| HOME | Service & Mods | Links | Downloads | Prices & Order |
here is our Dynaco ST70 page
our famous VTA70 driver PCB upgrade for your amp!
we've been selling this of selling this modification/upgrade for the ST70 since 1987 - 23 years now !!
we are also now offering your choice of our classic hi-gain version with 12AT7
tubes,
or a lower gain version using 12AU7 which has
revised resistor values to optimize the circuit for these lower gain tubes
see our customer comments on this mod/upgrade at the bottom of this
page!!
how to choose if you're not sure which one to buy . . . ??
if you have a preamp then the lo-gain version would probably be better, but if you go direct in or thru a passive volume control the classic hi-gain version would be better. Also, if you have standard efficency speakers (less than 92db) then the hi-gain, if you have hi efficency speakers (greater than 93db) then the lo-gain version
click here for NEW item -- ST-70 rebuild kit!
click here to go to complete amplifier kits
click here to go to our MK3 - MK4 page
click here to go to our Preamp page
click here to go to our downloadable Dynaco manuals page
visit our
new "Dynaco Tube Audio Forum"
Written Articles
ST70 modifications
comparison test - Glass Audio magazine article
non-USA buyers, please contact me by email first before placing your order!!
shipping to non-USA buyers will cost an additional $10 to $35 for shipping and customs paperwork!!email "tubes4hifi" for info info@tubes4hifi.com
add $10 for shipping fees
add $20 for shipping fees
add $30 for shipping fees
blank PCB with parts list, schematic, and manual is $39.00 including shipping in USA
PCB and parts kit is $88 (NOT including 3 driver tubes) including Priority shipping in USA
p classic hi-gain 12AT7 version<
PCB and parts kit is $89 (NOT including 3 driver tubes) including Priority shipping in USA
for the lower gain 12AU7/12BH7 version
VTA70 PCB classic HI-gain 12AT7 version, assembled and ready to install for $138
(free shipping in USA)
(NOT including 3 driver tubes,),
Plugs right into your ST70 amp.
VTA70 PCB LO-Gain version for 12AU7 tubes, assembled and ready to install for $139
this version is recommended if you use a tube preamp AND / OR you have very high effiecency speakers
(free shipping in USA)
(NOT including 3 driver tubes,),
Plugs right into your ST70 amp.
NOTE: the following items do NOT including shipping
unless
ordered with a kit above, if ordering separately
please add $5 to
your order for shipping
add $5 shipping fee for separate parts orders
add 3 JJ 12AT7 (ECC81) tubes for $33, these are great tubes for the classic hi-gain version!
add 3 JJ 12AU7 (ECC82)tubes for $33, these are great tubes for the lower gain version!
add 4 Electro-Harmonix EL34 output tubes for $56
Another option is a capacitance upgrade from our standard 88uF on board,
to 306uF on board, for an additional $12 !!
Another popular option is using 4 military-spec Russian PIO output coupling capacitors, these are type K40 rated 0.22uF at 500v, provide a real smooth sound for only $24 more.
In our opinion these provide a better sound than even the expensive AuriCaps. Possible shipping delay as we get these directly from Russia.
Another popular option is using 4 AuriCaps for the output coupling capacitors. these are 0.22uf rated at 400v and many consider them the most natural sounding of all for $52 more.
more parts to update your amp !!
new input
jacks $10 pair NICKEL PLATED
new input jacks $13 pair GOLD PLATED
new speaker posts $18 pair original type standard quad cap (30+20+20+20uF@525v) $38
here's an older page showing step by step conversion of ST70 to VTA70 with our mod PCB
here's a link to a wiring diagram for our VTA amp
here's a great photo of the internal wiring on a VTA70 amp, with the Triode/Pentode switches . . .
see Bob's page
to order an amp like this !!
contact us for any parts you may need for your Dynaco ST70
email "tubes4hifi" for info
our dealer on the east coast is Bob Latino. . . he offers NEW Dynaco ST70 KITS and ready-build amps
click here for his "buy-it-now" page brand NEW ST70 amplifiers, in KIT or ready to go!
you can send email to Bob Latino directly here for info on these complete kits or amps . . .
some additional info on our VTA70 PCB . . .
Our driver circuit is a modern all triode driver design, for totally neutral uncolored sound. One half of the first tube is used for each channel as a voltage amplifier. One each of the other tubes is used per channel as a combined phase splitter/driver in a long-tailed pair configuration. 13 db total loop feedback is used. Parts quality is top notch, with mil-spec tubes, metal film resistors, and propylene caps. There is an individual bias pot for each output tube, as well as a signal balance pot for the phase splitters. The bias is set for 40 ma, about 20% less than stock to reduce heat and conserve tube life. Open loop response of this design is incredible. It has flat frequency response from 7 Hz to 70 KHz, with good square waves from 7 Hz to 30 KHz. Open loop gain is 40. The PCB is 8.0" x 3.3". Max power output is 40 wpc.This board compares very favorably with the best of the competition, and is a better quality PCB for less money. For example, the Curcio board with comparable options (DC & AC balance, propylene caps) is about $40 more, and it is single sided. Ours is double-sided with plated thru holes. Now available in our classic hi-gain design using 12AT7 tubes, or our improved lower gain design using 12AU7 or 12BH7 tubes
customer comments
"I finished your mod and this is honest to god the first time
I ever enjoyed listening to an ST70..The ST70s to me have always
sounded kind of sloppy, but this mod tightened it up and the overall
tonal balance is much much much better. The biggest thing I noticed
was the lininerity of the sound and the focus of the instruments
possess an exponential difference now as opposed to the stock ST70.
The amp is tighter and much faster."
Bill (VTA70 mod)
"I have only run my ST-70 a few hours (w/ all tubes new), and let me
tell you how happy I am from the sweet sound I'm hearing.
Compared to stock, well no comparison.
Better highs, deeper and wider soundstage and tauter bass, more
transparent and better detail by a factor of 10. I heard an ST-70
with a Curcio upgrade last night driving the same speaker I have
and using a higly regarded preamp, and in my ears,
there is no contest. Thanks very much. A very happy customer."
John R. M.D. (VTA70 mod)
"hi roy
I put together the board of yours and then I wired it to my Dynaco ST70.
Let me tell you this is the most stable, accurate, fast, solid sounding
mod I've ever heard on a Dynaco... WOW.
I couldn't believe the drive they have. Oh by the way a friend of mine
had the Curcio modded amps and he heard these tonite and he said this is
a much better sounding design than the Curico."
mike (ST70 mod)
BEAUTIFUL WELL LAID OUT BOARDS AND EASY TO FOLLOW INSTRUCTIONS.EXCELLENT.A+++
Superior packing, very honest seller, A+'s all the way, very smooth transaction
Quality workmanship,quick shipping.Recommended!Thanks!
Nice amplifer, works great. It sounds better than my MC240! no problems!
Awesome product as promised!!!!! Nice and quick delivery!!!!!!
September 2005 comments
. . . posted on AudioGon by recent customers . . . .
VTA mod board Hi, I know all of you out there who are do it yourselfers(DIYer's) have done a mod or two on the most recongnized modded amps around, the Dynaco ST-70 and the Dynaco Mark III's. Well, I have bought just about every mod board available and have even done a few on others not sold mainstream from time to time. My favorite, until now, was the Kevin Kennedy(KTA HiFi) board until I tried on a whim, a VTA board from Tubes4HiFi. Immediately, with no warm up, this board was showing much promise and once it warmed up it was all there, period. After looking at the schematic and seeing what was done I was saying to myself and a very close friend who is an accomplished tech, was saying the same thing. "This board shouldn't be doing to the amp what it is doing." It took a marginal amp and made it great. I then had the urge to try this schematic on a pair of Heathkit W7's. If the Dynaco ST-70 is great, then the Heathkits are world class. These amps smoked the Dynaco from the beginning of the bandwith to the last and final note. There is a difference between the two amps besides the transformers. The Heathkits have solid state rectification where the Dynaco is tube rectified. I, at some point, just to be fair to Dynaco and its followers, am going to change the rectifier to solid state, just to compare apples to apples. I doubt it will make that much difference but one never knows. I am not a solid state lover in the rectifier but you just can't tell the Heathkits are solid state rectified with this board. This is a great mod board. Just try it! by Theschwrtz on 09-22-05
Follow ups VTA mod board I have tried the board in a pair of Heathkit W-7's. I bought two of them and didn't use the third 12AT7 of each board because the W7's are monoblocks. Also, when stuffung the boards only use pins 1,2, and 3 of the middle tube and all the parts associated with them because the input circuit shares both halves of the middle 12AT for the input of each channel on a Dynaco or any stereo amp. I also didn't use the bias supply on the board. I used the stock bias supply from the original Heathkit circuit. I put the board on standoffs and built a small wood sub chassis around the board for looks. It looks unusual but it looks good in my opinion. I didn't put any parts on the bottom of the board as described in the original picture on the VTA website. I was able to get the board down a bit lower to the chassis. If the new bias supply built on the board is used then you must put the bigger coupling caps on the bottom so you have access to all the bias pots when needed. That means you will need taller standoffs. Now for the sound. Let's just say I used the board on a few Dynaco's and I was happy with the results as compared to other mod boards and stock boards I tried. But when I put the boards on the Heathkits it took on a new life form. Dynamics in spades. Musical? None better! This is the best mod to an EL-34 amp I ever heard. The music is about as real as it gets with lifelike images that make you feel the musicians and singers are in the room for a personal perfomance just for the listener. The bass is extremely accurate and tight on the Heathkits. I felt it was a bit bloated on the Dynaco. Using a different feedback resistor and capacitor value helped but not like the Heathkits. Try this board! You will be glad you did and it is easy to install. stereovinyl 09-23-05
RE: VTA70 PCB kit It is a real winner - finished the amp in one day and everything worked perfectly and all was very quiet. All four 6ca7s balance at the same point on the pots (.40v after 12hrs of burn in) and remain stable. I put in some classic Eric Clapton, Eagles, Joe Cocker and David Allen Coe in the CD changer and WOW!! This thing is pure and really belts out a tight bass, with expanded mids and brilliant highs. It's been on continuously now for 3days playing a variety of old vinyl, along with DATs of CDs and live performances. I really think it outshines my MAC 225, and certainly beats any ST70 I have ever heard.
Roy, just a follow up to my recent order of a VTA board with the upgraded audio caps. I installed it last Sunday, which took no more than an hour. Fired it up, biased it per directions and everything immediately checked out O.K. (after warm up, the B+ voltage is settling at 439, 1 volt below the norm you set in your directions). It's driving a new set of Svetlana "winged C" EL34s, employing vintage Mullard 12AT7s. To be succinct, the sound is incredible - much more robust, with depth and detail far, far beyond what I previously was hearing from the amp (that isn't just me, even my thirteen year old Ipod-centric daughter commented on how "three dimensional" my system now sounds). It is even bringing out a decent soundstage from a satellite radio signal!!! Given that, listening to analog sources (vinyl and a vintage Kenwood tuner) is pure heaven. Thanks again for a great product.
> Roy - WOW - yours is some pc board !! > It makes vanalstines ultimate 70 board > sound terrible by comparison. Much thanks!! > John F.
http://www.audioasylum.com/audio/tubes/messages/19/198694.html I have used over 20 of Roy Mottram's VTA driver boards in Dynaco ST-70 builds for customers. They are extremely well built, have no open solder traces and in comparison to the Triode and Curcio boards - IMHO the VTA simply sounds better. The VTA board has individual bias controls (DC balance) for each output tube so a matched quad of output tubes is not really necessary. It also has AC balance and an onboard bias system with it's own power supply. It uses three low cost 12AT7 tubes and responds very well to tube and coupling capacitor tweaks. Bob Latino
http://forums.klipsch.com/forums/thread/833089.aspx I have the VTA MOD Dynaco ST70, and a freind of mine has the VTA MK3 mod, as far as I am concerned it is the best Dynaco upgrade ever, and it doesnt take a rocket scientist to install. check it out at www.tubesforhifi.com Dynaco tube amps and Klipsch are made to be together.
Just installed the board in my ST70 and I have to say it sounds superb! I had a previous upgraded board that's well regarded but sounds dull in comparison to your board. N. Haider, MD
Hi Roy, A note to let you know that I received the PCB and the parts I ordered. The PCB is absolutely outstanding as compared to the Curcio! It's clear that your intent was to give your customers a high quality PCB at a very reasonable cost.
I have only run my ST-70 a few hours (w/ all tubes new), and let me tell you how happy I am from the sweet sound I'm hearing. Compared to stock, well no comparison. Better highs, deeper and wider soundstage and tauter bass, more transparent and better detail by a factor of 10. I heard an ST-70 with a Curcio upgrade last night driving the same speaker I have and using a higly regarded preamp, and in my ears, there is no contest. Thanks very much. A very happy customer. John R. M.D.
I have only run my ST-70 a few hours, and let me tell you how happy I am from the sweet sound I'm hearing. Compared to stock there is NO comparison. Better highs, deeper and wider soundstage and tauter bass, more transparent and better detail by a factor of 10. I heard an ST-70 with a Curcio upgrade last night driving the same speaker I have and using a higly regarded preamp and in my ears, there is no contest. Thanks very much. A very happy customer. - J.R.
Hi Roy, Received your VTA ST70 mod, and I am thrilled. I must say, the quality and craftsmanship that have gone into this board are truly exceptional. You may be interested to know that before I ordered this board from you I did my homework, and investigated most of the mod boards being offered by other companies. Time and again, yours was rated by far the best, and now I can see why. I have loved the sound of tube amps since the 1950's, and have always strived to have the best sounding equipment(and generally LOUDEST) in my entire town. I didn't realize that part of your mod board INCLUDES additional power supply filter caps, When I finished the project, and powered it up according to instructions, and everything seemed just fine, but at first I thought there was something wrong because I couldn't hear any hum at all through the speakers. Then the music started. WOW! This is an amazing board you've designed. It has tons of power, plus great range. Amazing !! Thanks for going the extra mile for me -Peter S
This amp is absolutely LIQUIED. The sound stage is large and has wonderful detail! I would recomend this MOD for any ST70 Steve (VTA70 mod) Your board sounds really nice! I will recommend it to my friends with Dynaco Stereo 70's. To be honest the Dynaco just didn't cut the mustard in stock form but now it’s a whole new animal. Joe When I finished the project, and powered it up according to instructions, and everything seemed just fine, but at first I thought there was something wrong because I couldn't hear any hum at all through the speakers. Then the music started. WOW! This is an amazing board you've designed. It has tons of power, plus great range. Peter
Roy Just a note to let you know how much I enjoy the driver board I purchased from you. It made a night and day difference in the way the Dynaco sounded. I had heard people rave about the stock Dynaco ST70 so I bought one only to be disappointed by its sonic signature. I was assuming that it would have some bass and authority but it actually sounded very bad instead. Your circuit changes and your board brought it new life and authority that it should have had if it had been designed correctly in the first place. It ranks up with my "quicksilver" amps now and frankly if I had had the modified Dynaco first I never would have bought them. They sit gathering dust now while I use the Dynaco with you VTA70 modification. Best Regards, Joe T
Roy, Your ST-70 mod board is by far the best sounding one I've ever heard. I'm truly impressed by the improvement in sound and the other benefits of the board, like seperate biasing for the EL34's. I didn't expect anything good when I bought it, but had to try it as I've tried everything for the ST-70. I'll spread the word. And Thanks! Audiodyssey Anthony Cordero
Good afternoon, The amp is getting better and better, I put about 12 hours on over the weekend. I'm ruined. This was a second system. My main system is a pr of Magnepan MGIIIa's with Oddesey Mono amp's (high Current). My other system is a SET FI X 2a3 with fostex BLH. After listening to the Lascalla's and your upgraded amp board I cannot listen to the other systems.. It's like going to AM radio. I mean the bass the punch the dynamics the imaging the clarity. It's outstanding.
join the growing list of people that have been amazed and blown away by the incredible transformation this seemingly simple modification makes. It is a TOTAL TRANSFORMATION of the amplifer and the sound quality is unbelievably unbeatable!!
return to VTA home page
GoStats web counter