more lateral fets

For the three and more legged things
Post Reply
User avatar
ed
retired
Posts: 3641
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

more lateral fets

Post by ed » Sat Jun 09, 2018 3:35 pm

Oh the drilling, cutting, filing and bleeding...oh waily..
latfet pp.jpg
<waffle-mode)
This is a bit of a bitsa. It started life on paper as a simple platform to try and see what the sound of lateral fets was, if it could indeed be nailed down. The copious reports on the internet about how these lateral fets were the absolute best for audio caused my curiosity to lead me up the garden path yet again. Curiosity, oh waily waily. Originally a common drain complimentary pair of jfets into a common source pair of lateral fets...a la profet amp which I believe was the underlying base for F5. Well, it evolved, and the jfets were replaced by an opamp for simplicity. Matched pairs of jfets for the input are getting tricky to source, so I’ve left that for later.

I’ve decoupled the power supply to the extent that it now has two individual supplies for the input stage and the output...both way over specced as I intend to use this supply for other experiments...I still want to fiddle with the profet type front end and also a jfet ltp input stage. In a slightly different guise this whole amp could be the first 2 stages of a hockey puck amp.

Now for the irony.....

While researching SS in general I looked at various circuits and methods and came across the circuit for my aura 40 which I’d been using in the studio set-up for 20 years. Damn me, it was one of the original amps to use the new(at the time) lateral fets. I’d been listening to that sound for 20 years without a clue.

In true self-effacing style I took it to Steve’s last get together for a reality check...and yes, it is accountable.
</waffle-mode>

latfet ps.jpg
latfet baseback.jpg
There's nowhere you can be that isn't where you're meant to be

User avatar
ed
retired
Posts: 3641
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: more lateral fets

Post by ed » Mon Jun 18, 2018 2:07 pm

finished..just need to plug it in....pressure, what pressure...
latfet pp inside.jpg
There's nowhere you can be that isn't where you're meant to be

Cressy Snr
Oooo, Roberts Radio's sound nice
Posts: 7965
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: more lateral fets

Post by Cressy Snr » Mon Jun 18, 2018 2:10 pm

Remember to hide under the table Ed. :D
Happiness is not good for the economy Matt Haig.

Ant
Old Hand
Posts: 630
Joined: Mon Jul 31, 2017 6:45 pm
Location: Yorkshire

Re: more lateral fets

Post by Ant » Mon Jun 18, 2018 2:20 pm

Use a broom handle to hit the switch

User avatar
Mike H
Amstrad Tower of Power
Posts: 17753
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

Re: more lateral fets

Post by Mike H » Mon Jun 18, 2018 6:43 pm

Not a peep since .. :lol:
 
I never make the same mistake twice. Instead I prefer to fill my day with a variety of different mistakes

User avatar
ed
retired
Posts: 3641
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: more lateral fets

Post by ed » Wed Jun 20, 2018 5:03 pm

timid toad here......swidt

well the front end failed without so much as a puff of magic smoke....now adjusted the 16v balanced supply to 14v, a bit kinder to the opamps...but the back end tests ok, although it's only biased AB at the moment, hence timid toad....

it ran for about 45 mins and the sinks stayed at room temperature....I have plans for this case..mwahahamwahhaha
There's nowhere you can be that isn't where you're meant to be

User avatar
ed
retired
Posts: 3641
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: more lateral fets

Post by ed » Fri Jul 06, 2018 2:15 pm

either my ears are not as discerning as they used to be, or else I'm on to something here.

This is the pp amp I brought to Owston which seemed to go down quite well. At least no complaints were heard. As the pics show it's an absolutely stripped back and simple circuit. The aim was to listen to these lateral fets with as little or few components in the way.

I've been listening for the last week compairing in AB fashion to my F6 and 2A3, swapping over after every 2 or 3 albums, tedious I know.

I think I'm familiar with it now, and it's awesome. I can't really detect much difference between it and the F6 and it has a bit more control and detail at the extremes than the 2A3.

IMO it was a worthwhile exercise and I'm now going to put a complimentary JFET front end in(something like the BA-3 setup) and move the output stage a bit more into class A. I'm hoping for 20ish watts on 24v rails. I think I will also play with current clamps on the output pair instead of the clutzy fuse affair. I may even make some proper boards for this one.

onward....
ecx10n20pp-40.jpg
ecx10n20 cct.jpg
diet: the circuit shows the Hitachi output fets but the actual amp is running with exicons, a more or less drop in replacement.
There's nowhere you can be that isn't where you're meant to be

little eddy
Old Hand
Posts: 572
Joined: Sun Nov 09, 2008 2:06 pm
Location: Manchester

Re: more lateral fets

Post by little eddy » Fri Jul 06, 2018 5:53 pm

I'm following this with great interest after using the F6 last weekend and your observations. Keen to see:
  • What's the input sensitivity/gain likely to be for your target 20ishW?
  • And what dissipation and heat sinks you end up using with the output operating point.
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

User avatar
ed
retired
Posts: 3641
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: more lateral fets

Post by ed » Fri Jul 06, 2018 8:57 pm

Hi Mike

I'm planning on using J74/K170 for the input stage, hopefully I've got a few BLs in the box. Looking for idss of about 8ma.
I'm currently hoping for about 1.5/1.6v RMS to give about 13ish volts into 8 ohms, which is about 20 watts.
This is not planned to go too deep into class A, biased at about 0.4 amps, which should give about 10 watts per fet at idle, say 20 watts per side. The sinks that were on the case I took to Owston should be adequate.

this will be a departure for me as all the F series need those expensive sinks as they dissipate 2 or 300 watts. I'm looking at generating 50 watts max here, maybe less. I don't really need 20 watts output I'm just seeing what's possible.

I think the boss has twigged to what I'm doing and is hinting that I should have a clearout. There maybe 1 or 2 F amps for sale in the near future. I had planned on a major assault on ebay if that's the case. In the last 15 years of building amps I've only ever sold 1 amp so there are quite a lot to go, plus valves and transformers etc.
There's nowhere you can be that isn't where you're meant to be

User avatar
ed
retired
Posts: 3641
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: more lateral fets

Post by ed » Wed Jul 11, 2018 12:23 pm

Minor update to my previous ramblings....specifically where I said there wasn't much between the new latfet amp and the F6.

After lots more listening there is a big difference between them, to wit:

in it's current guise the latfet is a bit thin and 2 dimensional in it's presentation and there is a hint of sibilence on a lot of toppy recordings. There is bags of detail but that may be because it comes across as a bit bright.

It has long been said that the sound of any amp has more than a little bit to thank for the front end and in this case a move to a more substantial front end may change the entire flavour. A move further into class A on the back end will surely do no harm.

The current assessment has been prompted by much and repeated listening to mid 80s production excellence in the form of Peter Gabriel 'So' and Sting 'blue turtles' and Paul Simon 'graceland' and others together with Rachmaninof PC2 and much Dvorak.

with the little alpair monitors the F6 is still as good as I've ever had with normal speakers.
There's nowhere you can be that isn't where you're meant to be

little eddy
Old Hand
Posts: 572
Joined: Sun Nov 09, 2008 2:06 pm
Location: Manchester

Re: more lateral fets

Post by little eddy » Wed Jul 11, 2018 4:24 pm

You could have posted 10 minutes earlier before I ordered my pair of MoFo pcbs!

Still it sounds like you're persevering so perhaps all is not lost.
Thorens TD-125 & 'Snail' phono/pre, NAS/SBT, CS4398 DAC, Rocky KT66 amp, still messing with OBs.

User avatar
ed
retired
Posts: 3641
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: more lateral fets

Post by ed » Thu Jul 26, 2018 2:31 pm

minor update to the previous minor update....

further discovery has revealed that the sibilence and two dimensionality have now evaporated...it would seem that these exicon fets do change with the passage of time. I now have the amp in the main system, connected to the pair of vofos that weren't used at Owston.

I am happy for them to stay for the foreseeable. In a nutshell I am blown away by the sheer musicality of such a simple circuit running at tickover. Whether further changes appear with time passing remains to be seen, but at the moment I can thoroughly recommend these lateral fets......further proof that simple is best.

I will get around to putting a proper front end on and increasing the power, but I'm in no hurry as the current power and quality are adequate(Rolls Royce terminology).
There's nowhere you can be that isn't where you're meant to be

Cressy Snr
Oooo, Roberts Radio's sound nice
Posts: 7965
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

Re: more lateral fets

Post by Cressy Snr » Fri Jul 27, 2018 5:51 pm

Sounds like a success there then Ed. :)

Over the last couple of years I've come to the same conclusion: you can't beat simple for best access to the music.
Happiness is not good for the economy Matt Haig.

Post Reply