World-Designs-Forum  

Go Back   World-Designs-Forum > World Designs > WD Amplifiers
Register FAQ Members List Calendar Gallery Today's Posts Mark Forums Read

WD Amplifiers For discusson of World Designs Amplifiers

Reply
 
Thread Tools Display Modes
  #1  
Old 26th January 2015, 09:08 PM
Infinitely Baffled Infinitely Baffled is offline
Member
 
Join Date: Nov 2007
Location: Welshpool, mid-Wales
Posts: 38
Default Bi-amping: some questions.

Hello, all. I'm shortly going to be taking delivery of a pair of loudspeakers that, unlike my present ones, are equipped with 2 pairs of binding posts to permit bi-amping. I have used this technique in the past - before I discovered valve amps - with Audiolab integrated and power amplifiers. It was very simple and produced highly impressive results so I'm keen to try it with my current equipment. There are a couple of things I'm not sure about, though, and I would be very grateful if some kind soul out there could put me straight.

1. My pre-amp has only one set of output sockets (ie. to feed a single power amp). If I rig up some kind of splitter arrangement whereby I can take a set of output leads to each of the power amps in parallel, is the pre-amp going to take exception to that? I imagine that, in electrical terms, the pre-amp is going to see a completely different load with two power amps downstream. Might that be harmful?

2. The two amplifiers I propose to use for this venture are a WAD Kat6550 which I am currently building (I know, it'already a superseded model, but I've been sitting on it for ages and I 'm only just getting round to doing something with it) and a single ended triode set using 300B valves, which I also built from a kit (though not a WAD/WD kit) years ago. The SET amp is built as a single source integrated amp (which is to say, it has a volume control). If I go ahead with this idea I would plan to bypass, or even remove, this volume control. If I do that, should I replace it with something else to ensure that the components downstream of the volume pot are seeing a signal with the same electrical characteristics? If yes, what do I replace it with? Would it be a bad idea to leave the volume pot in circuit , but simply positioned fully open?

3. If I get past 1 and 2 and succeed in bi-amping the speakers, which amp do you consider I should dedicate to which driver? The speakers are 2-way designs, with a 1" silk dome Tonegen HF and an 8" doped paper bass/midrange driver made by SEAS, I think. I don't know off hand any more detailed specs for them or for the crossover, but I wonder if there is a general wisdom or rule of thumb to say which unit should get the whispy magic of 7 watts 300B output, and which should get its backside kicked with 35 watts of KT88s in push-pull config?

I would enjoy hearing your thoughts about any of this, folks. One thing, though: if you reply please do it as though you were explaining something to a slightly slow 8-year old. I genuinely have no understanding of how an amplifier works (I build them just by following the instructions slavishly), and my general understanding of electricity is rudimentary to an extent you guys wouldn't believe! To me, electricity is a sort of magic juice that goes in one end and makes the music come out the other - and I'm not exaggerating!

Anyway, I'd be pleased to hear from you if you have any words of guidance. Thanks and cheers. Infinitely Baffled.
Reply With Quote
  #2  
Old 27th January 2015, 07:51 AM
bob orbell bob orbell is offline
Senior Member
 
Join Date: Nov 2009
Location: kettering northants.
Posts: 1,957
Default Re: Bi-amping: some questions.

Hi there, quick answers, 1, no. 2, the amps should be the same?. 3, the low power to the tweeter and the high power to the bass. More to this the pre should be fine using splitter cables, the power amp's should ideally be the same, or at least the same input voltage so that the speaker drivers give the same volume, although a volume pot on the most sensitive amp. will give you some adjustment. I have in the past used Musical Fidelity amp's in Bi amp form and as you say the results were very good, I have also used two WD KT88 power amps to Bi amp my system, strangely,the results were very disappointing and I returned to one power amp, the sound being very good, I was and still am puzzled to this day about Bi amping with valve amp's. My advice to you is complete your 6550 and see how that sounds, I think that you will be very surprised. BOB
Reply With Quote
  #3  
Old 27th January 2015, 11:59 AM
davebms davebms is offline
Senior Member
 
Join Date: Nov 2008
Location: ware ,herts
Posts: 213
Default Re: Bi-amping: some questions.

hello all long time since i last posted !! ,, I have bi-amped with differant amps with no probs , i had 100w mono transistor amps on the bass and vtl tt25 on the top (the vtl did not have enough GO to do them all) i had to put a pot in a box to ballance the volume on the bass ,,, it worked well for a year or so,, then a speaker wire cam out and shorted the lot out,, sort off DIY ark welding
Reply With Quote
  #4  
Old 28th January 2015, 08:07 PM
Infinitely Baffled Infinitely Baffled is offline
Member
 
Join Date: Nov 2007
Location: Welshpool, mid-Wales
Posts: 38
Default Re: Bi-amping: some questions.

Many thanks, fellows. That's absolutely clear and v. helpful. I might try it anyway, but if I do not remove the volume pot in the single-ended triode amp, then it will be easily reversible if it proves disappointing. As you suggest, Bob, I will try them out first with just the Kat 6550 and see how that sounds. Are there any low-cost but worthwhile upgrades (or just things to avoid) that you would recommend for the Kit, given that it is still at the build stage? Regards. Inf Baff.
Reply With Quote
  #5  
Old 29th January 2015, 07:17 AM
bob orbell bob orbell is offline
Senior Member
 
Join Date: Nov 2009
Location: kettering northants.
Posts: 1,957
Default Re: Bi-amping: some questions.

I would build it as standard first so you can see what it is like, two things to bring to your attention, are first, if my memory is correct, then the mains fuse as supplied is ratted at 1.2amps, this will most probably blow at first switch on, it is not a fault on the amp but the current serge, 2.5amp is what most have changed the fuse to. Second see the FAQ section, rectifier flash over, this is worth doing at first build. Please report back when it is up and running. BOB
Reply With Quote
  #6  
Old 1st February 2015, 12:32 AM
Infinitely Baffled Infinitely Baffled is offline
Member
 
Join Date: Nov 2007
Location: Welshpool, mid-Wales
Posts: 38
Default Re: Bi-amping: some questions.

Thanks, Bob. Yes, I will. Cheers. IB.
Reply With Quote
  #7  
Old 29th February 2016, 07:13 PM
Infinitely Baffled Infinitely Baffled is offline
Member
 
Join Date: Nov 2007
Location: Welshpool, mid-Wales
Posts: 38
Default Re: Bi-amping: some questions.

Well, a little bit of a delay, but a short spell of medical recuperation prompted me to finish the build of this amplifier that several of you have been kind enough to advise me on. I completed the test measurements and hooked it up yesterday and to my absolute delight (and astonishment!) it works - perfectly as far as I can tell, but I shouldn't tempt fate. So first off, many thanks to all of you for the advice and encouragement at various points during the rather protracted build period.

Secondly, I promised to report back on how it all turned out. Well, to recap, it is an old WAD KaT 6550 kit that I bought back in 2004, I think, but sat on for years without doing anything with it. Following suggestions from bods on this forum I built it up close to standard, just substituting some better quality capacitors for the Orange Drops and some higher-rated resistors in place of the 560kOhm ones on the power valve bases. I used KT88 valves instead of 6550s. Oh yes, and I did the mod to avoid flash-over on the rectifier valves too.

The resulting performance is a real eye-opener! I am extremely pleased with it, and I have been listening to it for a good chunk of this afternoon. Presumably it will change as it soaks and burns in - for the better I imagine. However, the excellent sound poses some problems for me. I originally bought it to drive some electrostatic speakers in a second system, and I think it would have done a great job with them. But now I am downsizing and I don't plan on having a second system, so the amplifier doesn't really have a purpose. It has therefore become a competitor to my much-loved main amp for use in my flagship (and only) system - and its performance is already so good that it has me worrying about which one I ought to keep! Nice problem to have, I suppose.

I have been taken by surprise by how muscular and rhythmic the KaT sounds. It really takes a hold of the lower registers of the music and drives it along with aplomb. I tried it with some early Neil Young this afternoon and the effect was tremendous. But put some early music on and I quickly miss the airiness and light and shade that my other amp (a single-ended triode job) brings to the party. This is pretty standard, I guess, isn't it? It is naive to imagine that one piece of equipment will cover all the bases. It all comes down to the compromises and trade-offs that one is willing to make. And that is what I have yet to decide! Anyway, as I said, nice problem to have!


Thanks again, chaps, for all the help. It was a lot of fun.
Regards. Infinitely Baffled.

Last edited by Infinitely Baffled; 29th February 2016 at 11:02 PM. Reason: grammar!
Reply With Quote
Reply

Tags
bi-amping, kat6550, set

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT +1. The time now is 08:58 PM.


Powered by vBulletin® Version 3.7.3
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright World Designs