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Messages - JB074
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« on: June 18, 2018, 02:32:56 AM »
This ad got my attention (attached)
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« on: June 17, 2018, 11:38:45 PM »
...
I was unashamedly asking for *opinion* on heads you may have used that you like the sound of or conversely do not like.
...
My apologies, but I plead the hive-mind of the internet. Ask opinions on a ham sandwich and by the second page it's a full-blown smackdown on whether French Crullers are better than Danishes.
What kind of music do you play? I am assuming something Rock-oriented but I don't like to assume. If you lean towards the harder side, I don't think you can go too wrong with a Randall RG series. I can personally vouch for pretty much any Peavey heads for clean tone, and some TransTube heads have switchable loads. Beyond that, not sure.
I play a lot of varied stuff, from surf rock to slayer. I play a bit of country, a bit of 80's but most of my love is 70's hard rock. So you're all wondering why I don't have a plexi.... I mostly have 'clean' amps - blackface twin reverb, JC-120, Vox AC head, thr100 yam, katana 100 1x12. for dirt a heavily modded fm100H fender head, which is a one-trick pony. I'm looking for a slightly crunchy head for this vintage marshall 4x12 1960ahw cab. If it's a 50-100w head I will need to attenuate it, or it will need to have a low-power mode. And at least at this stage I'd prefer to drive the 16Ω cab without rewiring - not that it matters terribly for an SS output stage. I've spent many years repairing rackmount power amps and I don't need or want a huge gig setup. I have thought about reworking a small SS amp and putting a tube preamp channel in, but I can buy stuff like that off the floor in a shop too - Just throw some ideas out there - I don't care if it's a head for Jazz or a modded high gain unit - I'm just out of ideas.
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« on: June 13, 2018, 11:46:47 PM »
having said that, some smaller combos sound good...for a MArshall, Like an MG50 or variant. Someone else is going to punch me for saying that.
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« on: June 13, 2018, 08:42:52 PM »
I understand the implications of this particular cab.
I'm not afraid of Ω mismatching on an SS / hybrid - I know what occurs -
Hence my statement about the reactive load.
I'm not sure if I was clear enough about that or not.... but if the amp is clearly not suitable, some of which I am well aware already aren't without a reactive load - then the reactive load (power station / hotplate) will go between.
It may give me a chance also to test a UA Ox. Or an excuse to purchase one.
I had the idea of a JTM45 already, and the reactive load to enable me to dial it in at a slightly lower dB (trying to keep it around 100dB) but the philosophy was first, reactive load with what I have and 'see', second, purchase a new amp head, then maybe also an Ox, if I don't like the way the power station attenuates.
Most of my heads have a switchable output, some do not, and I am aware of impedance requirements.
Also the reactive load counteracts any mismatch between head and cab, so again, not concerned. Could also rewire as suggested. That's a far more obvious solution to direct input 'freedoms', which was on the cards down the track, after I've broken in the cab.
I was unashamedly asking for *opinion* on heads you may have used that you like the sound of or conversely do not like.
But if you feel that you wish to keep your opinions to yourselves, that's fine. Part of the logic for asking was exactly for the reasoning you mentioned. I am not interested in tubeheads forums with one-eyed love for fender vox marshall or some boutiquey brand, when it cannot be presented in an objective comparison environment.
thanks anyway, the points are valid for people who don't understand what damage can be done through a mismatch of impedance. Apologies if I was not clear enough - I thought I was speaking to an audience of peers and perhaps I was not clear enough.
5
« on: June 09, 2018, 08:32:54 PM »
Morning All,
I'm in a bit of a quandry -
Last week I purchased a Marshall 1960AHW 4x12 with the intent of running it from various combos or heads I have laying around.
Problem is, I do not specifically have any 'marshall' heads, for example JTM45 / plexi / jcm800 / jvm410 etc.
Now obviously a 4x12 can be brutal from a power handling capacity, but I'm looking for something in the 20-50w range in terms of a head.
There are so many heads on the market now that I just cannot keep track of them, much less have time to demo any.
I wish to avoid modelling amps, as they are not really my thing.
I already have fender bassman, twin reverb, JC120, AC30, and a boss katana 100, any of which I could plug into the cab, but I am not sure.
What I do know though, is that I am not an "orange" guy, and while I love a plexi as much as the next guy, I'll need a decent reactive load to keep the peace with the neighbours if I want to get the right crunch out of one - not to mention I like having my hearing.
So does anyone have a suggestion?
I'm halfway between a hybrid and all valve.
It's really easy to get lost in all the choices.
I guess the last option is to build my own again, but I'm sure those of you who work on stuff will understand what I mean when I say I just want to plug in and play.
hit me up with some suggestions - I know there are far too many out there to choose from.
Oh, just as background on tone - I play pretty much every genre except djent. I have LP's, strat's, hollowbodies and offsets. I don't have any P90's.
feel free to paste URL links to stuff you like, because I'm lost in choice.
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« on: December 17, 2017, 02:19:28 AM »
Just a prelim update. pulled the box down yesterday, took tray out, pulled drivers, cleaned the entire unit, there's 35 years of dust in there. was pretty abysmal. Luckily the cones were in good condition, the centre caps have taken a knock at some stage, but I was able to pull it back with vacuum. polished them up and re-lacquered them. Applied same to cabinet insides, and the edge trim/studs. Unit looks almost new except for a tiny nick in the grille cloth. then general dust removal, chassis cleaning, etc etc. Put the tray on the bench, started visual inspection. Then we had a massive thunderstorm, complete with lightshow, so the bench was vacated until the house ceased to become a lightning conductor. Lots of fun. Other half comes home from shopping, my 'free' time was subsequently schottky'd to her xmas planning requirements.  Will let you know how it goes DrGonz... When I get my 'free' time back...
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« on: December 17, 2017, 01:05:05 AM »
Some pics that display cosmetic differences of JC-120's of different pedigrees:
From top to bottom
- Very old version of the amp: Notice the chrome corners and the overall green-ish colour scheme.
- Somewhat newer version (approximately 1982 and onward): Notice the addition of "bright switch" feature, plastic corners and a grey-ish colour scheme. Jacks are now insulated type with plastic cover (instead of old plain metal jacks) and the potentiometers knobs are different too (they have varied slightly throughout the series' history). The Roland logo in the grille is also bigger.
- Even newer one: Bright-switches are now push-button -type, the Vib/Off/Chorus -toggle has been converted to a rotary selector -type. Speakers are different and no longer have metal dustcaps. At some point of the revision history the metal "lever" -type rocker mains switch converts to modern plastic rocker switch.
Samples of rear panels differences.
From top to bottom:
1. Very early version. Note the lack of rear cabinet panel and that the labels were silkscreened to the painted chassis. Controls from left to right: Mains/polarity switch, convenience AC outlet, Chorus/Vib F/S jack, Reverb F/S jack, Distortion F/S jack, two EXT speaker out jacks, line out jack (mono).
2. Newer version. A rear panel with label stickers is added (this was probably a cheaper solution than silkscreening the chassis). The control/jack arrangement is the same except that a fuse holder replaces the mains switch and that the convenience AC outlet is removed. A briefly earlier version (ca. 1976 and not depicted) still had both fuse holder and the convenience outlet. A Chorus trimmer potentiometer is also added to the far right.
3. Late 1970’s version. Controls from left to right: Mains fuse holder, chorus adjustment trimmer, two EXT speaker output jacks, line output jack, chorus, reverb and distortion footswitch jacks, two mains in jacks.
Here are some images I took of my "early-ish" JC-120. Despite everyone's best attempt to describe, This is obviously an early cabinet, with a pre-bright switch circuit. Inside however, is a later TA7122 driven preamp, and an 052-190A effects board. The two channel boards are disparate. I am aware someone has been inside before. - I came to this thread via my newbie post, just adding these pics FYI. Important for anyone troubleshooting these to be aware of the board revisions and serial number.
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« on: December 07, 2017, 05:02:32 PM »
I have a few years under my belt building and repairing hifi/tv so I should be OK.  I got the amp on the bench for only a few minutes yesterday. both channels ok. some minor hiss - more than I'd like, but not too bad. no 50Hz ac hum though. Got the factory service manual from Roland emailed to me, parts guy informed me of xmas closures and next shipment from japan not arriving till mid Jan, so I have plenty of time to let this sit on the bench over xmas. No distortion on 2nd channel, we have vibrato, but no chorus. I haven't put a scope on it yet. It needs a good clean. footpedal jacks are in need of a good clean, pots are all in very good nick. So I have a few places to start looking. Effects board is early ET-7 052-190 rev0 (s) Someone has been inside it before though - the pcb screws show signs of over-enthusiastic 'mechanic' work.
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« on: December 05, 2017, 12:44:30 AM »
Hi, New here. I googled JC-120 and ended up on an epic thread, had to join. It was a bit of a two-pronged attack - I was chasing a JC-120 and saw the thread, which made me feel a little better about troubleshooting. I subsequently found a JC-120 and picked it up today, for $150. It has a few issues, which I'm looking to sort out. Namely, the effects aren't working, but the amp is OK. Yet to strip it down and look inside, but I'm guessing new caps and possibly a coule of diodes/transistors. - maybe an FET/BJT or something - I will have to find the correct schematic first, but let's see how we go! Wish me luck. 
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