DIY Audio Projects Forum
http://diyaudioprojects.com/Forum/

4S Universal Tube Preamp Project (12A*7)
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628
Page 26 of 40

Author:  Chris65 [ 24 Sep 2016, 19:25 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

My second version of the 4S. After some discussion with Matt, to reduce gain the volume pot (50K) is on the input with 250kΩ resistors. Fitted with 2 inputs, switch for selecting heaters for 12A** & 6A** tubes and uses an octal rectifier, either 6X5GT, 5852, 6AX5GT or with adapters 7Z4 or 6BY5GA.

More volume control range now, running from around 10 o'clock to 2 o'clock at average listening levels. More depth & detail in the music too, can pick out those little details which were a bit veiled in the 1st version.

Author:  mwhouston [ 24 Sep 2016, 21:29 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Looks neat.

Author:  Danielk [ 27 Nov 2016, 07:20 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Hi, i built this preamp exactly as shown and it sounds great. One problem though, i tried about 10 12a.7 tubes, and every time the same channel is much louder then the other. Am i missing something?

Thanks,
Daniel

Author:  Gio [ 28 Nov 2016, 19:23 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

If the problem is consistently in the same channel, I would suspect a passive part. Check the resistors, but your input potentiometer is the more likely source.

Author:  mwhouston [ 28 Nov 2016, 20:31 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I've even miss-read a meter reading once and mistook 2.7K for 27K! Fortunately it was obvious when I played the unit. It just sounded wrong.

Author:  Aazero [ 20 Dec 2016, 19:46 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I have built this unit and it sounds awesome!! I'm not an expert but I have built a few things. Just wonder what kind of mods could be done to make this work for a phono preamp?

Author:  mwhouston [ 24 Dec 2016, 16:17 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Aazero wrote:
I have built this unit and it sounds awesome!! I'm not an expert but I have built a few things. Just wonder what kind of mods could be done to make this work for a phono preamp?

There are a number of phono preamp cct. around. I'd follow them. I've built a number of tube phono preamps. Apart from some more caps and generally two stages there is not much more in it.

Merry Xmas.

Author:  Bonsaimaster [ 31 Dec 2016, 02:20 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Quote:
After some discussion with Matt, to reduce gain the volume pot (50K) is on the input with 250kΩ resistors.

Do you have a schematic or drawing for the volume on the input and the 250K resistors?

Thanks
Bonsaimaster

Author:  Chris65 [ 31 Dec 2016, 08:01 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Sure, like this. R4 is the 250KΩ resistor & R3 is a 50KΩ potentiometer. R5 is also 250KΩ.
Attachment:
Revised 4S Pot Input.jpg

Author:  franck.forster [ 03 Jan 2017, 02:44 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Hello, This look like a very nice project, I am new to tube building and to Australia, I am interested in building the 4S any suggestion for a good part supplier in Australia, mainly for transformer.

Page 26 of 40 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/