Robban Posted October 12, 2022 Share Posted October 12, 2022 Hello musician friends! I have a Marshall JCM 2000 DSL head, and I have recently bought a Harley Benton G412a cabinet with Celestion Vintage 30 in it. How do I hook my amp to the cab to get the correct match up in Ohms? Grateful for answers! Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted October 12, 2022 Share Posted October 12, 2022 (edited) Cab switch to the right (8ohm mono...), plug into the 'Left/Mono' socket, and the middle output socket from the amp (N° 7...) with the amp switch to the right (8 ohm...). Enjoy. Edited October 12, 2022 by Dad3353 Quote Link to comment Share on other sites More sharing options...
Robban Posted October 12, 2022 Author Share Posted October 12, 2022 (edited) Thanks! Just a short question though, why not output socket No.8 from the amp..? Edited October 12, 2022 by Robban Quote Link to comment Share on other sites More sharing options...
FrankAtari Posted October 12, 2022 Share Posted October 12, 2022 5 minutes ago, Robban said: Thanks! Just a short question though, why not output socket No.8 from the amp..? Have faith and trust DadGuru... why will be revealed to you in your next life, if you re-join the forum. 1 Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted October 12, 2022 Share Posted October 12, 2022 25 minutes ago, Robban said: Thanks! Just a short question though, why not output socket No.8 from the amp..? '7' or '8', it matters not, but not both at once. Those two are wired internally together, so there's no difference. There are two to cater for the folk using two 16 Ohm cabs, so that, when they are plugged in together to '7' and '8', the amp 'sees' 8 Ohms (two 16 Ohms in parallel behave as one 8Ohms cab for the amp...). Hope this helps. Quote Link to comment Share on other sites More sharing options...
Robban Posted October 12, 2022 Author Share Posted October 12, 2022 Understood. Thanks a LOT for sharing your wisdom! 1 Quote Link to comment Share on other sites More sharing options...
Matt P Posted October 14, 2022 Share Posted October 14, 2022 just a quick aside, make sure that you use a proper speaker cable for the connection not a guitar/instrument cable, getting this wrong can cause serious damage to the amp (a friend fried the output transformers of his beloved laney head when he got this wrong) make sure the cable is marked as speaker and you'll be fine. Matt 1 2 Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted October 14, 2022 Share Posted October 14, 2022 12 minutes ago, Matt P said: just a quick aside, make sure that you use a proper speaker cable for the connection not a guitar/instrument cable, getting this wrong can cause serious damage to the amp (a friend fried the output transformers of his beloved laney head when he got this wrong) make sure the cable is marked as speaker and you'll be fine. Matt Yes indeed; this is an important point, which merits, perhaps, an explanation. Guitar (and other instrument...) cables have to carry very low-level signals, with very little current, and need protection from parasitic interference. To this end, they have very thin, flexible wire inside, enclosed in a metallic outer sheath, which keeps the unwanted noise out. Speaker cable, on the other hand, has to carry much higher voltage and current, and so much thicker wire and insulation goes into their structure. They are not, however, subject to picking up extra noise, and so do not have, nor need, the metallic sheathing of the instrument cable. What difference does it make..? An instrument cable used, wrongly, to cable an amp to a speaker is liable to heat up with the high currents that the amp puts out, as the thin wire, made for low signals, can't handle it, and is most likely to melt. If the inside wire melts, it will provoke a short-circuit between the inner wire and outer sheathing, which in turn will overload the amp. This could, if lucky, just shut down in protection mode, or, all too often, just bust the output of the amp, with ensuing 'magic smoke'. This is a Bad Thing, and can be expensive, or even dangerous. On the other hand, using, wrongly, a speaker cable to connect an instrument, will result in a lousy sound, with much buzzing, clicking and other extraneous noises. No physical harm, but a damaged reputation and a ruined concert. Each type of cable has its specific construction to cater for the use it is to be put to. These uses are not interchangeable, despite their having similar (jack...) plugs. Don't be fooled. Use instrument cable for instruments, and speaker cable for speakers. 2 Quote Link to comment Share on other sites More sharing options...
Matt P Posted October 15, 2022 Share Posted October 15, 2022 thank you @Dad3353 for the in depth explanation, i tried to explain it myself but i was trying to get the comment in when i should have been working so i was a little rushed. My friend did indeed let the magic smoke out of the output transformer of his Laney 50w head and unfortunately replacement transformers were not easily available at the time so it was broken for parts rather than being repaired ( i actually have a few of the valves sitting in a box somewhere.) Matt 1 Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted October 15, 2022 Share Posted October 15, 2022 4 minutes ago, Matt P said: ...My friend did indeed let the magic smoke out of the output transformer of his Laney 50w head ... Ah, probably open circuit there, then, rather than short-circuit. Valve amps do not like being worked hard with no load, so if the connection to the cab fails, for whatever reason... 'Puff..!' is often the result. A pity to not get it repaired, though, as those amps are splendid (we have a Laney VC50 Combo, which is very, very loud, and was toured around France for many years with no issues. Laney do some very Good Stuff.) Quote Link to comment Share on other sites More sharing options...
