New Approach to a Classic 30

[randomhitz]

Hi Everyone--I'm new here, been lurking for a while. I'm and old fart (62) who's been messing around with tube amps for a long time, but with spotty technical knowledge. I've logged quite a few hours with a soldering iron, but I'm finding it harder to find the motivation to tear into a piece of gear these days.

Here's my situation: For many years I just showed up for a gig with a 65 tele and a brown Fender Concert, but I was never that much of a tone tweaker. For various reasons that gear is gone now, but in my semi-retirement I have a renewed interest in playing (finally have time to work on becoming the guitarist I always wanted to be) and have discovered how much good tone influences one's playing. To that effect I've settled on a Classic 30 with JJs and a Cannibis Rex speaker. Both great improvements.

Here's where my thinking is going now: Even though I find myself gravitating toward cleaner tones in general, I still like enough dirt so it warms things up a bit and if I dig in i get some decent overdrive. I never play loud enough to get the clean channel on the Classic 30 to break up, so I'm stuck with the overdrive channel, which I still like better that overdriving the clean channel with a pedal. However I don't like the the more midrangey, bandwidth liimited basic sound of the overdrive channel compared to the clean but live with it by running an eq on my pedalboard to compensate.

What I would like to do is be able to blend the two channels. Looking at the schematic it looks like I could bypass the channel switching relay and just have the two channel combine into a resistive Y network. There's an R/C network that also gets switched by the channel switching relay bedtween the first and second gain stages of the overdrive channel. I'm not sure what this does but I wonder if this accounts for the different basic sound of the overdrive channel. What I would like to if possible is dedicate the channel swithching relay to switching the boost circuit, with appropriate modification to the boost circuit so it's not so ridiculously midrangey.

In addition the above mods I plan on doing the Blue Guitar tone stack and Fenderized front end mods. What I would like from the wonderfully helpful folks on this board is an opinion on whether the channel combining mod would work, as I would like to get all the mods done at one time by someone else. I feel technically competent to do the soldering work but I just don't think I have the oomph to get it done at this point (recovering from some health issues). Any chiming in would be appreciated. At this point I'm just looking for opinions on whether the idea is sound, not instructions on how to do it.

Thanks
Randy

[txstrat]

Hi Randy
that sounds like you would go for the ultimate versatile amp (=UVA -think of me when you make that a registered trademark- )
But it will leave you with sort of one sound at a time, wouldn't it?
Did you consider to tweak the clean AND the dirt channel both a bit to your taste? That way you'd still have two switchable sounds.

Matt

[tubeswell]

Steve Ahola's Tone stack mod is the cat's pyjamas for this amp. Last year I came up with an "SLO100" pre-amp mod for the overdrive, which doesn't exactly combine the channels in the way that an SLO100 does, but it sound better to me than the stock OD sound. For details see:

http://music-electronics-forum.com/s...ead.php?t=9416

If you thought about it a bit you could probably combine the pre-amp in a way that did give you a blendy channel thing like the real SLO100 front stages.

Working with the pc boards in that amp is finnickity.

[Enzo]

Not sure what you mean by channel combining. There is one channel through this amp. The dirt channel is made by inserting the extra tube into the path of the clean channel. (V2) A couple other small details switch at the same time. The difference in sound is mainly due to the signal running through the two additional gain stages.

[randomhitz]

Enzo--Sorry for the confusing terminology. It is a single channel amp with the option of inserting an extra gain section. As I read the schematic it looks like the output of the first stage is routed two places, throughVR1 to the relay switch that routes it directly into r14 and on into the input of V1b The output of V1a is also routed to the V2 overdrive stages. the two paths could be mixed together were it not for relay K1b. If K1b was not there the two paths could be combined with the blend controlled byVR1 and VR2 assuming the two signals remained in phase. From my limited knowledge a resistive Y network would minimize interaction between the two signal paths. I don't know how VR1 and VR2 gains would interact. They seem isolated enough stock.

To me the change in the sound of the overdrive channel is drastic enough in terms of less bass, less highs and more mids that I suspect a specific attempt to voice the OD channel so the signal cuts through better. I remember Steve A. tweaking the boost switch eq but not clear about whether he treated the overall frequency response of the OD section. I'm not sure what the purpose of C1 and R5 is, but I know their path to ground is switched by K1. Hope this makes clearer what my basic idea is.

Randy

[txstrat]

There is one channel through this amp.

Oops.
I didn't read the schematic. Please discard my last post.

[tubeswell]

It is a single channel amp with the option of inserting an extra gain section. As I read the schematic it looks like the output of the first stage is routed two places, throughVR1 to the relay switch that routes it directly into r14 and on into the input of V1b The output of V1a is also routed to the V2 overdrive stages.

It is a single channel amp with the option of switching in two more gain stages (comprising both triodes in V2), making four stages in total at the beginning of the pre-amp

the two paths could be mixed together were it not for relay K1b. If K1b was not there the two paths could be combined with the blend controlled byVR1 and VR2 assuming the two signals remained in phase. From my limited knowledge a resistive Y network would minimize interaction between the two signal paths. I don't know how VR1 and VR2 gains would interact. They seem isolated enough stock.

To me the change in the sound of the overdrive channel is drastic enough in terms of less bass, less highs and more mids that I suspect a specific attempt to voice the OD channel so the signal cuts through better. I remember Steve A. tweaking the boost switch eq but not clear about whether he treated the overall frequency response of the OD section. I'm not sure what the purpose of C1 and R5 is, but I know their path to ground is switched by K1. Hope this makes clearer what my basic idea is.

Like I said before, check out the SLO100 schematic. It has a permanent clean channel that uses two opto-isolators to switch in a couple of extra stages 'in parallel' with the 'clean' 'channel', the later of which stays connected throughout. The difference with the PV C30 is you end up with 2 or 4 stages in sequence at the start of the pre-amp, depending on the switch - with the SLO100 you have three in sequence and another one (that is always 'on') 'in parallel' with the 2nd two (of the 1st 'three') at the start of the pre-amp.

[randomhitz]

Thanks Tubeswell--I didn't see the thumbnail for the schematic the first time around, just the substitution list. looks pretty straightforward. Here's a quandary: After reading Steve A. rave on about how well the Soldano mod works in his Crates, I'm wondering if that would be a better modding platform for what I want, given the hassle of the C30 setup. I had it apart once when I first got it to see if I could figure out what the deal was with the reverb hum. It was definitely a pain to work on. The C30 has always had some basic hum in the preamp stages besides the reverb hum and I was hoping that could be solved when doing the tone mods. But I also know how tricky and time consuming the process can be. I was prepared to pay someone (I have no scope or other test gear at this point) to do the whole enchilada, but with the Crate option I would feel comfortable doing it myself.

[randomhitz]

I want to thank everyone who has replied so far. However, if I could, I would like to get some specific feedback on the idea of dumping the gain switching relay and using a resistive Y network to combine in parallel the output of gain stage 1 with the output of gain stages 2 and 3. I hope I'm being clear enough for folks to understand what I'm trying to do.

Thanks,
Randy

[tubeswell]

Thanks Tubeswell--I didn't see the thumbnail for the schematic the first time around, just the substitution list. looks pretty straightforward. Here's a quandary: After reading Steve A. rave on about how well the Soldano mod works in his Crates, I'm wondering if that would be a better modding platform for what I want, given the hassle of the C30 setup. I had it apart once when I first got it to see if I could figure out what the deal was with the reverb hum. It was definitely a pain to work on. The C30 has always had some basic hum in the preamp stages besides the reverb hum and I was hoping that could be solved when doing the tone mods. But I also know how tricky and time consuming the process can be. I was prepared to pay someone (I have no scope or other test gear at this point) to do the whole enchilada, but with the Crate option I would feel comfortable doing it myself.

The mod I did changes the voicing on the clean channel as well, so its up to the beholder whether you think its worth it or not. I hear what you're saying about how tricky that amp is to mod. I've modded mine umpteen bazillion times, and you got to have the patience and perseverance of a saint.

Re; the hum, switch the amp on and don't plug the guitar cable in. Turn the vol up - how much does it hum? The hum could be caused by your guitar cable (induced capacitance) or a poorly shielded guitar pick-up cavity. Try it with different cables and guitar to see how much the hum changes. I have found the C30 to be a pretty quiet amp hum-wise.

[randomhitz]

The hum is constant and static. It is not affected by whether there is any guitar or cable plugged into the input. If the gain is turned up the hum level stays the same as the white noise for the amplifier stages increases. plugging a jack into the effects return with eliminate it, suggesting the hum is in the preamp stage. Because the leve of hum is not affected by any of the tube gain stages it makes sense to me that one of the ICs in the reverb or effects/in-out sections may be to blame. The hum does grow as the reverb send is increased, but I've always assumed that a separate issue present on all C30s. Any thoughts would be appreciated.

[tubeswell]

Hum can also come from a bad tube. Since it appears before the PI (the FX return is before the PI), then try swapping out V1 and V2 with other tubes and see if that makes a difference.

[randomhitz]

The hum has been there from day 1 (I bought it used about 12 years ago). Done several complete tube swaps since then. I'll check it again though.