BASainty Posted November 17, 2015 Share Posted November 17, 2015 (edited) Correct me if I'm wrong but am I right in saying that running a head (lets say for arguments sake 500 watt at 4ohm and 250 at 8ohm) at the higher resistance would cause less stress and therefore wear and tear on it? My thought that a 500 watt (4ohm) head being run at 8ohm (250 watt) would cause less stress on the circuitry and less heat because its only having to use half its potential power. I know there are other factors that also contribute to wear and tear but this is just a theory that I had come up with while searching for a new head. Edited November 17, 2015 by 4StringFortress Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted November 17, 2015 Share Posted November 17, 2015 (edited) [quote name='4StringFortress' timestamp='1447765825' post='2910105'] Correct me if I'm wrong but am I right in saying that running a head (lets say for arguments sake 500 watt at 4ohm and 250 at 8ohm) at the higher resistance would cause less stress and therefore wear and tear on it? [/quote] For valve no. For solid state amps yes in theory. In practice I'd be surprised if there was a measurable difference in reliability for any decent quality amp over the time span someone would typically own one. Personally I'd run a 4 ohm load and just turn it down a bit knowing I've still got a little headroom left if I needed it. I see little point in second guessing the designers - if your nervous about running an amp within its design spec then honestly you need to use another brand that you have more faith in. Edited November 17, 2015 by bassman7755 Quote Link to comment Share on other sites More sharing options...
BASainty Posted November 17, 2015 Author Share Posted November 17, 2015 (edited) Ok cool. Was just looking at a HA3500 thats spent its life being played through an 8ohm cab. So was wondering if that would affect how reliable it is compared to one thats spend its life being played through a 4ohm load. I know the amount of use it has will be a factor and how well the head has been treated in general but this was purely a hypothetical question. Edit: I didn't end up buying it, I went for something new but was still wondering about the question. Edited November 17, 2015 by 4StringFortress Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted November 17, 2015 Share Posted November 17, 2015 [quote name='4StringFortress' timestamp='1447766882' post='2910123'] Ok cool. Was just looking at a HA3500 thats spent its life being played through an 8ohm cab. So was wondering if that would affect how reliable it is compared to one thats spend its life being played through a 4ohm load. [/quote] Cant see that being an issue, unless your amp has some latent fault that would only manifest itself at the lower impedance (which is highly unlikely). I'd give a right royal blow out at 4 ohm for a practice session and if it survives that then Id say your good to go. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted November 17, 2015 Share Posted November 17, 2015 FWIW it's not resistance, it's impedance, and the issue isn't power, it's current. The lower the impedance load the higher the current draw, which increases heat, and it's that heat which lowers component life. You often see questions about using lower impedance speakers "to get all the watts out of my amp", and that's usually not a good idea. As noted this doesn't apply to valves, where the load isn't the speakers, it's the output transformer. Quote Link to comment Share on other sites More sharing options...
LewisK1975 Posted November 17, 2015 Share Posted November 17, 2015 Very interesting thread this one, not something I'd considered to be honest - can see solid state and valves discussed above, what about digital amps? same as solid state? Quote Link to comment Share on other sites More sharing options...
BASainty Posted November 17, 2015 Author Share Posted November 17, 2015 [quote name='Bill Fitzmaurice' timestamp='1447770714' post='2910177'] FWIW it's not resistance, it's impedance, and the issue isn't power, it's current. The lower the impedance load the higher the current draw, which increases heat, and it's that heat which lowers component life. You often see questions about using lower impedance speakers "to get all the watts out of my amp", and that's usually not a good idea. As noted this doesn't apply to valves, where the load isn't the speakers, it's the output transformer. [/quote] Ahh right I thought it was impedance and not resistance but wasn't 100%. So what I said I correct? Running an amp at a higher impedance could prolong the life of certain components thus making the chance of any unexpected failures lower on a user amp? (As I said I know if an amp has been mistreated and knocked around that wont help either.) Quote Link to comment Share on other sites More sharing options...
BASainty Posted November 17, 2015 Author Share Posted November 17, 2015 [quote name='LewisK1975' timestamp='1447771211' post='2910180'] Very interesting thread this one, not something I'd considered to be honest - can see solid state and valves discussed above, what about digital amps? same as solid state? [/quote] I would of thought as digital amps will still have circuitry in them. I would of assumed a digital amp is the same as a solid state but I may be wrong! Quote Link to comment Share on other sites More sharing options...
Guest bassman7755 Posted November 17, 2015 Share Posted November 17, 2015 [quote name='Bill Fitzmaurice' timestamp='1447770714' post='2910177'] FWIW it's not resistance, it's impedance, and the issue isn't power, it's current. The lower the impedance load the higher the current draw, which increases heat, and it's that heat which lowers component life. You often see questions about using lower impedance speakers "to get all the watts out of my amp", and that's usually not a good idea. [/quote] To be fair though I think most people use a 4 ohm load because they want to run two cabs rather than to squeeze extra power from the amp. If your sat there looking at one amp and two cabs and thinking "hmm no I wont risk running them both" even though its within the amp spec then that is verging on paranoia IMO Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted November 17, 2015 Share Posted November 17, 2015 [quote name='bassman7755' timestamp='1447773420' post='2910214'] To be fair though I think most people use a 4 ohm load because they want to run two cabs rather than to squeeze extra power from the amp. [/quote]If you peruse threads you'll find that just as many use two cabs to get a lower impedance load in search of more power. They do get more output of course, but due to the increased sensitivity and driver displacement that two cabs gives, not more power. It's also not the least bit unusual to find those who want to replace the drivers in a cab to get a lower impedance load, again in search of more power. Of all the attributes of an amp power is the least significant, but you'd never know that by reading manufacturer advertising. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted November 18, 2015 Share Posted November 18, 2015 Stop worrying about it. Bill is of course spot on, the current increases as you reduce the impedance and with it the heating in the output stages of your solid state amp. However they are designed with this in mind usually with lots of output transistors working in parallel and lots of heatsinking and often a cooling fan. On top of this there will be protection circuits which detect temperature rises and reduce the output power accordingly. Digital (actually switching but who cares) amps are often more efficient than traditional solid state amps so don't get so hot, but the same principles are used. My reservation is operating amps down below 4ohms. Some amps won't handle that current and that really is a lot of amperage for components to handle. At least check before inflicting this on your amp. Generally you'd just use a different amp and speakers or double up if you want to engineer that much sound and I can't think you'd need to go to 2ohms outside of a specialist PA application. Wear and tear isn't something to think about with solid state amps. there aren't any moving parts (cooling fans excepted) so nothing to wear. Components will degrade over time but they'll do this anyway even if you keep the amp in a box. Some degrade slower and some quicker with no use but basically I doubt you'd see much difference between a 20 year old amp with heavy use at 4 ohms and one used rarely at 8ohms. Quote Link to comment Share on other sites More sharing options...
chris_b Posted November 18, 2015 Share Posted November 18, 2015 Heat isn't the enemy. All amps generate heat in their components and they are designed and built for that. Too much heat could be a problem but many amps these days have protection circuits built in to cut out if they go out of spec. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted November 18, 2015 Share Posted November 18, 2015 [quote name='chris_b' timestamp='1447837841' post='2910744'] Heat isn't the enemy. All amps generate heat in their components and they are designed and built for that. Too much heat could be a problem but many amps these days have protection circuits built in to cut out if they go out of spec. [/quote]There's a big difference between short term overloading that will cause protection circuits to trip and long term heat damage to components, for which there's no protection. Quote Link to comment Share on other sites More sharing options...
BASainty Posted November 18, 2015 Author Share Posted November 18, 2015 [quote name='Bill Fitzmaurice' timestamp='1447851324' post='2910907'] There's a big difference between short term overloading that will cause protection circuits to trip and long term heat damage to components, for which there's no protection. [/quote] And long term heat damage is what I was thinking about. Quote Link to comment Share on other sites More sharing options...
davehux Posted November 27, 2015 Share Posted November 27, 2015 [quote name='4StringFortress' timestamp='1447766882' post='2910123'] Ok cool. Was just looking at a HA3500 thats spent its life being played through an 8ohm cab. [/quote] Noone ever gets an HA3500 above 3 on the Master anyway, because it destroys buildings if you do, so I wouldn't worry too much about usage Quote Link to comment Share on other sites More sharing options...
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