Sujet : Re: New Pi 5 (Diversity - good or bad ?)
De : 186283 (at) *nospam* ud0s4.net (186282@ud0s4.net)
Groupes : comp.os.linux.miscDate : 18. Jan 2025, 05:30:11
Autres entêtes
Organisation : wokiesux
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On 1/17/25 6:10 AM, The Natural Philosopher wrote:
On 17/01/2025 06:01, 186282@ud0s4.net wrote:
No. He (and his dad) built his own guitar, but I think the pickups were P90s. The amp was always a (number of) Vox AC30(s), well known for a unique sound due to stuff you wouldn't be interested in
>
Hey, we're tekkies here - we're interested in lots
of stuff 🙂
>
From May's sound, it's clear the amp has a somewhat
exaggerated higher-end response with some interesting
harmonics. A lot of the older transistor amps had
a kinda 'hard' sound too and kinda heavier on the
odd harmonics. Dunno if that was inherent, or
by-design - intentionally emulating the AC30 sound.
The AC30 is a development of the original Mullard application note to use four EL84s - a small pentode - as a 25W power amplifier. Subesquent units used a pair of EL34s.
Being British, when it needed more gain, instead of adding an extra tube, they simply *removed the negative feedback* from the power amplifier.
You don't care much about distortion in a guitar amplifier.
Of course this had another effect, instead of just increasing the gain it increased the output impedance so much (~100ohm) that the loudspeakers were practically current driven, rather than voltage driven.
This had two effects. The first one was a result of the induction of the loudspeaker voice coil. Normally with a constant volatage, you get constant-ish output with frequency. But with a high impedance feed the loudspeakers got effectively a 6dB per octave treble boost all the way from somewhere around 1kHz. To tame this they added a simple 'tone control' that rolled off the treble only.
The other effect was that the loudspeaker cone was no longer tightly controlled by the amplifier - it was free to flap. And it so happens that the two 12" loudspeakers and the open backed cabinet had both a nice woodenish cardboardy sort of sound and a massive bass resonance peak at around 100Hz, which is very close to and lies between bottom E and bottom A on the guitar.
All this made for a classic 'boom and chink' sound perfect for the beat groups of the era, and all with as few valves (tubes) as they could get away with.
British amps sounded good because they were in fact BAD. Whilst a Fender is a reasonable copy of a hi fi amplifier of the period, British designs were over driven done on the cheap and had in many cases horrible distortion.
Well, for 'rock', a fair bit of distortion is desired
most of the time. However the intro to "Stairway" would
not have sounded so good with too much distortion added.
Sometimes you want something closer to Spanish guitar.
That's one of the coolest things about electric guitar,
they can sound anything from wood instruments up to the
coming of the Viking gods just by turning a knob or two.
The Marshall being the prime example of 'all of the above'. The classic 'attack' is caused by the amplifier having plenty of HT voltage - until you want to sustain power. Then the mains transformers sighs and gives up.
So a 'power chord' has a sharp attack and then sustains at lower volume...
Before the triode, there were MECHANICAL audio amps that
worked by various means. They were oft employed as public
PA systems - very popular at big political rallys because
the voice band was so piercing. Hitler woulda loved 'em.
http://www.douglas-self.com/MUSEUM/COMMS/trumechamp/trumechamp.htm https://en.wikipedia.org/wiki/Compressed_air_gramophone http://www.vias.org/crowhurstba/crowhurst_basic_audio_vol1_028.html The more common design was compressed air modulated by something
like a needle attached to the mic diaphragm - a spring would
counterbalance the air pressure partially - they were basically
class-A amps. Feed that modulated air into a big folded horn
assembly and some say you could get 120db.