Super Rocky

What people are working on at the moment
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#136 Re: Super Rocky

Post by Cressy Snr »

Paul Barker wrote: Wed Jun 03, 2020 9:27 pm
Cressy Snr wrote: Mon Jun 01, 2020 8:58 pm
Wonder if gapped, single ended output transformers have a sweet spot. I don’t know enough about them, but it seems the music snaps into focus at both ends of the spectrum, when these transformers are biased half way along their operating curve or am I talking crap and it’s just coincidence and it’s the power valves that have the sweet spot. Maybe it’s a bit of both.

I’m rambling again.
Don’t think so. Most noticeable change in transfomer performance comes when its saturated, that distortion you won’t miss. Transformers go from sweet to ... unimaginable high distortion.
Thanks for clearing that up Paul. Must be the valves themselves that were responsible for the differences.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#137 Re: Super Rocky

Post by Cressy Snr »

What a fun afternoon I’ve had. The Super Rocky is now living up to its “Super” nomenclature. Using the load line tool, I’ve set it up for KT120s and it’s now producing 8.25W per channel into a 2K5 load with distortion figures as follows:
2nd - 7.71%
3rd.- 0.14%
4th - 0.05% .............Impressive huh! :lol:

At lower levels, the model predicts a lot less distortion than at full output (which it would) and as the output swing reduces, the 3rd and 4th fall off rapidly before vanishing altogether around 3W, leaving only the 2nd remaining below that.

It’ll do 5W per channel into a 5K load, with less %THD, but interestingly, to me at least, the 3rd and 4th make up a larger percentage of the total, and I can hear it when I put the amp on a 5K load, as a sharpness to the presentation; something that the 2K5 load does not produce, when the amp is operated at the same volume level. Didn’t think I’d hear a difference like that but it was repeatable.

KT120s boogie like nothing else I’ve heard, apart from Simon’s copper anode GM70s at his place, a few years ago now.

So I celebrated with some bad-ass funk and boogie from my 70s soul and disco playlist.
Image

The KT150 triode model predicts only 3.6% H2 and 0.83% H3 at 8W using the same conditions as my KT120s are currently operating at. Half the distortion. Now that’s interesting.

A 6SN7 cascade and a bit of feedback would do wonders for the distortion figures of either valve. Of course that’s what mainstream manufacturers do with KT120/150 SE amps. If they didn’t they’d be run out of town.

Anyway, I don’t have to worry about that sort of stuff as I’m a cloth-eared bodger.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
JamesD
Old Hand
Posts: 997
Joined: Tue Oct 09, 2007 4:26 pm
Location: North Yorkshire

#138 Re: Super Rocky

Post by JamesD »

I love the look of your system its got a real cool retro vibe.

The chicken head knobs are brilliant

And its great that your honing in on better sound and why its better

Good stuff!
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#139 Re: Super Rocky

Post by Cressy Snr »

JamesD wrote: Mon Jun 08, 2020 5:57 pm I love the look of your system its got a real cool retro vibe.

The chicken head knobs are brilliant

And its great that your honing in on better sound and why its better

Good stuff!
Cheers James.

I’d gotten myself into a frustrating rut with the valve amps. It seemed that no matter what or how many I built, I just wasn’t moving forward to any appreciable degree, apart from the multiple power supplies.

There is an old saying in the teaching profession, that you can either have 15 years experience, or 6 months experience, repeated 30 times. With valve amps, I fall firmly in the latter category.

It is Paul’s exploration of distortion thread that lifted my feet out of the treacle, and once he’d linked to the valve loadline tool, I was away. Finding the distortion model on the same site was fortuitous and I haven’t really looked back since. Amazing what a week can do.

I love the styles of the late 50s/early 60s and the way I make the gear look is informed by the record players and radios and radiograms of my childhood. Our Ant has caught that vibe perfectly with the Lenco TT. It complements the other pieces beautifully.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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