OR120 headroom.. thoughts.

[OrangePaul]

Hi Andy (fellow orange lover lol)
12 is about right for the average output passive guitar I would say yes.
Must admit I was looking at the before and after vids on utube last night for the FJA modded OR120 overdrive and was starting to think we must be talking about totally different animals here lol
http://www.youtube.com/watch?v=nOUd2h98 ... K2WvfSEu84
http://www.youtube.com/watch?v=Yf6bjW5x ... 1AlInu7L2I

I use to use an electro harmonix wah, custom made distortion, pearl delay and midiverb 2 into my orange before I decided to put my rack setup together and cranked (distortion on and amp about 1/3 to half vol) I could maybe get something similar to the second link here. Lush feedback at will almost...them were the days lol.
As for the mesa i've not had it really cranked yet....not enough for the neighbours to come round yet anyway....if only they'd have gone away for the Easter hols lol
Yes I picked my Orange up in the mid 80's when they were been practically thrown away, in fact had 2 at one point, both none MV though.
Like yourself, I also used mine for bass initially then fretless bass after the Pino Palladino/Paul Young collaboration phase of things swept the 80's, but not for that long to be honest. I'd mainly used a cobra 90 bass head upto that point but soon switched to guitar after that.
My brothers amp is a Fender Twin Reverb which he bought new in roughly 76 (still in very good condition actually). Think the voltage selector knob on the back is red if thats what you meant. But no to be honest ive never heard it distort (master on full/ pot in), I just felt the orange on A, B testing into the same JBL's had far more punch and clarity at very loud bedroom levels.
Funny you should mention living in a studio because I was going to say that the only time I had my Orange cranked to full distortion was in a friends basement Rehearsal/Recording Studio on Londons Wapping Wall and i think we were that loud at the time that someone eventually in the building above must have set the fire alarm off in order to bring proceedings to a halt lol.
But yes for guitar as you say yourself for anything other than the biggest stage unpractical by todays standards...one of the reasons I switched over to a rack setup, that and having generally a low opinion of most foot pedals of that time at least in the 80's (but thats another subject lol)

Back to the original question then lol.....HeadRoom?

Borowman do you use active pickups on your bass? I would suspect you probably do because without them I wouldn't have thought you would have got a very 'full' bass sound from this amp alone. As I say though, I didn't use mine for very long and my bass guitars were only budget affairs...a Jazz copy and Vox fretless so probably pretty poor low output really. But maybe thats an option you could consider...quality passive pickups.
The best sound I got from my vox fretless in another band some years later was through a friends Trace Elliot Rig. It transformed my budget Vox into a Musicman!
That said my favourite recorded bass sound of all time is Geddy Lees valve sound on Permanent Waves and Moving Pictures....that unmistakable valve gritty growl....why did he ever change?? lol

Hey Andy what happend to JBL anyway. Did they price themselves out of the market?.. and yes we were miked but it didn't stop me struggling to hear an AC30 on stage firing at my knees with a 400watt 4x12 bass rig at head height behind me lol plus trying to figure the volume after the first song....it was an AC30 head and matching cab btw no tremelo model, a pretty nice amp really.

[a.hun]

Hi again Paul

Frankly I've no idea why JBL stopped making those great drivers. Possibly the same reason that Celestions (non 'vintage') Century speaker - another extremely efficient uncoloured full range driver - was discontinued after not so long - I'd guess they simply weren't selling well. I think the trend in recent years is more geared towards 'characterful' sounding speakers, so Celestion anyway are putting out more 'reissues' of lower wattage ones and where necessary updating them, eg the 50 watt alnico Gold.

The red knob 'Evil Twin' actually had red front panel control knobs, so not that then. I suppose a lot of the punch / clarity you were getting from the Orange could be down to the really useful presence control. That is something I always like to see on an amp as it gives a totally different sort of control to normal preamp tone controls. And the Baxandall tone circuit makes the OR120 way more versatile than people give them credit for. (Did you check out the link to those short Orange articles by fiveightandten BTW? Well worth reading!)


Yeah, staying at that studio was great fun. Gave me the chance to play with all sorts of different musicians and let me hear (and try out!) a lot of types of gear and get to know what they could really all do. For most of the time I was there there were only sheep around us so disturbing the peace wasn't an issue...

With the FAC I have never had any problems getting a full bass sound with decent passive bass pickups. To be honest though I set the amp controls up from scratch for each different room I almost invariably end up having it backed off one stop from full on. With my old bass 4x10 that got me a very full but punchy bass sound. My main fretless does have active circuitry, but since that is primarily for tone control not a level boost the actual outputs are similar. Never really needed to change the amp settings when switching basses during a set for example. Some (especially 18V) bass preamps can belt out a hefty level though. Be worth experimenting with the lower gain input if that was the case.

Really interesting to see that FJA Overdrive mod - thanks for the links! From the sound of it I'd say that they managed to keep the amps tonal character pretty well intact while giving it a decent hike in gain.
Neat, if exactly what I'd personally not need!
Especially impressive is that he doesn't seem to have killed the amps fantastic dynamics. Note at exactly 2:30 on the 2nd video how he goes from heavy drive to clean from the guitar BEFORE resetting the amp to clean. That is why I've always said that at proper working levels the old OR amps have about the best dynamic response to playing touch of any amps ever made. Just fantastic!

Yeah, ironically the OR120 these days is realistically too loud to be used 'as intended' for guitar, yet a bit too quick to overdrive for bass. Still worth trying to work around that though, and with the THD Hotplate you've got the perfect tool for guitar use IMO. One notch down and you've got (with healthy old power valves anyway) about a 50 watt amp - way more usable for most gigs. And with its ~180W RMS rating it is also one of the very few attenuators which can actually handle the amps full output properly!

Slight OT:Thread here on the first FJA Rocker 30 FX loop mod BTW:
http://forum.orangeamps.com/viewtopic.php?t=5180" onclick="window.open(this.href);return false;

IMO the R.30 is the only of the recent Orange models with much the same sort of 'feel' and dynamics as the old OR amps. Why I bought one of course! Sad to see it discontinued, but there you go...

Oh yeah, we're as one on the Geddy Lee sounds BTW. When I started playing bass I learned all his Rush basslines. Had 2112 practically sussed before I even got my first bass by retuning my old school fiddle from GDAE to EADG and playing it on my knee!

Last thing: I'd say the very best thing about my little 20W Boogie Subway Rocket is its cleans. Lovely!


Andy.

[markjazzbassist]

i got my 1972 OR120 (pics only) and i'm loving it. I've been getting great bass tone's with it (i'm a bassist, using a passive 69 fender jazz) and the headroom hasn't been an issue for me (use in-ear monitors).

I'm going to play around with some 12AT7's in the V1 or 2 spot to see if i can get some more clean headroom, but for now i'm satisfied.

In the future I'd like to change out the JJ EL34L's for some SED 6L6's to get some more low end. I have the FAC all the way left and still have the bass boosted using my orange obc410. I just can't seem to get enough low end out of these EL34L's.

the HF drive is at 0, this thing's got PLENTY of treble punch.

[a.hun]

Excellent! I'll just put in the traditional 'pics required' plea...

Honestly surprised that you aren't getting enough bottom end out of it with that bass cab though. Maybe the power valves are on the tired side. Lack of bottom end has never been an issue for me...

Going to 6L6s is probably a good idea. Ades thoughts on that:

(http://forum.orangeamps.com/viewtopic.php?t=7296" onclick="window.open(this.href);return false;)
Another tube that works well for bass in an OR120 is a 6L6. Those tubes will bias up in that amp just from turning the bias pot (with no resistor change) and they are fine at 500+ plate and 500+ screen. You will get the most out of them if you change the screen resistors to 470 ohm but this must be changed back to 1000 ohm if you put EL34`s back into the amp!

I'd certainly think you should get a shade more clean headroom with a12AT7 n there. Be aware of the tonal change though - they'll tend to give more bottom and top end relative to the midrange. Gives a smoother bass sound (a little closer to that graphic EQ 'V' sort of setting) but the mids may not punch through on stage quite the same. Worth trying though - you may well like it.

HF drive / presence at 0? Trying to remember, did you ever investigate having an 'L-pad' attenuator fitted for that cabs horn? Be a shame if you can't use the HF drive as it really is a great tone shaping tool too. Put it this way, I had the new DR103 running through a 1x15 bass cab only rated up to 3kHz and the presence knob got me plenty of sweet top end! Way more than the treble alone would get because the presence actually controls the speaker / amp interaction through a power stage feedback loop. If using a cab with a piezo I like to be able to tame it right down and bring all the tone controls into play. Just gets a more natural bass sound to my ears.

Enjoy the new amp!!!


Andy.

[markjazzbassist]

i put the 12AT7's in the preamp (2 of them) and I do have more headroom now. I can crank it up a lot more now, it made more of a difference than i thought. I'm still going to do the 6L6's eventually after these EL34's bite the dust, but it could be a while there. Thanks for the info!

I removed the horn on my cab, so no pad needed. Maybe i should clarify, my tone is VERY old school. Passive Jazz and Flatwounds. Think late 60's early 70's R&B, soul, Jazz tones. So i'm not into "grindy" or anything like that, hence the HF not being a big hit. I think it'll be more useful when i get the 6L6's in there though and I'm looking forward to experimenting then. The EQ is AMAZING on this thing. I've read those fiveightandten FAQs and they are very helpful to using the amp. It's really a tone machine in disguise

What is the word on the 12AT7's? I've got JJ's in there now, sounds good. Anyone try some others they like? (EHX, NOS Mullard, JAN Phillips, RFT)

the head i have is the one at the top of the orange amp field guide that amperex owned and modded (correct MV and standby). here's some pics

[OrangePaul]

Wow thats one very nice amp you've picked up there Mark. This is making me want to get my bass out of hibernation

[a.hun]

Wow thats one very nice amp you've picked up there Mark.

Sure is!

With you on the horn tweeter / presence thing now. You just need a good efficient LF cab to sit your 4x10 on and you'll be laughing all the way to the physiotherapist.

Beautiful amp - seriously nice score!


Andy.

[OrangePaul]

Just played my OR120 for the first time since we started this thread and realised there's more than a few things at play here on maybe why we disagreed so much originally lol.

I gave Nicks Orange Amp info link on tone controls/fac a read and was experimenting with some of the suggestions.(Thanks for the link Andy..its in my favourites )

My findings:

1. I've instinctively in the past gone for the 'biggest' cleanest EQ setting available on this amp (bearing in mind I can now easily verify this with the hotplate and gain setting)
These are (for me anyway) FAC fully left, bass around 3 o clock, treble flat or cut very slightly and HF drive around 3 o clock or more
2. Boosting treble ( for guitar anyway) seems to be the easiest way to distort this amp in that region where breakup starts (or possibly just revealing what we all know is already there lol)
3. I managed to get my passive seymour duncan/ ibanez, (set to humbucking , which I have recently raised....not because of this i might add lol) with some of Nicks suggestions distorting from about 10 o clock. I WAS quite suprised how easily actually lol.
4. When i'm playing clean i tend to usually switch to single coil, (maybe I finally need a Les Paul lol) generally have a light touch and roll back the guitar volume so the guitar filter cap comes into play, so thats another big factor there also.
5. Doing this with a telecaster (volume rolled back, middle/both pickup setting) it is possible (as you rightly say Andy) to get incredibly loud punchy cleans above even 12 o clock on this amp! with a light enough touch.


Also i used a distortion pedal when i gigged this amp. So when i was playing hard, the pedal would hide the fact that the amp was actually distorting (I always knew something was at play but thought it was more just the amp compressing and speaker interaction). The guitar I used back then was a Westone (budget superstrat/Trevor Rabin type thing)... not exactly low output but very warm (soft) in tone. All this coupled with the fact that I used it initially (and for most of the time actually) into JBL's which believe me....even at 9 o clock gain, made this amp dam bloody LOUD.

Still havent got to grips yet using this amp with the hotplate alone but had already started using that treble more in order to get more natural amp saturated tones. It can be such a wonderfull sounding amp but probably more difficult for guitarists to tame than bass players (cue ringing ears )
Think its time I did some valve experimenting next too. I have a spare set of mesa 12AX7-A tubes now also to play with lol. (they say Russian 2 with the mesa logo underneath- maybe sovtek??) Last owner fitted new electro harmonix in the Rectoverbs preamp stage, and Mesa tubes in the power and has given me the old set...he said they still worked fine. Could try them back in the Mesa too of course

[jontheid]

Bias the amp hot to get more clean headroom - the hotter the bias, the less crossover distortion at higher volumes.

You quote 35ma as your bias current, but this means nothing if you don't tell us your plate voltage.
What brand KT77s are you using? I use my head for bass (it is an Orange Super Bass) and Genalex KT77s only gave me 100W max output power, whereas Shuguang EL34Bs give me 150W.

Jon

[a.hun]

Bias the amp hot to get more clean headroom - the hotter the bias, the less crossover distortion at higher volumes.

Jon

Hi Jon.

Many don't find a hotter bias actually sounds better. As long as it is warm enough to be above the crossover distortion threshold biasing hotter still won't make it 'go away even more'. If it cold enough for crossover distortion it is clearly too cold of course.

For maximum sustained power AND long valve life though you are actually best to bias as cool as possible above that threshold for most big class AB amps. Biasing hotter means the valves will be running hotter at all power levels reducing actual efficiency. Whether that also happens to sounds better to you or not is a different matter. With most amps I find it doesn't.

Ade Emsley, Oranges designer does seem to agree with you about biasing OR120s on the hot side though. See his 2nd post here:
http://forum.orangeamps.com/viewtopic.php?t=7296" onclick="window.open(this.href);return false;

Were you being specific to these amps?


Andy.

[OrangePaul]

Bias the amp hot to get more clean headroom - the hotter the bias, the less crossover distortion at higher volumes.

You quote 35ma as your bias current, but this means nothing if you don't tell us your plate voltage.

Am I correct in believing that a 'hotter' bias equates to a lower plate voltage and that a medium value would be somewhere in the region of 500 to 510 volts ?

[jontheid]

Hotter bias equates to more power dissipated by the tube at idle (i.e. nothing being played on the instrument / no signal input)

Colder bias equates to less power dissipated by the tube at idle.

Things can get confusing using terms like 'increasing' and 'decreasing' the bias, as some people consider increasing the bias to mean making the bias voltage more negative, which means less power being dissipated by the tube at idle, and thus a colder bias. So I find it easier to talk of 'hotter' or 'colder'

The power dissipated by an output tube at idle is the voltage from the plate to the cathode x the current flowing through the plate, P=VxI

The maximum power dissipation allowed at idle is typically 70% of the peak tube dissipation power allowed (in a class AB amplifier). For a good explanation of why this is so, see here :

http://www.aikenamps.com/Why70percent.html" onclick="window.open(this.href);return false;

EL34s can dissipate 25W maximum power (note that this means that the tube itself can dissipate this, this is not related to power output). 70% of this is 17.5 watts.

We said previously that idle power dissipation = plate voltage x plate current at idle
Thus, for 70% max dissipation at idle:

17.5= plate voltage x plate current

You need to measure both of these to be able to set the bias accurately.

Firstly measure the plate voltage with the amp switched on, warmed up and plugged into a speaker of course. (this not for the faint hearted, as plate voltages are high enough to kill people, if you don't know what you are doing, don't even attempt this. And if your tech doesn't measure plate voltages when setting up yer amp, get another tech)

Then you substitute plate voltage into the above equation, and you get the plate current value that you need to get 70% max dissipation at idle.

Say the plate voltage measures to be 500V:

17.5=500 x plate current
plate current = 17.5/500 = 0.035 = 35ma

So now you measure the plate current at idle (various ways of doing this, see http://www.aikenamps.com/Biasing.html" onclick="window.open(this.href);return false;) and adjust this to give 35ma.

Now it should become apparent that just quoting a bias current of so many milliamps is not enough information as the actual power dissipated by the output tubes at idle is dependent upon the idle plate current and also the plate voltage.

Early 70s Orange amps can have high plate voltage compared with modern tube amplifiers, but I haven'tgot any typical figures.

[jontheid]

Further to the above, plate voltage at idle is not greatly affected by varying the plate current at idle (i.e. adjusting the bias point). This is because the output transformers' primary winding (of which on side is connected to the output plates and the other to the b+ supply) has a low d.c. resistance, so the idle current flowing through it only causes a small voltage drop.

[OrangePaul]

What purpose does the choke serve then in the power supply between the A+ and B+ outputs? All my formal electronic training is post valve technology, unfortunately for me lol

[Gladmarr]

The choke is in place to further resist any remaining AC ripple on the DC supply for the tube plates. It's not 100% necessary, and a lot of tube amps don't have a choke. It's more prominent in higher power amps. For example, Fender Champs don't have chokes.