Instrument tube / valve preamp

[Miso225]

Hello all!

I am browsing net for a long time now - looking for a good tube preamplifier that could be used for music instruments. I have managed to find very few at all, even less usable and none in final stage. I am just starting to work around tubes so the more details the better.

This one seems to be the best so far:

A Studio Preamplifier

Unfortunately as I have found out on this forum Mr. Nachbaur died...

I would like to know Your opinion about his setup and answers to few questions:

- what is NE2 (L1 - 3) parts? (probably stupid question but I am used to different type of schematics)
- how to tweak power supply? it is stereo so how to make it just fit for this preamp?

I am commited to build this preamp, but I need some help. In return I can post details from construction, PCB designs and measurements.

Thanks!

 

[Arnulf]

NE-2 is a neon lamp and it's the usual neon lamp symbol. You can use any type with similar holding voltage.

 

[rongon]

What type(s) of instrument(s) are you planning to use with this preamp? Electric guitar? If electric guitar, will it be for clean style (jazz, country, etc.) or distorted (rock, heavy metal)? Bass guitar? Bass viol w/ piezo pickup? Acoustic guitar w/ piezo pickup? Electronic keyboards? Other?

--

 

[Miso225]

Thanks for such a quick reply!

OK, about that neon lamp, what is holding voltage in this case?

I would like to use it for electric bass guitar and/or acoustic guitar with piezo pickup. I thought it is universal studio preamp but I understand there will be differences in input stage due to impedance. That rises question how to calculate imput impedance and how to adjust it for different use? And is the circuit capable of working with high impedance input such as piezo and with low as well? I mean not in same time I could build it with two different input stages and install switch to select between them...? Like on guitar amps where You have HI and LO input option...

 

[Ian444]

Most tubes have a fairly high input impedance so a low or high impedance guitar output should work fine. I think you are making this difficult for yourself. A very simple circuit copied from a guitar amp clean channel should do the job. One 12AX7, some pots for the tone and volume controls, a handful of resistors and caps, and a small high voltage power supply to suit, job done. For example, the input channel of an old Fender Bassman or Twin Reverb might be a good place to start, just to get the idea. You could even build it into a box like this, which I did 15 or 20 years ago. Yes it still works and last got used 3 months ago.

 

[Arnulf]

OK, about that neon lamp, what is holding voltage in this case?

My reference says "> 50V" for replacement of most NE-2 (3AD) types and "59V" for another. These are very imprecise devices anyway (they can easily differ by 20% among same model of devices) so any shoudl do unless you find some extremely exotic examples filled with some sort of gas mixture or completely different gas.

 

[Miso225]

Thanks Ian I will look at those circuits You suggested. If You have any links where I can find schematics or PCBs / parts list please let me know. But I think I will listen to You and start with very simple tube build as it is mi first and then move to more complicated one...

 

[Ian444]

This is a schematic of a Fender preamp I used for many years. The power supply was my own using 2 small common cheap transformers. If you search Google for "twin reverb schematic" you will find where the design came from, it is quite old now but still good, and once you have built something it is easy to try different circuits in it if you want to experiment. Most of the parts can be mounted on the tone control pots lugs. It will sound very good.

One thing to be careful of, a tube guitar preamp connected to a mixing desk or recorder may or may not sound good, in order to get a good guitar sound you still need to run the preamp into a poweramp into a guitar cabinet, and use a mic on the cabinet.