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4S Universal Tube Preamp Project (12A*7)
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628
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Author:  Suncalc [ 24 Feb 2018, 16:29 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

oloppolo wrote:
Can i try with 1uF?
Yes. This will improve the low end frequency response at the expense of bias recovery time. Be careful you don't overdrive whatever you driving and you should be fine.

Author:  oloppolo [ 12 Mar 2018, 15:36 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I have the best sound with 12at7 CVC valve (Mullard?) and amplifier F5 Pass.
I tried Rk at 1k, 1.5k, 1.2k. The best is with "original" 1.2k.

Author:  mwhouston [ 12 Mar 2018, 16:29 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Only over the last few years have I been using the 12AT7s but found I really like the sound. Originally 12AU7s were my preferred.

Author:  Suncalc [ 12 Mar 2018, 18:51 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

oloppolo wrote:
I tried Rk at 1k, 1.5k, 1.2k. The best is with "original" 1.2k.
Yeah, well I did put a little thought into the bias points. http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628&start=3

Author:  mwhouston [ 25 Mar 2018, 00:27 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Would someone please send me a link to the 6SN7 single stage preamp which Matt designed. I have lost my copy of the schematic. I'm sure it was on this thread.

Author:  Suncalc [ 25 Mar 2018, 21:42 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Mark;

The reason you couldn't find that post is because it's in the "Super simple single stage tube preamp" thread. Here is the link to that particular post:

http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3266&start=99

And for good measure, here is the schematic again:
Attachment:
4S-6SN7%20Circuit.jpg

Hope this helps. :)

Author:  mwhouston [ 25 Mar 2018, 22:46 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

No wonder I couldn't find it, thanks. What would total current draw be? I have a Hammond tranni good for 40mA total. Would this suffice?

Thanks.

Author:  mwhouston [ 25 Mar 2018, 22:54 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I should add I have another compact Cypress base and a 50 Year Treasure 6SN7. I was thinking a single stage 6SN7 preamp with Sophia Princess giant rec. tube. I have a slightly bigger tranni if this one is no good but would like to use it up.

Author:  mwhouston [ 26 Mar 2018, 02:24 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Just saw the 3.3V across Rk @ 1K. Therefore 3.3mA per channel. So the 40mA tranni will handle this easy.

Author:  john55 [ 29 Apr 2018, 10:51 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I'm using a Hifiberry DAC+ pro (2v rms out, 1K ohms approx output impedance) into a subwoofer plate amp (line in, input impedance 10K ohms) then signal passes through plate amp into 4S preamp and then into Lacewood V2. I want to attenuate the DAC output down to 1v rms. From what I can gather the 4S has a really high input impedance so no problem using say a 47K and 22K resistor for a voltage divider on the output of the DAC (these are the values suggested by Hifiberry), but with the plate amp input impedance at 10K I'm going to be way out (my understanding is I should be going for a minimum 1:10 ratio, output to input impedance). Can I use smaller resistors?, 1K and 470R for example. Will this cause me problems with the 4S preamp? Can someone advise me here. My reason for wanting to lower the DAC output is I THINK I'm clipping with the plate amp.

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