PP Amp kits qua Dyna ST-70?

[Downhome Upstate]

Got the itch to play with something for rock 'n roll. Anybody build the Triode ST70, the Dynakit Parts ST70 or the K&K rethink of that amp?

[Downhome Upstate]

And I guess I should throw mods of stock ST-70's in the mix, like the one from Welborne Labs. I didn't think to include those because I haven't found a stock ST-70 for sale at a good price. Ebay prices for these amps seem consistently pretty high.

[Paul Birkeland]

How much power do you need?

[Downhome Upstate]

How much power do you need?

Well, the room is 14w x 18l x 9h. The rig will be centered on the 14' wall. I don't have any speakers picked out yet. I was thinking about either factory refurb'ed Zu Omens - avg. 12 ohm, 97 db) at $999 a pair, or the Tekton Mini Lores (avg. 8 ohm, 95 db) at $650 a pair.

[Paul Birkeland]

With a room that size and speakers that efficient, an ST-70 is not going to be all that useful.

[Mike B]

Yeah, it will.

I drive 95 dB/W Tangbands with a 3.5 watt Stereomour.  It sounds wonderful, but it don't rock & roll.

35 watts would be better.

To really R&R I use 93 dB/W speaks and drive them with half a kilowatt each.  Yeah, that's close, but still not concert level.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Ffarm5.static.flickr.com%2F4014%2F4674991455_34f99bdeb1_b.jpg&hash=a03daa86a84a8cb966c70824f74ed6e33c12306a)

[Paul Birkeland]

I drive 95 dB/W Tangbands with a 3.5 watt Stereomour.  It sounds wonderful, but it don't rock & roll.
35 watts would be better.

If we take the Tang  W8-1772 as an example, specified excursion is 3mm.  Assuming a perfect 8" cone diameter, this will allow low-ish distortion performance at:

89dB @ 40Hz
93dB @ 50Hz
96dB @ 60Hz
99dB @ 70Hz
105dB @ 100Hz

These numbers hold for a sealed box or IB alignment.  A vented alignment can help the numbers around 50Hz, but not so much as you move up from there, and actually worse below.

This would suggest that ~8 Watts is a good power level for these drivers, though there's a big difference between linear Xmax and mechanical Xmax. 

[Mike B]

Yeah, with single drivers you can forget X max.  Just adds to doppler distortion.  Not good for rock & roll loud.  Not good for anything loud.

For loud you need at least a 2 way.

In my bedroom, 12 x 12 x 8 feet, they sound good to ~80 dB average at 3 meters.  I listen to ~67, got plenty of room.  Classic rock every night.  They give me tingles -

That badass system is in the garage.  It has brought tears to my eyes.  It hit's ~115 when the clip lights are blinking.

I don't do that much, not good for the ears.  Just a song or 2.  Once in a while.  For old times sake.  Damn it sounds good though -

[2wo]

Hey Mike, I think that with the speakers your looking at, it will work fine.

I know that when I drag the Streaght 8's out, and hook then up to an ST 70 size amp. It is pretty impressive...John

[Paul Joppa]

Football is a brutal game. Seattle, my home town, secured their position in the Super Bowl at home where we have the loudest fans in the league. I'm an acoustical engineer, so I may be the only person in Seattle who's not proud of that. I can guarantee that all 100,000 fans went home with some degree of permanent hearing damage.

Many serious rock fans are the same. And 35 watts is only 10dB more than 3.5 watts, not really enough to get to rock concert levels even in a modest size room unless you have fullrange horns at 112dB/w/m - which won't actually fit in a modest size room.

Nobody will care, but anything over 85dB-C sustained over a career will leave you just able to understand your corporate master's voice until the day you retire. At that point you become functionally useless to your corporate masters, so deafness is not an economic issue. Fortunately, even serious rock fans don't spend 8 hours a day for 40 years at rock concerts. Roadies and musicians however suffer the same fate as football players. It's a brutal game.

[Mike B]

Yeah Baby!

Yup, you know R&R.

I love my bedroom system.  It's on every nite when I go to bed.  I go to bed now at least an hour earlier than I used to just to listen to R&R.  The Stereomour & the Tangbands give me much of the garage w/o the hearing damage.  This system gave me insight to people who said they judged systems by how they sounded at low volume.

Yup, to get much of the same feel w/o the hearing damage is a good thing -

I don't think you can appreciate this fully w/o doing the 115 dB thing though.  It gives you insight to why they call guitars "axes", at that level they cut right to your soul.

[Paul Birkeland]

Seattle, my home town, secured their position in the Super Bowl at home where we have the loudest fans in the league. I'm an acoustical engineer, so I may be the only person in Seattle who's not proud of that. I can guarantee that all 100,000 fans went home with some degree of permanent hearing damage.

Ear plugs are pretty common in there these days, though at those levels, I'd want muffs and plugs.

[2wo]

At the last game, the guys on TV said that the record there was 135db ...John

[Downhome Upstate]

So, now that we've cleared that up, how about folks' experience with push-pull amp kits or projects based on used amps?  Any takers? What did you build or tweak, how much did you spend, was the result satisfying? How tweakable was it?

[Gerry E.]

Football is a brutal game. Seattle, my home town, secured their position in the Super Bowl at home where we have the loudest fans in the league. I'm an acoustical engineer, so I may be the only person in Seattle who's not proud of that. I can guarantee that all 100,000 fans went home with some degree of permanent hearing damage.

Loud fans + Century Link Field acoustical design (use link below) = loudest outdoor sporting event!   

http://www.businessinsider.com/seattle-seahawks-stadium-loud-2014-1

Gerry