API line amp as bass pre

a friend of mine is giving me his bass guitar now that he's just bought two fancy new ones so i wanted to do something nice in return. i thought a bass to line level type pre would be appropriate and found this circuit:

http://www.danalexanderaudio.com/ApiInfo/api2520_02.jpg

i'm looking at schematic number two and plan to build the 2520 on stripboard and use whatever bits i have laying around. probably a wallwart power supply to keep it simple.

just a few thing i need to know:
1) how much gain will i need
2) anybody foresee any problems or have any better ideas? (gotta be low cost because i'm poor)
3) i'm not really interested in making this super-clean sounding so any recommendations for output transformer ratio/brand?

cheers!

I think you should be considering the schematics from Bo Hansen instead.

http://web.telia.com/~u31617586


Although, having built the "straight into 2520" di, I should say that for bass guitar its very, very uninspiring.

Bo's active DI into input transformer api is absolutely brilliant though!

That bastard API opamp can drive seriously low loads! You can get something from ebay like this:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=270240753633


If you're seriously skint and you cannot buy any transformers, I'd suggest you go straight to the grid of a vacuum tube instead of the 2520

I'd recommend one of these:

http://www.geofex.com/FX_images/alembpre.gif

I built one for pretty cheap. I can't say strongly enough how nice these sound.

-Chris

great thanks!

i had considered the Bo Hanson one because everybody raves about them. which of the API/Hanson variations did you build?

the tube one looks great too, is it line level output? never built any tube stuff before.

what should the output of the power transformer be? i'm on 230 volts here so would need to take that into consideration when choosing step down ratio.

cheers!

err... actually it's probably step up to the B+ thinking about it.

[quote author="Mlewis"] which of the API/Hanson variations did you build?

[/quote]

Both the active DI and the "API 312 mic amp with DI input modification" from the page I linked. Like I said, to my ears no1 sounds brilliant, no2 crap!

With the active DI you need a separate microphone preamp to bring you to line level.

That schematic looks like fun chris, what's V1? 12AX7?

right... thanks.

V1 on the alembic is a 12AX7. I've actually got half the bits for the Alembic already so i've started putting it together. might build one of the hanson DIs with an API for myself one day though.

For the 50/25V electrolytics on the Alembic schematic, is it safe to assume that it's 50uF ?

anybody have a suggestion for what the power tranny should be?

M

http://www.moosapotamus.net/IDEAS/F2B/alembic.htm

I built my Alembic about 3-4 years ago, so I can't remember the details. I'm traveling now for work, but I will pop the top when I get home. I seem to remember the power transformer I used only costing about $20 from tubes and more. I also built the unit into a fruitcake tin using veroboard, so it cost me almost nothing.

-Chris

Chris you're a gentleman! thank you.

the power tranny and pots are all i need to get too so this is perfect.

OK, I popped the top:





I sort of did my layaout as I went along. Despite the closeness of the power transformer to the circuit, there really isn't any hum. I forgot exactly what the transformer's specs were, but I measured 12V for the heaters, 120V AC and 190VDC B+. I'm not sure why the B+ is measuring so high. The unit does give line level signal, depending on where you have the volume knob set.

Here are some sound clips comparing this to some other DI's. The first bass is a Rickenbacker 4001 lightly picked (pardon the bass' intonation). The second bass is a plucked Fender P with the brightest damned flatwounds I've ever used (D'Addario).

The alembic, volume = 6, tone stack all at 10. Bright=off. Straight into my line level in of my audio card.
Alembic

For a premium comparison, a G9 with OEPs and Sylavanias (I think)
G9

For a budget comparison, a Behringer Ultra-G DI into a Behringer ADA8000.
Behringers

Regards,
Chris

Chris... really sorry it's taken me so long to get back to you, I've been on fairly heavy duty sessions at the studio all this week so haven't even switched my computer on.

Downloading the clips now. Thank you so much for popping the top and taking the time to do this.

Interesting that you have 190VDC B+ because the link that i posted a few posts back stated B+ at well over 300vDC with 12V heater voltage. Maybe i'll try both if i can and report back.

Cheers!