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Ultra Gain Tube Preamp

Started by Minion, August 05, 2011, 01:31:38 PM

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Minion

This is a schematic of my new tube preamp ..... it"s very high gain and sounds great ... it is simular to most designs but also a bit different .....

I also have a PCB design for this preamp that I will post after I get the build instructions finnished ....

Cheers

J M Fahey

Nice.
Post pictures and MP3 when available.
Congratulations  :tu:

phatt

Nice work,, but I DO urr when I see so many circuits like this that just leave the tone output hanging from the end like that.

The loss is bad enough even when picked up by another stage but left like that you waste a lot of energy.
Remember these ARE passive hi Z tone circuits so they can't drive anything, cept another Very Hi-Z input.
Phil. 

Minion

Even with the tone stack at the end of the circuit the signal is still very very hot ......

phatt

#4
Here is the difference in output.
Green plot is Normal ,, using HiZ buffer.
Yellow trace is running the tone stack into a 10k load,, which is extreme but Could happen and the concept is best avoided especially if it's in a separate unit which might work with some gear but not with others.

In this example,, you are down 30 dB @100 hZ,, ouch!! :o

A buffer guarantees the same performance no matter what you plug into.

you may also come realize that you don't need to use so many gain stages,,,which helps keep the dreaded noise down also.

It's up to you? 8|
Phil.

Minion

Im running my Preamp into a LM3886 with an input impedance of 47k , I have a solid state buffer but I"m not using it because I tried it with the buffer and it really didn"t sound any different accept it was louder with the buffer but It is plenty loud enough allready , so loud that it clips the lm3886 with the Volume barely on ..... 

The circuit will be buffered anyways because I usually have my EQ and a couple pedals running through the FX loop ......

Thanx

mensur

After treble put 470K in series and 47K volume pot, or 1MEG/100K volume, this will tame off the signal and low the impedance.

Minion

Success !!! Ive been stumpted by this really bad hum problem so after a week of thinking on it I realized that I forgot to ground the circuit that runs the channel switching circuit ...
The channel switching circuit uses 2 5v relays to switch the 2 channels and the led indicator lites for each channel and runs off of a 6vac winding of one of the transformers that powers the tubes , it uses a footswitch that connects to the amp via a patch cord .....
After grounding the 6v winding the hum totally dissapears , sounds great and it loud as hell ....

I actually built this amp because the other amp I built died , but I come to realize tonight that it didn"t die at all , it was the 15 band EQ I bought that I used in the FX loop that died ....

go figure , you build an amp and it last longer than the store bought EQ that you bought to use with it ......  :)

J M Fahey

Quote
go figure , you build an amp and it last longer than the store bought (insert electronics guizmo here)  that you bought to use with it ......  Smiley

And what's so surprising about that?  :)  :D  ;D  :lmao:

Congratulations  :tu:

Minion

Here are a couple Pics of them amp .....


joecool85

Why "High" -> "Low" -> "Mid" and not "High" -> "Mid" - "Low" ?  Looks great though, I like the (I'm assuming) aluminum front plate.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Minion

hi , I did it that way because it was just a lot easier to wire up with the pots in that position ..... yes the front plate is aluminium , I got 3 of them at the local metal supermarket for about $12 ......
The rest of the chassis is from a old EQ I found in a junk pile .....

I"m going to redo the magic marker labeling at some point because it takes away from the amps awesomeness .... ;D

I also used some aluminum plate between the Power Transformers and the audio curcuits to shield some of the EM from the power transformers ....

You can"t see them in the picture but there are 3 seperate power transformers , I have a 235v transformer for the Plate supply that has a 6.3v tap that is unused and a 5v tap used for the Relay channel switching , it also has a seperate 12.6v 1A transformer for the Heaters and a seperate 100Va 2 x 18v transformer to run the LM3886 , there is also a 100mA 10H Choke .......
It was a lot of work trying to find away to fit all that stuff inside that Chassis ......

I"m now working on a 6V6 Power amp that I can use with the Line out on this amp to get that pentode tone ..... It"s allready built for the most part , just have to wire it up and find a chassis for it and hope it doesn"t catch fire ......

Cheers

phatt

Hi Minion,
             Mate,, great effort :tu: Just looked at the pics. Wow a lot of work in that one so glad you got it all working.
Forgot the ground ay?  Yep been there a few times. :-[
The ground is always the wire you forget to add :grr

One little thing,,, if I may be allowed?
Do I see Wires passing through holes with no grommets and around sharp metal edges?
can be an issue down the track. :trouble

Cheers, Phil.

Minion

Quote from: phatt on October 19, 2011, 09:07:25 AM
Hi Minion,
             Mate,, great effort :tu: Just looked at the pics. Wow a lot of work in that one so glad you got it all working.
Forgot the ground ay?  Yep been there a few times. :-[
The ground is always the wire you forget to add :grr

One little thing,,, if I may be allowed?
Do I see Wires passing through holes with no grommets and around sharp metal edges?
can be an issue down the track. :trouble

Cheers, Phil.

Thanx for the tip about the holes , there is enough slack on the wires so they hopefully it won"t be rubbing , I also don"t put it on top of my speaker cab because I don"t want to abuse it .... I will put some silicone glue around the holes to stop any rubbing .....

The amp has a sort of old school metal tone but It is hard to get the Clean channel to stay clean and be loud so I"m gona replace the two 12ax7 in the Clean channel with some 12au7 or 12at7 to get a cleaner tone ...... Using the Sonic Maximizer and EQ in the FX loop helps shape the tone quite a bit and makes it a bit more versitile .....

And the chanell switching curcuit works flawlessly , I made the footswitch out of a plastic project enclosure and a heavey duty push button switch and a 1/4 in female jack , it connects to the amp with a regular patch cord .......

It is by far the hardest project I have done which was componded by my total ignorance in Tube theory and my pathetic and dyslexic math skills .......

I will eventually post the PCB artwork , stuffing guide and wiring diagram I just haven"t had the time to finnish the stuffing guide .....

Cheers

tra

Quote from: Minion on October 19, 2011, 07:08:59 PM

I will eventually post the PCB artwork , stuffing guide and wiring diagram I just haven"t had the time to finnish the stuffing guide .....

Cheers

I wait eagerly!  :dbtu: