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   Dyna Stereo-70

Mods & Upgrades

Dyna Mark 2/3

Mods & Upgrades

Dyna PAS 2-3-X


CD12V Tube

Digital Processor

Daniel II

Reference Preamp


Phono Preamp

 Our Unparalleled Customer Service

Perhaps most important, you left me -- your customer, feeling respected -- never hurried or that my questions were bothersome or unimportant. It is a sad fact that most businesses, large and small, do not understand this -- one of the very basic principles of an enduring business relationship. You obviously do understand and I certainly wish you the best of luck in your endeavors. It is well deserved. DL

I cannot say enough good things about your web site and attitude about your business. I just left your site (again) after having read the "Why Upgrade" essay. What an honest and encouraging piece; and well written to boot. I will have to give one of your kits a try in the very near future. After running through your trouble-shooting guide, I'll let you know what I need... I'll probably have to start with that "cap replacement"... And by the way: your trouble-shooting guide is also incredible. Your time and effort is GREATLY appreciated. Thanks again, PH

I hope that you are experiencing incredible success in your business. Your customer service is amazing. Thank you very much for all your help. If you need any help from me ........ Once again, thank you. LH

Joe, I just wanted to say thanks for offering a thoughtful, logical approach for solving the problem I was having with my ST-70. Following your instruction I discovered the instability in my bias current was resulting from two tubes, an old one (the rectifier tube) and a new one (EH EL-34). Having now replaced both the bias current is very steady. As you may recall, when I called you I was questioning the pots. Thanks again for your guidance. I deem you, most generous, and greatly appreciated. Regards, G

Thanks again for the help. Your support of your products is exceptional. I will play with the coupling caps and see if I hear any difference. Having my homebrew pipedreams enables very small differences to be heard; they behave very much like a audio microscope, similar to horns. I should finish the complete rebuilds of my Mark IV's soon, and will let you know how I make out. Best Regards, DL

I have used Joe’s Curcio’s electronics for some 15 + years. I started with a modified Dynaco Stereo 70 and modified PAS 3X. Since then I’ve moved up to Daniel I and a pair of Curcio modified Dynaco Mark III ‘s and the Curcio DAC. Throughout the years Joe has stood behind his equipment and always was ready with advice. Not that his designs needed repairs, but they did require tube changes after 5+ years of steady use. The hall mark of Joe Curcio’s designs was wonderful imaging (both front-to-back and side-to-side) and lightening fast transients. However, once you get use the outstanding performance, all that metamorphizes into an involving sense of musicality. Frankly I though heard it all as far as the final word in musicality, and then I got a Daniel II Preamp with an enhanced phono section. First thing I noticed is how dead quiet it was even with volume knob set to 11-12 O’clock. The sound comes from the darkest background I have heard bar none. Yet all the high end was presented accurately and with musicality. Quite often with most electronics make you choose between musicality and accuracy. Curcio’s design gives you both accuracy and musicality. Well recorded voices are reproduced with effortless musicality that I never heard from my Vinyl. The punch and the dynamics while forceful are never exaggerated. My experience with the Curcio Daniel II is that this will be a pre-amp that you be upgrading your source components and speakers around in try to realize the full potential of the Pre-Amp. There is no Pre-Amp on the market that comes close to the performance of the Daniel II Pre-Amp at any amount of money. LL

Dynaco Stereo-70 Upgrades & Modifications

Just a quick word: after a week or so of careful listening, I must tell you that the amps sound fantastic. I want to thank you both for your efforts and your patience, because as far as I am concerned, it was all worthwhile. ... DM

I just wanted to thank you for your support and advise as well as congratulate you for not just an outstanding product, but for an informative and accessible website, as well as telephone availability. Saturday I was able to install the new driver board upgrade on my dynaco stereo 70 in a little bit over 3 hours. I had previously installed the capacitor replacement board. The sound is magnificent. You are absolutely right. Your modified PCB upgrade not only keeps the character of the original, but also improves on it. This is an impressive amp now; the music flows with the right amount of drive, the bass is plump and articulate, the tonalities are convincing and nuanced, but best of all the musicians performance is clear and engaging unlike most pieces of electronics out there. I am running the amp through a pair of spendor s3/5 monitors, and feeding it from a Quad QC-24 tube preamp, and is a great combination. I am curious now about the more powerful dynaco mono blocks... Thank you again for putting more better music in our lives! Best regards, RF

I'm writing primarily to thank you. My cousin used your kit to modify one of my 2 Dynakit ST70 amplifiers. He suggested that I write to you with my impressions and thanks. You gave him some email advice a few months ago and I'd like to express my appreciation for this as well.  Now, I'm not an audio engineer, but simply a fan of recorded music. So I'll deal with subjective rather than objective, measurable assessments. The improvements my system has gained with your modification are, to my ears, quite measurable. I'd been running 2 ST70s, 'bridged' into mono, for about the past thirteen years. For about the past year I consolidated (good, operating) tubes and ran just one Dynakit.  My system consists of a Linn LP12, Ortofon cartridge, Sonic Frontiers Anthem 1 pre, JVC XL-Z1010 cd player, Dahlquist DQ10s and of course, the ST-70 with Curcio modification, as of this past Tuesday. It's an aging system, but I'm tickled pink to see some of my components still mentioned by the audio press, which I've ignored for most of the past fifteen years or so. Here's what the mod has done in order of magnitude:
1. The Curcio mod has separated what was once a mass of instruments and vocalists into coherent 'compartments'. This is
actually the biggest difference, and the first thing I noticed. Never a particular fan of this before (I tend to seek out sound staging), but now that I hear it I want to keep it. This difference also means that two or more things can be playing at once and I hear them...separately. It's a real revelation, and quite unexpected. 
2. The Curcio mod has extended the bass floor quite noticeably. I can tell this, because the floor shakes much more. But there are also bass NOTES. That means that I can now hear Eberhardt Weber's acoustic bass render differences between notes. The thumps are no longer just low-ish thumps, but notes. I hear bass notes. For a guy with a pair of DQ-10s, this is quite an accomplishment. I hear all sorts of little things happening down there. I've discovered why Jaco Pastorius is a genius, he does all kinds of interesting things in the nether regions of bass. On Joni Mitchell's "Blue" the opening drum can be heard as more than just a dull thump. I always thought it was someone's foot tapping on the floor. Now it sounds like a drum. Cassandra Wilson's "Strange Fruit" has bottom, real bass depth. It's quite frightening in a way. I can now play disco, if I really wanted to. My daughter will be so pleased.
3. The Curcio mod has extended the high end frequency floor. This is not as easily discernable as the bottom octave differences noted above, except for the fact that: a. I get more soundstaging. b. I get more image depth. But my system sounds brighter. This means I have to do something about my cd player, cause on some recordings, I get speaker fatigue. Maybe I should drop the little Dahlquist piezo tweeters into Lake Ontario..
4. The Curcio mod has given the system more detail..or, to put it more clearly, I now hear the very beginnings and endings of guitar strums, vocalists take breaths in-between passages, I hear small things in the mix not previously there, like bells for instance. Paul Simon's "Rhythm of the Saints" album has all this STUFF going's very subtle, but it's very definitely
there. Singers lick their lips, tinny guitars sound tinny, fat guitars sound fat. I can hear the musician's fingers running up and down the frets, I can hear when the strings are sustained for an extra moment in an piano passage. Hell, that I can hear that at all makes the whole thing sound more real and enjoyable, and that's the point of the whole exercise, isn't it? 
5. The Curcio mod has made my system able to reproduce the studio on some recordings. Here I think I'm being limited by my speakers, but I can definitely hear 'the room' on Kate & Anna, Roches, Simon, Jazz at the Pawnshop, Joni Mitchell, etc... it doesn't make bad recordings sound better though. I can hear the 'switch' from room to room, for example on "Blue" the difference in rooms between the piano track "My Old Man" and the next track, "Little Green" is quite easily heard. I can hear when a vocalist gets too close to the mic, I can hear more studio crap, I can hear whispers and asides in live recordings with much more clarity...that I'm not sure I want to hear. 
6. I don't know if I'm imagining this one. The Curcio mod seems to have done something to the tempo on some recordings. The Roches seem to be speeding up and slowing down between choruses. They do this intentionally, I realize. I think I noticed this first when I got the Anthem preamp, but it's much more apparent now. The Indigo Girls and Joni Mitchell and others do this as well...
These are only preliminary impressions but I'm certain about their authenticity. Thanks again, RR

Hi Joe,
It's been a couple of week now since I finished upgrading my st-70 with your kits for power supply and driver board. After a period of time for break-in, and finding an appropriate interconnect and power cable, I can tell you that I am very comfortable with the sound my system is making. It's very musical and natural in a way that my high end solid state gear was not. Thanks for making these kits available and thanks for your help on the couple of occasions when I needed direction. It was comforting and essential to know that your help was just a phone call away. Best regards, G.

I have a fully modded ST70 and a PAS using both the driver and the power supply boards and love the sound. Tight bass, extended highs, very detailed and very 3D. I often listen at night with all of the lights turned off and frequently get startled out of my seat from hearing something in the music that sounded like it came from outside, or behind me. It's an unusual experience (a good one for sure). Joe provides exemplary service to his customers and his products are top rate.
I'm getting ready to fully mod a pair of MkIII's and can't wait to get them into my rig! My Impressions:
1. Sound is accurate and detailed. Not warm or cold, but right in the middle. Very wide, 3D soundstage with individual musical elements placed appropriately within the soundstage.
2. The rebuild is fairly straight forward. It is a full rebuild, the only items reused are the transformers, chassis, quad cap and some of the hardware. The replacement boards fit nicely. I used the premium semi-pack semiconductor upgrade as well as upgraded some caps with Wima's. The instructions that are included were slightly unclear for me, so spend some time and read through carefully.
3. Customer service with Curcio products is second to none. I was a complete electronics beginner when I rebuilt my ST-70 and had sent numerous newbie emails to Joe Curcio for assistance. Joe replied himself to every email answering my questions. He even provided some phone support when I was really stuck. That says much about a person/company commitment to their customer. KS

I rebuilt an old ST-70 using the full Curcio mod (power supply and driver boards) in 1992. The transformation was not subtle. I can't imagine anyone who has a system that can use a 30 WPC amplifier not being thrilled with this unit. The CAE mod has real, tight bass, smooth mids, and natural highs. Compared to a stock unit, well, there IS no comparison. I've also built and have extended listening experience with the Van Alstine and Audio Research mods. The AVA mod sounds good within its design parameters: bandwidth limited. The ARC sounds close to the CAE but is fond of eating 6L6 output tubes and is no longer available. Curcio's approach is certainly valid from an engineering standpoint. The regulated power supply provides strong legs to support the audio sections. Some may take issue with the 6DJ8 / 6922 tubes (4) in the phase splitter / driver section but I hear none of this tube's purported sonic signature (harshness, coldness, excessive sibilance) in the amp's overall sound. I have not had to replace a tube since the modification and it still sounds great. I highly recommend it. Regards, S

I am fellow LS3/5a owner, I have owned my speakers since 1978 and have been pleased with them since day one. Through the years I have had the opportunity to listen to many preamp and amp combinations, solid state and tube alike. Luxman Tube and Solid state, Audionics C22, Theta tube preamp, NAD 3020, APT Holman, DB Systems, All Dynacos, McIntosh, Haffler, Audio Research, Mark Levison, Old Marantz and HK, just to mention a few. I can truthfully say I like what I have now better than anything I've heard, and for a lot less money except the NAD 3020. I've noticed many owners inquiring about the best amp to use with the LS3/5a's. I whole heartedly suggest taking a look at Curcio Audio Engineering ( Dyna ST-70 (FULL MOD amplifier) and the PAS (FULL MOD preamplifier) -Tremendous Combo. I finished my Curcio ST-70 amp about 2 years ago and the PAS about year later. I used the preamp section of a NAD 3020 until I finished the PAS - the PAS brought the ST-70 to a level I think most of us aspire to. Imaging is Unbelievable - on good recordings the LS3/5a's completely disappear - the depth is perfect - timbre right on - with the right tube combinations RCA 6fq7- Mullard EL-34(dual getter) for the ST-70's and a well balanced 12at7 (RCA or Telifunken (more money) for the line stage of the PAS they will SING. The ST-70 allows you to use a lot of different driver tubes - this gives you a lot of latitude when trying to get the sound that you like. I think these units will be the best price to performance our fellow LS3/5a users can purchase. These units are a great value and I don't mean cheap - I mean the biggest bang for the buck. If you get a chance, check these units out - you won't be disappointed. Oh by the way, I think Mr. Curcio also listens to LS3/5a's. To my ear this is the perfect combination for the LS3/5a's.
Equipment: Rogers Ls3/5a, Curcio ST-70 complete mod, Curcio PAS upgrade with DACT Volumn and selectors switched, Linn LP-12 - Grace 707 and Denon 103D Verion Step - up ,Marantz 63SE, Quad 57 ELS, Onkyo T-9 Tuner
Silver Sonic Speaker Cable, Belden 89259 IC's, Thanks, JB

I've used Curcio's St-70's since '92, one built with boards purchased from Sonic Frontiers, another built with stuffed boards purchased from Curcio Labs ( actually he built the entire amp, in return for a late delivery! How's that for service!). I've ended up wiring the outputs in triode on both of these amps. Simply put, I find the sound quality superb whether running pentode or triode, though the sound is a bit sweeter, the imaging a bit tighter, in triode mode. I have no comment about the bass as I've never used these amps full range; I tri-amp, using the Curcio's on mids and highs. Compared to an ARC D-76 (upgraded with MIT's, Holco resistors, and new 'lytics throughout), the Curcios offer far greater resolution of detail, again, better imaging (not EVEN close!), and much sweeter string reproduction without loss of "air" or, on excellent source, the natural string "bite." Some of this may be a reflection of my preference for EL-34's over 6550's, but, objectively, it is far more likely attributable to the power supply regulation - "total" plate regulation is, in my experience, something of a novelty, but, in conjunction with everything else, seems to manifest an order of magnitude improvement in sound quality - once more, most noticeably, with image specificity. I should also like to add that Joe Curcio has been more than willing to respond to any technical queries I've posed, and has been most gracious in dealing with my sometimes just plain stupid questions. One man's opinion. B

The 7199 tubes finally gave in and the cost to replace them was not to far from just getting a new driver board. I chose Joe Curcio's design for several reasons. First, this man really loves tweeking Dynaco gear and second the man is a saint. He helped me with several other problems my unit was having. I was even emailing pics of PC boards to him at one point. But mainly his driver board design employed newer technology while still maintaining the spirt of the true Dynaco design.
It was little hard to compare because the original design was pretty darn good. But I listened to some CD's that I was very familiar with. Again clarity and distortion wasn't a problem before but WOW there really was a difference. I tried several setups with direct input with the Dynaco FM3 tuner and a Marantz 2230 as a tuner preamp. I listened to a Pink Floyd song and actually heard a female technician giving directions in the background. On the Beatles White Album you can hear the usual chairs creaking and background "stuff". Beethoven's Pastoral, my favorite,was hauntingly beautiful. The change over from fragile soft passages to swelling crescendos were glowing and warm with detail incredible deep but subtle. It was almost like 3D sound. Loud rock is loud but the detail was still there even at increased volumes. One particular favorite rock album "Days of the new" is a very detailed piece, and it sounded wonderful with deep base and strong mids. Thanks Joe! C

Dynaco PAS 2-3-X Preamplifier Modifications

Now for the sound........Massively increased soundstage and instrument separation. I think clearing up the signal paths with new wires and jacks probably did that trick. The board looks very professional. My amp looks brand new. Thanks for some high quality products and high quality service. I'm one happy customer. J

You were right once again. Your PAS line stage with generic PP caps surpassed my XX PAS preamp w/ quad regulation in every area of performance. PWB is laid out very well. Looks like a lot of thought went into this design. Good Job. GL

I feel this is one of the last preamps I'll ever own. I'll try others but will always keep this one. I giggle everytime I listen to this thing. I'm always amazed at the sound this preamp kicks into my old Dynaco. Anyone who says Dynaco has it shortcomings sonically doesn't have the right preamp. And I will stand behind that 100% C

I owned a PAS also, and used Curcios line, power, and phono boards to upgrade it. I am the type of person thats goes through a lot of gear, trying to find something that really improves my sound. I kept the Curcio modded PAS longer than any preamp I have ever owned. About 3 years. It never failed to impress me over that time. I sold it only after building a Curcio Daniel full function preamp.

Dynaco Mark 3 Power Amplifier Upgrades & Modifications

I have successfully completed your modification using driver boards and capacitive upgrade for my aging dynaco m3 monos. The conversion was straight forward and was done in my kitchen. The impact on the sound was spectacular. Prior to the mod i liked the dynaco amps for their midrange liquidity and tolerated the bloated base and explained the missing highs as vintage tubey sound. After the mod was completed the midrange liquidity embraced the higher frequencies with new detail and without glare. The capacitor power supply upgrade tightened up the the base with more impact and grip. My wife (with more sensitive female ears) clearly voiced her pleasure that it was like having a new amp in the house. The step up was unbelievable for the cost and few hours of meddling with the circut guts.It brought new life to a very good midrange amp. I replaced the phillips 6dj8 that you provided with russian 6h1n tubes and I liked them better in my modified amps, but those are individual choices anyway. Thank you for your great contribution in design to the pleasure of music and sound appreciation. JH

I received the Amps on Friday and hooked them up right away. The change from the original amps is really nice. I was looking for a little more bass. This modification gave me not only more bass but it is really tight. It also seem to have picked up more soundstage, much deeper and the highs are less shrill. I may also be hearing things but the detail is really much clearer now then before. Needless to say I am as happy as a pig in slop. I also just bought a matched quad of Electro Harmonix 6550EH from the Tube Store. As soon as I receive them I am going to install them and set the bias. In your experience what will these tubes add. Once again thanks for all your help and patience, I definitely am pleased with the results. Regards, RV


CD12V Reference Tube Digital Processor

My first impression, and fairly immediate, is the palpable presence of everything. Music is occurring in a space and not on a surface. RL

The DAC is better than the Norh CD-1. It is also better than Classia DAC1. I have compare the CD12V with the Muse 2 Plus DAC today afternoon with my friends. CD12V is 100% better than Muse DAC. CD-12V with the following ‘cheap system’ combination, it  products the sound like S$15000 to S$20000 system ( in term of sound quality). The sound is very realistic, the same comments  on your web site “just plain you are there realism”. They don’t believe (has never can’t across) that the DAC make a such huge  improvement in sound. The KLH speaker ( Indoor / Outdoor and Multi-purpose 3 ways 4” Speakers) sound like a big speaker  system. They are also comment that CD12V is first and final investment to everyone whom should make. Regards, ACW (Taiwan)

BTW I have been enjoying my CD12V tube processor with the Daniel II (all in one chassis) for over 6 years. Never a glitch. I have been using the I2S output from an Audio Alchemy DTI 2.0 to drive the Phillips chipset directly, and it sounds wonderful. I now have an SACD player, and the CD12V gives it a VERY close run for its money. Thanks so much for providing this circuit.  (An SACD processor would be marvelous, if ever the DSD signal is made available by the transport manufacturers.) JJ

I am very satisfied user of the Vacuum Tube Digital Processor......The analog design is excellent. MR

Mr. Curcio, i just wanted say your dac is truly amazing. it doesn't sound at all digital and is blowing me away. DR

Hi, Joe,
I have been the happy owner of a CD12V for the last couple of years. Since you did a minor repair job for me a while ago,  the DAC has been performing flawlessly. The sound never leaves me wanting.  Thank you,  D

For your infomation my brother and myself really has been enjoying more music now with the introduction of the DAC into our set. Keep up the good work and surely I am going to write some review of the finer point of your DAC in one of the forum what they have been missing and your DAC really beat some of the expensive and well established one like MUSE 2. Please keep me posted of the progress and if there upgrade on the DAC. I am now very excited to know and hear what kind of improvement will the pre-amp offer when fixed to the system. I hope it will bring more present, clarity, tighter bass and transparent. Best Rgds  AB


Daniel II Reference Preamplifier

.. I have been listening to it with great pleasure and have never had the feeling I wanted to replace the pre-amp. This cannot be said of the other components in my system. HH, Netherlands

I am very much enjoying the Daniel II I completed in Jan and the ST-70 rebuild completed last year. Your designs, combined with speakers of my own design, have made it possible to come very close to some very pricey "all-out" systems I have heard (bettering many, in fact...), for what is really very little money. BC

I would like to take a moment to tell you how happy I am that I decided to build your Daniel II preamp. It has exceeded my expectations in every way, and they were high (based upon my experience with your DAC). I won't go into details that you have heard before, but I can find no shortcomings. TC

First thing I noticed is how dead quiet it was even with volume knob set to 11-12 O’clock. The sound comes from the darkest background I have heard bar none. Yet all the high end was presented accurately and with musicality. Quite often with most electronics make you choose between musicality and accuracy. Curcio’s design gives you both accuracy and musicality. LL

Well recorded voices are reproduced with effortless musicality that I never heard from my Vinyl. The punch and the dynamics while forceful are never exaggerated. My experience with the Curcio Daniel II is that this will be a pre-amp that you be upgrading your source components and speakers around in try to realize the full potential of the Pre-Amp. There is no Pre-Amp on the market that comes close to the performance of the Daniel II Pre-Amp at any amount of money.

I have been listening to Joe Curcio's Daniel 2 pre-amp with the new SOVTEK 6922's. The sound is stunning. This has to be the quickest pre-amp (in terms of transient response) and can reproduce an acoustic guitar or violin with amazing timbre. The sound-stage is very good without some of the negative attribute one sometimes assigns to a "tube sound". .... This has a richness and timbre. P

Sarah All Tube Reference Phono Preamplifier

In 1981 I built Curcio's original Daniel preamp and used it until just recently. I just built the newly designed Curcio Sarah phono preamp which I use with a passive line stage. I really like the Sarah, it is a very nice step up from the Daniel 1. I have not heard the Daniel II, but Joe indicated that he felt the Sarah's phono stage was superior and he was thus thinking about converting the Daniel II to a line-only unit. By the way, I purchased the Sarah after I had done some extensive comparisons with the Lehmann Black Cube and the Wright Sound WPL-10V. IMHO the Curcio designs are sonically superior - offering better resolution and a more neutral sound. Also, the Sarah is EXTREMELY quiet for a tubed phono stage - almost as quiet as the dead silent Lehmann SS

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