?'s re: Roland BC-30 Amp... Fogman? Anyone?

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I have an opportunity to buy a Roland Blues Cube 30 Amplifier.
Here's some specs...

What I see on the Internet are going for $200 and up (this model is discontinued).
The seller is asking $175 on a consignment sale at a local shop.
The guy at the shop today told me he thought the lady would be willing to go $150

Here's the catch... ... the Lead Channel works but the Clean Channel does not.
The input jack is loose and one knob has a small chip out of it.
I suspect she dropped it on it's head or dropped something on top of it.

I played it today at the store and it sounded just fine with the one working channel.
I tried out a couple of different guitars (different pickup configurations).

I'm no electronics expert... I can solder... I know what a capacitor looks like as well as a resistor, etc.

I feel competent enough to remove parts and solder in new ones.

I only have a multimeter... no scope or fancy diagnostic gear.

I'm wondering if I could open up this thing and maybe find a loose connection or a condenser or capacitor or the like that is definitely blown and replace it.

This is why I called out for Fogman!
But anyone is welcome to post an answer or opinion.

I figure for the money... this one channel amp might even be worth it as it is.
I was thinking of going back Monday and having who ever is at the store, contact the lady for me.
I want to know what she did to it.
I was told she just used it in her house for practice/lessons, but I don't know if she was teaching or being taught.

Anyway, I'm really wondering what the chances are of me opening up this amp and finding the problem with the other channel and then being able to fix it?

Thanks.

It sounds like a cool amp for what it is, but I don't know a whole lot about amps. So it's basically a little fake tube amp?

Yeah, it has some electronics in it that help create a 'sort of' tube effect I guess?

I'm hoping Fogman will see this post because I think he may know something about electronics.
Of course, there might be others here too that can give me an opinion on whether I should attempt to track down the problem with the other channel.

It does sound nice on the one channel that works, plus it's a 12" which is better than my little MicroCube I usually practice on.

I'm getting set up so my pedals are all plugged into my Crate half stack which is in my bedroom.
I like to crank that one up every-so-often when I get tired of the little cube.
But the MicroCube (Roland also) really puts out some sound!

I just want something a bit bigger to carry around to jam sessions, etc., when I get good enough and brave enough to do so!

For vacations or taking my music to work... I have my Line6 PocketPod and the MicroCube.

I figured I could afford the $150 right now and I don't know of another 30watt 10" or 12" that I could buy for this price.

I'd avoid the Roland amp, as it sounds to be a transistor amp that uses what is most likely a compression circuit as well as a clipping diode to simulate tube overdrive. This amp also most likely uses PCB construction with the control pots mounted directly on the PCB. --Depending on the quality of the PCB layout and circuitry traces, this can be a problematic thing.

OTOH, these still go for cheap, and utilise true point to point wiring, which makes them easy to work on as long as you are experienced with working around HIGH VOLTAGE DC current, and take care to discharge the PSU filtering caps. Mostlikely the filter caps will need to be replaced as these are already quite old.

Unlike the Roland that you want, these are all tube designs, and are fairly popular amongst people who mod guitar amps because they are cheap and will yeild good tones. You will have to install a .25" Tipring jack and perhaps to some tonestack modification to them. --Expect to encounter voltages @ 500VDC inside this thing.

There are some reveiws of the finished results here and here.

I would suggest sticking with the CHB series amps, as they all use tubes that are in current production. -- Mine has a 6EU7 in the V1 positon, which is a variant of a 12AX7 with a differant pinout. Other than that, these use current production tubes. The CHB uses 6L6GC output tubes which are used in many current tube designs, and the CHB-35's and CHB-100's use 7868 output tubes, which are a 7591 (Used in a lot of 60's Ampeg designs) variant with a 9 pin (Noval) base instead of the more common octal socket. Schematics are available for download here

For playing at home, 10 watts of rated output is sufficient, 35 watts will make you heard above a fairly loud drummer, and 50 and 100 watt amps are sufficient for playing live in a LOUD band. Remember, tube amps are rated in watts of undistorted output power, anything more doubles the output power, and causes the power amp to compress and clip, which is pretty much the way that guitar players have always played.

Bear in mind also that a lot of cheaper transistor amps are designed with obsolescence in mind, and will be crap in a few years, while older tube amps will virtually last forever with proper care and maintanance. --Most of the really desirable guitar amps are 35+ years old.

If you get one of the Bogen's chances are that you will save some of the cash that you spend on the Roland, even after you do some work on it, provided that you have to equipment and knowlege to work on the amp yourself. --Watch for electrolytic caps that are leaking white or grey crud, have ehat appears to be a tiny white or grey bubble near either of the leads, or appears to have bubbles, or bulges on it's body, these have gone bad and will need to be replaced with caps of the same values.

Also, I cannot stress this enough, the electrolytic caps in a tube amp are capable of storing voltages sufficient to cause injury and even DEATH should you touch the leads to them, so if you don't know how to properly discharge all the caps in a tube amp, leave the work to somebody who can.

Furthermore, I would most likely want to leave a lot of work on one of these to somebody who has a good reputation with tube amps, as you'll need at least this equipment to work on tube amps :

A dummy load resistor of comparable wattage handling to test and set the bias of the amp, without blowing the output transformer through running the amp speakerless with an open load.

A multimeter and an oscilliscope ( for the above)

A variac (to properly charge and form new or long unused filter caps)

Last edited by Fogman on 18 May 2008, 11:32 am, edited 1 time in total.

Also, I'd like to add a link tothis MP3 file. The guitarist of the band, (Rifle Sport, a somewhat influential early 80's punk band from Minneapolis) is a member of a pro audio forum that I'm a member of, and their first demo was posted there for download with his graces.

He converted an old Bogen ( either a CHA-50, or a CHB-50) to use as a guitar amp,as he couldn't afford a 'real amp' when he was initially a member of the band. All guitar tracks on the demo, including quite obviously the track posted here were recorded using the Bogen, which he still has.

I dunno..unfortunately I did have a Peavey Deuce for about 20 years. Sounded great, could wipe out the rest of the band (which they took a dim view of). however, one thing to consider; while tube amps are great sounding, they have this huge chunk of iron in them (transformers, more than meets the back... that will tend to tire you out if you have to schlep them along any great distance.

I got some pop-out casters (wheels) for it, which helped a lot.

Frogman, that was extremely informative! Even though this thread doesn't directly apply to me, I'm trying to learn more about amps, so thank you for all the info.

Do you know of any good books about these old tube amps? I'm going to need an affordable one that I could use to play live with a semi-loud band. I had an opportunity to buy a 1969 Marshall mk2 for $2,000. I really liked that amp - used to use it all the time. But I need something less expensive.

Older Peavey's are built solidly, though they're not the greatest tonally speaking. Other solidly built transistor amps are made by Acoustic Control Corp(Acoustic), Sunn, Kustom/Kasino, Traynor's old TS series, 80's Marshall Transistor amps, Roland JC series, Gallien Krueger, HH, Ampeg's Transistor amps from the 70's, and a few others.

Barring that, though, most Solid State guitar amps aren't built to last. All of them sound horrible when they clip naturally due to the fact that transistors produce odd order harmonics when they clip. --This is why the better ones from the 80's utilise special overdrive circuitry that utilises audio compression and clipping diodes to produce distortion.

Tube amps, OTOH, produce even order harmonics when overdriven to the point of clipping, and have a very dynamic, natural compression due in part to the limitations of tube technology, as well as power supply design.

A transistor amp will produce a very clean signal up until it exceeds it's design limitations, and will sound horrible after that point is reached, and may also fail if pushed hard and long enough. Part of this, is because transistors have peak output power that is much greater than their clean output, and when they are pushed into clipping will eventually overheat and fail catastrophically. Part of this is due to the fact that the PSU in a transistor amp is built for the amp to run clean, unclipped signal, and when the amp is clipped, it is actually drawing more power than the PSU can supply, leading to a loss of voltage. This loss of voltage is called PSU sag. Transistors are very susceptible to a loss of voltage, and will be damaged if the voltage loss is prolonged.

You also need to know a bit about electronics to repair a blown transistor amp because they are designed with componants that are more relieable than tubes, and are designed with the belief that they will not need to be replaced, therefore, the transistors are mounted directly to a PCB. There is also a great variety of transistors that are used, and have been used in the past. --Finding a matched set for a 30 year old amp can be a very problematic thing, much less matching the new ones with transistors that have had 20-30 years hard usage and the resultant spec drift.

Tube amps OTOH, will produce clean signal as well, though when pushed beyond the design limits they will compress and distort predictably with even order harmonics. When tube amps clip, their output will double, beyond that, they will simply compress the signal. When a tube amp is pushed to the point that the PSU sags, the resultant voltage drop will not destroy the tubes, you will simply get more distortion from the amp, as well as an interactive 'touch response' from the amp. --When playing an electric guitar through a tube amp, you are not only playing the guitar, you are also playing the amp as well.

Furthermore, tube amps are engineered taking the inherant fragility/unreliability of the tubes into account, and therefore are easy to maintain. There are only a few specific types of tubes used in amplifiers, and they have for the most part been in production since the late 1940's/early 1950's. Changing tubes in an amp that is cared for properly is a simple process on the order of changing a light bulb, and once the tubes are changed in an amp that is properly maintained, is like having a brand new amp again.

Some of the most desirable tube amps are Fender Amps from the late 50's to the early 60's, as well as Marshall amps (Actually a british close copy of a 1959 Fender Bassman) from the 60's and early 70's, and the pricing of these amps reflects their desiraility as well as scarcity.

That being said, Pakled is quite correct that tube amps are heavy. Unlike transistor amps which only have one transformer, Tube amps have two of them. The PSU on a transistor amp turns AC voltage into DC voltage (usually quite low). On a Tube amp, The PSU turns wall voltage into high voltage, (In North America usually quadruple, sometimes quintuple the AC current) at high resistance. This high voltage/ ohmage must be converted back down to voltages/ohmages appropriate for the speakers, therefore, a stepdown transformer is needed. This will add weight to the amp,however, the only places you should be carrying the amp is to venues/practice spaces/abodes from your vehicle.

Avoid Aspen Pittman's 'Groove Tubes' amp manual for the overpriced POS that it is, the schematics available in that book are readily available for downloading through searching via Google.

Also '69 Marshall's are really good amps, I have no idea of the wattage of the one that you had the opportunity to buy, though I would probably assume that it's a 50 watt head at that price. The amps that Marshall made in 1969 were essentially the same as the amps that they made in 1968, once you get past the fact that the 69's had an anodised aluminum control panel versus the gold plexiglas control panel on the 1968. These amps usually sell for quite a bit more than the $2,000 price that you quoted, unless it's had major componants replaced, or it's been horribly modified to the point where it's lost it's intrinsic worth.

Instead of getting the '69 Marshall, (even though it's a fantastic amp) consider looking at a Traynor YBA-1A, or a YBA-3. The YBA-1A is a 45 watt amp, and the YBA-3 is a 120 watt amp. Both of these amps use a schematic that is essentially the schematic that Marshall copied from Fender, and utilise the same EL34 power tubes that Marshall uses. -- They won't sound exactly like a Marshall, but they will come quite close tonally for a LOT less cash.

Also, another cool amp that you might want to look at is an older Ampeg V-2, or a V-4. They utilise a Baxendall tonestack ( Not unlike the now trendy Orange amps) as well as an active semi-parametric midrange control for great tonal versatility. The V-4 head was also loaded into a 2x12 open back cabinet not unlike a Fender Twin and badged as VT-22. The downside of the VT-22 though is that it weighs a bit more than a Fender Twin. The VY-22 weighs 88 pounds. The Rolling Stones used V-Series Ampegs in the early 70's, and they can be heard using them on thier live 'Get Yer Ya Ya's Out' release.

That being said, Ampegs are very loud amps with a bit more LF response than a Marshall, somewhat like an Orange in that regard. The best ones are the early ones that don't have the distortion circuit, and have a toggle standby and power switches. --Later V-Series Ampegs are distinguished by their white rocker style standby and power switches. V-Series Ampegs are also significantly cheaper than the price you were offered for the Marshall.

Also, if you're adamant about have a vintage Marshall for cheap, I cannot help you, though since you are interested in schematics, you might want to look here to buy very close copies of 60's Marshall amps either fully assembled, or in Kit form to build yourself. --Their fully assembled replica of a '68 Superlead (100 watts) is slightly more than the $2k that you were quoted on the '69 Marshall, without any of the potential headaches you could face buying an old amp.

FOGMAN COMES THROUGH AGAIN!


I followed your links about the bogens, then followed the links on those pages, then followe...... you get the picture I hope

I appreciate your warnings about the high voltage... just like in the old t.v. sets I used to open up when I was young/curious/stupid/... and incredibly LUCKY!

I sorta wished you hadn't posted that stuff though Fogman... with my ADD/HD... who knows how many of these amps I'll start collecting with the idea to 'eventually' get them converted to build all those guitar amps I am now dreaming about! LOL

Oh well... at least I no longer have a wife to roll her eyes and shake her head at me when I start talking about.. "This GREAT NEW IDEA AND PROJECT I'M GOING TO START ON TODAY!".
At least she won't have to suffer either

I've already been dreaming about building my own effects boxes and have been doing some sporadic research about it.

Alas... I do not own an oscilloscope nor do I know how to really use one.
I have a rudimentary knowledge of sound waves, sound forms(?), clipping, etc., but probably not enough to really understand what I would be doing by moving this part and rearranging this circuit... etc....

I'm going to look through all that stuff though about the amp conversion.
I hear what you say about tube vs transistor.
I have always wanted to own a nice tube amp, so maybe all this will actually inspire me to build one... sooner than later.

I'm also going to have to look around for someone local who knows about this stuff and maybe willing to do some work for me?

Anyway.. thanks a lot!
Although I don't want to dismiss the capabilities of anyone else on this website... I just knew you probably had some really good ideas about this amp business...


THANKS FOGMAN!

thank you for the explanations, makes me wish i wasn't a total dud with circuits

though im still thinking of replacing the pickups on my bass(or just getting a new one), and now about pedals (id like to distort the hell out of my bass, sorta like 'napalm death' - 'scum', except maybe a tad brighter) though im about as lazy as i am cheep

Yes, thank you for all the useful info! I really should have gotten that 1969 Marshall and worked out a payment plan with my friend - he would have done that. He paid a lot less for that amp (no more than $500). Obviously, whomever sold it to him had no idea what it was worth! I don't think it had been modified at all, and it worked great - almost too loud to play at home, even with the volume as low as possible. Too bad he changed his mind about selling it.

I will look for a Fender or Marshall tube amp. What do you think about the Vox tube amps? I almost got one of those a while ago; I think it was from the 60's.

What you want is one of these



Vox's sound nice, especially the old JMI era Top Boost AC30's. AC50's were a class AB design and sound good as well. If you can find an old AC100, though beware as those were very unstable Amps. The bugs were worked out and the amp that best represents high powered Vox tone was branded as 'VAMP Power' as Tom Jennings lost the rights to the 'Vox' name. --Marc Bloan used them for most of the old T Rex stuff. The later Vox amps made by Dallis Arbiter, and later Rose Morris in the UK, and were differant from the JMI stuff. They featured Solid state rectification, and the later Rose Morris amps used Fane speakers that produced an entirely differant sound that the original alnico magnet Celestions used in the JMI amps. Needless to say, old Vox AC30's aren't cheap, and neither are the reissue ampd from the 90's, and the earlier part of this decade. I am suspicious of the quality controls on the current AC30cc, as these are fairly cheap Vox amps made in China. --Original AC50's are a bit cheaper than the original AC30's because they don't appear as much on what are considiered to be classic recordings.

That being said, if you want tones that come close to Vox's along with also having a High gain channel as well, you might want to look for an old Bedrock amp. These were really high quality amps made in Nashua NH, and later Framingham MA, from the Mid 80's to the mid 1990's. Most of their amps output 50 watts, with some smaller amps appearing in the early 90's. Allegedly they also made 100 watt amps in the 90's as well, though they are quite rare, and I have never personally seen one, much less played through one. The 50 watt amps, as well as the 20 watt amps that they made later do sound pretty good, though.

Early Bedrock amps were branded as 'FRED' amps until around late 1986/ early 1987, when they changed the name to 'Bedrock', FRED's may possibly sell for a higher price due to their scarcity. Aereosmith used Bedrocks in the late 80's and Beastie Boy's used one on 'Check Your Head' and 'Ill Communication'.

Also, I would still suggest an Traynor amp, as these used also used the same basic circuit that Marshall copied from the 1959 Fender Bassman. Look herefor more info on them.

OH NO! We've unleashed the FOGMAN!

I have to say Fogman, I find that generally speaking, once I get 6 or so words into anything you write about this sort of stuff... I'm lost! ... but that's okay since I love checking out your links and learning more.

I'm heading down to the Bay Area/ Oakland today and tomorrow and I'll be dropping in to any thrift stores I see, maybe a few pawn shops, and definitely a couple of music stores I know about.

Not sure if I'll find any killer deals... at least any that I can afford... but it's fun just to look around anyway.

Now.. if I could only carry all the information that I might find valuable to help me know when I do stumble upon a deal...

With all the manufacturers and models of amps out there, I'm afraid I'd pass up too many good deals out of pure ignorance.

btw.. I have started looking around locally for a p.a. type tube amp. I checked the local used stereo/electronics shop but the guy said he didn't have anything like that in the building... BUT... he's going to go through his storage between now and the end of the month and he might have something in there.

I may have also located a guy who builds effects boxes, and another who does amp work.

This is getting TOO exciting... here I go... off on another project!

I was able to feel a little bit techy yesterday when my jack on my Ibanez started acting up.
After opening up I saw the really crappy soldering job someone did... BIG GLOBS of solder... and very short wires.
I suspect someone worked on this before and trimmed the wire for the jack until it was almost strung tight.

Luckily I found some shielded wire at an electronics store that is working just fine.

But it'll be a big leap from that little job to building a tube amp!

I have to say I'm the opposite! Once I get 6 or so words in, I'm completely enthralled and I can't stop reading! And then I want to go back and read everything again and take notes!

This time, for example, I don't even have a response because there's so much information to consider carefully, and I need to thoroughly research everything to be sure that I understand correctly.

I can say that it is reassuring to hear that there are plenty of options! I had been under the impression that my amp choices were basically just Fender vs. Marshall vs. Orange. Or something of much lower quality that would frustrate me like my little Peavey practice amps currently do. I don't care about having an amp with a famous name; I just want one that will do the different things I need it to do - loudness with decent control over tone.

Yeah, knowing you, your going to have this really well researched.
You have a great mind for that sort of thing.

My frustration comes in when I really get excited about a project but drop it for something else later on.
I often do this without realizing I'm doing it.
Then later on, I run across everything I compiled or collected for the project before dropping it.
It just reminds me that the project is still waiting.

For the Bogen amp project, here's what I am figuring my steps should be...

1) read through the material again and take notes.
2) create a file to keep all this written material in
3) create a checklist of the physical steps necessary to convert the amp
4) find someone who can do the work that I cannot... for example discharging the caps. Until I find out how it's done, I'm not sure I can do it at home.
5) start shopping for everything I need, but do it with a shopping list made up from my notes.
6) once I have everything, then create a space and time to actually get to work on it. Follow my notes and outline so I go step-by-step

I'm really interested in doing this.
If you are too Kim, I'll keep in touch about what I am doing.
If there's anyone else here who wants to take a serious crack at building their own amp, maybe we can start a builder's group.

I'm wondering if I should just see what's available for P.A. type tube amps or start looking for an amp that takes one of the tubes still readily available today?