Basically I'm thinking of making one for my freshly made speakers.
I would be looking for at least 25Wrms per channel.
I don't like the look of them with the transformers on top of the chassis is it possible to mount them inside as long as they are suitably electrically and magnetically isolated properly? Or is this not the reason for no having them inside the chassis?
How much am I looking at price wise?
Where are the sorts of places I can my kits from in the UK?
Why go for tube over chip? And would I really benefit from it as I jsust payed £300 for the speakers I have made?
Thanks
Boscoe
I would be looking for at least 25Wrms per channel.
I don't like the look of them with the transformers on top of the chassis is it possible to mount them inside as long as they are suitably electrically and magnetically isolated properly? Or is this not the reason for no having them inside the chassis?
How much am I looking at price wise?
Where are the sorts of places I can my kits from in the UK?
Why go for tube over chip? And would I really benefit from it as I jsust payed £300 for the speakers I have made?
Thanks
Boscoe
Hi Neighbour!!
You may not need 25W, I changed from a 150W SS amp to a ~9W SE amp and didn't notice any lack of power!
Tube will sound better than SS for a number of reasons, mainly due to the vanishingly small number of correctly designed SS amps.
You can make an amp that uses toroids that will fit under a chassis - but usually the most room is available on top with the tubes!
You may also find it cheaper to buy a chinese amp like the Yaqin MC-10L and mod it rather than buy a kit or all the bits separately.
How did you arrive at 25 WPC?
Can you tell me the SPL rating of the speakers you built?
A chip amp may have some advantages over a tube amp. Tube amps are typically more expensive to build. The advantages are more aesthetic, but you get some exceptional performance from a properly designed and built tube amp.
An exceptional tube amp will be indistinguishable from an exceptional solid state amp as far as performance differences. It's like having your pick between a 2010 Porsche Boxster S and a 1966 Jag XKE. Performance is similar, but the Jag has a lot more style.
Looks good for choice then. You can measure them with a cheap multimeter! Switch to AC voltage, connect to the speaker leads and play as loud as you want. I'd be very surprised if you use more than 1 Watt
My speakers are 87dB/Watt and go way loud enough on 9W.
Switch to AC Voltage (lowest range).
Read off the voltage on the display!
Into a 8ohm speaker 8V is about 8Watts, 4V is 2Watts, 2V is 0.5Watt, the formula is Power (Watts) = V x V / R (R = resistance, nominal 8).
It's a rough estimate of power but good enough for the purpose.
BTW: Read the safety topic in this forum (listed at the top) before considering working on a tube/valve amp.
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Let's assume the speakers are 8 Ohms nominal, 90 dB. sensitive and that their impedance curve is reasonably flat, as tube amps "dislike" speakers with dips in the impedance curve, especially in the deep bass. Complex crossovers tend to produce the unwanted dips.
Paul Joppa has given us a useful rule of thumb. Joppa's rule states in an "average" listening space an amp/speaker combo should be capable of producing 102 dB. SPL peaks at a 1 M. distance. Applying the rule to 90 dB. sensitivity tells us you need 16 WPC. A push pull amp employing EL84s or 6V6s will not get there. An PP amp built around EL34s, 7591s, or 6L6s will get there and then some.
Paul Joppa has given us a useful rule of thumb. Joppa's rule states in an "average" listening space an amp/speaker combo should be capable of producing 102 dB. SPL peaks at a 1 M. distance. Applying the rule to 90 dB. sensitivity tells us you need 16 WPC. A push pull amp employing EL84s or 6V6s will not get there. An PP amp built around EL34s, 7591s, or 6L6s will get there and then some.
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I've got an old oscilloscope. I used it to look at the signal on my speakers. I have some DIY speakers at nominally 89dB sensitivity, close enough to your 90dB. For normal listening the average (by eye) amplitude of the music was always equivalent to well UNDER 1W. Of course if I want a loud rock n roll that's a different prospect but in a typical listening room I'd doubt you need more than you can get from most tube amps including the flea watt kind. Good thing about a tube amp is that many of them tolerate peaks an transients very well so you don't suffer very much from these things if you do get a low powered amp. It means you won't get 102dB peaks. Your ears will thank you for this when they are still working fine in your old age.
I've only built one tube amp, a 6AS7 SE amp. I put all the transformers except for the mains power transformer inside the chasis where they can't be seen. I did this because they are all ugly. Only the power transformer has a nice painted cover. I have found that my power transformer gets pretty warm so having it on top is good. The other transformers don't get warm and they are all find inside the box. You do have to be careful about how they are positioned and oriented to prevent magnetic fields coupling between them and other parts of the circuit - or you'll get hum, or worse.
Hope this helps.
I've only built one tube amp, a 6AS7 SE amp. I put all the transformers except for the mains power transformer inside the chasis where they can't be seen. I did this because they are all ugly. Only the power transformer has a nice painted cover. I have found that my power transformer gets pretty warm so having it on top is good. The other transformers don't get warm and they are all find inside the box. You do have to be careful about how they are positioned and oriented to prevent magnetic fields coupling between them and other parts of the circuit - or you'll get hum, or worse.
Hope this helps.
90 dB is not bad.
At 1 Watt = 90 dB at 1 meter from the loudspeaker.
At 2 Watts = 93 dB
At 4 Watts = 96 dB
At 8 Watts = 99 dB
At 16 Watts = 102 dB
At 32 Watts = 105 dB
At 64 Watts = 108 dB
At 128 Watts = 111 dB
At 256 Watts = 114 dB Close to Peak of a live symphony orchestra
So, 250 watts would get you to the performance level of a live symphony in loudness without distortion from the amp.
At 25 Watts you top out at 103 to 104 dB, which is loud, but not as loud as a live performance.
Sound pressure levels drop off at the square of the distance. So, as you get further away so too does the reduction in volume.
At 1 Watt = 90 dB at 1 meter from the loudspeaker.
At 2 Watts = 93 dB
At 4 Watts = 96 dB
At 8 Watts = 99 dB
At 16 Watts = 102 dB
At 32 Watts = 105 dB
At 64 Watts = 108 dB
At 128 Watts = 111 dB
At 256 Watts = 114 dB Close to Peak of a live symphony orchestra
So, 250 watts would get you to the performance level of a live symphony in loudness without distortion from the amp.
At 25 Watts you top out at 103 to 104 dB, which is loud, but not as loud as a live performance.
Sound pressure levels drop off at the square of the distance. So, as you get further away so too does the reduction in volume.
And conversely:
By UK law, employers must start to take measures to save the hearing of their workers in workplaces where noise reaches 85 decibels or more. This means that the noise has to be monitored, and hearing protection provided for those who request it. After 90 decibels the noise exposure has to be reduced in addition to providing free hearing protection devices to workers.
So 90dB in an average sized room is pretty good. I used a 'scope to measure some unbearably loud stuff from a regular 86dB/Watt speaker and managed a peak power of 12Watts, or 6Watts RMS.
It's not the average power that counts, it's the peak power that you want to consider.
Ideally, your amp should not clip at any listening level. If it does, it is introducing distortion.
If your 8 Watt amp is set so that your average listening volume is 8 Watts, every time you introduce a music peak above the average, it is distortion that is heard.
Check that requirement. I'll bet it is sustained levels, not peak levels. A train whistle 500 feet away hits 90 dB.
Incorrect. Lundahl transformers, bith OPT and power, will easily fit INSIDE a 88mm high box (2RU) - we do it in both of our commercial poweramps. You can see pix on my website.
Regards, Allen
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