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Super simple single stage tube preamp
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Author:  mwhouston [ 12 Jun 2011, 18:24 ]
Post subject:  Re: Super simple single stage tube preamp

dtsup1 wrote:
Mark, can you please post the schematic with your modifications, as well as a linear power supply?
I want to build this.

Can't find the cct. on the net so I'll re-draw. The PS is my own design and build but I will draw that too. Just remember this preamp has low gain but good sound.

Author:  Gio [ 12 Jun 2011, 18:47 ]
Post subject:  Re: Super simple single stage tube preamp

mwhouston wrote:
the HT is stated at 300V (I'm using 250V). With the one I'm using Rp=20K the FB R from output cap to grid is 330K and my output cap is 470nf. These are the only differences.

Mark, what tube are you using? With the 6DJ8 family B+ is noted as 150-180V.

Cheers

Author:  mwhouston [ 12 Jun 2011, 18:59 ]
Post subject:  Re: Super simple single stage tube preamp

Nothing that exotic. I have a mix of 12AU7s. one from the Conn organ company which came from a yanky organ, an Australian made Phillips and a Zaerix - English sold but E.German made. All pre-loved with 80% emissions.

Author:  Gio [ 12 Jun 2011, 19:18 ]
Post subject:  Re: Super simple single stage tube preamp

You can probably adjust the resistor values for better performance with the 12AU7. How much gain are you looking for? Also, what will you be driving? This is high output impedance.

Cheers

Author:  mwhouston [ 12 Jun 2011, 19:20 ]
Post subject:  Re: Super simple single stage tube preamp

Enclosure has had the only top coat it will get. With the acid etch primer underneath a second coat is not required. I used Woodlands Grey which is the same on the top and bottom plates of the Silver Dragon. Drying takes days. The light mark on the top is just the light coming through the window, not a bad spray job!!

Attachment:
SSTAmpVss.jpg

Author:  mwhouston [ 12 Jun 2011, 19:26 ]
Post subject:  Re: Super simple single stage tube preamp

Gio wrote:
You can probably adjust the resistor values for better performance with the 12AU7. How much gain are you looking for? Also, what will you be driving? This is high output impedance.

The input is coming out of the preamp section of a surround sound amp center channel and it will feed a 120W Hugh Dean Naksa SS amp. So load should not be an issues.

Author:  dtsup1 [ 12 Jun 2011, 19:38 ]
Post subject:  Re: Super simple single stage tube preamp

I'd do fine even with a gain of 1X as the Elliot P3A amp has sufficient gain to drive the speakers.
I just purchased some new speakers - Mardaunt Short MS45Ti which will be sent today.
These were made in 1987-1989 and use a titanium tweeter and 2X 8inch midbass units. In pristine condition!

Author:  mwhouston [ 12 Jun 2011, 19:44 ]
Post subject:  Re: Super simple single stage tube preamp

dtsup1 wrote:
I'd do fine even with a gain of 1X as the Elliot P3A amp has sufficient gain to drive the speakers.
I just purchased some new speakers - Mardaunt Short MS45Ti which will be sent today.
These were made in 1987-1989 and use a titanium tweeter and 2X 8inch midbass units. In pristine condition!

Got an image

Author:  mwhouston [ 12 Jun 2011, 21:44 ]
Post subject:  Re: Super simple single stage tube preamp

Mistake number 3.

I read 470R as 470K. That was four wrong resistors. All fixed. the preamp is flat from 10Hz to 130Khz and has a gain of 3db. It will swing 11Vpp with a load of 22K with 5.5V in. I will publish the square waves soon.

Author:  mwhouston [ 13 Jun 2011, 01:49 ]
Post subject:  Re: Super simple single stage tube preamp

Take a look at the SQR wave shots. All excellent. The bottom SQR wave is from the preamp. See in the 10khz shot even the oscillator is not producing a perfect signal. With the correct resistors now in the preamp has plenty of gain, more than enough to drive my 3W SET into clipping. After some further listening time I now know I have to make one for myself. Bass, mids and highs all excellent.

Attachment:
100hzpng.png
Attachment:
1000hz.png
Attachment:
10khz.png

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