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Preamp EQ styles

Discussion in 'Pickups & Electronics [BG]' started by Derek Balonek, Dec 17, 2012.

  1. I've been wondering what style of EQ some of the production model pres have.

    There is a schematic for the NTMB floating around. It uses inductors for the mids.

    I haven't found any others though. I would assume most use standard active style controls, like a graphic EQ. A few use variable filters, like the Alembic, ACG, and Wal. I would assume the Glock and Aguilar are similar to the EQs in their respective amps.

    Do any of them use older amp topologies for their EQ? I'd think some of the East pres might, but otherwise I doubt it. Any that use a Fender/Marshall tone stack, or a Baxandall? The EQ (even flat) contributes to the tone considerably. Using a vintage tonestack may add an interesting flavor.

    I've heard the stereotype that active basses sound more 'hi-fi' quite often. The buffering may have something to do with it, but I think that the EQ has an effect too. I don't think anyone would call a Fender preamp 'hi-fi'.
  2. jbrew73


    Dec 24, 2006
    Would you consider the Sadowsky preamp modern sounding?
  3. Hactar


    Sep 25, 2011
    Boulder, CO
    I'm guessing there are a number of preamps out there that use simulated inductor (gyrator) EQ designs.

    Or were you discussing amplification topologies in preamps? i.e.: A, B, A/B, (I don't believe there exists a class D preamp, although I'm sure it would be a hit with the marketing department).

    I know that an Alembic F2B circuit is simple J201 (JFET) input/output stages and a 3 band Fender tone stack in the middle. Speaking of which, J201s are excellent for instrument preamps.
  4. Honestly, it's difficult to say without having access to schematics, which few manufacturers publish. Most manufacturers just tell you their frequency centers, and that's only part of the story. The Q and the shape of the shelving bands are subject to variation. I don't recall off hand, but some things are common with DIY builders, such as Baxandall. Do a search within DIY communities to see what's popular.

    As far as amplifier classes go, I don't see any practical reason to use anything but a Class A. Class AB Push/Pulls do not have the same highly-linear transconductance, and are subject to crossover distortion, turn-on delays, etc., negating the fact that they are more efficient amplifiers. Class A is more than sufficient for a preamp gain stage, anyway, since there is very little power to begin with. A Class D design would be a bit silly, and wouldn't be likely to catch on, considering the general dislike of digital things for onboard bass circuits. Class C would offer far too much distortion. (Works well for megaphones, though.) The other classes don't really apply to audio applications.
  5. I was mostly focusing on tonestack variations. Amplification class is not too varied. If discrete, it's probably class A. If there's an opamp, I would assume it's AB. The EQ was my focus though, sorry if I wasn't clear.

    The basic idea was, "Do bass preamps use vintage tonestacks?" Now that you mention it, I have seen Bax in a few DIY designs. I think I've even seen it in home audio. I forgot about the Alembic F2B too.

    I do agree that J201s are nice. I'm a fan of FETs in general.

    I'd say the Sadowsky can be modern. I honestly haven't listened to it too much. From the descriptions I've heard I'd put it more modern than vintage.
  6. jbrew73


    Dec 24, 2006
    I was just curious on that because the sadowsky preamp is based on the blackface fender tone stack from what I've seen. Also on my early comment I probably should have ask if it was hi fi sounding. I would also consider the sadowsky bass as a modern or hi fi sounding instrument. It just seems odd to me that the preamp uses a vintage tone stack to get what I consider a modern sound.