abbey road d enfer said:
Thank you sir
On my way
Just a quick question regarding the switches... I suppose a MBB switch with the resistor is preferably since there will be a load at all times? Or am I wrong here?
Best regards
// John
Guitar amp switching
- Thread starter johnheath
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Help Support GroupDIY Audio Forum:
Thank you sir
On my way
Just a quick question regarding the switches... I suppose a MBB switch with the resistor is preferably since there will be a load at all times? Or am I wrong here?
Best regards
// John
abbey road d enfer said:
Hmm... wouldn't that require four speakers? I mean each amp connected to common of the switch... That would be easier just to have speaker connected to each amp but then the choice of selecting speaker for each amp would be gone wouldn't it?
Best regards
// John
Bo Deadly
Well-known member
That could be an important part of a better solution.johnheath said:
Bo Deadly
Well-known member
The one that doesn't make your tubes flash blue.johnheath said:What is that better solution?
squarewave said:
Well... as the situation is now you are obviously seeing something that I don't. I guees a very simple solution to it all would be to being able to just switch the amp and have a similar speaker cab connected to the both amps... yes that could easily.
The question is in fact if there is a simple solution to being able to switch between the amps... and the speakers.
If this is a too hard nut to crack for please just say so... I can take it, but I was in fact just asking for advice
I know that you are a person with high level of knowledge and in absolutely most cases gives very good and constructive answers to who ever.
Best regards
// John
Bo Deadly
Well-known member
Trying to switch a load and not have it change at all is actually quite hard. I think that's primarily why you're not getting the answer you're looking for.johnheath said:If this is a too hard nut to crack for please just say so... I can take it, but I was in fact just asking for advice
The requirement that you have to be able to switch while the amp is on is a major problem. So just don't do that. If you turn the amp off (or to standby), then a simple AB switch would work. You could just use the circuit you posted or buy an AB switch.
squarewave said:
Thank you sir
Yes, I have settled for the "standby mode" solution... I won't go further than that. I will build a small bow with it and suitable heat sinks for the resistors... I actually think that I have it all laying around in the work shop.
Best regards
// John
clintrubber
Well-known member
FWIW, you might have already seen this one:
the Palmer TINO "TwoINOne" might not be exactly what you're looking for,
but perhaps might provide some info or inspiration?
the Palmer TINO "TwoINOne" might not be exactly what you're looking for,
but perhaps might provide some info or inspiration?
Bo Deadly
Well-known member
A secondary reason I think you're not getting the answers you're looking for is because I don't think you're really thinking things through. For example, the resistors were to try to deal with switching a live amp. But if it has been decided that you'll never-ever switch the amp unless it's off or in stand-by (just like you would never pull the speaker cable out of a live amp), then you don't need load resistors at all. Right? And, as others have suggested, it's not clear that 620 ohms would prevent a failure anyway. And, even if you did use them for whatever reason, the heatsink requirement depends on the power they dissipate which is something that you can compute using ohms law. For a 50W amp tha'ts 20V / 8R = 2.5A * 20V = 50W. So if you used 620R resistors that's 20V / 620R = 0.032A * 20V = 0.65W. Under a watt. Depending on the specific resistor used, that probably doesn't need a heatsink at all. So like I said at the end of my last message, use and A/B box and just never-ever switch the load while the amp is on.
The "8 Ohm" do not have to be exact. 2:1 either way may lead to a Common Value. 10r is convenient. (However 8r power resistors are sold as Dummy Loads rated for more power than most tube amps.)
We could observe that ALL tube amps survive heavy beating at speaker bass resonance which is often 50 Ohms. And power in 50r is maybe 1/3rd the power at 8r. (Not 8/50 because the amp is lossy at nominal load, and light-load voltage rises more than a transistor amp.)
We could observe that ALL tube amps survive heavy beating at speaker bass resonance which is often 50 Ohms. And power in 50r is maybe 1/3rd the power at 8r. (Not 8/50 because the amp is lossy at nominal load, and light-load voltage rises more than a transistor amp.)
squarewave said:
Thank you sir
I have been thinking about this as well... I mean that never switching the live amp should not be that tricky.
I has been an interesting discussion though... and as in all discussions you pick up some facts her and there so it is good.
Best regards
/ John
See attached schemo.johnheath said:
There's only one point to take in consideration; with both amps off or both on, their outputs are connected together. The risk of damage is not considerable, but if you want to avoid it, you have two possibilities:
1) Be very cautious
2) Use interlocking switches; I would recommend that. The best interlocking switch is a rotary switch IMO.
Attachments
Speaker switcher/swapper ,attenuator and dummy load all in one box seems do-able, passive di transformer so the soundguy gets a balanced ungrounded feed , maybe you could hijack 48v phantom from the desk to power the relay if you needed remote capabillity but loose the ungrounded advantage by doing so .
Not realistic. Such a typical relay needs about 500mW to energize.Tubetec said:
Max available power from phantom is only 170mW.
No. The relay coil can be completely floating from the audio circuitry.
moamps
Well-known member
You can't leave a tube amp unloaded, even without signal.moamps said:
moamps
Well-known member
It's loaded with another speaker.
