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Why does a Fender Blues Deluxe lose bass on the drive channel??

Discussion in 'Amp Central Station' started by jasper6120, Jun 7, 2018.

  1. jasper6120

    jasper6120 TDPRI Member

    36
    Aug 9, 2011
    NSW Australia
    I quite like the sound of my blues deluxe. I've done a bunch of Fromelle style mods and replaced the speaker and its sounding really nice to my ears. But one thing that is still bugging me is how I can get a rich full bass response from the clean channel but I lose it as soon as I hit drive? I have bass tone pot on about 7 when I am on the clean channel and need to crank it up to 12 to get the same amount on drive.

    What is the fix for this? Is there a cap somewhere that filters out the bass for the drive channel? Is it an issue with the preamp valves? I don't have the coin to flash around on too much valve auditioning. I have an Electro Harmonix 12AX7 on V1 and Sovtek 12AX7LPS valves in V2 and V3.

    Is it on purpose? Like, if they had more bass on the drive channel would it muddy up the drive?

    I never thought I'd like the drive channel, but it turns out with these mods I'm getting really happy with it. Just a bit more bass response from that channel and I'll call it a job done :)
     
  2. Guran

    Guran Friend of Leo's

    Mar 20, 2007
    Sweden
    Bass is cut before drive because too much bass going into the drive stage will give a very flubby and farty drive.

    In the schematic it looks like C4 is the high pass filter, and that it is bypassed, via RY1B, in normal mode/channel.
     
    JustABluesGuy and bblumentritt like this.
  3. jasper6120

    jasper6120 TDPRI Member

    36
    Aug 9, 2011
    NSW Australia
    Ahh okay. Do you think it would be useful to try some different caps in C4? Blues Deluxe drive channel often gets a bad rap for being thin sounding. C4 looks to be 750pf stock.
     
    Last edited: Jun 7, 2018
  4. Chicago Matt

    Chicago Matt Friend of Leo's

    Age:
    69
    Aug 23, 2014
    Woodstock
    Interesting thread. I found I liked the clean channel on my BDRI a lot, but the drive channel was useless to me. I ended up using only the clean channel and then a pedal for drive. I will be interested to read answers to this...
     
    Alamo likes this.
  5. Wrong-Note Rod

    Wrong-Note Rod Poster Extraordinaire

    Mar 4, 2009
    atlanta
    for the same reason so many overdrive pedals are notorious for it as well

    I'm guessing that bass frequencies at the same level will sound "bad" so they are intentionally pulled down.

    This is why I USUALLY like a two channel amp that has separate tone controls for each channel, or, always run pedals and the overdrive pedals either dont kill the bass like that, or have an actually bass tone knob that I can control.
     
    3-Chord-Genius and 8barlouie like this.
  6. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    Look at Marshalls. They are pretty well known for their lack of low end, and this is the exact reason.
     
  7. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    In particular, look at Jimmy Page’s tone settings on that big Marshall. He runs the bass down to nil, iirc, as do many other Marshall users, in order to avoid getting lost in the mix with the bass player.
    Re:Blues/Hot Rod Deluxe/DeVille Amps. They are biased notoriously cold at the factory. I have adjusted the bias while owners play, and their eyes go wide when a hotter biasing yields more richness, warmth and harmonic content. I never question anything about one of these amps without making sure that the bias is adjusted to somewhere above 50% of max plate dissipation.
     
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  8. jasper6120

    jasper6120 TDPRI Member

    36
    Aug 9, 2011
    NSW Australia
    The bias is reasonably hot on this amp and yes that's a big improvement from factory settings. The thing that bugs me is mainly that the two channels are not really usable together. Either one is too bright or the other is too muddy. A bit of uniformity would be nice.

    I haven't heard that many tele tones I love out of Marshalls. I'm sure they're out there but combining a bright guitar and a bright amp sounds like a recipe for industrial deafness. I guess I'm going to creep up on this high pass filter slowly to avoid flatulence. Might try a 1nf silver mica in C4 (C53 on the reissue schematic) and see how the drive and bass response is.
     
    Last edited: Jun 7, 2018
  9. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Those tone controls are there for a reason. Here is one of the icons of Tele players...through an early Marshall.


    And...here is another....



    Fwiw, the Blues/Hot Rod Deluxe and Deville are loosely based on the same amp that Jim Marshall cloned when he built the first reissue Fender......the amp he cloned was the 5F6A Bassman.
     
    JustABluesGuy and Wrong-Note Rod like this.
  10. michiganguitar

    michiganguitar TDPRI Member

    Age:
    59
    30
    Sep 15, 2017
    Metro Detroit
    I’ve played a couple HRDIV’s at the store lately and noticed the same thing. Switch to the drive side and the low end completely disappears. I understand it’s to help with the flub/fartiness but it’s too much, imo. If you crank up the bass, when you switch to the clean channel, it’s too hot. I haven’t used them in a live setting so maybe it works fine there, idk. It just seems to drop the low end more than other amps I’ve tried.
     
  11. Fearnot

    Fearnot Friend of Leo's

    Jan 17, 2010
    Decatur, GA
    What Fender is saying is, "if you want low end, get a bass player."

    It's a conspiracy to sell more P-basses.
     
    Dennyf, drlucky, Asmith and 2 others like this.
  12. JustABluesGuy

    JustABluesGuy Friend of Leo's

    Age:
    60
    Sep 2, 2016
    Houston, TX
    If you want to fix that, just set the clean channel the way you want it, and then use a Tube Screamer for your distortion.

    Oh, wait! The TS cuts bass and boosts mids so that you will cut through the mix better in a live situation.

    Hmm... maybe thats why they do it on the drive channel? I almost always have more bass available than I care for, and tend to roll it back, often to zero, even when not playing with a bass player, and also tend to run my mids a bit high already. My amps are all single channel amps as well, so I don’t have this “problem”.

    Are you trying to tweak this amp for gigging or for solo home use? That makes a difference. A thinner tone will sound weak alone, but often sits much better in a mix.

    I wouldn’t mod an amp to sound great “in isolation”, unless I didn’t ever intend to gig it as well.

    The bass cut sounds to me like a “feature” rather than a flaw. If it the feature isn’t useful to you then tweak away. I’m not able to do any circuit mods myself, and try to stick with amps that need nothing more than a speaker upgrade or tube swap.

    Anyway, good luck with getting it right where “you” want it, and be sure and post updates!
     
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  13. JD0x0

    JD0x0 Poster Extraordinaire

    Age:
    28
    Feb 22, 2009
    New York
    It's because of the intentional bass cut as other have mentioned. By using smaller coupling caps, you avoid 'farty' bass and blocking distortion, which sounds unpleasant, for most people. I find, as with drive pedals, they usually cut the lows a bit too sharply. It's totally possible to have a bassy OD tone that doesn't flub out, but it takes some tweaking. To keep things simple you could just tweak the coupler for a bit more bass, but not enough to make things mushy. I usually find 3.3nF is a good ballpark value for a high gain stage. Keeps things full, but trims off the 'flub'

    On pedals, they tend to set the -3dB low end cutoff around 750hz, which is pretty high. You lose some of those nice low mids, along with the bass. I tend to set the low pass -3dB corner frequency around 350hz on TS and similar pedals. Same deal as above.. trims enough to tame the mush, but keeps things ballsy. I hate stepping on a pedal and listening to all my lows get chopped off. I think I tend to notice it a bit more, too, because my speaker cabs can reproduce low frequencies very well for 'guitar cabs'
     
  14. printer2

    printer2 Poster Extraordinaire

    May 24, 2010
    Canada
    The thing with bass cut in the lead channel is that the designers do not know how much gain you are going for in a lead situation. Going for a slightly hotter sound will allow for more bass than a maxed out cut through any mix setting. Don't see why a knowledgeable person couldin't tack a capacitor onto the leads of the cap in the circuit (wit adequate soldering skills) and find the amount of lows they can live with. I was going to put in a tone control in the lead channel of a pedal I am building but I ran out of room.

    JD0x0 snuck his post in there before me, seems he has the same idea.
     
  15. jasper6120

    jasper6120 TDPRI Member

    36
    Aug 9, 2011
    NSW Australia
    Okay so I had a quick peak at the circuit and the amp today. Unless I'm reading this incorrectly - the 750pf cap in C53 couples to the 510k resistor in R44 to create the high pass circuit. The equation to identify the point where the low freqs begin to be attenuated is HZ = 1 / ([2pi x R[ohms] x C[farads]). Punching in the deets gives an attenuation point around 400hz. I put the multimeter on the 510k resistor in R44 and it came back as 96k (despite correct 510k colour code). That would give an attenuation point around 11khz! But surely that would be unbearably lacking in low end. Mine has a reasonable amount, could just do with more. The plot thickens...

    On a side note, it looks like there was a tracer leading to the C53 cap over to R52 that has been scratched off the board (second pic) that would have been to cut the bright switch out yes?
     

    Attached Files:

  16. Guran

    Guran Friend of Leo's

    Mar 20, 2007
    Sweden
    You are taking DC readings of the resistor(s). R44 is in parallell with both R6 and R52. That gives 98.7k (with volume all the way down). Well in the ballpark.

    Oh, that was my post #3000. I hope it was helpful! :)
     
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  17. jasper6120

    jasper6120 TDPRI Member

    36
    Aug 9, 2011
    NSW Australia
    Ahh! I'd over looked the parallel resistors. I'm still pretty new to schematics. To open up the bass response a bit more, do you think it would be best to try higher value caps or higher value resistors? And congratulations on your 3000th post!
     
  18. Guran

    Guran Friend of Leo's

    Mar 20, 2007
    Sweden
    Higher value cap (as others suggested).

    I missed this part. Yes, that look weird. I'm in a bit of a hurry right now, but that looks like drive channel wouldn't work unless there has been other mods done. Like disabling K-1B so that it's always in nc position. But then you shouldn't have this bass cut... And if that mod was done, there would be no reason to cut the trace to the cap, as it would be bypassed... Weird!

    Gotta go now.
     
    Last edited: Jun 8, 2018
    jasper6120 likes this.
  19. jasper6120

    jasper6120 TDPRI Member

    36
    Aug 9, 2011
    NSW Australia
    Sweet deal. I think I'll start by running a 300pf (500v) cap in parallel with the 750pf and see if anything is better. The schematic says 1kv but the Fromel mod uses a bunch of 500v silver mica caps where the schematic lists 1kv caps so I think it'll be okay. Touch wood..
     
  20. jasper6120

    jasper6120 TDPRI Member

    36
    Aug 9, 2011
    NSW Australia
    Hey all. I figured I should let you all know where I'm at with this.

    I just put a 1200pf capacitor into C53. It did the trick, the bass response is about the same between the clean and drive channels now. It did change things in a few ways. Firstly, it is letting a bit more signal through to the drive channel. Where I used to have the gain on 7 for a slight breakup I now have it on about 5.

    Also, the mid control seems to have overlapped into treble territory. The treble pot seems not to have as much influence over the tone as it used to and its harder to wind out the brightness. Does anyone know why this would be? The amp has a .015uf cap in the mid control, would a .022uf cap step it away from the treble frequencies a little?

    The tone of the drive sounds fine. Not mushy at all, but I am playing a nocaster through it. I imagine it would probably get mushy with humbuckers. I think maybe 1000pf might be a good compromise.
     
    Last edited: Jun 13, 2018
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