FET-2B Bass Preamp, my first "design"

[nego_veio]

oh, ok. There is an (already reported) error in the Guero's layout, the 25n cap should be 2n5. My mistake. Now they are basically the same tonestack, but the Guero one is rescaled to try to lower the noise. Any report if this was sucessful?

[fatfoohy]

If anybody wants it, i just drew up a schematic using this altered tonestack, but using 12au7s instead of jfets, im probably gonna start a new thread once i get the schematic up just to get check it out, it runs off of a nine volt power supply, but i bumbed it up to run the heater at 12 volts, and then the plates at 41, hopefully there's nothing wrong with the schematic, i'll post it around 4, im at school right now

[Jarno]

The F2b works great for bass, but the schematic in there is that of a blackfaced dual showman amp, so not specifically a bass amp. I've built a pimped version of the F2b and it sounds awesome, it's my main bass preamp. I've also built the Fet2b, and didn't like it for bass, but it's probably good for guitar if you're looking for a clean preamp.

[Brymus]

Yeah there are clones of the original F2B here in this forum and elsewhere on the web.
the reported (I have never played one) perks of the F2B was the two channels which were identical but could be run in series for OD and the fact that the plates of the 12AX7s were run at 300V,giving it alot of headroom and punchy tone when used for bass.
If you search the Alembic site there was some good info over there on it (at least when I was going to build one)
And I think DIYaudio had a couple of threads dedicated to the F2B as well.

I think its great you guys are offering so many varients based on the original, FET emulators are great IMO and so are low voltage tube projects.
I hope (really want) to see schematics,layouts,pics and sound clips of these completed builds guys.

[fatfoohy]

http://viewmorepics.myspace.com/index.cfm?fuseaction=user.editAlbumPhoto&albumID=1723865&imageID=29146739
Here is my 12au7 F-2B schematic, if anybody has any interests or issues with the circuit, i started a thread right here  http://www.diystompboxes.com/smfforum/index.php?topic=84932.0

[nego_veio]

Jarno, what you changed in the f-2b to pimp it up for bass?

[meffcio]

Anyone suggest a good 5-band tonestack for that thing to use with bass guitar? I want to build a simple preamp for my friend bassist, and I don't know what thing is better for bass guitar - this, or the FET Twin?

[Jberg]

A few questions from a noob.  First, what are the trim pots for instead of a fixed resistor and where should they be set?  Second, will this drive a speaker by itself? If so, what should the Ohm and watt ratings on the speaker be? 

Thanks!

[Davelectro]

A few questions from a noob.  First, what are the trim pots for instead of a fixed resistor and where should they be set?  Second, will this drive a speaker by itself? If so, what should the Ohm and watt ratings on the speaker be? 

Thanks!

Trimpots are usually set around 4.5V.

This is just a preamp. It can't drive a speaker by itself.

[Ben N]

The F2b works great for bass, but the schematic in there is that of a blackfaced dual showman amp, so not specifically a bass amp. I've built a pimped version of the F2b and it sounds awesome, it's my main bass preamp. I've also built the Fet2b, and didn't like it for bass, but it's probably good for guitar if you're looking for a clean preamp.

Back in the blackface/early silverface era, THE Fender amp for bass was the Dual Showman, with it's 80-100 watts, big iron, and humongous 2x15" cab. Fender's only "bass" amp was used by bass players only in garage bands, since at 50 watts through a pair of 12" speakers it was woefully underpowered to compete with 50-100 watt guitar amps, organs and drums. However, if you didn't need a lot of bells and whistles (like Reverb), the Bassman made an excellent guitar amp. (I've still got mine, and it sounds like God!) So, typically, if a little perversely, it was not uncommon to find Fender driven bands using the Dual Showman for the Bass and the Bassman for the guitar (at least until Fender came out with a 100 watt Bassman.

Truth be told, Fender didn't really compete seriously in the bass amp market. But the preamps of the DS and the Bassman are very similar.

[Jberg]

So I would need to run this into a power amp? then it will drive a speaker?

[markmcconachie]

What do you guys think about putting this inside a passive bass?
Replacing the existing EQ?

[blacktransistor]

Hi!!!!

days ago, I designed a FET version of the bassman  100, which has 2 normal inputs and two bass instrument, the section of "normal", is almost identical to the schematic (some minor variations) but the section "bass instrument "is different, this is because the tone stak uses the" deep switch "and not" bright switch "unfortunately I could not try my circuit, but the sound of FET-2B bass is amazing!

[JebemMajke]

I ve included both deep switch and bright switch in my build. And I've found that deep is more useful than bright.

[Michal_R]

Hi, I made this preamp. Temporarily tested it on a downtuned guitar. Sounds great, but is this normal that after twisting all EQ knobs to 0, sound disappears (volume pot does not work)?

[slacker]

Yes, that's normal with this style of tonestack. If you look at the schematic you'll see that if you turn the bass and mid all the way down they are zero resistance so the bottom of the treble control is then connected to ground and acts like a volume control for the treble, turn it all the way down and you get no sound.

[Michal_R]

Thanks. Just as I thought, but I wanted to make sure. Is there any way that the sound did not disappear?

[Ben N]

Yes, Michal. If you put a fixed resistor in series with your mid pot, that will set the floor for loss through the tone stack.

[SILVIAO]

Hello is my first post, and i have one question about type of capacitors and volume potenciometer, is logaritimic or linear?Thanks .

[mth5044]

Volume pot is likely log. Type of capacitors - not sure what you're asking, but I used film for ones that were electros.