Last year I picked up a used McIntosh MC275 Series V off Audiogon for my main system. I have always been a tube amp lover for may years. After playing the Mac for over a year in my main system, I was looking for another tube amp for my smaller system downstairs which presently uses an older Pioneer receiver. When we have a party or friends over we mostly use the downstairs playroom. The kids are gone and no one but adults touch my gear. After looking around the net, I came upon the VTA ST-70 and ST-120 kit amps on the Tubes4hifi web site. I am fairly handy and had built some tube kits in the '60's. I sent Bob Latino an Email with a few questions. Within an hour an Email came back with detailed answers to my questions about cap upgrades and the VTA stepped attenuator. He even gave me his phone number in case I wanted to talk by phone which was nice. To make a long story short I ordered his VTA ST-120 amp kit without tubes but with both of the capacitor upgrades and the VTA stepped attenuator. I paid with Paypal that night and the very next day (a Tuesday) received notification that the kit had been shipped. I received the kit the very next day in NY. It was very well packed. I checked all the parts against the parts list that Bob provides and everything was there. I brought everything to my workroom. It would have to stay there until Saturday when I would have time to work on the kit.
On Saturday I started the assembly and found the manual to be very well written with good detail. The two photos that Bob sends along were really helpful too. Step by step the amp just came together. The only minor problem I had was the assembly of the supplementary cap module. Nothing wrong with the instructions, it just seemed a little tedious try to hold the cap with one hand and solder with the other. I put in about 6 hours on Saturday and another 6 or 7 hours on Sunday. By Sunday night I was done. I placed the three driver tubes in the amp and connected my old KLH 6 speakers and my CD player to the inputs. Flipped the switch on the amp and all the driver tubes lit up. Shut the amp down and placed the two left channel Genalex Gold Lion KT88's that I had bought separately and an old Stromberg Carlson 5AR4 rectifier that I had laying in a box of tubes. Everything lit up and I biased the left channel. I walked over to the left speaker and put my ear to the grille cloth and heard a barely audible hiss. A foot away from the speaker I could hear nothing. Shut the amp off. I inserted the right KT88's turned the amp on and biased the right channel. No blown fuses, no noise, nothing. Turned the Oppo CD player on with one of my Steely Dan SACD's. Out of the silence came Steely Dan sounding MUCH better than what I got with the old Pioneer receiver and through 40+ year KLH old speakers.
The next weekend I brought the amp upstairs to try in my big system which has B&W 683 speakers and the Mac MC275 amp. I first played the Mac MC275 with my Cary SLP 03 preamp (another Audiogon buy) to remember the sound of the amp. I then swapped in the VTA ST-120 but bypassed the preamp and used just the stepped attenuator for volume control. It immediately sounded different and the difference was in wider soundstaging. The sound was more "holographic" on the VTA ST-120. The 120 also had a cleaner and more extended top end. It made my Mac sound kind of "dull" by comparison. Maybe the bypassing of the preamp gives the VTA amp an advantage? The gain of the amps was very similar and the ST-120 at its rated 60 WPC sounded just as strong as the Mac's 75 WPC. Later the next day, I had an audio friend come over and listen. He brought over some his vocal jazz SACD's. He was also amazed that the little VTA ST-120 sounded as good as it did considering that Mac costs about 3 to 4 times the price of the 120. He also agreed that the top end was better on the 120. Now I am in a quandry? I don't know now whether to keep the MC275 in my main system or replace it with VTA ST-120 and bring the Mac downstairs? For the meantime I am going to keep the 120 in my main system and let it break in completely. I will also try the ST-120 through the Cary preamp when I have the time. Bob mentioned that if I turn the attenuator all the way clockwise there is no attenuation and the audio signal passes from the input jacks directly to the input circuit. In a month or two I will have to bring one of them downstairs. DrewK
On Saturday I started the assembly and found the manual to be very well written with good detail. The two photos that Bob sends along were really helpful too. Step by step the amp just came together. The only minor problem I had was the assembly of the supplementary cap module. Nothing wrong with the instructions, it just seemed a little tedious try to hold the cap with one hand and solder with the other. I put in about 6 hours on Saturday and another 6 or 7 hours on Sunday. By Sunday night I was done. I placed the three driver tubes in the amp and connected my old KLH 6 speakers and my CD player to the inputs. Flipped the switch on the amp and all the driver tubes lit up. Shut the amp down and placed the two left channel Genalex Gold Lion KT88's that I had bought separately and an old Stromberg Carlson 5AR4 rectifier that I had laying in a box of tubes. Everything lit up and I biased the left channel. I walked over to the left speaker and put my ear to the grille cloth and heard a barely audible hiss. A foot away from the speaker I could hear nothing. Shut the amp off. I inserted the right KT88's turned the amp on and biased the right channel. No blown fuses, no noise, nothing. Turned the Oppo CD player on with one of my Steely Dan SACD's. Out of the silence came Steely Dan sounding MUCH better than what I got with the old Pioneer receiver and through 40+ year KLH old speakers.
The next weekend I brought the amp upstairs to try in my big system which has B&W 683 speakers and the Mac MC275 amp. I first played the Mac MC275 with my Cary SLP 03 preamp (another Audiogon buy) to remember the sound of the amp. I then swapped in the VTA ST-120 but bypassed the preamp and used just the stepped attenuator for volume control. It immediately sounded different and the difference was in wider soundstaging. The sound was more "holographic" on the VTA ST-120. The 120 also had a cleaner and more extended top end. It made my Mac sound kind of "dull" by comparison. Maybe the bypassing of the preamp gives the VTA amp an advantage? The gain of the amps was very similar and the ST-120 at its rated 60 WPC sounded just as strong as the Mac's 75 WPC. Later the next day, I had an audio friend come over and listen. He brought over some his vocal jazz SACD's. He was also amazed that the little VTA ST-120 sounded as good as it did considering that Mac costs about 3 to 4 times the price of the 120. He also agreed that the top end was better on the 120. Now I am in a quandry? I don't know now whether to keep the MC275 in my main system or replace it with VTA ST-120 and bring the Mac downstairs? For the meantime I am going to keep the 120 in my main system and let it break in completely. I will also try the ST-120 through the Cary preamp when I have the time. Bob mentioned that if I turn the attenuator all the way clockwise there is no attenuation and the audio signal passes from the input jacks directly to the input circuit. In a month or two I will have to bring one of them downstairs. DrewK
