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4S Universal Tube Preamp Project (12A*7)
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Author:  Suncalc [ 26 Jan 2017, 17:50 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

jdrouin wrote:
I'm not sure about input and cable capacitance, as I haven't measured them and don't have the tools for it, but I think they're low. I'm going to make a pair of short interconnects (about 1 foot) between the 4S and power amp, using solid 18awg copper wires. There are no capacitors in the power amp between the input jacks and input tubes (5842).
I looked at the schematic and you should be ok with the volume control on the output. This is assuming that the volume control on the TSE schematic is either left at full volume or omitted. So long as the CM plus cable capacitance is less than 90µµf (which it really should be) the lowest your high frequency rolloff will get is 25kHz.

Author:  jdrouin [ 26 Jan 2017, 18:05 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Suncalc wrote:
jdrouin wrote:
I'm not sure about input and cable capacitance, as I haven't measured them and don't have the tools for it, but I think they're low. I'm going to make a pair of short interconnects (about 1 foot) between the 4S and power amp, using solid 18awg copper wires. There are no capacitors in the power amp between the input jacks and input tubes (5842).
I looked at the schematic and you should be ok with the volume control on the output. This is assuming that the volume control on the TSE schematic is either left at full volume or omitted. So long as the CM plus cable capacitance is less than 90µµf (which it really should be) the lowest your high frequency rolloff will get is 25kHz.


Thanks very much. I was wondering what the threshold for low CM & cable capacitance is, so this information is helpful. I've got to do some reading on that for sure, as it's not something I'd even considered before.

Yes, I'm planning to remove the existing volume control altogether. For the next project after the 4S, I want to build a pair of "classic" 6SN7 --> 300B mono blocks (i.e. Fi Primer or JE Labs 300B), and according to the datasheets the 6SN7 has much lower grid to plate, grid to cathode and heater, and plate to cathode and heater capacitances than the 5842. So unless I'm mistaken, the 4S should be OK in front of those amps too.

Will either start a build thread or post pics of the finished product. Thanks again for the helpful input.

Author:  invaderzim [ 26 Jan 2017, 18:08 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

mwhouston wrote:
invaderzim wrote:
I'm looking at using this preamp with a SS one that lists 10k for input impedance. It is the amp camp amp: http://www.firstwatt.com/pdf/art_amp_camp_1.pdf

are there any issues I should be aware of or tweaks I should make?

Thanks,
Trevor

Not amp camp and it will not work well with your SS power amp. The input impeadance is too low. There is another design of a two stage version where the second stage is a cathode follower. This will work much better. Or do as I do, add a Pass B1 to the output of any 4S build.



Thanks, Someday I'll learn to ask the questions before I order parts.....

If I add the Pass B1 buffer what do I put in place of the volume control on it since I already have one on the 4S?

Author:  mwhouston [ 26 Jan 2017, 23:13 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I have to pot between the 4S and the B1.

Author:  davesatu [ 10 Feb 2017, 22:33 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Wanted to write and say thank you to all those finishing with Matt for developing this project. It has proved to be a winner sounding wonderful from first time switched on. My base line pre was by B.Rozenblit from a Glass Audio magazine article way back in 1991. With even less circuitry this new one sounds as good and probably better. Have listened with 2A3,45,300B and Matt’s 6EM7 SET’s plus a 6V6 push pull. All great. Pics here and yes it’s not the best looking but was built except the transformer with parts on hand. The case is a Retex from Spain 9x7x3 inches. Only concern was using a plastic ABS case but no problem as it is dead quiet. I always switch power amps from the connected pre hence the white power outlet.

Wiring preamp circuits point to point without hum can be difficult. Using a driver PCB mounts everything including Alps blue pot and balance control with it’s circuitry. I need balance as all recordings are different and my speaker placement favours one side. Space was made for some Russian PIO coupling caps which make a huge difference. You can now fit anything.

PCB’s can make placement of critical components such as grid resistors easy and needed areas kept apart. I was thinking of having this board made in China. Five copies for about USD44 including HK Post to me is the go. Perhaps if Matt is happy with that approach we could fine tune it and provide PCB’s at cost to those who show interest. Happy to help.

Thanks Matt

Author:  gonzalo guerrero [ 29 Mar 2017, 01:08 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

can i use a 6np1 in this preamp?

Author:  mwhouston [ 29 Mar 2017, 02:44 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

gonzalo guerrero wrote:
can i use a 6np1 in this preamp?


I would say no. But there are/is a schematic for a 6N1P preamp. I hope to build one.

Author:  Chris65 [ 29 Mar 2017, 06:29 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

gonzalo guerrero wrote:
can i use a 6np1 in this preamp?

6N2P can be used with appropriate heater wiring.

Author:  Alex Q [ 17 May 2017, 14:44 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Hi everyone,
I have a spare 100K ALPS Blue Velvet POT can i used this for the 4S,Can i used 6CG7 for this preamp?
Thanks!

Alex

Author:  Suncalc [ 17 May 2017, 17:40 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Alex Q wrote:
I have a spare 100K ALPS Blue Velvet POT can i used this for the 4S
Unfortunately, 100kΩ is too small to use in this design as is. However, if you replace the 250kΩ pot in the design with just a 250kΩ resistor, you can put the 100kΩ pot on the front end and it will work fine.
Alex Q wrote:
Can i used 6CG7 for this preamp?
The reason for this amp is to allow the use of a series of tubes. However, the 6CG7 (6SN7) is a different beast. Here is a design for a 6CG7/6SN7 version which, coincidentally, will also make use of your 100kΩ Alps potentiometer.

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

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