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Thread: My Fender Hot Rod Deluxe mods!

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  1. #1
    Forum Member
    Join Date
    Feb 2007

    My Fender Hot Rod Deluxe mods!

    Hi everyone,

    I've just finished some mods to my HRDlx that I want to share.

    I bought my amp used almost a year ago.
    - The first thing I had to change has been the speaker: the original speaker was broken (it produced a kind of distortion when playing bass notes), so I decided to go for a Celestion Vintage 30, as it is my favourite speaker and it is also stock on the limited edition version of this amp. Very helpful to smooth out the sound (I really hate shrill sounds), very useful for distorted tones.
    - Next I changed the tubes, as they still were the stock ones (the amp is from 1998) and I had read about how much the sound of this amp could improve. I didn't want to spend a lot of money, I had just bought the new speaker, so I chose Electro-Harmonix for all the tubes, because I read a lot and they seemed to have the best quality/price ratio. I got a 12AT7 for V3 (the phase inverter), to tame the volume a bit. Compared to the stock tubes, the sound did improve, but it was almost a year ago, so I don't remember. Not a radical change at all, though.

    Now the most recent mods.
    NOTE: I didn't want to mess with taking the board out of the chassis, so I worked on the components side of the PCB. Whenever possible I soldered new components in parallel to the existing ones (for example to increase a cap value or decrease a resistor value). When not, I cut the component pretty near its body, in order to leave a long bit of the component leg to solder the new component to. This way my mods are all easily reversible.

    - I did the reverb mod This is a must, IMO. Now the reverb is much more usable.
    - Changed C11 (390p) to 1n. Now more highs are shunt to ground at the end of the drive channel.
    - Changed C1 (47u) to 22u. A bit less bass and gain are fed to the following stages.
    - Added a 10n cap in parallel to C23 (1.5n). More bass to the drive channel.
    - Added a 180k resistor in parallel to R9 (220k) in order to get 100k here. This way less highs are blocked at the beginning of the clean channel (note that as a collateral effect you also get more gain, as we're reducing a resistor between gain stages).
    - Added a 470k resistor in parallel to R12 (130k) in order to get 100k, the standard value in Fender tone stacks. However, after checking again with the Tone Stack Calculator, I realized this mod increases bass and bass-mids (I had inverted the curves in my mind) rather than decreases them. So I might go back to 130k.
    - I tried cutting R105 out, because it looks like an added component to the standard Fender tone stack, but I ended up soldering it again into place, because its role is to tame the bass a bit. I also read in another thread of this forum that it is better to keep it.
    - Unfortunately, I couldn't do the middle pot mod (soldering the wiper to the bass-pot-side leg) because the big C6 cap in front of it isn't letting my soldering-pen tip go there. This is a pity, as that mod allows a better control over the overwelming bass of this amp. Edit: my recent thoughts about this mod in the following thread:
    - I added a 22u cap in parallel to C8 (1u). I did this because I noticed the More Drive setting was harsher than the normal Drive. As the More Drive differs from the normal Drive setting by two added cathode bypass caps (C8 and C9) in the last two gain stages, I thought this was the culprit, because I know that a cathode bypass cap smaller than 22u alters the frequency response of the gain stage (the smaller the cap, the more you have an increase in gain only for treble frequencies). C9 was already 22u, so no problems there.
    I'm happy with this mod, now the More Drive is really an extension of the Drive setting. You also get even more maximum gain in More Drive: I like this, because it allows me to keep the drive knob lower, so I have a bigger highs-blocking effect from that pot.

    Most of this mods are inspired from the Blues Deluxe schematic, but also from other Fender amp schematics. I played a Blues Deville 4x10" once at a gig and I think its clean sound was superior to the HRDlx, although it also had different speakers.
    As you can see, the aim of these mods is to reduce the bass/increase the highs in the clean channel and to increase the bass/reduce the highs in the drive channel. This is to cure the harsh sounding drive channel (most of all) and the rather dark sounding clean channel. As most of the circuit is shared between the two channels, I decided to give priority to the clean channel, which is the one I use more because I mostly have pedals for my distorted tones. At the same time, I tried to give the clean channel more sparkle in order to be able to keep the treble and presence knobs lower, as this improves the drive channel tone.

    I'm very happy with my mods!! The clean channel improved and, most of all, the drive channel is now more than usable. I'm looking forward to trying my amp loud at a gig to confirm the improvement.

    Thanks for reading this, I hope it will be helpful to someone!


    Edit: I played the amp extensively today and I'm really stunned with the improvement in sound!! Now my strat really plays like a strat, both clean and "drived" (the stock amp didn't do its justice)!! I was about to change its neck single coil but now I'm happy again!
    Last edited by shredgd; 11-16-2007 at 10:39 AM.

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