robocorpse Posted February 26, 2011 Share Posted February 26, 2011 What about wiring a 10 watt 8 ohm resistor across a jack plug and leaving it plugged in all the time unless you have a speaker connected? that way if you do accidentally unplug the headphones, there is no chance of running the output TR unloaded. Quote Link to comment Share on other sites More sharing options...
icastle Posted February 26, 2011 Share Posted February 26, 2011 [quote name='robocorpse' post='1142319' date='Feb 26 2011, 01:39 PM']What about wiring a 10 watt 8 ohm resistor across a jack plug and leaving it plugged in all the time unless you have a speaker connected? that way if you do accidentally unplug the headphones, there is no chance of running the output TR unloaded.[/quote] But wait! I have a cunning plan.... Why not use a 10W 8Ω loudspeaker across a jack plug and leave it plugged in all the time... Quote Link to comment Share on other sites More sharing options...
robocorpse Posted February 26, 2011 Share Posted February 26, 2011 [quote name='icastle' post='1142342' date='Feb 26 2011, 02:08 PM']But wait! I have a cunning plan.... Why not use a 10W 8Ω loudspeaker across a jack plug and leave it plugged in all the time...[/quote] I was replying to OPs earlier comment: "So I can run it without a cab? That would be convenient." No need to be so condescending... Quote Link to comment Share on other sites More sharing options...
icastle Posted February 26, 2011 Share Posted February 26, 2011 [quote name='robocorpse' post='1142581' date='Feb 26 2011, 05:48 PM']No need to be so condescending...[/quote] It was not intended to be in any way condescending, sorry if you took it to be. Quote Link to comment Share on other sites More sharing options...
mart Posted February 28, 2011 Author Share Posted February 28, 2011 [quote name='robocorpse' post='1142319' date='Feb 26 2011, 01:39 PM']What about wiring a 10 watt 8 ohm resistor across a jack plug and leaving it plugged in all the time unless you have a speaker connected? that way if you do accidentally unplug the headphones, there is no chance of running the output TR unloaded.[/quote] Thanks for the suggestion. I had been contemplating something like this - it would seem a quick and safe fix. And a lot more convenient than a speaker. Quote Link to comment Share on other sites More sharing options...
umph Posted February 28, 2011 Share Posted February 28, 2011 [quote name='mart' post='1139896' date='Feb 24 2011, 01:07 PM']I've just bought myself a tiny valve head. It says, as you'd expect, that you should connect a speaker before turning the head on. It also has a headphone socket, and when you plug headphones in, it cuts off the sound to the speaker. Does this mean I can use the head with no speaker attached if I'm using headphones? My understanding is that an amp needs a load, and a valve amp especially needs a load. But if the headphone socket cuts off the signal to the speaker, then surely it's disconnecting the speaker, in which case I don't need it connected in the first place. Am I right?[/quote] what amp is it? It could be switching the amp onto a dummy load. Quote Link to comment Share on other sites More sharing options...
mart Posted February 28, 2011 Author Share Posted February 28, 2011 [quote name='umph' post='1144483' date='Feb 28 2011, 02:10 PM']what amp is it? It could be switching the amp onto a dummy load.[/quote] It's a Blackstar HT1RH. (I've now edited my OP to include this information since it was buried further down in the thread). Quote Link to comment Share on other sites More sharing options...
umph Posted February 28, 2011 Share Posted February 28, 2011 just realised what amp it is, no need to worry about a dummy load. It'll be fine. Quote Link to comment Share on other sites More sharing options...
mart Posted February 28, 2011 Author Share Posted February 28, 2011 Because of the small output? Quote Link to comment Share on other sites More sharing options...
umph Posted February 28, 2011 Share Posted February 28, 2011 [quote name='mart' post='1144606' date='Feb 28 2011, 04:19 PM']Because of the small output?[/quote] aye and high impedance on the primary, the ecc82 shouldn't be all that picky Quote Link to comment Share on other sites More sharing options...
mart Posted February 28, 2011 Author Share Posted February 28, 2011 [quote name='umph' post='1144607' date='Feb 28 2011, 04:21 PM']aye and high impedance on the primary, the ecc82 shouldn't be all that picky[/quote] Thanks. I have to admit that I don't understand that , but it sounds like you do, which gives me confidence in what you say! Quote Link to comment Share on other sites More sharing options...
mart Posted March 2, 2011 Author Share Posted March 2, 2011 So I finally got a response from Blackstar: [quote]Thanks for the enquiry. We recommend that you have a speaker load attached but the speakers will be disconnected when the emulated output is in use. Hope this helps.[/quote] I can't say that I feel very enlightened by this response, but at least I'll stop complaining about them not replying! Quote Link to comment Share on other sites More sharing options...
mart Posted March 7, 2011 Author Share Posted March 7, 2011 (edited) Having mulled this over, I definitely want to make up a dummy load, i.e., a jack connector wired to a resistor. Would this 10ohm resistor from Maplins do? [url="http://www.maplin.co.uk/10-ohm-to-30-ohmmetal-film-0.6w-resistors-341331"]http://www.maplin.co.uk/10-ohm-to-30-ohmme...esistors-341331[/url] Edited March 7, 2011 by mart Quote Link to comment Share on other sites More sharing options...
icastle Posted March 7, 2011 Share Posted March 7, 2011 [quote name='mart' post='1152339' date='Mar 7 2011, 11:20 AM']Having mulled this over, I definitely want to make up a dummy load, i.e., a jack connector wired to a resistor. Would this 10ohm resistor from Maplins do? [url="http://www.maplin.co.uk/10-ohm-to-30-ohmmetal-film-0.6w-resistors-341331"]http://www.maplin.co.uk/10-ohm-to-30-ohmme...esistors-341331[/url][/quote] Nope. It'll only handle 0.6W. If you want to do that you should be looking at something like [url="http://www.maplin.co.uk/10-watt-wirewound-resistor-2181"]these[/url] - the do an 8.2Ω one - you need to order part number H8.2R. Quote Link to comment Share on other sites More sharing options...
mart Posted March 7, 2011 Author Share Posted March 7, 2011 [quote name='icastle' post='1152509' date='Mar 7 2011, 02:15 PM']Nope. It'll only handle 0.6W. If you want to do that you should be looking at something like [url="http://www.maplin.co.uk/10-watt-wirewound-resistor-2181"]these[/url] - the do an 8.2Ω one - you need to order part number H8.2R.[/quote] Well, the amp is only rated at 1W! Seriously though, thanks - that 8.2Ω one looks ideal. I just need to save up a further 37p Quote Link to comment Share on other sites More sharing options...
icastle Posted March 7, 2011 Share Posted March 7, 2011 [quote name='mart' post='1152532' date='Mar 7 2011, 02:40 PM']Well, the amp is only rated at 1W! Seriously though, thanks - that 8.2Ω one looks ideal. I just need to save up a further 37p [/quote] Oh god - I thought it was 10W! In that case what you need is something like [url="http://www.maplin.co.uk/3-watt-wirewound-resistor-2173"]this[/url]. It's bigger than what you really need but at least it's available in a reasonably close value without wiring loads of smaller resistors in parallel. W8.2R is the part number. Quote Link to comment Share on other sites More sharing options...
mart Posted March 7, 2011 Author Share Posted March 7, 2011 Even better! Thanks again! Quote Link to comment Share on other sites More sharing options...
umph Posted March 7, 2011 Share Posted March 7, 2011 [quote name='mart' post='1152621' date='Mar 7 2011, 04:00 PM']Even better! Thanks again![/quote] If you've not got a fan on it i'd recomend something larger. Your amp will do 1W rms and a few more overdriven and if you're running the resistor near it's limit it'll get hot Quote Link to comment Share on other sites More sharing options...
mart Posted March 8, 2011 Author Share Posted March 8, 2011 [quote name='umph' post='1152785' date='Mar 7 2011, 06:39 PM']If you've not got a fan on it i'd recomend something larger. Your amp will do 1W rms and a few more overdriven and if you're running the resistor near it's limit it'll get hot[/quote] Even though the amp isn't putting any signal through the resistor? (Since I only want this dummy load for when I'm using headphones, and the amp "disconnects the speaker" when the headphone socket is in use). I must admit I'm a bit lost on this, but if I had a speaker connected there would be no sound, so surely with a resistor in place instead of the speaker, the resistor will be getting no current through it. Or am I missing something again? Quote Link to comment Share on other sites More sharing options...
icastle Posted March 8, 2011 Share Posted March 8, 2011 [quote name='mart' post='1153493' date='Mar 8 2011, 10:22 AM'] Even though the amp isn't putting any signal through the resistor? (Since I only want this dummy load for when I'm using headphones, and the amp "disconnects the speaker" when the headphone socket is in use). I must admit I'm a bit lost on this, but if I had a speaker connected there would be no sound, so surely with a resistor in place instead of the speaker, the resistor will be getting no current through it. Or am I missing something again?[/quote] If you unplug the headphones then the signal will expect to find a loudspeaker to work with. A resistor works by converting an applied voltage into heat and needs to be of a large enough size to dissipate 1W (as opposed to the 10W I thought it was!). If it helps, think of these resistors as the 'posh' electronics equivalent of the old fashioned bars you used to get on an electric fire. A 1W resistor [b]would[/b] do the job, but if the amp was overdriven then that 1W resistor could get very hot (you could apply more than 1W to it) so using a larger wattage resistor is the easiest way of putting a load on the amp which won't get too hot and has very little chance of failing. Quote Link to comment Share on other sites More sharing options...
mart Posted March 8, 2011 Author Share Posted March 8, 2011 Ok, that makes sense. So let's see if I've got this right: While the headphones are plugged in, my tiny resistor should be ok. But if I accidentally unplug the headphones, or forget to plug them in, and carry on playing, then that resistor may get too hot. So a bigger resistor (that can shed more heat) will guard me against that possibility. Quote Link to comment Share on other sites More sharing options...
icastle Posted March 8, 2011 Share Posted March 8, 2011 [quote name='mart' post='1153926' date='Mar 8 2011, 03:11 PM']Ok, that makes sense. So let's see if I've got this right: While the headphones are plugged in, my tiny resistor should be ok. But if I accidentally unplug the headphones, or forget to plug them in, and carry on playing, then that resistor may get too hot. So a bigger resistor (that can shed more heat) will guard me against that possibility.[/quote] Yep, that's pretty much right. This resistor is just a coil of wire with a ceramic shell around the outside of it - if it gets too hot then the coil will burn out and you'll end up with no load (it'll 'blow' like a light bulb) and that's bad news. A higher wattage resistor can cope with a higher load going across it and (in your scenario) has very little chance of overheating and blowing. Quote Link to comment Share on other sites More sharing options...
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