PaulWarning Posted August 16, 2019 Author Share Posted August 16, 2019 4 minutes ago, Chienmortbb said: Many of their amps were designed around MOSFET output stages and these were easy to scale up to higher powers. The BLX130 that I had spaces for extra output MOSFETs suggesting that the same PCB was used for a number of models. As electronics engineer I must say they well engineered, maybe over engineered, by the standards of the time. I had the mosfets replaced in my AH250 a couple of years ago, could this explain why it's so loud? Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted August 16, 2019 Share Posted August 16, 2019 MOSFETS have as number of advantages over bi-polar transistors especially as they act more like thermionic valves in mnay ways. They are also inherently safe. That is as temperature increases, the MOSFET will become more resistive, reducing the output current and hence dissipation and heat. Bi-Polar transistors allow more current to pass as they get hotter and can suffer from thermal runaway until they go pop. The downside is that the power supply voltage for a MOSFET amp needs needs to be higher for a given output. So you need a beefier power supply but if there is enough available it might have a bit more real ,p[ower available at volume but as I always say, a watt is a watt so if they were louder then there must be some way to measure it. 1 Quote Link to comment Share on other sites More sharing options...
PaulWarning Posted August 16, 2019 Author Share Posted August 16, 2019 (edited) 8 minutes ago, Chienmortbb said: MOSFETS have as number of advantages over bi-polar transistors especially as they act more like thermionic valves in mnay ways. They are also inherently safe. That is as temperature increases, the MOSFET will become more resistive, reducing the output current and hence dissipation and heat. Bi-Polar transistors allow more current to pass as they get hotter and can suffer from thermal runaway until they go pop. The downside is that the power supply voltage for a MOSFET amp needs needs to be higher for a given output. So you need a beefier power supply but if there is enough available it might have a bit more real ,p[ower available at volume but as I always say, a watt is a watt so if they were louder then there must be some way to measure it. so, when it gets hot the volume could go down? I did think this might be happening, thought it was a fault. My SMX is the fanless model, just the heat sink Edited August 16, 2019 by PaulWarning Quote Link to comment Share on other sites More sharing options...
T-Bay Posted August 16, 2019 Share Posted August 16, 2019 And whilst comparatively ‘safe’ they can and do explode if abused/ coupled to faulty circuits. Having been three feet away from one that went bang, my underpants will confirm the energy released when they do go. I have been a target shooter for many years and it sounded very similar to a rifle report. Quote Link to comment Share on other sites More sharing options...
LukeFRC Posted August 16, 2019 Share Posted August 16, 2019 4 hours ago, Chienmortbb said: MOSFETS have as number of advantages over bi-polar transistors especially as they act more like thermionic valves in mnay ways. They are also inherently safe. That is as temperature increases, the MOSFET will become more resistive, reducing the output current and hence dissipation and heat. Bi-Polar transistors allow more current to pass as they get hotter and can suffer from thermal runaway until they go pop. The downside is that the power supply voltage for a MOSFET amp needs needs to be higher for a given output. So you need a beefier power supply but if there is enough available it might have a bit more real ,p[ower available at volume but as I always say, a watt is a watt so if they were louder then there must be some way to measure it. Does that extra resistance add anything to the sound? Like gentle compression of some kind? Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted August 17, 2019 Share Posted August 17, 2019 9 hours ago, LukeFRC said: Does that extra resistance add anything to the sound? Like gentle compression of some kind? Yes a MOSFET acts more like a valve and compresses when pushed ina pleasing way. I think some people that say they love Class A/B mean MOSFET A/B. Quote Link to comment Share on other sites More sharing options...
stewblack Posted August 17, 2019 Share Posted August 17, 2019 2 hours ago, Chienmortbb said: Yes a MOSFET acts more like a valve and compresses when pushed ina pleasing way. I think some people that say they love Class A/B mean MOSFET A/B. Thank you. Quote Link to comment Share on other sites More sharing options...
onehandclapping Posted August 17, 2019 Share Posted August 17, 2019 Back before I retired I worked in a music shop for 20 years,and we sold Trace bass rigs,the one I fell in love with was the all valve V4.I never thought any of the other Trace (transistor,mosfed) models I tried compressed/sounded like that. Quote Link to comment Share on other sites More sharing options...
2elliot Posted August 19, 2019 Share Posted August 19, 2019 This is off to an electro wizard tomorrow for a fiddle.... 1 Quote Link to comment Share on other sites More sharing options...
TimR Posted August 19, 2019 Share Posted August 19, 2019 As said above, loudness is frequency related. The power measurement is taken using THD Total Harmonic Distortion figure in %. So some manufactures will measure at a specific frequency with a specific amount of distortion, others at a different frequency and different distortion. Each manufacture will measure at whatever gives them the best marketing results. So someone could sell an amp that does 500w but 0.1% distortion and someone else an amp that does 500w but only 0.01% distortion. One will be louder than the other... Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted August 19, 2019 Share Posted August 19, 2019 (edited) Old (analogue) Trace amps are conservatively rated for RMS not 'music power' or any other such misleading calculation, and have big hefty transformers with reasonable regulation. They also use a design for the power amps that gives hi-fi levels of quality, so you get maximum headroom with minimal distortion, possibly less than 0.1% at rated output. <Just looked carefully at my amp and see I've been talking bollocks so I'm editing this> I'd assumed it was a 150W amp because (1) everyone knows the 1110 combo was 150W and (2) the transformer is marked 39V 0 39V - the later AH150 was rated as 40-0-40 AC input. But I was just musing at how big the transformer is when I noticed the amp isn't actually powered from the 39V terminals, but from a pair marked 50V. That explains why the DC rails are at 69 - 0 - 69V. This probably also explains why a 150 watt amp is so loud... So... this amp is a very early 1110 combo, it has a MPB2 PCB marked 'Issue 2', with two mosfets and a fan. The issue 4 AH150 board has FOUR mosfets, 40-0-40V supply and no fan. The Issue 4 AH250 board has four mosfets, 46-0-46V supply and a fan. At the least I am tempted to add another pair of mosfets... they can drop straight into the board. Edited August 19, 2019 by Stub Mandrel Quote Link to comment Share on other sites More sharing options...
radiophonic Posted August 19, 2019 Share Posted August 19, 2019 I'm not really adding anything here, but I had one of the 150W heads with the GP11 pre, running into a 1048 cab, back in the early 90s and it was just stupid loud. I never really thought about it at the time since all gear was BIG, but both of the guitar players were running valve heads into 4 x 12 cabs - one had a Fender Dual Showman FFS. Nothing went through the PA. I never struggled to be heard and I never went past about 2 O'Clock on the big red knob. In retrospect I think we're talking about proper engineering. Big output transformers and conservative measurement. At the time I just wanted an AH350 cos it had the UV blacklight. I don't miss lugging that cab about though! Quote Link to comment Share on other sites More sharing options...
ahpook Posted August 19, 2019 Share Posted August 19, 2019 My old 150W GP7 head was very loud. I ran it into an old Peavery 4x10 and never had any problem being head. At all. Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted August 20, 2019 Share Posted August 20, 2019 16 hours ago, Stub Mandrel said: Old (analogue) Trace amps are conservatively rated for RMS not 'music power' or any other such misleading calculation, and have big hefty transformers with reasonable regulation. They also use a design for the power amps that gives hi-fi levels of quality, so you get maximum headroom with minimal distortion, possibly less than 0.1% at rated output. <Just looked carefully at my amp and see I've been talking bollocks so I'm editing this> I'd assumed it was a 150W amp because (1) everyone knows the 1110 combo was 150W and (2) the transformer is marked 39V 0 39V - the later AH150 was rated as 40-0-40 AC input. But I was just musing at how big the transformer is when I noticed the amp isn't actually powered from the 39V terminals, but from a pair marked 50V. That explains why the DC rails are at 69 - 0 - 69V. This probably also explains why a 150 watt amp is so loud... So... this amp is a very early 1110 combo, it has a MPB2 PCB marked 'Issue 2', with two mosfets and a fan. The issue 4 AH150 board has FOUR mosfets, 40-0-40V supply and no fan. The Issue 4 AH250 board has four mosfets, 46-0-46V supply and a fan. At the least I am tempted to add another pair of mosfets... they can drop straight into the board. I found the sane thing when I had a BLX130? The board was just asking for another pair of mosfets and, if I remember rightly, two resistors. Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted August 20, 2019 Share Posted August 20, 2019 2 hours ago, Chienmortbb said: I found the sane thing when I had a BLX130? The board was just asking for another pair of mosfets and, if I remember rightly, two resistors. The TE board already has the gate resistors in place. 🤣 Unfortunately no holes in the heatsink or I could probably do it without taking the board out of the case! Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted August 20, 2019 Share Posted August 20, 2019 Digging a bit it seems I have an amp with a 200W/300W into 4 ohm PSU and a 150W power amp (with fan), such things were not unknown back in the day. Amps like that could be the origin of the 'TE Watts' legend. Well please because I'm now only 2 fets short of a 300W TE combo. Who needs walls? Quote Link to comment Share on other sites More sharing options...
TheGreek Posted August 20, 2019 Share Posted August 20, 2019 A lot of this discussion could have been recited to me by Stanley Unwin..... 1 Quote Link to comment Share on other sites More sharing options...
hooky_lowdown Posted August 20, 2019 Share Posted August 20, 2019 Old solid state watts are not the same as newer one's. I recall the very old Acoustic (brand) SS amps were rated comparable to tube watts. So a 100w Acoustic amp head was as powerful as a 100w tube head = bl**dy loud! A 100w head these days = fart. 2 1 Quote Link to comment Share on other sites More sharing options...
Count Bassy Posted August 21, 2019 Share Posted August 21, 2019 On 19/08/2019 at 18:58, Stub Mandrel said: and have big hefty transformers See, you knew the secret all along. 1 Quote Link to comment Share on other sites More sharing options...
Soledad Posted August 21, 2019 Share Posted August 21, 2019 18 hours ago, hooky_lowdown said: So a 100w Acoustic amp head was as powerful as a 100w tube head = bl**dy loud! That's been my long time impression. Either I have become desensitised to SPL (hearing loss then), or modern amps are less loud watts for watts. I definitely remember the Acoustic 360 / 361 rig being massively loud, befor that a Hiwatt 100 (OK, with 2 412s) silly loud. And in all my experience the Traces I have used belong to the brave old school... LOUD. A word for the 7 band graphic - really well chosen frequencies, lots of mid shaping available. Very few current class Ds offer the same degree of EQ, and when they try it just seems complicated. 7 sliders, job done. Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted August 22, 2019 Share Posted August 22, 2019 On 20/08/2019 at 18:58, hooky_lowdown said: Old solid state watts are not the same as newer one's. I recall the very old Acoustic (brand) SS amps were rated comparable to tube watts. So a 100w Acoustic amp head was as powerful as a 100w tube head = bl**dy loud! A 100w head these days = fart. Smoke and mirrors my friend, smoke and mirrors. Quote Link to comment Share on other sites More sharing options...
hooky_lowdown Posted August 22, 2019 Share Posted August 22, 2019 1 hour ago, Chienmortbb said: Smoke and mirrors my friend, smoke and mirrors. Do some research my friend. Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted August 22, 2019 Share Posted August 22, 2019 Trace Elliot could give Cuadrilla run for their money... who needs fracking? Quote Link to comment Share on other sites More sharing options...
fleabag Posted August 22, 2019 Share Posted August 22, 2019 (edited) I believe the Acoustic 360 was a preamp into the 361 powered cab, giving 400 watts @ 4 ohm so could probably easily keep up with a 100 watt valve amp. That is, i should add, the revised 360/361 rig Edited August 22, 2019 by fleabag Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted August 23, 2019 Share Posted August 23, 2019 20 hours ago, hooky_lowdown said: Do some research my friend. 45 Years as a Electronics Engineer involved lots of research but I am always willing to learn. Point me to your sources and I will gladly study it. 3 Quote Link to comment Share on other sites More sharing options...
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