Something stirs in the Undergrowth

Dedicated to those large boxes at one end of the room
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#286

Post by IslandPink »

Yeh, maybe it's a combination of the heat and reading Mark E Smith's autobiography :D

I put another layer of bendy MDF on one side this afternoon .
I almost did it 'nicely'...but not quite. More filler/epoxy/whatever . The sound waves won't care exactly what it's made of, anyway .

ILPS
"Once you find out ... the Circumstances ; then you can go out"
chris661
Shed dweller
Posts: 2556
Joined: Mon Feb 22, 2010 7:29 am
Location: Sheffield

#287 Re: Amps ( or lack of )

Post by chris661 »

IslandPink wrote:Come on guys ...
Why the ...'k would I want to run highly efficient horn speakers from SS amps ? I mean the whole point of doing this thing was to be able to run 2A3 or 45 type amps to get the lowest distortion and highest audio quality !!
The only SS option I might ever consider is driving low bass and bass/mid from the Passlabs F4 . With any other SS amps you are literally 'down in the noise' at this sort of output .

As regards the driving impedance, you'll see if you look at the Hornresp data for the bass/mid horn I've used about 1.8R on all the sims . The bass/mid horn is not as picky about driving impedance as the Tapped horn , in that case as Chris pointed out, you need the lower impedance, and 0.3R from Pass F4 + cables should be ideal .

Anyway, what about the 'optimum' driving impedance for critical damping ? - it does not have to be as low as possible . I refer you to a recent post on JJ's blog for a reminder on that one :
http://hifiheroin.blogspot.com/2011/03/ ... dance.html

Rant over, I think :o
MJ
SS amps, like all the amps here, are a means to an end. Needless to say, when it comes to noise etc, valves themselves have challenges to overcome that simply aren't present in SS designs.

I'm curious: according to Hornresp, how much does the response change from, say, 1.8 to 5 ohm equivalent series resistance?
As Nick said, any output impedance is possible (provided, I suppose, you put the feedback around the output transformer), but measuring then fine-tuning could be fun.

For any speaker designed to be driven by a voltage source (ie, most of them), an output impedance close to zero is required. The number of loudspeakers specifically intended for valve use (or any other topology with high (>4ohm) output impedance) are in a small minority, so it can be said that, most of the time, a low output impedance is necessary.

The blog post seemed rather inconclusive to me: just seems to say that you should match your amps up to your speakers, which leads me neatly to my initial point: you might want to try your horns with all SS amps, too: they would provide a better approximation of a voltage source than the alternative SETs.

It's getting late, so apologies if I've put my foot in something without hearing the accompanying squelch.

Chris
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#288 Re: Amps ( or lack of )

Post by pre65 »

chris661 wrote:
, so apologies if I've put my foot in something without hearing the accompanying squelch.

Chris
Victor Meldrew and the dead Hedgehog ? :lol:
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#289

Post by brig001 »

Maybe in all discussions like this we should adapt this old saying:
Just because it is old doesn't make it good, and just because it is new doesn't make it better.

to:
Just because it is valve doesn't make it good, and just because it is solid state doesn't make it better.

Looking like a top job with the horns BTW, not sure I'd get away with making something like that <insert jealous smilie>

Brian.
Neal
Shed dweller
Posts: 2299
Joined: Fri Aug 03, 2007 10:57 am
Location: From the land of the Bodgers

#290

Post by Neal »

Interesting, been trying to get my old rusty brain cells working and I seem to recall that although a high damping factor is theoretically ideal Triodes have a workable o/p impedance and being inherently linear don't require gobs load of feedback like SS to work correctly. No feedback also means the amps response isn't skewed by a reactive 'speaker load...so although not an ideal voltage source the benefit of no f/b far outweighs the negatives.

Also, I think this was in one of the old WAD supplements, many issues in the Bass with valve amps (loose flabby, over blown etc) are more likely due to a very LF instability somewhere in the amp...I think Andy Grove came up with a new Kr bypass scheme that resolved some of these problems.

On another tangent I thought SS devices where more like current sources than voltage sources, their voltage swing being effectively limited by the supply rails to the o/p devices but being still being able to deliver high current peaks...
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#291

Post by IslandPink »

I'll just try a few of the points raised ( must get onto some soldering ! )

I think my curtness is related to the fact that 10 years ago someone demo-ed a small SET amp ( 6B4G ) to me, and it blew away every SS amp I'd ever heard . From that point on, I started building valve amps , and from time to time I hear SS amps and generally they don't get close . Generally I'm not listening to the bottom octave, I'm after tone, transparency , realistic presence on vocals and instruments , and microdynamics .
But, generally, I'm open to new designs too, so that's why I decided to build the Pass F4 , because people like Nick had told me it was very close to a valve amp. Jono Noble also highly rates the F5 .. so we'll see.

My point I was trying to make, also, was that at typical <30mW output , any solid state amp is going to have to be really sorted with respect to noise, and have none of the typical class AB or B switchover noise . Narrows down the choice, I think .

What aspect do you think I'm going to miss out on, from having a slightly higher driving impedance ? ( 1.8R into 8R speakers ) .
Bear in mind I've run the upper horns ( GPA288 on Azuras ) from the 300B amp with 6.8R and 22R series resistance as an experiment . Other than the change in level, it was hard to tell any difference with 6.8R ; with 22R there was a slight loss of dynamics and tone .

I attach a couple of FR sims of the bass/mid horn with 1R and 5R driver . The differences are small and could mostly be equalised with changes to the back-volume .
Attachments
1 ohm driver
1 ohm driver
5 ohm driver
5 ohm driver
"Once you find out ... the Circumstances ; then you can go out"
brig001
Old Hand
Posts: 550
Joined: Sat Nov 13, 2010 9:56 pm
Location: Back home in Preston now

#292

Post by brig001 »

Lots of class A solid state (including the Pass range) which would suit and have no nasty crossover distortion, but since your power requirement is so low, maybe an SET with the output transformer wound specifically to give a low output power is the way to go.

This is outside my experience, but if you took a "normal" output transformer and compared it with one with less turns on the secondary; at the same output power to the speaker, would the effects of hysteresis etc. be reduced giving lower distortion?

Probably talking rubbish, but food for thought.

Brian.
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#293

Post by Mike H »

No that does make sense in that the impedance ratio is higher. So like 10k primary instead of 5k primary.

BTW I did realise this topic is more like a "diary", albeit the rest of us seem like we are trying to be helpful by chipping in :D
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#294

Post by IslandPink »

I'm in danger of becoming like Romy the Cat, on this thread :
http://www.goodsoundclub.com/
Whose system is the ( or one ) inspiration for this .
I was warned by Chris Vry ( Paul knows who he is ) that you should really treat Romy's site as a blog .

In fact he has experimented with non-standard turns ratios to optimise the various channels , to subtly alter the character of each section .
http://www.goodsoundclub.com/Forums/Sho ... ostID=4973
I decided this was one step too far, especially as I realised that my three valve-powered channels are all about 109dB/w and might be fine-tuned just with small series resistors on the speakers ( hence the above experiment ).
Romy's speaker system is somewhat more complicated :
http://www.goodsoundclub.com/MacondoAcousticSystem.aspx
ILPS
"Once you find out ... the Circumstances ; then you can go out"
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8874
Joined: Mon May 21, 2007 9:42 pm

#295

Post by Paul Barker »

Yes it's not a place for a wife.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8874
Joined: Mon May 21, 2007 9:42 pm

#296

Post by Paul Barker »

Yes it's not a place for a wife.
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#297

Post by IslandPink »

You're sounding a bit like Mark E Smith there Paul ( you might need to look up The Fall if you don't know what I'm on about !) .

Have you spoken to Chris lately Paul ? - He was close to being a father last time ( in April ) I phoned him. He's gone very quiet on the E-mail !
"Once you find out ... the Circumstances ; then you can go out"
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8874
Joined: Mon May 21, 2007 9:42 pm

#298

Post by Paul Barker »

Probably too much of that activity which leeds too fatherhood.

When we were trying for children was best time of my life.

Chris was also full of ideas about compression horns.

He was more of a long term enthusiast gathering parts of an idea over a decade but none completed. He had bits of the best audio dreams you could ever want in his flat.

The Martin Logan panels were the best sounding panel I heard with the 212 powering them. The front Lowther style horns like Orris just didn't do anything for me, just as none of those at vsac. When he waxed lyrical about compression was his greatest enthusiasm.

A great playground for the single life! Wander what will come of it all now?Probably too much of that activity which leeds too fatherhood.

When we were trying for children was best time of my life.

Chris was also full of ideas about compression horns.

He was more of a long term enthusiast gathering parts of an idea over a decade but none completed. He had bits of the best audio dreams you could ever want in his flat.

The Martin Logan panels were the best sounding panel I heard with the 212 powering them. The front Lowther style horns like Orris just didn't do anything for me, just as none of those at vsac. When he waxed lyrical about compression was his greatest enthusiasm.

A great playground for the single life! Wander what will come of it all now?
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8874
Joined: Mon May 21, 2007 9:42 pm

#299

Post by Paul Barker »

Strange things happen when I post from my phone!
User avatar
andrew Ivimey
Social Sevices have been notified
Posts: 8307
Joined: Mon Jun 11, 2007 8:33 am
Location: Bedford

#300

Post by andrew Ivimey »

from your phone, your phone, phone,phone, one!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
Post Reply