Well I've finished an amp that is rated @ 30 watts max based on .037 ma x 2 output tubes @ 410 plate volts and it sounds really great- To me. However, I gave it a blast test today and hesitated to turn it all the way up due to the fact, as I approached max power the speakers just didn't sound as though they were responding in the right way. It sounded to me like the speakers were coming close to the blow out zone. A sort of flapping loss of clarity sound.
For purposes of the discussion let's assume the amp is functioning properly.
My question is: Could a 30 watt amp blow 4 12's rated at 420 watts? These speakers were packaged in a B-25 cabinet and unmarked but still, that short of the rated power?? I do understand they may have stated peak music power or something like that, but still, that short of expectations?
Now, what kind of circuit flaw could cause that same problem if the speakers were in fact okay?
Thanks for the consideration,
Ccat.
For purposes of the discussion let's assume the amp is functioning properly.
My question is: Could a 30 watt amp blow 4 12's rated at 420 watts? These speakers were packaged in a B-25 cabinet and unmarked but still, that short of the rated power?? I do understand they may have stated peak music power or something like that, but still, that short of expectations?
Now, what kind of circuit flaw could cause that same problem if the speakers were in fact okay?
Thanks for the consideration,
Ccat.
It's unlikely that an amp like this could drive your speakers full range to a high volume level. Probably it was clipping badly.
Have you heard your speakers sound ok with other amps?
I'll have to try that
I've got the MosFet amp I was using. I'll have to try that or, more easily connect the scope up and check the output. This build is a power amp only so the clipping would have to arise from the phase inverter I suspect.
Thanks,
Ccat.
I've got the MosFet amp I was using. I'll have to try that or, more easily connect the scope up and check the output. This build is a power amp only so the clipping would have to arise from the phase inverter I suspect.
Thanks,
Ccat.
The usual type of power supply in a small tube amp can't store enough energy for driving wide range speakers loudly.
Silicon diode rectifiers and much larger capacitance help.
Multiplying voltage and current in the no signal bias condition is not how the power rating of a power amplifier is determined. What you have calculated is the waste heat in the output tubes.
What is the primary impedance of the output transformer? Is the load properly matched to the output transformer secondary?
Not a good idea. Have you connected the amp to any other speakers?
Normally no, but what makes you think the speakers are rated at 420 Watts? Have the speakers ever been connected to a known working amp?
In answer to your questions
Loudthud:
Multiplying voltage and current in the no signal bias condition is not how the power rating of a power amplifier is determined. What you have calculated is the waste heat in the output tubes.
Well I guess I'm off the the Internet of things to determine power calculations... (This now introduces several other questions such as- That's an awful lot of wasted power? and if I lower the bias how will that affect the what? Headroom, tone, cost of tea in China?
I'll have to put together a dummy load and start scoping the amp. Once I get some data I'll put that up in the area this amp is posted under in Instruments? It is a new build.
The decision to use that particular bias level came from a bias chart.
What is the primary impedance of the output transformer? Is the load properly matched to the output transformer secondary?
I believe so as the transformer employed drove 6L6 tubes in the past- albeit at 660 Plate volts and the design was exactly the same.
Quote:
Originally Posted by colorcat
For purposes of the discussion let's assume the amp is functioning properly.
Not a good idea. Have you connected the amp to any other speakers?
No but it sounds great until I approach MAX volume...
Quote:
Originally Posted by colorcat
My question is: Could a 30 watt amp blow 4 12's rated at 420 watts?
Normally no, but what makes you think the speakers are rated at 420 Watts? Have the speakers ever been connected to a known working amp?
The speakers came out of a B-52 Cab rated at 420 watts. I just don't recall if that was Peak Music Power or what.
Another question that has entered the possible realm is: Could the output transformer be cutting out due to design limitations on frequency response?
rayma
It could be insufficient supply reserves but I based those values on the original design. Not to say that was correct either and the rectifiers are silicone.
These are great directions to look in. Thanks for all the feedback.
Here is the build thread and finished schematic with voltage levels: http://www.diyaudio.com/forums/instruments-amps/265261-sunn-sceptre-style-build-3.html
Ccat.
Loudthud:
Multiplying voltage and current in the no signal bias condition is not how the power rating of a power amplifier is determined. What you have calculated is the waste heat in the output tubes.
Well I guess I'm off the the Internet of things to determine power calculations... (This now introduces several other questions such as- That's an awful lot of wasted power? and if I lower the bias how will that affect the what? Headroom, tone, cost of tea in China?
I'll have to put together a dummy load and start scoping the amp. Once I get some data I'll put that up in the area this amp is posted under in Instruments? It is a new build.
The decision to use that particular bias level came from a bias chart.
What is the primary impedance of the output transformer? Is the load properly matched to the output transformer secondary?
I believe so as the transformer employed drove 6L6 tubes in the past- albeit at 660 Plate volts and the design was exactly the same.
Quote:
Originally Posted by colorcat
For purposes of the discussion let's assume the amp is functioning properly.
Not a good idea. Have you connected the amp to any other speakers?
No but it sounds great until I approach MAX volume...
Quote:
Originally Posted by colorcat
My question is: Could a 30 watt amp blow 4 12's rated at 420 watts?
Normally no, but what makes you think the speakers are rated at 420 Watts? Have the speakers ever been connected to a known working amp?
The speakers came out of a B-52 Cab rated at 420 watts. I just don't recall if that was Peak Music Power or what.
Another question that has entered the possible realm is: Could the output transformer be cutting out due to design limitations on frequency response?
rayma
It could be insufficient supply reserves but I based those values on the original design. Not to say that was correct either and the rectifiers are silicone.
These are great directions to look in. Thanks for all the feedback.
Here is the build thread and finished schematic with voltage levels: http://www.diyaudio.com/forums/instruments-amps/265261-sunn-sceptre-style-build-3.html
Ccat.
'Generally' PA and Guitar gear have proper RMS ratings, as otherwise they die while still under warranty.
But even with imaginary ratings, an 18W amplifier isn't going to make them cough at all - if anything it's too small to drive them reasonably.
I don't have the slightest doubt that the problem is your amplifier - don't you have another speaker you could try? - a HiFi one for example, again 18W is too low to damage pretty well anything.
No point in guessing.
You have a scope, according to your posts.
Check the new amp into a dummy load (resistor) while looking at it on the scope with a sinewave around 1kHz going in and measure the actual p-p voltage, take 1/2 of the p-p, multiply by 0.707 and use that value to figure the power into the resistor's ohmage value. That is the true power of the amp.
Then you can run into your speakers and with the scope connected note when you are at or near clipping (the same p-p voltage).
In the event that it starts to sound really bad before clipping, and the waveform in the previous test was not distorted, then you may be running out of drive voltage from the previous stage(s). A scope - again with the dummy load connected - will tell you that too.
Then you will know where ur problem is.
Until then, don't guess and muck about.
_-_-
PS. the bias on this amp should be for class AB, so quiescent probably on the order of less than 1 watt. The amp is in the 30 watt range, unless the supply voltage is high enough then the top end is about 50 watts. Regardless, this is a difference of <3dB.
PPS. The power supply, solid state or vacuum tube, big caps vs. small caps will have very little influence on if the amp can make a reasonable amount of undistorted power... the output iron also will have nil effect unless ur trying to run a low bass signal and seriously saturating the core.
PPPS. The speakers - how are they wired?? IF they are all wired in parallel, then the power is equal to the rating of ONE speaker. If it is a series parallel with 4 speakers then the rating is equal to TWO speakers. 4 in series is 4x the power of a single speaker. Regardless a 30-60watt amp ought not to be too much drive for reasonably good speakers - of course if these are 15watt cheeze speakers in a box marked 420watts (sounds likely, btw), then they may indeed be overdriven.
You have a scope, according to your posts.
Check the new amp into a dummy load (resistor) while looking at it on the scope with a sinewave around 1kHz going in and measure the actual p-p voltage, take 1/2 of the p-p, multiply by 0.707 and use that value to figure the power into the resistor's ohmage value. That is the true power of the amp.
Then you can run into your speakers and with the scope connected note when you are at or near clipping (the same p-p voltage).
In the event that it starts to sound really bad before clipping, and the waveform in the previous test was not distorted, then you may be running out of drive voltage from the previous stage(s). A scope - again with the dummy load connected - will tell you that too.
Then you will know where ur problem is.
Until then, don't guess and muck about.
_-_-
PS. the bias on this amp should be for class AB, so quiescent probably on the order of less than 1 watt. The amp is in the 30 watt range, unless the supply voltage is high enough then the top end is about 50 watts. Regardless, this is a difference of <3dB.
PPS. The power supply, solid state or vacuum tube, big caps vs. small caps will have very little influence on if the amp can make a reasonable amount of undistorted power... the output iron also will have nil effect unless ur trying to run a low bass signal and seriously saturating the core.
PPPS. The speakers - how are they wired?? IF they are all wired in parallel, then the power is equal to the rating of ONE speaker. If it is a series parallel with 4 speakers then the rating is equal to TWO speakers. 4 in series is 4x the power of a single speaker. Regardless a 30-60watt amp ought not to be too much drive for reasonably good speakers - of course if these are 15watt cheeze speakers in a box marked 420watts (sounds likely, btw), then they may indeed be overdriven.
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You'll hear high excursion bass drivers "fart out" when they hit their mechanical limits. This happens at about 1/2 rated RMS (thermal) power rating.
Guitar speakers usually have much less excursion than bass drivers. They'll hit their mechanical limits much sooner.
The "flapping loss of clarity" seems to indicate this.
Guitar speakers usually have much less excursion than bass drivers. They'll hit their mechanical limits much sooner.
The "flapping loss of clarity" seems to indicate this.
Sorry @bear - don't get that at all. Four 105 watt speakers wired together gives you a cab rated at 420 watts - it doesn't matter whether they are series, parallel or series-parallel. The combined impedance would be different, according to the connection, of course.
I've moved this to the build Thread
http://www.diyaudio.com/forums/instruments-amps/265261-sunn-sceptre-style-build-3.html#post4166923
It probably makes sense to continue this on the Thread related to the actual build as all the technical details are there. I wondered about the speakers at first but the problem must be in the amp.
Ccat.
http://www.diyaudio.com/forums/instruments-amps/265261-sunn-sceptre-style-build-3.html#post4166923
It probably makes sense to continue this on the Thread related to the actual build as all the technical details are there. I wondered about the speakers at first but the problem must be in the amp.
Ccat.
This thread is probably dead but I was browsing threads and came across this one. Malcolm Irving is absolutely correct about speaker power handling. It doesn't matter whether speakers are wired in parallel, series or series-parallel, all you do is add up total wattage of the speakers when multiple speakers are used. Not sure where bear got his info.
Hi,
I know what Bear is talking about but he expressed it poorly for some.
If you can't see what he's getting at it is about what you can
expect from drivers and a reasonably load tolerant amplifier.
rgds, sreten.
I know what Bear is talking about but he expressed it poorly for some.
If you can't see what he's getting at it is about what you can
expect from drivers and a reasonably load tolerant amplifier.
rgds, sreten.
Thanks for responding sreten. I understand what you are talking about. If you read the OP's first post, he was wondering if his speakers could not handle his amp's power. The thread then evolved to address the real issue. Then bear stated in his PPPS that if you wire speakers of the same power rating in parallel then the power is equal to the value of ONE speaker, which is not true. No matter how you wire speakers, you add up the total. I agree the main problem that is happening is what you and bear said but all of bear's PPPS statement regarding speaker wiring is not true. Total impedance is another matter altogether. Will the amp handle the various impedances with different wiring?
Sorry, I was a bit hasty when I said "all" of his PPPS was wrong. The third scenario about adding up the four in series to get the total was correct. Sorry about that.
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