My new boo-teek preamp

[fdeck]

This is the circuit that I have been fiddling with for a while. Everything is from my spare parts bin. I will post a schematic soon. It's my attempt to find out how a DIY bass amp would sound with a simplistic discrete design. So far the feature set is:

Input gain stage
Active bass / treble control
Active semi-parametric midrange
Master volume
Final gain stage

If you count carefully, there are nine transistors.

Yeah, yeah, how's it sound? So far I have only played with it at moderate volume in my workshop to confirm that the controls function.

[UncleFluffy]

Nice. Like the build style - I'm normally more of a stripboard man for prototyping, but that's incredibly neatly executed.

[Interceptor]

I'm a kind of old RF guy - love the dead bug construction. It looks just like something out of one of the old ARRL Handbooks. Beautiful!

Simple circuits are the hardest to optimize. I'll bet a Capitol beer Francis has a good one here!

I'd love to give this a whirl.

Jim

[Passinwind]

Post yer clips!

Very cool build Francis...that's about as far away as possible conceptually from my newest build that I'm currently finishing up. I love all the different takes we see on DIY stuff here on TB.

[bongomania]

Thumbs up!

[JimmyM]

Close that lid or you'll never be able to sell it for $3000

I like the look of it, F...I'm all for having as few parts as possible. Except for tubes...those are necessary.

[Christian Waiau]

Originally Posted by JimmyM

Close that lid or you'll never be able to sell it for $3000

I like the look of it, F...I'm all for having as few parts as possible. Except for tubes...those are necessary.

if he added a couple tubes... he could still sell it for $3k! ...tubes dont even need to be part of the circuit..

[johnk_10]

i like too. once you get it all sorted, all it would take is a a little dab of silicone here and there to make it roadworthy and vibration-proof for some of those 'floating' components. nice work!

[jokerjkny]

that is PTPTPTPTP if i ever saw one... nice nice.

[chicago_mike]

what type of trannies? J201's? Oh, and, get rid of that green meanie

[Jim C]

The creativity on this board never ceases to amze me.
Beauty; here's to hoping the tone is exactly what you like.

[oerk]

That's certainly a nice take on point-to-point.

I'm looking for a simple preamp like that myself, can't wait to see the schematic!

[Eric Perry]

Subscribed...

[greenboy]

Hey fdeck,

Great schtuff! Let's see some projected EQ center and Q specs, input, S/N and noise and so on.

[Morfman6]

so cool! subscribed!

[PSPookie]

Very tidy indeed.

I'd love to see/hear graphs and clips.

Nice work

[fdeck]

Thanks for the many kind and encouraging words!

Here's the schematic:

http://personalpages.tds.net/~fdeck/bass/ebpresche.jpg

I should offer some caveats. First, I didn't use exactly these component values, because I had to use what was in my parts bin. Second, there's a problem, because a circuit like this will suffer from tolerance variations in the parameters of the JFETs. Typical fixes include selecting parts, adding bias adjustments, or putting up with it. I chose the latter, in order to get the circuit built.

I am on the fence about the bass / treble control, since a passive James circuit would also work there. The active circuit should provide better noise performance.

Next steps include:

1. Document the design
2. Testing, after I coax Windows 7 to run my testing software
3. Record some clips with my crummy bass
4. More careful parts selection
5. Lay out a printed circuit board
6. Share the results

Critique is welcome!

[svtb15]

NICE!

[UncleFluffy]

In the Baxendall circuit, are J5/J6 there to provide a virtual earth?

[greenboy]

I thought it was Baxandall - Peter James Baxandall, Her Majesty's Secret Audio Service ; }

That'll help when you are googling ; }