Those are more like Marshall values. I dont think they work well in Fenders. The only change I'd do is R12 to 100K and C5 to .022.Originally Posted by Alcaraz
Those are more like Marshall values. I dont think they work well in Fenders. The only change I'd do is R12 to 100K and C5 to .022.
Ok! Thank you JAM! I'll start from the basic mods then and leave those!
In my previous message I was about to write: "You forgot a 100k resistor for R12 ;-)". Then I decided not to write it, because, that mod actually increases bass, which is not what we want with this amp. However, again trying to go as close to a standard Fender circuit as possible, I did that mod in mine (you can read it at the beginning of the thread), and the mod is still there. I did the mod together with something else, so I can't judge about it alone, but at least it doesn't sound bad! It narrows the mid cut achievable with the mid pot, if you want a further technical explanation (not that I have noticed that, though...). However lowering it to 56k is too much, IMO. Again, the standard Fender tone stack slope resistor is 100k.
Those C7 and C5 stock values are Fenderd standard, too. Why changing them?
Doubling C7 will give you a permanent bright function, which might not be helpful with your drive sounds. However, the bright switch of vintage Fender and also Mesa amps actually adds a cap in parallel to the 250p one. So if you're only using this amp for cleans and you like a vintage Fender amp with the bright switch on, you might like that mod. As it is a simple paralleling mod, you might try it temporarily and then go back to stock.
Reducing C5 to 22n will cut some bass and give you more mids. This is theorically in the "right" direction for this amp, but I think it will change the whole character of the amp a lot.
However, if you look for "duncanamps tsc", you will find a freeware program that allows you to see how the different values in tone stacks affect the frequency response. It is very nice, and it will guide you through the most appropriate mods for your tastes.
Giulio
I dont know amout Mesas, but Fenders use a 120pf cap across the volume contol for the bright, not a parallel 250pf with the existing 250pf in the tone stack. I have seen the additional cap used as a 'mid boost' however. It's a matter of taste ultimately.
That's why I wrote "a cap" and not "a 250p cap" ;)
Mesas use a 750p, in fact.
Giulio
Thanks again! I'll start from C11, C1 and R9. I'll also try the R24 cap and the trimmers that Thom suggested for R42 and see what I can get.
I cut R103 and now the reverb is great! :)
I had 250pf on my mind, which I've seen used, but my point is it doesnt add brightness. The Gxx series Yamaha amps (SS) did a similar thing for a 'pull fat' for example.
Last edited by JAM; 02-20-2008 at 09:07 PM.
I use EL84s in my HRDx and it rocks. No soldering and completely reverseable at a gig in 1 minute flat. Just like the manual says, no rebiasing needed - I checked before and after and it was dead on. If you want sound clips, I've got them.
Cheers
"I bet your Momma was a tent-show Queen ..."
I'd love to hear som nice clips JJGross :)
I am having trouble finding a good place to get caps. Can anyone recommend a place?
One seems to be a problem. The C11 cap is listed on the schematic as 390 pF @ 1kV. I can't find anything that is rated for 1000 V.
I already cut R103 and the reverb is much more manageable, sounds great.
That cap could be changed to a 47pF, I did that.
Shouldn't need more than a 500V rating.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Are you sure for C11? Seems like that would let even more high signal through to the drive channel. I already have problems with highs in the drive and want to cut out more highs in the drive. Most people are suggesting an increase at C11 to 1.4 - 1.5nF
C11 is basically a 'bright cap' on the MV. As a bright cap, 390pF seems quite excessive.
Going to a 1.5nF is the same as 1500pF. Really excessive, IMO.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
I see that a lot of people are complaining about their drive channel being muddy and the decrease you suggested to 47pF is a typical mod. I seem to have the opposite problem with my HRDx and have too much high chimey sound in my drive channel. Since I can increase the value on C11 by adding a cap in parallel, that's what I'll try first to see, if I don't like it, it's easy to remove. For the mod you suggested, I would have to replace C11, which I might try later.
At any rate, where do you get your parts from, I would like a recommendation for a good place to order them online as all of my local electronics shops have been put under by Radio Shacks.
http://www.mouser.com/
http://www.tubesandmore.com/
http://www.tedweber.com/
Thanks, JAM.
I usually order from Mouser, too. Try both caps to see which you like better, they're really cheap.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Maybe you are referring to another cap, C11 shunts high frequencies to ground!
Giulio
HUGE WARNING !!!
I opened my amp, and see that 3 resistors aren't at schematic's value (11 august 95, rev B.)
all values are in first stage of normal and drive volume....
So R9 is not 220k but 270kOhm on PCB.
R52 is not 180k but 240kOhm on PCB.
it change a little bit the cut-offs frequencies....
moreover, R44 is not 180kOhm but 56kOhm instead.this later control the gain of first stage.
So, before doing any mods to my amp, I will do some further calculations :)
My PCB is dated 2002.
Take care.
Largol.
let me know if you discover something else....
Maybe...of course, my Hot Rod hasn't been a Hot Rod in a loooong time, so I forget some of what I did.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Mine's from the 2002 rev. and it has some value changes too. But I think you only have to recalculate a R value from the proposed changes.
OK, I got home from work today and the parts I ordered were here.
So I got right to making the mods.
Added 1nF in parallel to C11 for a total of 1.390nF
Replaced C1 with 22uF
Added 180k in parallel to R9 for 100k
(cut R103 a few days earlier)
This really made a big improvment and the drive channel is pretty deacent now.
I was planning on adding 3.2nF in parallel to C23 but the existing cap was installed all the way down to the insulation with no room for me to jumper anything on. The legs were snipped way to short to try to pull it away from the board. I'll have to totally replace it to a 4.7nF but I didn't order that cap.
Thanks everyone for the great thread and the help.
I'm a bit confused by what you say Falco, I explain why:
The best improvement you made is C1 lowered to 22uF, it's a typical fender Anode tube biasing...
having R9 fixed at 100kOhms is to block hum in clean channel 'cos 72 Hertz is the high-pass
filter frequency (assuming you didn't do a change at C10 value). Well, why not, but it's for the clean channel!
regarding C11, it forms a low-pass filter with the master potentiometer. So at first sight and if i'm not wrong, it's calculated frequency made by fender was 4080 Hz. It means it let frequency pass to the next stage,from close to zero Herts up to 4080 Hz which (to my point of view helps cutting a ripple in the eminence legend 125 speaker's respons-curve)
So why change that C11 value to lower the cutt-off frequency of that low-pass filter ?
Is it to make the drive channel darker, with more bass ?
I need explanations, I want to mod my amp but that C11 value is critical beacause it's close to the power-amp section....
Thanks for your answers.
Regards.
Largol.
Got the answer to my question, it's to tame that high chimey drive sound! I should have read the whole posts....
Glad I could help, lol.
I'm waiting for the components to do it. I'm going to try the "Y" with the trimers and de cap too.
It was said before in the thread that changing C23 value may cause intermodulation distortion, isn't it? So I would leave the original value.
I think the initial mod at C23 stated was to increase to 10nF, this was too large. A smaller increase say to 4.7nF was suggested, this is also the mod listed at the Unofficial Hod Rod Deluxe web page.
My amp's overdrive may be sounding good enough now that I won't change C23.
I have two Hot Rods and I have been tweaking them ever since i got them about 3 months ago. I'm a frustrated EE and was looking for a project. I began by buying the HRDX from some guy in Bakersfield CA on Ebay. He said it did not work. I played it for about 3 hours before it finally crapped out. I hung out on Jason's site and did every mod but the input jacks. I replaced all the signal caps with Orangedrops and beefed the thing with all of Jason's wisdom. While playing it, it crapped out again. I opened it up to find one of the zener diodes (16v) actually heated up from R77/78 nearby on the circuit board and popped off the board! Hot enough to soften solder. When it did, the voltage (wrong polarity) hit the 8 pin dip chips and burned them up.
I ordered new zeners, and dip chips then devised an off PC board R77/78 mod. I remote mounted 50W resistors (bought from Mouser) on a piece of aluminum angle (bought at Home Depot). The mod is perfect, no trouble ever since. I read a lot of people concerned about noise but not a sound, even at gig levels. These stock 5W resistors are a major cause for these amps hitting the dumpster. They put so much heat on the PC board that they turn black. Fender really cheaped out on the 16V circuit. This is a simple mod. If anyone is interested, let me know.
I have a 4X10 DeVille that i bought with a road case for $200. It also has issues! I will do the R77/78 mod on this one next.
Just bought a 65 DRRI on craigslist. It is sweet! It works so i need another project?
Student of the Blues
Sounds like a kit-build is in your future!
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
Am I the only one who thinks any mod to these amps short of gutting the chassis and building in a good circuit is like putting lipstick on a pig?
...cue the horse in the cape...
Several guitars in different colors
Things to make them fuzzy
Things to make them louder
orange picks
no - your probably not.
But no need to kill a good thread that is allowing some peole to get and share information that is helpful for them. No need to do the "Dog pile on the rabbit " bit.
Kenny Belmont
>:^{I)>
This has been an interesting an informative HRD thread.
But in the end, a rebuild is usually in order. It's just the PCBs...they can't handle repeated mods.
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
I discover my amp is a "2nd" revision schematic, dating from year 2002.
It was checked and approved the 19 september
2002.
It leads me to change my mods. I have done the master volume mod: 250k pot log, R25=142kOhm, C10 remains the same, C11=150pF, so i don't change roll-off frequency , I might had like a lot of forumer a 1 nF in // to C11.
So the main difference with 1st rev of the amp (schematic from year 1995) is the incerased value of R9=270k (instead of 220k), R52=240k (instead of 180k), C23 and
C18 remains unchanged....
The normal/bright switch applies to tube V2-A and not V1-B like in 1995 amps...
It means that the bright switch is applied after the tone stack and not before like in older version of the amp!!
Does that revision matters concerning the bright switch ?
any comments or ideas ?
By the way I lowered C1 and C56 to 22uF instead of 47uF. It's much more a traditional Fender value for biasing correctly cathod.
Best regards.
Largol.
I've just made some of the mods and I have to say I can't believe this amp could sound so good!
I changed C1 to 22uf and R9 to 100k and the clean channel is awesome! Now it really sounds like a Fender, very close to a Deluxe Reverb, but I feel it with more body. I tried a low gain tube in V1, but I like a 7025 on V1 lowering the gain with C1.
For the Drive channel I tried the C11 mod with 1nF and 1,5nF and fixed it a bit but still wasn't a good overdrive sound and the More Drive wasn't good at all to my ears. But the trimmers mod ˛Thom suggested works great! You can eq the drive channels to sound really good both! And you can get a clean sound very very close to the clean channel rolling back the volume. I couldn't believe it when I heard it!
Now I don't need overdrive pedals anymore! Believe me! Just try!
Thank you very much Giulio and ˛Thom for that mods!
I have to say that I play my hot rod almost every day for more than 2 years and not a single problem!
I'm glad it worked for you as well!
Giulio
I'm really confused on what to add to my lovely amp.
had trouble to understand how to do the Y modification.
And why adding a 5,6nF in // to R24, what's the exact purpose?
thanks.
Largol.
I can mod as far sa I want I just bought a special liquid to make again the copper foil, delaminated from PCB!
No need to have a turret board, NT Blues Guitar :p)
What fun is that, then?
"...pray do not imagine that those who make the noise are the only inhabitants of the field;
that, of course, they are many in number; or that, after all, they are other than the little,
shriveled, meagre, hopping, though loud and troublesome, insects of the hour."
-Edmund Burke
I found a special liquid that is conducting electrons, replacing copper foils when damaged!
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