systemtruck
Well-known member
Just posting there that I’ve built an RCA BA-2 and an original Putnam 610, and have done some preliminary testing just on voice. I also set up my “new” UA Solo 610 so that this was a 3 way shoot out. My personal goal is/was to meet or beat my own Solo 610 with a new build that i could make 8-12 units of and turn it into a console. Originally i was going to use the BC-3/BC-6 type segments, such as the preamps and booster amps and line amps, etc, but the more i learned about the sounds of single ended and of no-NFB, I ended up being recommended by @emrr to check out the BA-2. I also have the parts to build a Gates SA-134 soon, which is single ended but does have a (seemingly) small amount of NFB which i plan to experiment with eliminating.
But for now, comparing the old Putnam 610 (as reverse engineered by John Hinson), the new Solo 610, and the RCA BA-2…
I’ll take the BA-2 as the winner here.
It is pretty close though, they’re all wonderful sounding. All 3 of these are VERY nice preamps and fit the character of dark and warm and wooly, a very vintage and vibey sound. But there is something more “magical” and present about the BA-2. It has that classic vibrational character that sounds like an old radio voice yet still is full fidelity. And as impossible as this sounds, the BA-2 is wide open and natural but also perfectly compressed. As @emrr has mentioned before, the BA-2 forms its own limiting when you hit it hard. I could hear some of this just testing on voice and it is really awesome, and I can only imagine how much more rich it will sound once I’m sending electric guitars and drums into it.
For both of these builds, the input transformer is the Cinemag CMQEE-3440-A, and the output transformer is the Cinemag CM-27101 with the standard gapping that they offer for that one. I’m looking forward to utilizing the other two input options on the 3440, as right now I’m just using the 150 ohms. There is also the 37.5R, and the 600R. I do have some ribbons with ultra low output impedance options on its own transformer, so im looking forward to hooking that up to 37.5 and seeing how much more gain there is. As it stands now though, the 150 input provides just enough gain for the BA-2 to do vocals at good levels going into a standard audio interface. Surely with any louder sources the BA-2 would need to be turned down. The Putnam 610 is louder for sure, and is so similar to the level of the Solo 610 that one would have to do a proper sound source test setup to compare. The BA-2 hovers below them, many 10 dB under them.
Unrelated to the RCA world… I’m very curious about who out there has actually used an original Putnam 610, and maybe even compared it to the new Solo 610. Since I’m using very similar iron to the new Solo 610 ( i believe that Cinemag provided UA with their 27101 during some stretch of new wave of 610 development and maybe even production, and i think maybe the 3440), my Putnam 610 and Solo 610 sound quite similar. I wouldn’t yet say one is better than the other, and I didn’t build the EQ section of the circuit at all, so perhaps the “off” setting of the EQ section imparts just a slight amount of treble and/or bass differences itself so all of this is not perfectly representative of an original Putnam 610 in the ‘flat’ position. But already they are very very close in timbre. I’m really splitting hairs with his point so it’s probably moot.
Also, my Putnam 610 build is just slightly noisier than the Solo 610 and BA-2. But the noise might be something I’m causing with my regulated test supply setup, since it sounds like a faint higher buzz that we associate with an mild grounding issue and not like a mains related or rectifier related hum. It’s a very very quiet buzz and you can only hear it when you crank the headphones during silence. So i can probably work that buzz out of it. Even with vocals you could probably ignore it. However, i used the same test power for the BA-2 which doesn’t have this noise.
This BA-2 build is already very quiet. I’m guessing that once a permanent power situation is hooked up it would beat the Solo 610’s noise performance too.
So there we have it. 3 terrific preamps so far, but the BA-2 has noticeable character that the 610’s don’t quite have. The 610 design implements multiple stages of NFB and uses noval tubes, and the BA-2 has zero NFB and uses octal tubes. Not that the 610’s sound pinched or forced because they really don’t and the amazing sound of the Solo 610 is what sent me on this mission to begin with, but the BA-2 simply is more natural and open and rich and beats both of them in my book.
I’ll update again when i have the Gates SA-134 built. Some day soon i will do a real recorded comparison of all 4 of them. That is when I’ll also make the call on the console build. I’m guessing at this point that it will be 12 BA-2 channels and the Gates SA-134 pair as master channels even though i haven’t even heard them yet. But i also recently discovered the RCA 86-A / 96-A which can be built with modern iron and offers some compression which would be convenient on the master section.
But for now, comparing the old Putnam 610 (as reverse engineered by John Hinson), the new Solo 610, and the RCA BA-2…
I’ll take the BA-2 as the winner here.
It is pretty close though, they’re all wonderful sounding. All 3 of these are VERY nice preamps and fit the character of dark and warm and wooly, a very vintage and vibey sound. But there is something more “magical” and present about the BA-2. It has that classic vibrational character that sounds like an old radio voice yet still is full fidelity. And as impossible as this sounds, the BA-2 is wide open and natural but also perfectly compressed. As @emrr has mentioned before, the BA-2 forms its own limiting when you hit it hard. I could hear some of this just testing on voice and it is really awesome, and I can only imagine how much more rich it will sound once I’m sending electric guitars and drums into it.
For both of these builds, the input transformer is the Cinemag CMQEE-3440-A, and the output transformer is the Cinemag CM-27101 with the standard gapping that they offer for that one. I’m looking forward to utilizing the other two input options on the 3440, as right now I’m just using the 150 ohms. There is also the 37.5R, and the 600R. I do have some ribbons with ultra low output impedance options on its own transformer, so im looking forward to hooking that up to 37.5 and seeing how much more gain there is. As it stands now though, the 150 input provides just enough gain for the BA-2 to do vocals at good levels going into a standard audio interface. Surely with any louder sources the BA-2 would need to be turned down. The Putnam 610 is louder for sure, and is so similar to the level of the Solo 610 that one would have to do a proper sound source test setup to compare. The BA-2 hovers below them, many 10 dB under them.
Unrelated to the RCA world… I’m very curious about who out there has actually used an original Putnam 610, and maybe even compared it to the new Solo 610. Since I’m using very similar iron to the new Solo 610 ( i believe that Cinemag provided UA with their 27101 during some stretch of new wave of 610 development and maybe even production, and i think maybe the 3440), my Putnam 610 and Solo 610 sound quite similar. I wouldn’t yet say one is better than the other, and I didn’t build the EQ section of the circuit at all, so perhaps the “off” setting of the EQ section imparts just a slight amount of treble and/or bass differences itself so all of this is not perfectly representative of an original Putnam 610 in the ‘flat’ position. But already they are very very close in timbre. I’m really splitting hairs with his point so it’s probably moot.
Also, my Putnam 610 build is just slightly noisier than the Solo 610 and BA-2. But the noise might be something I’m causing with my regulated test supply setup, since it sounds like a faint higher buzz that we associate with an mild grounding issue and not like a mains related or rectifier related hum. It’s a very very quiet buzz and you can only hear it when you crank the headphones during silence. So i can probably work that buzz out of it. Even with vocals you could probably ignore it. However, i used the same test power for the BA-2 which doesn’t have this noise.
This BA-2 build is already very quiet. I’m guessing that once a permanent power situation is hooked up it would beat the Solo 610’s noise performance too.
So there we have it. 3 terrific preamps so far, but the BA-2 has noticeable character that the 610’s don’t quite have. The 610 design implements multiple stages of NFB and uses noval tubes, and the BA-2 has zero NFB and uses octal tubes. Not that the 610’s sound pinched or forced because they really don’t and the amazing sound of the Solo 610 is what sent me on this mission to begin with, but the BA-2 simply is more natural and open and rich and beats both of them in my book.
I’ll update again when i have the Gates SA-134 built. Some day soon i will do a real recorded comparison of all 4 of them. That is when I’ll also make the call on the console build. I’m guessing at this point that it will be 12 BA-2 channels and the Gates SA-134 pair as master channels even though i haven’t even heard them yet. But i also recently discovered the RCA 86-A / 96-A which can be built with modern iron and offers some compression which would be convenient on the master section.
