Problems with my new Black Spirit 200 Amp Head

I have had a chance to play with the amp head connected to the speakers as well as through power in. I am not happy with the stability of the connections so would like to solder to socket terminals and speaker terminals. I have a Weller soldering and some experience so I am not worried about the job. However I have the 2W 120 ohm resistor, but I am not certain how it works. I understand its dangerous to have the combo amp powered on with the amp head connected (too much power to speakers), I'd like to understand how the resistor prevents the overload. Also, the resistor should be soldered over the input wires from 212r on the socket, correct?

Matt

No Matt, the problem is not too much power to the speakers.  You have put in place a switched socket which should disconnect the speaker from the combo amp output totally when a plug is inserted in the new socket from your BS200.  The combo amp is now left with no load attached at all and this is a very dangerous thing for a valve output stage if it is powered up like that.  A signal will now cause very large voltage spikes, (flyback spikes), in the output valve circuitry.  It can be damaged severely by running with no load at all.  The 120ohm resistor is there so that if that condition occurs by accident there is at least some load there, even though it is very mismatched, which should prevent the largest of spikes in the output stage.  This is not about damage to the speaker, it is about damage to the combo amp.  It seems counter-intuitive to say an amp can be damaged by having no load on it to drive but it is true.

I'll just make sure about your connections for absolute safety.  The combo amp output wires must be connected to the two terminals which are isolated and left connected to nothing when a plug is pushed in.  The speaker should be soldered to the two terminals which are lifted when the plug is inserted.  Make sure you can understand what I mean by that and get that point absolutely right.  You then need to have the resistor soldered across the two terminals of the socket which the combo amp output wires connect directly to.  When the plug is inserted the combo wires are now not connected to the speaker but are left connected to the new resistor.

The +ve of the speaker and the +ve of the combo amp output cable should both go to the terminals furthest from the socket hole so they follow the tip of the plug.

I hope the picture makes everything clear.  Check out the area ringed in red.  Just make sure to correctly identify the pair of terminals which is connected to the plug and the pair which are isolated when the plug is in.

Just finished up soldering the connections. All went well, amp head and speakers sound great utilizing Speaker Out from BS200. Just a note, at 20W output I really have to crank up the volume and gain. I'm wondering about setting it the BS200 output to 200 watts, and keeping the volume real low. Looking on the net I found the following quote: "For instance, this is a quote from Sweetwater's website regarding matching amps with speakers. "The general rule of thumb is that an amp should be rated at about double the power of the speaker it must drive.""

I certainly wouldn't go by that advice on amp/speaker relative power from Sweetwater. I wouldn't drive any of my speakers, (right back to precious 1960s original G12H), with an amp that had twice the power. It's fine while you keep control and keep the volume down. There will always be the temptation to give it "just a little more". Having a very powerful amp with less powerful speakers is not a problem as long as the amp isn't running at that power but there will always be slips and accidents and these can get costly.

Certainly try the BS200 at the 200W setting, as long as you are very careful to start with the volume very low and progress up to your level gradually as you can hear the effect. Bear in mind that, the whole idea of having that 20W setting is not to put a limit on what the amp puts out at the same settings on the Gain and Volume control. The idea is to limit power in order to stretch the control travel you can use. I would absolutely expect that you will use the full range for the Gain and Volume and I wouldn't see it as a problem. Effectively, (not practically but the principle holds), now full volume is only giving out 20W not 200W so you need to use the full 1-10 whereas before at 200W you may only have been able to use something like 1-3. You now have finer control over the amp. It's a bit like having a gearbox where you can drop down a gear, run the revs higher, but only get a fraction of the speed out of the car. You drop to 20W, turn up the controls to suit, and have your tone at a fraction of the full power of the amp.

Remember, you only have a 100W solid state amp with matching speakers. (My apologies, I forgot that for a couple of posts and spoke as though it was a valve amp. It won't make any difference to what you have done, the process is exactly the same, it will just mean the amp is a bit less touchy about its loading than I made out.) Valve amps do have the ability to give out a fair bit more than their rated wattage while solid state amps limit sharply. With that in mind speakers for a budget solid state amp can be a little more "conservatively rated" than for a valve model. The problem we have to consider is not how much sound level you get out of them, it is literally the electrical power burning out the speaker coils. They heat up in use and if this goes above a certain limit the coil gets damaged and the speaker if ruined. You must make sure that doesn't happen. The simplest way is to control the output level to safely below the speakers' rating.

As I said, if you are not getting enough sound level out then all you can do is to use 200W and be VERY CAREFUL. If the problem is that you aren't comfortable with the idea of having to set your Gain/Volume controls up high then you can stop worrying, that is how it should be.

I've just checked out that Sweetwater quote. You got it wrong, (I must admit I suspected you must have). That section is about PA Amps and Speakers not guitar. PAs must run without distortion so you need to have unused headroom in your amp for the signal peaks to remain unclipped. Having a 200W amp would mean you would not be running it over considerably less than that for PA as it will start to overdrive and distort which sounds horrid for vocals.