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

4S Tube Preamp with 12AU7 Cathode-Follower Output Stage
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=5186
Page 8 of 9

Author:  Gab [ 04 Dec 2018, 08:19 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

What kind of resistor value have you used on the heater circuit ? The original 4S power supply diagram uses two 100R between the heaters and the ground, but the cathode follower adds two more heaters. Does it change the values ?

Author:  tizman [ 04 Dec 2018, 13:28 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Those two one 100 Ohm resistors are there between each leg of the heater supply and ground in order to create a pseudo centre tap. They don’t change if you add more tubes to the heater circuit. Just use the same value.

Author:  tizman [ 04 Dec 2018, 13:36 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Gab: Do use a bigger enclosure than I did (or smaller capacitors!). It’s best to have more room between the parts of the circuit in order to avoid oscillation by keeping a reasonable gap between components. I still haven’t corrected my hiss issue, although it is greatly reduced, despite the grid stoppers I added. Also, I probably have too much gain. You could also build a cathode ffollower without the gain stage if you really don’t need the gain and just need the buffer.

Author:  Gab [ 04 Dec 2018, 16:36 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

tizman wrote:
Gab: Do use a bigger enclosure than I did (or smaller capacitors!). It’s best to have more room between the parts of the circuit in order to avoid oscillation by keeping a reasonable gap between components. I still haven’t corrected my hiss issue, although it is greatly reduced, despite the grid stoppers I added. Also, I probably have too much gain. You could also build a cathode ffollower without the gain stage if you really don’t need the gain and just need the buffer.


I already built my 4S in the enclosure that I had at the time of my last comment. It is roomier than yours though. You can see what it looks like in my project tread
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=6392

Author:  tizman [ 04 Dec 2018, 20:36 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Looks great. Very nice job. Mine looked pretty good, but ended up being pretty useless, as all my DIY amps have preamp sections and volume pots, and the 4S doesn’t work with either of the SS amps I have because of high output impedance. Adding the cathode follower made it too noisy to use at all in my application. I’ll probably strip it for parts at some point. Also, there is very little action or movement in this thread, so support is going to be minimal. If I were you, and I had an operational 4S that you are happy with, I would build a seperate buffer so it doesn’t mess up the perfectly good preamp that you have. I think that for me, the high sensitivity of my speakers was the biggest problem. That and a too tight chassis. Also, fewer stages are always better. That is always true in my experience.

Author:  eldarvanyar [ 18 Jan 2019, 09:40 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

I have a Quad 606 Power Amp which is Solid State.

Input Sensitivity: 500mV
Input Impedence: 20Kohm

Can you please tell me what I would need to do, caps spec etc to make it work with it?

Also is there any advantage or disadvantage in build the 4S and building the CF output stage separately?

Thanks

Author:  ILoveHiFi [ 19 Jan 2019, 13:38 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

eldarvanyar wrote:
I have a Quad 606 Power Amp which is Solid State.

Input Sensitivity: 500mV
Input Impedence: 20Kohm

Can you please tell me what I would need to do, caps spec etc to make it work with it?

Also is there any advantage or disadvantage in build the 4S and building the CF output stage separately?

Thanks

Output cap of 1uF for cut off at 8hZ, 2.2uF for cut off at 3.6hZ nice and low which I recomend
https://www.electronicproducts.com/RC_F ... lator.aspx

The output cap needs to take b+ of the schematic and using geniune metalised polypropene will maximize sound quality.
Olny advantage in bujlding seperatly is can use for diffrent projects, IMO no one wants to build a cf stage seperatly, with more length wire and extra chassis your picking up more noise and wasting allot of not needed money.
CF stage is easy dosen't take up much space if you want to put one just for every project.

Author:  ILoveHiFi [ 20 Jan 2019, 05:53 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Perosnall practicall listening and scope testing shows that if you like low and you want to get the best low always have to have cut off freq at 5hz or lower, cutting off at 10hz will chopp small ammounts of lows off.

Author:  eldarvanyar [ 25 Jan 2019, 05:37 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

Sorry to ask this,
would it be possible to draw up the complete circuit of the 4S with this included in the diagram for us newbies and list extra required components to complete the build?

Thanks

Author:  Suncalc [ 26 Jan 2019, 12:47 ]
Post subject:  Re: 4S Tube Preamp with 12AU7 Cathode-Follower Output Stage

eldarvanyar wrote:
would it be possible to draw up the complete circuit of the 4S with this included in the diagram for us newbies and list extra required components to complete the build?
The single channel schematic is shown in the second post in this thread (repeated below).
Attachment:
4S-Buffer Preamp.jpg
The power supply is from the original 4S project page linked here: http://diyaudioprojects.com/Tubes/Universal-Tube-Preamplifier/.You need the resistors shown on the schematic and you need to choose an output coupling cap based on what type of amp you intend to drive. You need to build one power supply and two signal chains for a stereo preamp.

Does this help?

Page 8 of 9 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/