Building a clone of Hiwatt DR506 preamp

Discussion in 'Amps [BG]' started by magic papa, Dec 25, 2013.


  1. magic papa

    magic papa Gold Supporting Member

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    Hi,

    I'm planning to build a clone of the DR506 preamp section. It's preamp only, I want to plug it into a digital power amp.

    Got the schematics from here: http://hiwatt.org/Schematics/DR_506Input.gif

    Basically I'm going to remove the phase inverter (V4) and draw the signal from the cathode follower (pin 3 on V3). Otherwise I'll leave it as it is (perhaps add a mid control to the tone stack and a channel switcher).

    Can anybody comment on this idea please? Namely - taking the signal off that pin and plugging it into a power amp (through a cap)? The output impedance with a 1M resistor should be about 0.6k, which I assume is fine.

    It is stupid or should work?

    Many thanks

    MP
  2. BioWeapon

    BioWeapon

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    I'd give you my opinion but I think your link is a smiley?
  3. magic papa

    magic papa Gold Supporting Member

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    The link is not a smiley (?). Should open a PDF with a diagram. And yes - I'd like to hear your opinion.

    Here is a GIF version: http://hiwatt.org/Schematics/DR_506Input.gif
  4. Bassmec

    Bassmec

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    Happy Christmas!
    Of all the Hiwatt pre amp designs one of the very best built in Southend on sea was instead of hylight was, the Roost SR it was a Mid seventies very small firm that had a whole 8 employees including the van driver, who probably used to work for hylight as well.
    Chop the pre amp out of this four ecc83 design and you will see off a Dr201 pre amp in a few ways:
    [​IMG]
    :D:hyper::bassist:
  5. magic papa

    magic papa Gold Supporting Member

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    Yeah, that looks like a guitar amp although at these times it was really hard to tell one from another. Very similar preamp.

    So you are saying I should get the signal from the V3a cathode and chop off the V4 and the rest?
  6. Passinwind

    Passinwind Charlie Escher Supporting Member

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    It'll probably work a lot better if you use a 12AU7 for the cathode follower, with optimized resistor values. ;)

    Personally, I'm a big fan of using a stepdown transformer with something like a White follower driving it. The Jensen web site details that approach.
  7. BioWeapon

    BioWeapon

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    Guess the mobile app is bugging... weird. I call for bug fixes!

    Edit: I can see it when quoted... huh.
    Edit: it's a smiley again but I can see the url while editing. Who do I contact about this? Haha :)

    Looks like passin's already got your answer.
  8. scf4003

    scf4003

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    I wish I had the skills to build this preamp but it's way out of my league.
  9. BioWeapon

    BioWeapon

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    I wish I could too but I don't know enough about tubes. I find solid state amps wayyyy simpler.
  10. magic papa

    magic papa Gold Supporting Member

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    Tube preamps would actually make great beginner circuits if it wasn't for potentially lethal voltages.

    So I won't encourage you to try it if you don't feel confident. It's just about safety however, I doubt the rest would be out of your league if only you're handy with a soldering iron.
  11. magic papa

    magic papa Gold Supporting Member

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    Did you have an output stage like this in mind?
    http://www.jensen-transformers.com/datashts/10k611m.pdf
  12. Passinwind

    Passinwind Charlie Escher Supporting Member

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    Yes, or John Broskie's Aikido topology if you don't mind using two tubes. PM me and I'll send you a schematic of how I built mine, or take a look at John's Aikido kit manuals and articles on Tubecad.com. If you use either approach you will never be wanting for headroom and drive current, at least in my experience. Broskie's power supply boards are pretty handy too.

    I think Jonathan Greiner (JGR) uses that transformer with just a single section 12AU7 cathode follower though.
  13. BioWeapon

    BioWeapon

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    It really doesn't look that hard, in fact it seems like an easy project.
    But... Unless you already have a power supply you're out of luck, no? I'm currently in the midst of designing a power supply for an amp project I'm working on because I couldn't find any plans.

    Do you already have a supply, seeing as those ECC83/12AX7 tubes take over 300v?
  14. magic papa

    magic papa Gold Supporting Member

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    Power supply should be quite easy, it's just the matter of finding the right transformer or yes - you'd be out of luck ;) Happens to me all the time because I'm in Australia @ 240V, so my choices are sometimes limited.

    Anyway, I'm lucky this time because I found this one: http://www.edcorusa.com/p/601/xpwr012. Gives me plate voltage, filament supply and an extra 5V winding to drive LEDs and relays. Th only thing about it is that it's quite bulky and won't fit into a 2U rack case :crying:. But I can't have everything I guess. Might get a head cabinet or something similar to house the preamp.

    And here is the power supply from the same site I go the preamp schematics http://hiwatt.org/Schematics/DR_PS0506.gif, there is really not much to it, just a rectifier and some caps to smoothen it up. I'll add an extra rectifier bridge for the 5V circuit and that's pretty much it.

    The 12AX7 tubes have max plate voltage of 300V. The power supply normally would give you much more than that and how much the tube really gets depends on the plate resistor and bias.
  15. BioWeapon

    BioWeapon

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    Sweet!
    I'm using the rectifier, cap, limiter, and transformer method for a smooth DC output.
    I'm glad I only need a 120 v source!
    Anyways, best of luck - oh and, pics of the final result please? ;)
  16. magic papa

    magic papa Gold Supporting Member

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    Thanks, I'll post the pictures/soundclips, but this thread will be long dead by then ;-). I haven't started ordering the components yet and projects like that are definitely a good patience training.

    It had happened to me that by the time a component arrived I actually forgot what it was for :).
  17. MAMMOTHvolume

    MAMMOTHvolume

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    you'll wanna swap the 83 follower for an 82 and it might be best using a step down transformer. You don't need 300v for this circuit, you're looking to get 1V~ out of it
  18. magic papa

    magic papa Gold Supporting Member

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    Yes, that's what Passinwind suggested too. This looks like a nice output stage (thanks Passinwind):

    http://www.jensen-transformers.com/datashts/10k611m.pdf

    I'm thinking about replacing V3 with it. I'm also not sure why the two halves of V3 are coupled with a resistor (1m8) and a cap (10n). What's the significance of it? Is the cap just a coupling cap?

    I think for the Jensen circuit I would need to recalculate the resistors for the higher HT value. I'm guessing the outputs stage is trying to be linear, so it would need to stay this way.
  19. magic papa

    magic papa Gold Supporting Member

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    Sorry to respond to my own email, but I now think this may be a treble-boosting coupling.
  20. MAMMOTHvolume

    MAMMOTHvolume

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    why do you want a higheer ht? it's a mid range boost

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