off topic : tube amp

Hi, sorry, it’s off topic, it’s for a friend , as i know that here are people with fine ears , can somebody give thoughts about :


I love valve / tube amps - I use a pair of EL34 based mono-block amps I designed and built myself as general purpose / monitor amps. The output power rating can look a bit miserly by comparison to transistor amps, but ~ 30W is fine for any normal sized room, with plenty left to annoy the neighbours. You do have to be a little more selective in your choice of speakers - most will work just fine, but its always a good idea to audition the speakers / amps together if possible to identify / eliminate any potential mismatching problems. As usual, there is a lot of BS that gets talked about different amplifiers / system components etc etc (this is audio after all) but all I can say is that I built mine as an experiment - and I liked the sound so I use them.

thanks, this friend is building the speakers, so he’s trying to find the " good relation " between the amp and the speakers ( considering the amp’s choice )…

theres alot of BS when it comes to speakers and amps.

1 of them being you will blow up a speaker using a smaller amp than the rated power rating of the speaker. try blowing up a 1000w speaker with a 50 watt amp, the amp will die before the speaker, 500w speaker 50w amp same deal.

generally with amp/speakers there are 2 main trains of though, match the continues power . so a 500w speaker with a 500w amp, or match the peak power, so a driver that a driver rated with a peak of 600w you would want a 600w amp.

general rule just dont clip your amps, if your amp/speakers are close enough you shouldnt blow drivers,

what blows speakers? over working them not over/underpowering, though power a 100w speaker with a 1000w amp youw ill blow the speaker much easier than with a 200w amp.

and thats not even taking into consideration that alot of manufacturs speaker ratings can sometimes not really mean anythhing usefull.

1 of them being you will blow up a speaker using a smaller amp than the rated power rating of the speaker. try blowing up a 1000w speaker with a 50 watt amp, the amp will die before the speaker, 500w speaker 50w amp same deal.

VAST oversimplification and often wrong in the world of live audio, sorry.

A 50W amp might not (Depending on how bad you are clipping it), but a cranked up 500W amp in an effort to get speakers ‘louder’ might. For right now I will focus on professional audio, particularly in a live context, rather than amp design which is not my forte (Live audio most certainly is).

There is primarily two things that can damage a driver. Overexcursion, or Overheating. Overexcursion comes from driving to much power into a speaker, so the first thought is, of course then you would want to go lower power on the amp. The issue is you may clip your amp as a result of underpowering the speakers, long before you actually drive the speakers into overexcursion, and speakers generally handle brief (Key word is brief) periods of overexcursion fine. You would think this would prevent damage to the speakers, but you would be very wrong, as the end result is that in clipping you are generating a LOT of HF material, which means that in a multiple driver cabinet (Pretty much any professional cabinet designed for live audio) you are now sending MUCH more power into your HF driver, and will overpower it and cause it to pop in an extreme enough case.

The other issue that comes from clipping the amp has to do with the second damaging factor to speakers, heat. When you clip a sine wave, you can end up with a waveform much similar to a square wave depending on the severity of the clipping. Along with generating much more HF content, this has the added complexity of causing the LF driver in particular to stop moving as it hits what is effectively a DC signal briefly at each clip. The driver in actuality depends on movement to cool off, so the more severe the clipping, the closer to a DC signal you are sending, and the more heat builds up in the driver, until it starts to tear itself apart from the extreme movement combined with the weaker construction from heat.

So no, the thought of a speaker will die sooner from a small amp than a large one is not a myth. It is in fact backed up with both testing and science. The general rule of thumb accepted is to match the amp to the speaker at 1.5x-2x the RMS power rating. (RMS being another misnomer when dealing with complex audio signals, often times this will be labeled as ‘continuous’ or maybe even ‘program’ rating on the speaker data sheet, marketing departments don’t quite agree with using the same terminology sadly. So a 400W Continuous rated speaker, is best paired with a 600W to 800W amp, and then restrictions on the input side of the amp to make sure you don’t clip the amp, or overdrive the speakers.

If your speakers do not get loud enough with said restrictions in place, you need better speakers.(Another simplification sorry, that is an entire different topic in itself).

Now all that being said, as I mentioned above, this post approaches things from the live sound operators’ standpoint, not from the standpoint of amp design, where intentionally generating clipping can be beneficial, and often times there aren’t HF drivers in the same realm to think about, so it works well to use a much smaller amp with more powerful speakers I would imagine, but honestly I don’t deal with building amps, just micing them and running the live sound FoH and/or Monitors:)


Specifically with valve / tube amps, matching the speakers to the amp is more important, than for example it might be with a transistor equivalent. In general, tube amps are designed with less negative feedback (often a necessary consequence of having less open loop gain to begin with - amongst other things). This can mean that a relatively complex load presented by a speaker can have a more significant effect on uniformity of frequency response and in some cases stability than it might with an equivalent - well engineered - transistor based design. Matching speakers to tube amps is not just about matching nominal impedances for optimum (theoretical) power transfer. Speaker design itself (even just the enclosure - and very much more so the drivers, obviously) is a complex task definitely best left to experts. Almost always you will be better off buying speakers made by companies which specialize in making speakers, than you would be by building them yourself.

Thanks for your expert advices, i transmit …
may i ask differently : have somebody here experience with this amp ( dialogue-one )… or is it considered as BS ? :slight_smile:

Good post Seablade!


For the theory i recomend this place:
its a source of a Knowledge :slight_smile:
Other thing which is really Nr.1:It is important to listen to it.
So, go there to Bright Audio wizards sit in the room, plug some speaker/boxes play some cd´s and listen.
A/B listening ( must doo it) between this “tube thing” and some simple
transistor amp or active monitor boxes ( Neumann KH 120 A is a cream in ears :).

It is more complex to match this tube thing to good drivers! And it costs!!
I would stay with Neuman (all the stuff is matched and ready in the box) costs less!!!
However, we all love the tubes.
Im sure :slight_smile: