moo-fi

SET amps

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Since I have had a down turn in the works department, I am in the unusual position of having time on my hands. There isn't much call for a live sound for some reason at the moment. 

So I need a project to do, considering building a 45/2a3 amp with a proper power, anyone aware of any decent reading on the subject? From a casual glance it seems to be as much an art as actual science. 

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The art of picking and balancing your compromises mostly!

Sent from my BLA-L09 using Tapatalk

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Try DIYAudio forum, there'll be a motherlode of circuits argued and pored over there.

Sent from my BLA-L09 using Tapatalk

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Maybe have a search over on the bottlehead forum there are some threads on converting their 2a3 amps to use 45 and I'm pretty sure several builders have documented the process you might find some useful info

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39 minutes ago, Jazid said:

Try DIYAudio forum, there'll be a motherlode of circuits argued and pored over there.

Sent from my BLA-L09 using Tapatalk
 

Indeed, spending some time there already. Makes a nice change from class D schematics that I usually work with. 

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Posted (edited)

I agree with James about DIY forum. Plenty of schematics there, but just Google anything.

SETs are relatively straightforward, but you need decent transformers and you need constant current sources. You'll also find that getting the buggers quiet is a major issue.

Edited by rabski
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Pre amp duties will be carried out by a silver wound Slagle autoformer, which I built a while back for a uni project. 

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I'd be more worried about the lack of power at the other end. 4-5 watts is about right. Lovely watts though!

CCS is ideal, but not the end of the world. The trick with any DHT is to get it quiet but not lose the 'magic' in the process. Have a look at Bartola valves as well. Ale's stuff is preamplifiers, but there's a lot there about filament and choke supplies that's universal.

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For speakers I have inherited a set of fostex in some form of back horn,  I have been told they might be a Dallas horn but need some attention. 

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6 minutes ago, moo-fi said:

For speakers I have inherited a set of fostex in some form of back horn,  I have been told they might be a Dallas horn but need some attention. 

That'll be lovely :love:

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They are in walnut and we aren't talking veneer.  A church was skipping them, so I rescued them with a suitable donation. Suspect the drivers are beyond repair but the cabs seem to be in good condition. 

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Lucky so and so!

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I've acquired quite a selection of DHTs as I'd like to try some of the preamp designs. Only glued one together so far as a breadboarded 2P29L design. I assumed things like Ale's use of CCS for anode supply was a tweak to get the best, and that regulated filament supplies were similar. Possibly not. Keith and Richard here have 26 based preamps and will confirm they can be a real pig to get quiet. I've breadboarded a couple, but all they've done so far is to demonstrate why choke loading isn't ideal and why even relatively clean DC filament supplies are still massively noisy.

It'll have to wait though. I really do need to clear some of the other stuff first...

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Heard Keith's at one of our Welsh bake off's along with his 845 power amps. This is one of the reasons I started looking at DHT's, the other is the aforementioned horns which are crying out to be used. 

Quiet power supplies are an art form, everything needs to be considered and is the area which I am most concerned about.

The basic amplifier circuit is about as basic as it gets, which also means there isn't any hiding place for poor PSU design. 

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1 hour ago, rabski said:

I agree with James about DIY forum. Plenty of schematics there, but just Google anything.

SETs are relatively straightforward, but you need decent transformers and you need constant current sources. You'll also find that getting the buggers quiet is a major issue.

I'm just starting to look into a Tubelabs 845 SE amp.  More power and complexity than you want, I think, but he does simpler designs.  Like this - http://tubelab.com/designs/tubelab-sse/

My question will be, can the  845 SE drive Quad 2805s properly?

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