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  • #16
    Preventive measures like those are like seatbelts in your car - until the need arises, they sit there in the way. DOn't worry about it, I was just pointing out the reason they are there.
    Education is what you're left with after you have forgotten what you have learned.

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    • #17
      Cathode bias mod...

      Daz,

      What's the address to Steve's site? I'd like to do that cathode bias mod.

      Thanks,

      Dave

      Originally posted by daz View Post
      The first mod i'll mention because i felt it was a huge improvment was to cathode bias the amp. It's actually a very simple mod. there's a gif schematic on steves site that shows the changes, but enzo recommends one difference that i found to be better......a 100 ohm cathode resistor instead of the recommended 60 ohm. This mod really opens the amps tone up and makes it transparent and much more pure and organic like a simple tube amp. the next was the C4 swap as mentioned. The mods recommend a 680 or 820 PF cap, and i found the 620 worked much better. It helps the lead channel a lot and drops the gain down a bit. the processed nasally sound is gone. The last was the input where i simplified it to a classic fender or marshall input. theres loads of garbage there that i think caused the amp to not take pedals very well.

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      • #18
        Wow.......this is almost a year old post ! Would have never seen it if i didn't get email notifications when someone posts in a thread i posted in !

        http://blueguitar.org/

        You may have to spend a lot of time looking for it because he has a ton of small text files and such and i recall the CB notes were buried in the site. Look to the "ftp" link.

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        • #19
          New old C30 - needs a tweak or two

          Hi. I had a Peavey Classic 30 about 15 years ago and I loved it. Having been through a slew of different Fender and Mesa amps since then, I have just manage to get an old (1994), tweed C30 on eBay in pretty good condition.

          Recently, I have been modding a Epi Valve Junior and decided to do a scratch build using tag strips and 'best' components, so I have got a little amp that I consider to be the best sounding amp I've ever owned - unfortunately, it is not powerful enough to play with at gigs without sounding 'stressed'. I have tried lining it out into the C30 via its FX return, which is okay but I would like to tweak the C30 to get more 'sparkle' on its own. It sounds dull in comparison to my SE 5 watter.

          I like a clean(ish) sound so I'm not really interested in the drive channel. I do play blues but it is of the vintage electric variety - T-Bone Walker, Jimmy Reed, Muddy Waters so I'm after the bright sound old old Fender amps with just a hint of grit.

          I have found Steve Ahola's mods at blueguitar.com and I'm going to do the input and tone stack mods and change most of the caps to Orange Drop or micas. I have changed the EL84s to JJs and the 12AX7s to Electro Harmonics. I have a new Celestion V60 in there.

          Question is, what is the best mod to add 'sparkle' to the C30's clean channel - cleaner highs, more transparency, slightly more scooped mids?

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          • #20
            Hi Joey

            I have a C30 I've modded ad-infinitum. Steve Ahola's mod to the tonestack and boost does the most for this amp (But it does alter gain - I put a 120K at the Plate of V3A to compensate). I also did the 'fenderising input' mod but with a sheilded cable from input jack to Grid pin of V1A - I used the 68k grid stopper here. I also put a 22pF RF bleed cap to ground at the input jack

            I also replaced all the plate resistors in the pre-amp with metal film.

            I upped the B+ and B++ by lowering R59 and R60. I have tried various combinations in here and at present have both at 8K2. This adds a certain vintagey tone to the clean channel without changing the PI too much. I have a modified Plessey/Celestion Bulldog in the amp at present. It gives the best sound yet.

            In the OD channel I didn't like the stock OD sound, but I haven't quite cracked it yet. I dumped C7 altogether and made R9 into a 1M grid load resistor. I also dumped R13 and C16

            I kept the 1k5/22uF cathode combo at V1A and V1B, and at present have the Rk at V2B at either 2k2 or 4k7 (I think?) with a switchable 10uF cathode bypass cap (which sounds too bassy). I have the cathode combination at V2A at 1k5 (or 1k - can't remember which) and 1uF. I don't like this OD setup much as its only any good on the bridge pickup, so I'm still comtemplating the OD channel. At the suggestion of Amp Kat I tried the SLO100 values at one stage, and the OD sounded pretty darn good with that, but lacked the fenderyness in the clean channel, which I got upset about, so I undid it. I still am contemplating revisiting the SLO100 values solely in V2A and V2B (solely because I really liked the result in the O/D channel) but with a switchable cathode bypass cap in V1A to keep the 1k5/22uF if I want it.

            I did the 'proper' presence (see schematic) and MV mods, and did a resonance mod by changing R56 for a 500kA pot. These give quite a bit of flexibility to the tone manipulation. I liked these so much that I eventually hacked the amp around quite a bit to fit all the knobs and switches on the back where they can easily be got to (see photo). As I prefer the controls where I can reach them relatively easily, and as it is my favourite gigging amp of all time and I never want to part with it, I don't care about what others think - they'll never get an opportunity to buy it. :-)
            Attached Files
            Building a better world (one tube amp at a time)

            "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

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            • #21
              Thank you for the details tubeswell. Much appreciated.

              I'm not too concerned about the OD channel. I don't understand your SLO100 reference. Are you referring to the 150K cathode resistors. These are usually 100K in Fenders, are they not?

              From my experience, R19 is a critical component to the voicing of any amp with a TMB tone stack. I have a three-way switch there on my VJr giving 100K, 68K, 47K which gives various degrees of treble and bass separation. I might try that here too.

              I am a bit loathe to add extra pots but I can squeeze in a couple of 3-way miniature toggles. Would tinkering with the 'presence' resistor values give me the sparkle that I'm after or is it all those small caps going from signal path to ground that is creating the wet blanket effect?

              Comment


              • #22
                Originally posted by joey View Post
                Thank you for the details tubeswell. Much appreciated.

                I'm not too concerned about the OD channel. I don't understand your SLO100 reference.

                I was talking about adopting all the resistor and cap values that are in the Soldano SLO100 O/D channel for the C30 O/D channel. The SLO100 preamp has a topology that is similar to the C30 preamp. The middy sounding O/D channel in the SLO100 sounds quite nice to my ear. I am thinking that it would be good to try this in the C30.



                Are you referring to the 150K cathode resistors. These are usually 100K in Fenders, are they not?

                The Cathode resistors in Fenders are typically 1k5 (not 150k). The Plate (Anode) resistors in Fenders are 100k.



                From my experience, R19 is a critical component to the voicing of any amp with a TMB tone stack. I have a three-way switch there on my VJr giving 100K, 68K, 47K which gives various degrees of treble and bass separation. I might try that here too.

                Be interested in your opinion of the results



                I am a bit loathe to add extra pots but I can squeeze in a couple of 3-way miniature toggles. Would tinkering with the 'presence' resistor values give me the sparkle that I'm after or is it all those small caps going from signal path to ground that is creating the wet blanket effect?

                The caps in the NFB don't go directly to ground in the stock configuration, there is a 10k resistor blocking the path, so the stock combination acts as a tone control. Chucking a 10kN pot mod in at R70 allows diversion of the signal from the NFB that gets through caps C53 and C54 in the stock configuration to ground. When the pot is open in the modded configuration the 150R in the mod then stops them from being reduced in value to the point where they would only bleed high frequency from the NFB to ground. The presence mod shown on the above schematic works alot better than tinkering with the 100K resistor at R57. I have tried a pot substitute for R57 initially (as per Steve Ahola's orginal mod notes) and it doesn't do much at all (I suspect due to the fact that there are all those other caps and resistors in the NFB loop). The ultimate in 'sparkle' would simply be a switch that just opened the NFB loop (I'd say between the R57 and C36 junction). I didn't want to do this because I wanted to keep the resonance mod working. Hence I went to some lengths to alter the cab to enable the chassis to be situated forward of the stock position by 22 or so mm. This gives more protection to the knobs and switches I have added on the back. Peavey should build all their classics like this in any event, to make it easier for guys like me to mod their amps. ;-)
                Cheers
                Last edited by tubeswell; 03-02-2008, 02:40 PM.
                Building a better world (one tube amp at a time)

                "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                Comment


                • #23
                  The Cathode resistors in Fenders are typically 1k5 (not 150k). The Plate (Anode) resistors in Fenders are 100k.
                  Sorry, I'm getting cathode and anode muxed ip as usual What would be the effect of changing the 150Ks to 100K?

                  >From my experience, R19 is a critical component to the voicing of any amp with a TMB tone stack.

                  The Ahola mod changes this to 56k
                  I see that, but a typical Fender (or most other) TMB tone stacks would have .047µF at C14 and 100K at R19. Problem is that the C30 isn't as easy to work with as a tag strip build so I want the options hooked to switches.

                  The caps in the NFB don't go directly to ground in the stock configuration, there is a 10k resistor blocking the path, so the stock combination acts as a tone control. Chucking a 10kN pot mod in at R70 allows diversion of the signal from the NFB that gets through caps C53 and C54 in the stock configuration to ground. When the pot is open in the modded configuration the 150R in the mod then stops them from being reduced in value to the point where they would only bleed high frequency from the NFB to ground. The presence mod shown on the above schematic works alot better than tinkering with the 100K resistor at R57. I have tried a pot substitute for R57 initially (as per Steve Ahola's orginal mod notes) and it doesn't do much at all (I suspect due to the fact that there are all those other caps and resistors in the NFB loop). The ultimate in 'sparkle' would simply be a switch that just opened the NFB loop (I'd say between the R57 and C36 junction). I didn't want to do this because I wanted to keep the resonance mod working.
                  Is the tone brighter with the 10K(R70) in play or when it is shorted across? From what what I understand, C53/C54 are shunting treble to ground thus feeding back a treble cut signal that would boost mids and lows???

                  ... I went to some lengths to alter the cab to enable the chassis to be situated forward of the stock position by 22 or so mm. This gives more protection to the knobs and switches I have added on the back. Peavey should build all their classics like this in any event, to make it easier for guys like me to mod their amps. ;-)
                  I noticed that in your photo. I would be inclined to have the knobs pointing downwards so that that isn't necessary but I see that you have added a speaker jack? in that position. My plan is to replace the stock speaker jack socket and pedal socket with better quality units. The stock speaker jack seems to be flaky in my amp. As I'm putting in an 8 Ohm speaker instead of a 16, I am going to wire the external jack for series to connect a 8 Ohm external speaker in series and hook up the internal speaker to the 8 Ohm tap. I'm not quite clear what Steve Ahola is suggesting in his notes but when I connect an internal 8 Ohm speaker to the stock external socket, the connection is poor and sometimes cuts out completely.

                  Anyway, putting extra knobs and switches in would only be a temporary stop-gap situation so that I can make variations without continually taking the PCB out and in. When I get the tone I want, I will let them be.

                  Isn't it amazing that we can have this dialog from opposite corners of the World

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                  • #24
                    The amp is more lively (i.e. brighter) when the 10kN is open.

                    The effect of changing a 150k plate resistor to 100k is to incease the plate voltage, which decreases the gain/cleans up the signal from that gain stage.

                    I wired the internal speaker to a 1/4" socket so I could either run 1 x 16 Ohm or 2 x 16 Ohm or 1 x 8 Ohm speaker configurations from the amp. either as a combo or a head.

                    I too had problems with the extn speaker socket as it eventually wore out with time, and the plugs wouldn't make proper contact with the ground terminal in the socket. So I simply replaced the socket with a locally available switching socket and wired it to the same configuration as stock.

                    In the stock setup, the 16 Ohm tap runs through the 8 Ohm socket via a socket tip switch when the 8 ohm socket is unplugged. When you insert a plug into the 8 ohm socket, it disconnects the 16 Ohm tap and connects the 8 Ohm tap, putting both the 'internal' speaker and the extn speaker in parallel. With the Ahola internal speaker socket mod, you can simply disconnect the 16 Ohm internal speaker and run an 8 Ohm speaker/cab only from the 8 Ohm socket this way.
                    Last edited by tubeswell; 03-03-2008, 03:24 AM.
                    Building a better world (one tube amp at a time)

                    "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                    Comment


                    • #25
                      Had to let you guys know, I just got together with a local musician, working on some recording (he has a studio in town), doing guitar lessons and repairs, maybe minor amp repairs but definitely nothing heavy duty, and he has a Classic 30. First time I hooked up my Super Reverb he listened for about 30 seconds and asked why he couldn't get that kind of bass out of his C 30. It had almost no bass at all, which is why I passed up a chance to buy one for $150 several years ago. Now I'm kicking myself, I didn't know then you could modify them at all...

                      I got online and looked up what the knowledgeable folks here had to say, found this thread pretty quick, since it had just popped back up on the first page, and printed out the pdf file from BG.

                      Changed out just the bass cap, it wasn't hard to find at all but wasn't easy to get to, since i wanted to bend the board as little as possible. (it's a 30 minute drive to the nearest place to get the caps I don't have, won't be able to get over there till next week at the earliest).

                      Put in the orange drop, .047 I think it was, or .47 I don't have the printout in front of me as a reference, but anyway that's the only one I had so I soldered it in, put everything back together and turned it on for a sound check about two minutes before the owner came back from running errands...he walked in and I was playing my Squier strat through his C 30, soon as he looked to see what I was plugged into since my amp wasn't there, it stopped him in his tracks and his jaw fell halfway to his knees.

                      EDIT: It's a .047, just realized I have the PDF file on this computer...CRS strikes again...

                      He talked about it all day, needless to say he was very pleased with just the swap of the one bass cap, it's literally a different amp now. Night and day. I'm not sure if I'll swap the other caps in the tone section, we'll have to listen to it a few times and see how it goes. This might be the only change made, it really does sound great, he loves it. I'm not into seriously modding anything to begin with and he just wanted more bass, so this might be the only change made.

                      So I had to get back on here and tell you folks thanks a bunch, it was way cool to see the look on his face when he realized that was HIS amp he was hearing. (I didn't pull this as a surprise, we had discussed doing the mod, he just didn't know I was doing it yesterday while he was out of the shop).

                      You guys are great, thanks very much for the knowledge you share and the time you donate to doing it. He LOVES the amp now. Can't stop talking about it, plugs in and plays it any time he has an excuse to...or just wants to show it off when someone comes in and starts talking amps.

                      Thanks. He's a happy camper.
                      Last edited by Paleo Pete; 03-15-2008, 12:35 PM.
                      Why do I drive way out here to view the wildlife when all the animals live in town?

                      My Photography - http://billy-griffis-jr.artistwebsites.com/

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                      • #26
                        Pete, can I ask which cap you replaced? The mid and bass caps are both .022µF in the stock C30 and in the mods I have seen. I have also read somewhere that for more bass it is the mid cap C19 that should be increased NOT C18 which is attached to the bass control.

                        In any other amp, I would just hook another .022µF in parallel with the stock caps with crocodile leads but I really wouldn't want to run a C30 out on the table!

                        Comment


                        • #27
                          Sorry, missed your question and it took a couple of days before I spotted it.

                          I changed C 18, bass cap. Going to probably do the mid and treble later, but have to wait until I have a chance (and a good reason, with gas over $3) to go to the larger town where I can get the 270pf cap I need.

                          It sounds great right now, but still not as warm as my Super Reverb, but just the bass cap made a huge difference. He still shows it off any time a guitar player comes in the store.
                          Why do I drive way out here to view the wildlife when all the animals live in town?

                          My Photography - http://billy-griffis-jr.artistwebsites.com/

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                          • #28
                            Originally posted by Paleo Pete View Post
                            Going to probably do the mid and treble later, but have to wait until I have a chance (and a good reason, with gas over $3) to go to the larger town where I can get the 270pf cap I need.
                            FWIW I used a 330pF as the treble cap and a 390pF as the boost cap (I found mica caps sounded better to my ear - other guys swear they make no diff.). When the boost is engaged, this makes 720pF for the treb cap/boost combo - less of a mid boost, more of a bright boost, and definitely more useable. I found the stock boost too harsh.

                            Another thing I liked was an Alnico Bulldawg - uprated to 35W RMS with a new celestion cone - gives lovely tingley highs and excellent bass, with a hint of ever sooo-slightly papery/woody quality and a nice quack to my strat. A recone is alot more individual sounding - (you never quite know what you're going to get) and cheaper too (Mine was $160NZ all up). I just used it at a gig tonight - rocks the house (unmiked).
                            Attached Files
                            Building a better world (one tube amp at a time)

                            "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                            Comment


                            • #29
                              Cool, thanks for the info. I've been planning to use the recommended 270pf treble cap, (mica) but haven't gotten as far as thinking much about the boost yet, and until I can get the gain pots cleaned up enough to make it usable I won't really know, but from the little I've heard while it was working some the boost sounds fairly decent so far stock. I hate to have to pull the chassis again to clean two pots, but unfortunately I hadn't tried it yet and didn't know they were really dirty until after I swapped the bass cap and put it back together. So far spraying contact cleaner down the stem hasn't done a lot of good, but has cleaned them up a little.

                              I'm sure I'll have to bite the bullet and open it up again, but hoping to put it off until I have a chance to go get the treble cap (30 minute drive so I need more reason than a $1.50 cap) and do that at the same time.
                              Why do I drive way out here to view the wildlife when all the animals live in town?

                              My Photography - http://billy-griffis-jr.artistwebsites.com/

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                              • #30
                                I use 22n/22n orange drop in tone stack with 270pf polystyrene in treble and 56K slope. But boost mode is more complex: 345pF polyester Philips paralleled to 270pf and using the second circuit: 68K paralleled to 56K slope (30K aprox.).
                                With this system the apparent loss in bass produced by the emphasis in middle frequency is avoided and the whole tone bumps.
                                Regards

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