Should i build F5?

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Graeme
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#1 Should i build F5?

Post by Graeme »

Ok, i seem to have a few audio plates spinning at the moment LOL.

For a while ive wondered about the firstwatt amps.
Now i seem to be bi-amping my tannoys ill need an amp for the bass.
If that whole set up stalls, i plan to have a second system in the lounge anyway.

So, ive been looking at other amps. I was going to buy an old quad, but there not that good (33/303) and nothing else takes my fancy.

So, for an amp to run bass duties (1k and under) or if not, a lounge amp for TV/cd, should i build an F5?

Looks pretty simple thanks to LOADS of back up, a well troden path, and pcb's available. Should be do-able for what, £400?

Or, should i look elsewhere?
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IslandPink
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#2

Post by IslandPink »

I built the F4 amp with a view to using as a bass amp in a multi-amp set-up.
I haven't got far enough with the project ( speakers I mean ) to say for certain I couldn't have got away with something cheaper, though, eg. a T-amp with a better power supply.
The advantages of the F4 and F5 being class A and low or zero feedback is that they'd have the same sort of soundstage/space properties to a valve amp, and be closer to the distortion spectrum too .

On the other hand I think £400 is on the low side as an estimate for an F5 . You might be able to do it, for that amount, if you have a suitable chassis and some big heatsinks that are just right for the job.

I think I spent at least £600, maybe £700, although that included a custom-made aluminium chassis that cost about £200 - plus some anodising - from local businesses .

There are things that add up - like caps in the power supply that are man enough for the current involved after the rectifiers - you can easily pay £10 a piece for 4 caps .
But the F5 does sound very good - probably a bit cleaner, tonally, than the F4 from what I've heard at Owston . It's a good amp to have in reserve for when you're re-building your main valve amp .
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IslandPink
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#3 Pics

Post by IslandPink »

For info Graeme, pictures of mine start about here :
http://www.audio-talk.co.uk/phpBB2/view ... c&start=30

I got the PCB's from Peter Daniel in Canada , via DIY Audio.
The matched set of solid-state stuff , I think, came from a guy in France who had changed his mind about the F4 and done something else.
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Graeme
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#4

Post by Graeme »

It had crossed my mind F5 might be overkill for a bass amp.

As for costs, i can get PSU caps for pretty much free, hard wired PCB.
With enough searching i'd say £70 for TX, say £50 for pcb by the time i pay shipping etc, £30 for matched SS stuff. Heatsinks would be scavenged/wait for something cheap on ebay, or ordered from australia (my friend is coming over later this month, but might be too soon) so say £20-£60 then say £150 for any oversights, other components etc. Bit of scrap ally to make a case.

I'd say it could be done if done slowly hunting for bargains.

If i bought a 303/405 i'd end up throwing money at it in mods.

T amps ive not even looked at.

The set up at the mo, bi amped with a modded 405-2 on the lows is only better ever so slightly in the mids but is a bit better tonaly in the bass. Maybe a bit more control too.
My main amp (modded kel84) isnt too bad down low, but i think bi-amping shows enough prommise. Just need to decide what amp to build/use.

Whats the deal with T amps then?
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colin.hepburn
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#5

Post by colin.hepburn »

Here's a link to diy audio store for the F5 Boards
http://www.diyaudio.com/store/amplifier ... lones.html
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Graeme
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#6

Post by Graeme »

Ive been all over the diyaudio store, f5 build threads, theres even whats basicaly a manual.
Various people have made sure these amp can be built pretty easily :)

Part of me want to build it anyway, would be fun, but fullfilling the 'bass amp' quota for alot less money would free up cash for all the other aspects im still playing with.
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#7

Post by grog »

i'd say go for it,
I've just finished the Pass PLH amp (twist on the JLH theme) 15W class A
it sounds rather good to be honest, and i'm planning to build the F5 once i finish the 300b SE i'm working on now,

if you don't like the F5 sound, then there are plenty of alternative Pass designs using the same heatsinks, output devices, PSU etc...
remember the power supply and number of output devices are scale-able depending on how much power and what impedance you will be driving,

i was planning on an V5 turbo variant, keeping the ~23v power supply, but doubling up on the output devices for more bias and the ability to better drive 4 ohm loads.
most speakers (drivers) are nearer 4 ohms, regardless of what the manufacturer admits!
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#8

Post by brig001 »

A couple of questions:
How much power do you need?
Can you still get all the components for an F5?

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Paul Barker
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#9

Post by Paul Barker »

Nick made me one but I am such a Luddite with solid state I don't know which it is, is it the F4 or the F5? I think it may be the F5.

different league to a T amp entirely.

A little low on sensitivity, needs an active preamp, probably Nick's present regime of his 2a3 preamp which I glean he has mutated into a 6as7 from things he's said between the lines.

I prefer my 6em7 amp but there isn't a whole lot in it. But to get my 6em7 amp into the lead I have had to use a Black Gate shunt regulation and direct coupling. A bogg standard valve amp with RC coupling and CLC power supply, the Pass amp probably noses ahead.

My 6EM7 amp has great bass at the level it is meant to work. I put it down to the choke input and shunt regulation. The Pass amp is not required to take over that duty in my setup.

the Pass amp is not really required to supplement a good valve set up, it is an entire amp in itself, and it does the job better than some valve amps and not quite as well as others.
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Ali Tait
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#10

Post by Ali Tait »

I'd venture to suggest - fun of the build aside - this may be a bit overkill just for a bass amp?

I run an active system at the moment, using two Temple Audio Bantam Golds. These are similar to a Tripath amp, but using a more up to date Analogue devices chip. Do great bass to my ears. Small, about the size of four stacked cd cases, pretty cheap (180 quid plus postage) and very good sound IMHO. Cheap to run too.

Try one, you may be surprised by how good they are.
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Ali Tait
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#11

Post by Ali Tait »

Graeme
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#12

Post by Graeme »

A couple of points raised there.

F5 sensitivity.
This had concerned me. I use a passive pre, my main amp has no need for a pre.
Matching the 2 amps might be tricky, might have to have an active pre channel for bass and passive for top.
Could be hassle to set up.

The f5 being good, well, there is always the possibility its just all round better than my valve amp. In which case i'd swap, then probably be in the market for another bass amp LOL.

As for the little bantam gold, seems good, i need to get over my initial irrational dislike of these things due to how little you seem to get for your money.

I think so far, my initial enthusiasm to build F5 is now in question. I need to sell a couple of bits before i can do anything, maybe ill get the money together, see exactly what my budget is, keep my eyes open for bargain parts and see how things look in a week or so.
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#13

Post by grog »

I use the PLH with a B1 buffer pre-amp (also Nelson Pass design ~1.0 gain) and the gain is ok,
I use up to setting ~50 of my 64 step attenuator,
I believe the F5 has more gain than the PLH, so i think you should be ok.
you might need to attenuate the input of your other amp to match though.
read the F5 Turbo article and it explains a lot more about the F5,
it lists alternative transistors, ways to increase the gain a bit, various methods of tweaking the design.
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Ali Tait
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#14

Post by Ali Tait »

Graeme, good thing with the Gold, it has a vol pot, so setting gain is no problem.

I agree you don't seem to get much for your money, but they are well made and use decent components, sound good too.
Graeme
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#15

Post by Graeme »

Ill have a look. I'd ignored anything 'turbo' for 2 reasons.
Firt, i thought it was all just about more power which im guessing i dont need. Second, i HATE people putting the word 'turbo' on stuff (unless its turbocharged). I guess its ironic, but i thought that died out in the 90's.
Almost as bad as putting 'i' in front of everything since the ipods popularity.
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