations.
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