Orange Terror Bass

[65basser]

Anyone have a schematic for an orange terror bass amp? Just looking to tweak the EQ a bit. Thanks.

[Brian Swatton]

I'm also looking for this circuit. I have one with s/c PSU transistors that someone else has tried to repair, but it failed again shortly after. At nearly £40 for the pair, I'm don't fancy just changing the transistors without info.

[J M Fahey]

Don't think it's much of a "tweakable" amp.
It ***LOOKS*** like the "real Terrors but it'd all digital stuff, end to end.
I bet it has some DSP chip in the preamp doing everything and of course, all SMT construction.
They seem to have a tube there.
Well, maybe, don't think it changes the rest very much.
Of course, if it happens to have a discrete preamp and somebody wishes to post it, he's welcome .

[Brian Swatton]

Hi Juan, thanks for the response.

No it's not too bad like that, no SMT or digital stuff that I can see, though the amp is class D. I'm used to working with SMT anyway. I've found some data on the class D chip used, so can get an idea whats going on there. The PSU is a very basic switched mode, just a free running oscillator and a half bridge driver in the chip, no regulation even as far as I can tell from the chip data sheet. I haven't dismantled too far yet, I've been hoping to find a circuit.

It would be useful to try and get the two parts up and running individually if possible. I know the PSU has been repaired before and blew up again very shortly afterwards.

[J M Fahey]

Fine.
Well, if you someday happen to get it, please post it here.
I happen to be also interested in replacing my EI iron transformers with some kind of SMPS, but being a minimalist at heart, I don't want anything fancy, just the basic functional equivalent.
Just offline rectifier > inverter > rectifier .... end of story.
The PSU you describe looks like that

PS: any amp guts pictures would be interesting
PS2: and of course, *anybody* who happens to have that schematic, is encouraged to post it here
PS3: what would the SMPS chip be? Maybe your amp uses basically the datasheet suggested circuit or something *very* close.

[Brian Swatton]

The PSU IC is an IR2153, basically just a 555 type osc with a half bridge driver. I don't think that will be too much of a problem to get going and load up. I spent quite a few years as a test engineer for an SMPS manufacturer fortunately. I'm a bit more concerned about the amp section taking it out again as I don't think there's much in the way of s/c protection (if anything) and the devices are quite expensive.

The amp itself is based around 2 x IRS2092, there are datasheets for that which will help a bit too.

I have tried Orange, but they will only share tech data with authorised dealers. If I get hold of a drawing I'll post it here unless I've agreed to an NDA to get it.

I'll consider posting some pics too, I'll be getting it on the bench later to get the amp out and do some checks on that. I'm going to try and arrange some external supplies to tentatively power it up if there are no immediately obvious faults.

[Brian Swatton]

As requested, here's a few pics :

With the fan cowling removed, showing the PSU section:


A more birds eye view of the PSU:


The underside, showing pre and power amp boards:


The power amp board removed:


I did get the PSU running, though with the wrong FETs in at the moment. I'm getting about +/- 52v out with no load. I get a pretty rapid temperature rise above 200v input though, not sure why yet. I'm trying to confirm what devices should actually be fitted now, when the unit was bought in there were a pair of s/c FQA28N50 in a bag with it. Actually fitted were a pair of IXTQ30N50L2, also s/c.

[J M Fahey]

Wow, thanks a lot.
At first I thought the 4 TO218 transistors were the power output ones, then saw the 6 TO220 on the other side, so now I think the 6 smallers are output (Class D) and the 4 larger are pPSU inverters, is that so?
And the 4 leg pack to their left, looks like a rectifier.
Line/Primary side or secondary?
Thanks for posting.
PS: as of "overheating over 200V", maybe the switching MOS don't stand that, although their coding seems to indicate otherwise, or you still have problems on the secondary side, either the PSU itself or the power amp.
After all, *something* killed it the first time !!

[Brian Swatton]

Yes, the 6xTO220 are for the amplifier.

Looking at the PSU from the front, going from left to right there is a bridge rectifier for the mains input, the 2 power FETs then 2 output rectifiers for the high current +/- rails.

It's an odd temperature rise, they sit at about 30'C below 200v, but as I increase it just a few volts above that I see them rapidly rising to 70'c within a few seconds, at which point I switch off. I want to get the right devices in before I make too much of that, I've just got a pair of STW45NM50 at the moment as I had some here and just wanted to see how things would wind up with an auxiliary supply on the IR2153.

[Brian Swatton]

Just thought I'd provide a bit of an update on this unit for anyone interested.

I'm pretty confident of all PSU elements, apart from having the correct FETs.

I put some of the IXTQ30N50 in and the heating in them was much, much worse. Gate drives were very rounded, input capacitance much too high. I went back to the 45NM50s for more checks. These have the best input C and RdsOn of the 3 device types. Gate drive is still a little rounded, but nowhere near so bad. Of course, slower rise times here mean the FET spending more time partly on, and so dissipating.

Trawling through forums I've found there were a few batches of the Terror Bass that were suffering quite a lot of blown fuses. Orange was providing replacements pretty quickly and seem to have been aware of an issue. Batch numbers 0411 and 0111 are two I remember. The batch number is the last four digits of the serial number, I have an 0111 here. Unfortunately I can find out nothing more about the issue or fix.

As I have not seen a drawing, or cannot even confirm what the PSU FETs should be, I think I'm going to have give up and recommend the customer contacts Orange. They won't help me at all as a tech.

This in no way affects my opinion that Orange amps are pigging ugly and probably smell of wee.

[Steve Conner]

Oh no, SMPS with no short circuit protection... :O

The STW45NM50 seems like a reasonable replacement as it has 117nC gate charge, the FQA28N50 had 110. The only remaining question is whether those were the original devices. I'd expect a circuit like this to work fine with the very popular IRFP460A or IRFP460LC.

Did you check the output rectifiers? Maybe one is damaged and is breaking down as you get over 200V DC bus voltage.

[nickb]

Just a random thought. Could the temp rise above 200V be a result of a bust (or missing) snubber network? Check the waveform on the primary side of the transformer for spikes.

[Steve Conner]

Good call.. Another unsettling thing I've seen is that modern MOSFETs switch so fast, they can exceed the dv/dt rating of isolated gate driver chips such as the IR2153, causing the chip to go crazy and blow the FETs. A snubber network would probably help to stop that.

[Brian Swatton]

Thanks for the interest guys.

I did try with all output rectifiers disconnected - well, txfmr lifted and just the primary connected. I got identical results.

I used a sense transformer today to look at the current waveform through the winding - a nice symetrical triangle with a little glitch at the peaks where I guess both FETs are briefly off. I actually took some pics earlier to show a colleague



The voltage waveform is a square wave, I don't have a pic of that.

[Steve Conner]

Nice waveform, but what's the magnitude of it? Amps p-p? I can think of a lot of faults that would give the same waveform, just a lot bigger than it should be.