DRRI bright cap question

Discussion in 'Amps and Cabs' started by Presc, Jun 30, 2008.

  1. Presc

    Presc Member

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    I know clipping the bright cap on the vibrato channel of a DRRI is a common mod many have done. While I am getting a good sound with my pedals, there is a bit of fizz on the top end that I would like to get rid of. From what I understand, clipping the bright cap will get rid of this.

    Here's my question: I like the vibrato channel much more than the normal. The normal channel sounds flat to me, the vibrato channel is much "springier". Does clipping the bright cap change the unaffected sound of the channel? Will it make my vibrato channel more like a normal channel with reverb? Because I don't want that.

    Thanks!
     
  2. Deadduck

    Deadduck Member

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    I'm no amp expert so I'm just going to repeat what I've read and my experience with my DRRI.

    It is my understanding that the vibrato channel has two stages of gain vs one for the normal channel. So the vibrato channel won't sound exactly like the normal channel. But clipping the bright cap will dull the tone down more like the normal channel.

    Personally, I've found that with some good tubes (NOS Mullards and JAN GE and Tung Sol Reissues), proper biasing, and a better speaker (mine had the Emminence, replaced with a Weber 12F150B), clipping the bright cap is not necessary. At least I'm happy with my second channel.

    Another way to get the normal channel sounding better is the so-called Fritz mod, which puts the channels into phase so they can be jumpered, and also adds reverb and tremelo to the normal channel. http://www.fenderforum.com/userphotos/index.html?recid=48201

    I haven't done this mod as I'm pretty clumsy with a soldering iron, but I may have it done one day. I'm happy with my amp now, but I only use the vibrato channel.
     
  3. Presc

    Presc Member

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    I'm not unhappy with the way my pedals are going in (some are better than others), but there's just a tiny bit of hair on the top end that I'd like to get rid of without really changing the voicing of anything else. Mine has the Jensen C12K, not the Eminence btw. Previous owner had recently rebiased with JJs pre and poweramp tubes and a NOS tube in the tremolo (unsure which). I've had it for about a year. Thanks for the ideas.
     
  4. 5E3

    5E3 Member

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    :agree with DeadDuck

    I recently lifted a leg on the bright cap @ C10. It doesn't make the Vibrato channel sound "just like" the Normal channel, but it does remove some of those ice-pick highs.

    If you can get a tone you like with tone controls, pedals, speaker, tubes and re-bias, I suggest you leave the cap @ C10 alone. If you decide to make the C10 mod, just touch the bottom of the PCB solder drop for one leg of C10 and lift it gently out of the hole. This way it is easy to put back, should you change your mind later.
     
  5. smolder

    smolder Gold Supporting Member

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    I just read the latest issue of ToneQuest this weekend and it addressed this exact problem. If I remember I will try and look it up this evening and pass it along.
     
  6. Rick1114

    Rick1114 Member

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    Deadduck is right on with regard to the DRRI Normal vs Vibrato channel info. If you find the normal channel "flat" sounding, then running it through the reverb/vibrato circut will add that 2nd gain stage and it will sound hotter. This is not mentioned much, but the normal channel also has a .047 coupling cap, which makes it a little darker/fatter sounding, but besides that, the channel will sound like the vibrato channel with no bright cap if you do the Fritz mod. It's a 1 wire mod, but it shouldbe done by someone familiar with electronics (draining filter caps and soldering).

    I like the Vibrato channel with the bright cap, but I don't think I came to that point until I put an eminance RW&B speaker, the right tubes and I went the extra mile and upgraded the filter caps (F&T), Tone stack (Mallory), and PI section (PS Series). I could be wrong but I think the raspiness I used to hear on the top end went away with cap changes. I wouldn't do all that again because the PCB doesn't hold up at all. I'd curious what the tonequest report said...

    Rick
     
  7. tommytomcat

    tommytomcat Member

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    To answer your question.. Cliping the bright cap on the vib ch will make that channel a little closer to sounding like the normal ch, but it won't be nearly that drastic. Go to a music store that has a super reverb.. (or any 60-70's vintage fender with a bright switch).. play it and flip the bright switch up and down. That will give you an approximate idea of what the difference will be. Also note, the more the volume is turned up the less effect the bright cap has. (turn it up 3/4ths way and it's like it's not there). BTW, does the fizz go away when you roll down the guitar's tone knob?

    Strange.. I've never heard of anyone who owns a BF or SF DR feel the need to yank the bright cap.
     
    Last edited: Jun 30, 2008
  8. Blues_N_Rock

    Blues_N_Rock Member

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    Following along this line of discussion, is the ice pick brightness sound in a DRRI more predominant with humbucker pickups versus single coil or stacked single coil pickups? If so, is it because the HB PU has a higher DC resistance? Thanks
     
  9. Presc

    Presc Member

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    Well, I sort of hear the problem with the powertube overdrive by itself - it's a bit raspy on the top end. At the lowest of volumes on the amp, the fizz is definitely more apparent, but it never totally disappears. And that's really my only issue, I have never found the amp to be an ice-pick in the ear or anything. I run treble on 4, bass on 7 with a G&L Legacy, single coils. And like I said, my sound is pretty good, but there's a hint of hair on the top end when I step on my pedals (Fulltone OCD and Barber Direct Drive) that makes it sound not quite as clear or smooth as things could be.

    Just some thoughts (I don't know much about electronics/circuits)...is there some "intermediate" value cap that one might put in that's sort of halfway in between clipping the current cap and keeping it? I would be having a tech do it the next time I change tubes/rebias so it might even be cool to have a bright/dark switch like on a SRRI or TRRI. Speaking of which I should go play one of those and see if I like what the switch does.

    It is interesting that no one ever does this on the BFs/SFs. I wonder if by nature the RI is harsher which compels people to do the mod.
     
  10. mbratch

    mbratch Member

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    Yes, different cap values can be used to adjust how much brightness to allow. To add a bright switch without defacing the amp, you can install a push-pull volume pot. :)
     
  11. mbratch

    mbratch Member

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    I solicited this poll on it over a year ago. :)
     
  12. Rick1114

    Rick1114 Member

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    You can try different values, but it's a PITA to experiment with this amp (taking apart the PCB takes a while) and the solder pads fall off. Being a glutton for punsihment, I tried a few value in the bright cap and went back to stock (.047) eventually. I tinkered with this amp quite a bit and found the stock values sounded best, but parts need to be upgraded to get rid of that harshness in the top end. Start by getting rid of that Jenson speaker - I put it back in for a second once and it was horrible. I like the RW&B, but there are plenty of good options. I think upgrading the filter caps to F&T's helped a lot too, but my amp was already 8 years old and probably gigged by previous owners, so it may have needed it anyway....

    Has anyone tried a push/pull pot in one of these. Iw ould love to try that but it looks like you would have to be merlin to install it in this amp (the pots are attached to PCB and theres no room).
     

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