Ay Caramba... maybe dual wound for a parallel configuration?
I think we have now crossed from a quixotic endeavor to a Pyrrhic design battleground.
And no, nyet! I'm not gonna use my one working tube amp in this experiment. I wonder what a burning output transformer smells like...
But yes, those tubes driving the 16 ohm taps sound very nice. Really nice. And being Svetlanas, I wonder if I can get replacements for them.
You mentioned speakers. I wouldn't connect your experimental parallel amplifier to any speakers you care about. It's almost 100% that you will damage any speakers you hook up to this monstrosity.
I have a feeling you'll be smelling some magic smoke pretty soon. Not a putdown, but a right of passage.
Not all my spectacular mistakes were decades ago. About 4 years ago I was looking at a high powered amplifier that had gross distortion on the negative swing of one channel. Good clue, right? I had the unit powered up with no safety precautions; no current limiting resistors or light bulbs (my favorite), just powered up with 140 volts on the rails. I was poking around with the VOM, being mindful of the high voltage so as to not get a shock. I went to measure the voltage on one of the driver transistors, and one of the output transistors (enormous Sanken Darlingtons with 6 emitters and internal emitter resistors) went up in a plasma arc. There was nothing left but a couple of the leads still soldered to the board and a small piece of the case. Further examination revealed that 3 of the 4 driver transistors (T220 with no heat sink) had unsoldered themselves from the board. I could yank 2 of them right off the board without unsoldering them or heating them up.
You are overlooking a very important reason why power doesn’t always double when reducing the load by a factor 2.
The output stage has to operate within its SOA, if not it will blow up.
For that reason, current limit circuitry is added to the design to prevent this from happening and also to make the amp short circuit proof.
Power supply that fits the bill then has to be designed to support the maximum allowable current, a bigger supply doesn’t bring that much.
So, thinking that the power figures are the result of manipulation of a marketing dept is dead wrong.
For the same reason it's not possible to simply relate the maximum power to supply voltage.
Hans
And then there is the loose / intermittent connector factor on one of the two amps.
Which additional heat?
For the power supply voltage - current - delivered power, and for power transistor current , voltage and dissipation (hint: dissipated heat), the following conditions apply:
2 x 45W is exact same as 90W bridged.
2 x 60W is exact same as 120W bridged
that´s how bridging works.
Nothing personal here, simple Math 101
In case it isn´t crystal clear:
bridging (keeping the 2:1 impedance ratio which applies to such topology) does NOT create increased dissipation, hence no additional heat.
Well, you are right, mostly. There's still a marketing side... look at AVR ratings.
And true, current limiting is an issue, which is actually why I brought up, to being with, the idea of paralleling two ampliers.
Ay... forget the bridging part.... your initial claim was that power doesn't double as the load is halved. That indicates some sort of current limiting.
it's in your own post.
I did smoke a $250K board back in the early 80s.
Yes, watching a diode go into plasma is an alarming thing to experience.
Oddly, there was no smell, the lab had very good ventilation. Only sound of caps popping up alerted me to turn around and look.
BTW, speaking of smell.. we used to have a ritual. Whenever someone powered up a brand new piece of equipment in the lab we'd walk behind the test station, right next to the inlet to the cooling fans, and burnes some insulation off a wire. It was fun then.
We used to smoke a lot of hardware in that lab. It was our job, really... if we smoked it then it meant a redesign otherwise it might smoke at the customer's facility, or worse, in flight! We also had to fill a lot of paperwork. :-(
I have a feeling I completed my right of passage a long time ago. ;-)
I have some 20-30 posts in this miserable thread, please quote which one you are referring to.
Verse and chapter.
And why "forget the bridging part"? , I am copypasting the brochure for your amplifiers and they mention it.
Post #251
Your comment (and my reply) was about doubling power into halving the load.
Stop before you start calling anything "miserable"... seriously, keep the attitude in check here. Just keep it "professional". After all, no one is asking you to post anything.
What exactly are AVR ratings.
All that marketing dpts do is to stay a bit on the safe side, that’s all.
Looking at Stereophile tests, most claims are pretty close to the measured results.
Hans
For stereo amplifier ratings, the FTC demands to know all channels driven, after one hour at 1/3 power conditioning, power, resistance load, frequency range (20-20Khz) and THD.
But for multi channel amplifiers (as in AVRs) there is no such requirement, so we're sort of back where we were before the early 70s. Back to "music" power and IHF (I think it was called) ratings. So, often the AVRs will claim a huge rating for ONE channel operation at 1Khz, and then in footnote sections they will rate it in stereo and "all channels" driven.. with a complete -sometimes- frequency.
Also, many AVRs caution not to drive into lower than 8 ohm loads. Indeed many such AVRs have a "low impedance" switch which limits the current (and power). If you look at the AVS Forum site you will see a lot of discussions about this.
And yes, I'm not making any claim the numbers are fake, you can rate it anywhere on the curve. Just look at how Pass Labs rated the XA25, which was a very conservative number.
https://www.stereophile.com/content/pass-laboratories-xa25-power-amplifier-measurements
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FTC no longer has any preconditioning requirement, but must run at 1/8 power with pink noise into X ohms without shutting down or tripping a breaker (or blowing out) to carry an FTC rating. The similar very short term rating is AES. For that, up to 1% distortion is allowed and that means it’s already half a dB or more into clip. Current draw (from the wall) is rated into that same 1/8 power - NOT a full power sine wave. It’s better than the old IHF rating, but not by a whole lot.
For about 100 watts AES, it may be 85 FTC. And have AES ratings at 4 ohms, while having no FTC rating at 4 (but possibly at 8).
For about 100 watts AES, it may be 85 FTC. And have AES ratings at 4 ohms, while having no FTC rating at 4 (but possibly at 8).
Yeah, it looks like it the 1/3rd preconditioning rule got dropped this year. I missed that.
Sad, as it was a particularly difficult test, if an amp could survive that you knew it could deliver the power while playing Spinal Tap at 11.
THIS year? It’s been that way a while now. I think it had to do with making all these bigger and bigger multi kilowatt amps. At 1/3 power they draw way the hell more than 20 amps off the wall. That would mean requiring special circuits for professional use, and they would never really draw that much except maybe a few seconds at a time. Some HAD 30 amp plugs, but they were few and far between. Many would draw 50 or 80 amps. Of course, nothing could do this all day but it didn’t need to. At 1/8 power which is more typical of most use they squeak in at 15 or 20 amps. Even Spinal Tap at 11 is closer to 1/8 power than 1/3. Some of that ghetto bass would be up there, but only in the sub channels. If you’re running a real pro setup and run into that kind of program material, you just don’t run at minimum impedance. Most “2 ohm capable” pro amps will run at 1/3 power, 8 ohms, all day. Even if they would shut down or otherwise misbehave at lower ohms.
How about subwoofer amps... I guess most have gone to class D for that reason, huh?
God forbid you run two subwoofers in parallel. Oh wait...
Hmm.... I was just looking through the design of the F4... guess what, it has a parallel mode.
I quote:
"In mono parallel operation, you can achieve up to 100 watts output into a 2 ohm load" which is four times the 25 watt rating as a stereo operation into 8 ohms.
https://www.firstwatt.com/pdf/prod_f4_man.pdf
See pages 8 and 9.
https://www.firstwatt.com/f4.html
Which is precisely why I wanted to parallel the Parasound amps... but I guess that voltage amplifiers are not quite up to the task?
And, yes, as a matter of fact, I want an F4. No, not to run two of them, just one, in stereo. I got the preamp gain, so it's time to try a pure current amplifier.
I quote:
"In mono parallel operation, you can achieve up to 100 watts output into a 2 ohm load" which is four times the 25 watt rating as a stereo operation into 8 ohms.
https://www.firstwatt.com/pdf/prod_f4_man.pdf
See pages 8 and 9.
https://www.firstwatt.com/f4.html
Which is precisely why I wanted to parallel the Parasound amps... but I guess that voltage amplifiers are not quite up to the task?
And, yes, as a matter of fact, I want an F4. No, not to run two of them, just one, in stereo. I got the preamp gain, so it's time to try a pure current amplifier.
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Again, reducing the speaker impedance....no-one here is disputing that.
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