AudioNervosa

Self Medicating => DIY Electronics => Topic started by: P.I. on July 08, 2020, 05:15:49 PM

Title: My Dyna ST70 (?) Project...
Post by: P.I. on July 08, 2020, 05:15:49 PM
Here is the VTA (tubes4hifi.com) 9 pin input board.

I just ordered the octal version for my other ST70.  We'll hear...

Tubes here are TAD 12BH7.  Kind of my goto tube for 12AU7 applications that require the best sonics.
Title: Re: My Dyna ST70 (?) Project...
Post by: S Clark on July 10, 2020, 11:14:17 AM
Okay, you caught my attention.  Is this a board with an improved layout, a better design, or just better components.  The Dyna sold a bunch of kits back in the day, but how do they stack up against competition today? 
I took a look at the tubes4hifi.com website.  Any idea how their phono preamps compare to competition today? 
Title: Re: My Dyna ST70 (?) Project...
Post by: P.I. on July 10, 2020, 10:50:15 PM
Okay, you caught my attention.  Is this a board with an improved layout, a better design, or just better components.  The Dyna sold a bunch of kits back in the day, but how do they stack up against competition today? 
I took a look at the tubes4hifi.com website.  Any idea how their phono preamps compare to competition today?
Complete redesign of the input circuitry.  Uses 12AU7 Triode variants instead of the crappy 7199 pentode tube.  It uses a constant current source in the phase splitter stage to give better linearity.

The circuit designs really good.  I wonít post it because because of my respect for intellectual property rights.    I went with Takman carbon film resistors for their musicality and with the lowest noise components that I could source in the power supply. 

The power supply has 20ppm temperature coefficient components instead of resistors often used that are 700ppm or even worse.  You know my advocacy for low noise power.  I build a company on this!  In keeping with my power supply philosophy the choke is rated at 3H @ 250ma instead of the original 1.75H @ 200ma.  With the other mods Iím making the power supply will be much stiffer than the original.

The A470 output transformers are very good.  It was interesting to see the changes in measurements that cryo brought about...   like I said elsewhere, they are the only original parts except the chassis.  Iím going to have todo some as work changes to accommodate the larger choke and polypropylene power supply caps I am using.

I have no idea about their phono stage.  Talk to Don.  He knows everything about it.  He builds an upgraded version:

http://www.dsachsconsulting.com/custom%20tube%20phono%20stage.html
Title: Re: My Dyna ST70 (?) Project...
Post by: Nick B on July 10, 2020, 11:33:26 PM
Okay, you caught my attention.  Is this a board with an improved layout, a better design, or just better components.  The Dyna sold a bunch of kits back in the day, but how do they stack up against competition today? 
I took a look at the tubes4hifi.com website.  Any idea how their phono preamps compare to competition today?
Complete redesign of the input circuitry.  Uses 12AU7 Triode variants instead of the crappy 7199 pentode tube.  It uses a constant current source in the phase splitter stage to give better linearity.

The circuit designs really good.  I wonít post it because because of my respect for intellectual property rights.    I went with Takman carbon film resistors for their musicality and with the lowest noise components that I could source in the power supply. 

The power supply has 20ppm temperature coefficient components instead of resistors often used that are 700ppm or even worse.  You know my advocacy for low noise power.  I build a company on this!  In keeping with my power supply philosophy the choke is rated at 3H @ 250ma instead of the original 1.75H @ 200ma.  With the other mods Iím making the power supply will be much stiffer than the original.

The A470 output transformers are very good.  It was interesting to see the changes in measurements that cryo brought about...   like I said elsewhere, they are the only original parts except the chassis.  Iím going to have todo some as work changes to accommodate the larger choke and polypropylene power supply caps I am using.

I have no idea about their phono stage.  Talk to Don.  He knows everything about it.  He builds an upgraded version:

http://www.dsachsconsulting.com/custom%20tube%20phono%20stage.html

Speaking of Donís phonostage, I will be offering mine for sale within a week or two. I will post the ad on AN first. Sorry to deviate a bit...
Title: Re: My Dyna ST70 (?) Project...
Post by: _Scotty_ on July 10, 2020, 11:57:34 PM
If any of the tubes take notion to spontaneously fail what happens to the solid components in the signal path down stream from them.
Are drivers in the output stage protected and are there modern equivalents to them available.
Scotty
Title: Re: My Dyna ST70 (?) Project...
Post by: Folsom on July 11, 2020, 07:11:02 AM
When it comes to tubes a little resistance here and there seems to be your friend... seems like some designers avoid it.
Title: Re: My Dyna ST70 (?) Project...
Post by: P.I. on July 11, 2020, 07:29:17 PM
If any of the tubes take notion to spontaneously fail what happens to the solid components in the signal path down stream from them.
Are drivers in the output stage protected and are there modern equivalents to them available.
Scotty
Judiciously placed fuses will protect the important parts and pieces.  I am using all modern tubes. NOS is too expensive and very difficult to maintain SQ from device to device.

Edit:  At 72 my ears are past ďprime timeĒ.  Being able to get matched quads for much less than the cost of a single NOS tube.  A single NOS Genalex Gold Lion KT77 is $270.00 from Brent Jesse.  I bought a matched quad from Antique Electronics Supply for $180.00 during a 10% off sale.  When I checked them on my Heathkit tube tester (newly rebuilt with modern parts) they were within 2%.