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Post by humanbn on Jun 11, 2008 8:11:11 GMT -5
Hello,
I want to change out the IC chip in my Hotrod Deluxe so that I can hopefully get a fuller, thicker, fatter sounding distortion from the second channel. My problem, however, is that I don't know which chip that is and I haven't been able to locate anyone else's information on how to locate it. Does anyone have any suggestions or helpful tips that may lend me a hand?
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Post by ChrisK on Jun 11, 2008 17:44:41 GMT -5
Since there are three "IC chips" in the amp, you need to whittle it down to what you actually mean. Since the gain of opamp-based circuits is dependent on the gain setting components and not the opamp, aside from opamps with enhanced open-loop gain (which can help frequency response in a closed-loop circuit), there aren't "hotter" opamps like there are hotter preamp tubes. There are in tubes since most tube stages are open-loop circuits. Opamp modules (the precursors to the IC-based ones) were developed to get around the crappy issues with tubes. This is a round about way of asking just what "a fuller, thicker, fatter sounding distortion" means. Do you want it to distort earlier (at a lower input level) and hence to distort more, or do you want a different frequency response. I'm fairly certain that these all point to a "stouter" sound, but clarity is. Also, what does "the second channel" mean in terms of what the channels are called on the amp? It depends on what "it" means.  You betcha! Here is the link to the Fender amp schematic on the Fender web site. If one goes to www.fender.com & support & amp_schematics....... www.fender.com/support/amp_schematics/pdfs/Hot_Rod_Deluxe_Schematic.pdfU3 is used as comparators for mode/channel select. U2 is used in the reverb signal path. U1 is used for the preamp out and power amp in. (Sorry, this is NOT an all-tube signal path.) Opamp gain set is by external resistors. Gain may be changed by changing preamp tubes or their gain stage resistors/capacitors. Otherwise, it appears that the external gain setting resistors for one of the ICs could be modified. Until more clarity is given, I don't know what much of this means. |
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Post by sumgai on Jun 11, 2008 17:45:48 GMT -5
bean,
My first question to you would be: how do you know that changing "the IC chip" will give you the desired results?
Got a link to where you heard/read this little tidbit?
sumgai
(Edited, for reasons shown below.)
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Post by humanbn on Jun 11, 2008 21:29:39 GMT -5
I haven't heard of this from anywhere. The way the distortion sounds on this amp makes me think that it is just that, distortion, and not overdrive. I am hoping that the second channel operates more as an effect pedal plugged in line with the signal rather than actually overdriving the tubes. If this is case than I should be able to alter how the signal is affected. It's only a thought. I really don't like that channel.
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Post by humanbn on Jun 11, 2008 21:32:14 GMT -5
ChrisK, I fail to understand what you mean by the word "it". It, to me, would be the sound eminating from my speaker.
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Post by sumgai on Jun 12, 2008 4:26:10 GMT -5
Actually, if one looks carefully at the Poweramp In jack, one sees that the signal goes directly from Pin 4 of K2a (one of the Channel select relays) to C24, which passes it on to the grid of the Phase Inverter, V3a/b. Only when the Preamp Out/Poweramp In jacks are used do the two halves of U1 enter into the signal path. (It's interesting to note that the Reverb circuit is in parallel with the Preamp Out/Poweramp In jacks, which means that U2 will also be in the signal path when you use Reverb, no matter if anything is or is not plugged into the Poweramp In jack.) BTW, I went back and looked at my previous schematic source (it wasn't the Fender site)....... turns out that the link said one thing, but sent me to another amp's schematic instead. That'll teach me to double-check where I am on the intertubes at all times.  Several design "differences" jump out at me here, but to keep things short and sweet, I'll only say that there is just one channel here, regardless of Fender's labeling ("TremoLeo", anyone?). V2b is inserted into the path to give more gain, and the relays make other circuit changes to offer more control of this additional gain. (Note the different capacitors/resistors for the Drive and Volume controls. Maybe Fender thinks this is enough to make it sound like a different channel?) The "More Drive" feature is actually nothing more than a simple changing of the bias voltages found on the cathodes of V2a and V2b, via the pair of FET's, Q1 and Q2 respectively. Seems simple enough, nothing too exotic here, eh? Where I'd first start looking for "fuller, thicker, fatter" tone would be the tubes themselves. Preamp tube V2 is your prime suspect. Next, try V1 and V3, then if you're still searching aboot, go after the power tubes. But the preamp jobbies are cheaper, so start there. If you can afford it, try a variety of tubes in each slot, they'll act and sound a bit differently, perhaps one will sound more appealing to you. If you do end up with new power tubes, don't forget to have them biased before you take everything out on the road! HTH sumga |
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Post by humanbn on Jun 12, 2008 20:46:51 GMT -5
Sumgai,
Thanks for the input. I have changed the tubes already and though that did help it's still not where I want it to be. I'm going to build a new cabinet for the amp and put in a new speaker soon so maybe I will be closer to what I want then. I really like the clean tone I get from this thing and running an overdrive pedal in line with the signal from my guitar sounds nice; however, when I kick in the built in distortion it fuzzes up the sound but also seems to thin it out (almost like the EQ is all messed up when I do this). Maybe I should just invest in a second pedal. I just hate to do something like that. I have little problem understanding how to modify my guitar or my pedals but when it comes to my amp I'm in the dark. I just don't understand what's going on in there.
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Post by sumgai on Jun 13, 2008 17:43:38 GMT -5
hb,
What those two FETs are doing, as they are engaged/disengaged by the footswitch, is to bypass a resistor (for each stage of V2). This resistor is in series with an AC bypass capacitor on the cathode of those tube stages. An old trick to increase gain, at the expense of tone, is to increase the cap's value, which is what this bypass mechanism is effectively doing.
If you're not comfortable in there, take the unit to a qualified tech, and show him C8 and C9, and tell him you want them changed. I'd reduce their values by half, to start out. Also, changing the values of R23 and R24 might be helpful, perhaps double the values, again to start. There's lots of room to play here, and the interaction amongst just these four components will have a large effect on your overall tone.
HTH
sumgai
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Post by humanbn on Jun 15, 2008 10:40:42 GMT -5
Sumgai,
Thank you for the incite. I am trying to figure out how you can look at the schematic and tell what these resistors are doing. I can look at it and tell what the symbols represent (resistor, capacitor, etc...) but as far as understanding what function each one serves I don't yet grasp. Could I ask you to recommend a text for me to pick up on this subject? I would like to better understand so I don't just come here and ask some one else to do the thinking for me. Thank you again. I will try switching out these resistors soon.
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Post by sumgai on Jun 15, 2008 12:42:48 GMT -5
hb, I don't have anything that I'd recommend as an all-around tutorial, I only google for specific things when I need them, like now.  Here's a page that explains very well what happens when you bias a tube with both a resistor and a capacitor on the cathode - saves me a lot of typing.  www.tpub.com/content/neets/14178/css/14178_43.htmRemember that in most cases, there's no additional resistor between the cap and ground, yet there is one in your amp. (Actually, one per stage of V2, labeled as R23 and R24.) For your purposes here, once you understand the theory behind C8 and C9, the reason for shorting those resistors with the FET's will become obvious. ;D HTH ........... And no problem about asking questions, that's exactly why we're here, and why we stick around.  sumgai |
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Post by 4real on Aug 22, 2008 1:37:09 GMT -5
I could have started a new thread...but I see there is one already... Here is a link to the "Unofficial Hot Rod Deluxe Website" with a bunch of mods... studentweb.eku.edu/justin_holton/faq.htmlI don't mind messing with guitars, but amps and especially tube amps do kind of scare me  The HRD is one of the most popular amps ever...and I got one about a year ago and I love the clean channel and the reverb is superb... Almost everyone hates the drive and more drive channels. These are tube stages so they got to be good right...wrong! I use the clean channel and a distortion box of choice to get a dirty sound...you are still overdriving the tube clean channel but more control than the channel switching. People have devised mods for the channels...I don't know enough about them, but not as easy as changing a chip though. A big problem is the sneaky and cynical use of a linear pot in the volume control. These amps are a loud 40 watts, plenty to play with a drummer or small band...however, to give the illusion that the thing is louder than it really is, fender put a linear pot in there so that the majority of gain is between 0 and 2 on the dial...as they go up to 12...that's not a lot of usable range. The consensus is that this was done so that when people try them in a shop they put it on one and get blown away...2 is very loud...so they figure it must continue to get louder. Unfortunately, changing stuff in these is tricky as the pots hold the circuit board and everything up in there with special pot holding brackets!~  Above is a solution to sounding even louder and bigger...I have a 15" extension speaker in a closed/ported bass box. With this the amp pushes a lot more air and I have to turn down all the way to...errr...1.25 instead of 2. Also puts the amp up safe off the floor and the controls at a convenient height. The clean channel on these amps are beautiful and it does seem a waste to have these extra tube stages going to waste... If anyone has one or especially done mods or knows about valve amps...encouragement would be required before I hack into this thing...still that volume control is a temptation, there are probably a bunch of hidden sounds at various gains between 1 and 2 and it would make life easier to control...well volume anyway... pete |
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