Bass guitar preamp

zafira1981 · 24th July 2006, 08:39 PM

Hi!!!!

I'm looking for a tube bass-preamp schematic. Does anyone have a circuit ? I searched for half hour and didn't find anything.

Thanks!!!

Mikael Abdellah · 24th July 2006, 11:07 PM

I am searching for info on the exact same subject. So far I haven't found much. Im looking to build a VERY simple preamp, preferably with tubes.

Mikael Abdellah · 24th July 2006, 11:30 PM

Why don't we try and figure something out together? The only thing I've come up with so far is a 6N1P and BUF634. I can't find much info on signal levels and such. Do you have any idea what the normal signal level from a passive bass pickup is? The gain of the 6N1P is 33, and from what I can figure out that seem to be roughly 15dB.

zafira1981 · 25th July 2006, 02:52 AM

Hi!!!!

I dont know how much I can help to design a tube amp. What I can offer is some tube manuals/datasheets, my father used to build tubes stuff. But he dont know about hi-fi, only radio amps......

I Think that I have lot of 12ax7 tubes for the project.

I will use an active bass guitar so I need both inputs. I dont know how to design a preamp for bass, I dont know nothing about impedances of bass pickups.

If there is anything i can do, tell me. I also have some tube manuals, schematics, but they're like 30 years old.

thanks!!!!

Mikael Abdellah · 25th July 2006, 07:32 AM

Just tell me what kind of features you want. Im going to buy my first bass guitar in the next 2 weeks. I have never played any kind of string instrument before, so you probably have a lot of things to teach me about what kind of effects and tone controllers would be nice to have. My first idea was to just build a small gain stage with a low mu (gain) tube and just a buffer but it looks like the signal might me a bit high to start with. I was aiming for just a bit over normal home stereo equipment line level but assuming closer to 2-300mV from the guitar Im afraid i will blow up the opamp or buffer on the output. I cant do any measurements before I get my bass.

Jarno · 25th July 2006, 07:44 AM

You could try to build the one in the picture. It's a very simple schematic and sounds very good indeed, I recently built one myself. The original Alembic unit has two identical channels (which are modelled after Blackfaced Fender amps). I built a preamp with only one channel, and added "bass-shift" and "treble-shift" functions like present in the Mesa Boogie Bass400. I have built that preamp as well (a long time ago), and didn't like it much.

I did redesign the powersupply with DC heater supply, and B+ with a overkill amount of capacitance (had a bunch of caps lying around).

The preamp is easy to build and sounds super, I would say a fine candidate for a first project (if you treat the HT with the appropriate amount of caution).

Jarno · 25th July 2006, 07:47 AM

And this is the Mesa Boogie Bass 400 schematic:

Mikael Abdellah · 25th July 2006, 08:13 AM

Looks nice and simple but since you use both halfes of the 12AX7, wont that produce way too much gain? Have you measured you "maximum" output signal voltage?

Jarno · 25th July 2006, 08:36 AM

Hello Mikael,

I am not much of an EE guy (rather ME) so I didn't measure anything, but this schematic is built by Alembic so I just considered it a finished design. I did hear someone say there is a mistake in the schematic somewhere.
But you are right, when using my (active) bass, the output is quite "hot", I am thinking of adding a 6db pad.

zafira1981 · 25th July 2006, 01:07 PM

thank you all for the replies !!! interesting schematics.

I think I will build the preamp stage of this one:

As a power amplifier, I have a LM3886 gainclone,... do you think that I can use the output of the master pot as output to feed the gainclone?

thanks!!!

24th July 2006, 08:39 PM	#1
zafira1981 diyAudio Member Join Date: Jan 2005 Location: Argentina	Bass guitar preamp Hi!!!! I'm looking for a tube bass-preamp schematic. Does anyone have a circuit ? I searched for half hour and didn't find anything. Thanks!!!

25th July 2006, 08:36 AM	#9
Jarno diyAudio Member Join Date: Sep 2002 Location: Rosmalen, The Netherlands	Hello Mikael, I am not much of an EE guy (rather ME) so I didn't measure anything, but this schematic is built by Alembic so I just considered it a finished design. I did hear someone say there is a mistake in the schematic somewhere. But you are right, when using my (active) bass, the output is quite "hot", I am thinking of adding a 6db pad. __________________ Oemptempa petoempetapap

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24th July 2006, 11:07 PM	#2
Mikael Abdellah diyAudio Member Join Date: Jan 2003 Location: Sweden	I am searching for info on the exact same subject. So far I haven't found much. Im looking to build a VERY simple preamp, preferably with tubes.

24th July 2006, 11:30 PM	#3
Mikael Abdellah diyAudio Member Join Date: Jan 2003 Location: Sweden	Why don't we try and figure something out together? The only thing I've come up with so far is a 6N1P and BUF634. I can't find much info on signal levels and such. Do you have any idea what the normal signal level from a passive bass pickup is? The gain of the 6N1P is 33, and from what I can figure out that seem to be roughly 15dB.

25th July 2006, 02:52 AM	#4
zafira1981 diyAudio Member Join Date: Jan 2005 Location: Argentina	Hi!!!! I dont know how much I can help to design a tube amp. What I can offer is some tube manuals/datasheets, my father used to build tubes stuff. But he dont know about hi-fi, only radio amps...... I Think that I have lot of 12ax7 tubes for the project. I will use an active bass guitar so I need both inputs. I dont know how to design a preamp for bass, I dont know nothing about impedances of bass pickups. If there is anything i can do, tell me. I also have some tube manuals, schematics, but they're like 30 years old. thanks!!!!

25th July 2006, 07:32 AM	#5
Mikael Abdellah diyAudio Member Join Date: Jan 2003 Location: Sweden	Just tell me what kind of features you want. Im going to buy my first bass guitar in the next 2 weeks. I have never played any kind of string instrument before, so you probably have a lot of things to teach me about what kind of effects and tone controllers would be nice to have. My first idea was to just build a small gain stage with a low mu (gain) tube and just a buffer but it looks like the signal might me a bit high to start with. I was aiming for just a bit over normal home stereo equipment line level but assuming closer to 2-300mV from the guitar Im afraid i will blow up the opamp or buffer on the output. I cant do any measurements before I get my bass.

25th July 2006, 08:13 AM	#8
Mikael Abdellah diyAudio Member Join Date: Jan 2003 Location: Sweden	Looks nice and simple but since you use both halfes of the 12AX7, wont that produce way too much gain? Have you measured you "maximum" output signal voltage?

25th July 2006, 01:07 PM	#10
zafira1981 diyAudio Member Join Date: Jan 2005 Location: Argentina	thank you all for the replies !!! interesting schematics. I think I will build the preamp stage of this one: As a power amplifier, I have a LM3886 gainclone,... do you think that I can use the output of the master pot as output to feed the gainclone? thanks!!!