My rack mount ST-120 build

First off, I want to say a BIG 'thank you' to Bob for all his help.  I made several dumb mistakes, and Bob was always super quick and helpful with his responses.  This is was my first tube amp build.  I ordered the ST-120 kit from Bob without the stainless chassis because I wanted to make mine rackmount.  I kept the layout mostly the same except for a few minor things: I staggered the power tubes, I put small jacks behind each of the power tubes for the bias measurement, etc.  I machined the top plate (1/4" thick aluminum) on my Bridgeport.  The front wood piece is Bolivian rosewood.  The volume knob is machined brass with an Amboyna burl insert, and the decorative brass ring around the power switch I also made.  I opted to install two 80mm cooling fans inside the chassis.  I used the standard RCA input jacks but opted for Speakon output jacks for the speakers.

The amp sounds fantastic and creates wonderful sounding music through my speakers.  80 Hz and below is handled by several other QSC sub amps.  I have all this equipment in my garage.

Dave

Hey Dave,

Great looking build! I like the location of the power switch & volume control. Any chances to see pictures of the internal wiring of those components? Also it would be nice to see where you have your I/O routed.

As an IT admin and an ex live concert sound support crew member, I'd move the amp to the very top.

Let the tubes see the heavens! The heat will rise and not harm your other rack components.

Cheers,

Aguaazul

Hello Aguaazul,

    Thank you very much for the kind words - it's greatly appreciated.  I've attached a few more pictures.  For the outputs, I have two sets of speakon jacks: one for 4 ohm, one for 8 ohm speakers.  Input jacks are just regular RCA jacks.  Ideally, I'd have XLR jacks for balanced inputs on the back, but I'm not savy enough to figure out the balanced to unblanced circuitry.  
    Regarding what you said about moving the amp up to the top - I understand 100% where you're coming from.  This thing really does put out a lot of heat.  Not shown in the pictures, I actually have two 120mm fans blowing air across the transformers and tubes.  They are mounted slightly above and behind the transformers.  I have two internal 80mm fans that blow air into and out of the enclosure itself. When I run the amp, I always leave the rack door open.  With all that said, I do like your idea of putting this amp near the top.  I'll look into that - thank you for the suggestion!
    What kind of amp/speakers are you running?  Since you used to do live sound, are you using any pro-audio gear in your setup?

Thanks again,

Dave

Hi Dave,

First of all congratulation on the quality of the build, the miusic from tubes are magical.
I've been running VTA M125s since 2014 and would never part with them. I also installed the upgrade board on my 1966 ST-70, which made a whole lot of difference than the stock board.
Mills River is about 90 miles south of me, I'm in Upper East Tn.

TM

10-E-C wrote:Hi Dave,

First of all congratulation on the quality of the build, the miusic from tubes are magical.
I've been running VTA M125s since 2014 and would never part with them. I also installed the upgrade board on my 1966 ST-70, which made a whole lot of difference than the stock board.
Mills River is about 90 miles south of me, I'm in Upper East Tn.

TM

Thank you for the nice words!  Would you be willing to post some pics of your M125's?  It's funny you mentioned that - I'm thinking about getting a pair.  I like my ST-120 so much that I want more.  What are you using for speakers?

Thanks again and have a great weekend,

Dave

dasa2131 wrote:Hello Aguaazul,

    Thank you very much for the kind words - it's greatly appreciated.  I've attached a few more pictures.  For the outputs, I have two sets of speakon jacks: one for 4 ohm, one for 8 ohm speakers.  Input jacks are just regular RCA jacks.  Ideally, I'd have XLR jacks for balanced inputs on the back, but I'm not savy enough to figure out the balanced to unblanced circuitry.  
    Regarding what you said about moving the amp up to the top - I understand 100% where you're coming from.  This thing really does put out a lot of heat.  Not shown in the pictures, I actually have two 120mm fans blowing air across the transformers and tubes.  They are mounted slightly above and behind the transformers.  I have two internal 80mm fans that blow air into and out of the enclosure itself. When I run the amp, I always leave the rack door open.  With all that said, I do like your idea of putting this amp near the top.  I'll look into that - thank you for the suggestion!
    What kind of amp/speakers are you running?  Since you used to do live sound, are you using any pro-audio gear in your setup?

Thanks again,

Dave

Hey Dave,

Thanks for posting the photos. It's cool to see the I/O and routing.  Nice use of the fans, if you used a deflector on the back of the rack, perhaps you could blow some exhaust air across the transformers & tubes, that would help cooling your ST-120, it's worth a try.

You have a very good looking build for sure!

We have a few speakers that we use for our dedicated 'Stereo' system.
We Bi-AMP a set of Bozak 1968 Symphony's using a VTA ST-120 for the Mids & Tweeters & a Carver A-220 Solid State Amp with high damping factor for the dual woofers per speaker. We use the Bozak N-106C Electronic Crossover.

Also in the mix is a set Klipsch Heresy I with fresh Crites Crossovers.

We also have a nice set of Dynaco A-25's, very natural sounding. They are in need of a crossover refresh.

I have a Pioneer D-23 - 4 - Way Active Crossover that we plan on using on the big Bozaks, the existing ST-120 (Mids) - Carver A-220 (Woofers) plus a fresh ST-120 for the 8 Speaker Tweeter Array (up to 12KHz) & a 1968 Dynaco ST-70 w the VTA driver board for a set of Silk-Domed Super-Tweeters that sit on top in dedicated enclosures for 12KHz & Up. I've been working on that setup for many moons and it's finally getting close!

No pro gear in the dedicated stereo setup.  When we get the D-23 with 4 amplification systems in place, I'll use REW Room Acoustics Software to get the levels right.

Cheers,

Aguaazul

Bob Latino wrote:Hi Dave,

Nice work on your custom VTA ST-120 !

Bob

Thank you Bob! I can't tell you how much I appreciate your incredible customer service. Every time I power up the ST-120, I have a big smile on my face.

Thank you again!

Dave

aguaazul wrote:

dasa2131 wrote:Hello Aguaazul,

    Thank you very much for the kind words - it's greatly appreciated.  I've attached a few more pictures.  For the outputs, I have two sets of speakon jacks: one for 4 ohm, one for 8 ohm speakers.  Input jacks are just regular RCA jacks.  Ideally, I'd have XLR jacks for balanced inputs on the back, but I'm not savy enough to figure out the balanced to unblanced circuitry.  
    Regarding what you said about moving the amp up to the top - I understand 100% where you're coming from.  This thing really does put out a lot of heat.  Not shown in the pictures, I actually have two 120mm fans blowing air across the transformers and tubes.  They are mounted slightly above and behind the transformers.  I have two internal 80mm fans that blow air into and out of the enclosure itself. When I run the amp, I always leave the rack door open.  With all that said, I do like your idea of putting this amp near the top.  I'll look into that - thank you for the suggestion!
    What kind of amp/speakers are you running?  Since you used to do live sound, are you using any pro-audio gear in your setup?

Thanks again,

Dave

Hey Dave,

Thanks for posting the photos. It's cool to see the I/O and routing.  Nice use of the fans, if you used a deflector on the back of the rack, perhaps you could blow some exhaust air across the transformers & tubes, that would help cooling your ST-120, it's worth a try.

You have a very good looking build for sure!

We have a few speakers that we use for our dedicated 'Stereo' system.
We Bi-AMP a set of Bozak 1968 Symphony's using a VTA ST-120 for the Mids & Tweeters & a Carver A-220 Solid State Amp with high damping factor for the dual woofers per speaker. We use the Bozak N-106C Electronic Crossover.

Also in the mix is a set Klipsch Heresy I with fresh Crites Crossovers.

We also have a nice set of Dynaco A-25's, very natural sounding. They are in need of a crossover refresh.

I have a Pioneer D-23 - 4 - Way Active Crossover that we plan on using on the big Bozaks, the existing ST-120 (Mids) - Carver A-220 (Woofers) plus a fresh ST-120 for the 8 Speaker Tweeter Array (up to 12KHz) & a 1968 Dynaco ST-70 w the VTA driver board for a set of Silk-Domed Super-Tweeters that sit on top in dedicated enclosures for 12KHz & Up. I've been working on that setup for many moons and it's finally getting close!

No pro gear in the dedicated stereo setup.  When we get the D-23 with 4 amplification systems in place, I'll use REW Room Acoustics Software to get the levels right.

Cheers,

Aguaazul

Aguaazul,

It sounds like you have very ambitious plans. Have you ever looked into using a MiniDSP as an active crossover? I'm close to buying a MiniDSP OpenDRC-DA8 to act as a crossover and timing/phase alignment for my subwoofers. I have 14 ported subs in my garage which are grouped into 6 unique channels for time/phase alignment. Currently I'm using a Behringer DCX2496 for this, but it's a little clunky when applying PEQ's and time/phase alignments. The cool thing about the OpenDRC-DA8 is that it can use both IIR and FIR filters. The FIR filters can be applied which allow linear phase filtering (no phase shifting).

Just a thought,

Regards,

Dave