Tubelab Simple P-P

[tubelab.com]

From post 298, it appears very little is required to convert to PPP. See the left hand photo. Looks like one wire jumper is added, and one resistor is removed.

There are several ways to make a Simple P-P into a Simple PPP.

The easiest way is to build a fully functional Simple P-P and just wire the two channels in parallel, then use the 16 ohm taps (paralleled) with an 8 ohm load. THis method uses two OPT's per channel which only makes sense if you already have the OPT's.

Another way is to wire the two channels in parallel but use one OPT per board. This requires one OPT of half the impedance and twice the power rating. For EL84's this would be a 3300 to 4000 ohm OPT rated for 30 to 50 watts. With 6CW5's this would be a 1500 ohm OPT which may be hard to find. I am using a 6600 ohm OPT with my 8 ohm speakers connected to the 16 ohm tap. This reflects a 3300 ohm load to the EL84's.

Both of these methods use a seperate driver and phase splitter for each amp. In theory the two front ends could be mismatched leading to some "detail smearing". So, it is possible to use one input secion to drive both power amps through seperate phase splitters (thats how the amp in the picture is wired).

It is also possible to use one input section to drive the two power amps through a common phase splitter. Just lift the ends of the coupling caps for one channel closest to the front edge of the board and run jumper wires to the corresponding caps in the other channel. The unused tube can be left in place for looks, or removed.

I have tried all 4 methods and I think one of the last two methods sound the best. I am not sure which of the two works best. They are very close.


I have one more day of chasing grandkids, or letting them chase me, then T
they leave. I will start the long drive home Thursday or Friday.

[Moko]

Hi I have been following this thread for a while now and would really like to build a simple P-P but I have a few questions.

1. Can you buy a board & the parts to complete it yet? If so how much would the kit be with shipping to the UK?

2. The Edcor transformers look a really good deal, does anyone know where you can buy them in Europe? Failing that how much would shipping etc. be to the UK?

3. Another question again for any UK builders do they have any suggestions for some good local Mains & Output transformers?

Thank you in advance for any info you may have.

[bigjppop]

I must admit, I would have thought there would have been a little more "action" on the Simple PP threads recently but this one hasn't seen much in the last 8 months; any new builders out there? Any of you original builders have any "long term" reviews you want to post on this amp? I'd love to hear some more thoughts/experiences/debate on this project.

[rknize]

George was saying that the PCBs haven't been selling as well as he expected. Mine is in my shop and is usually on while I'm in there. The only issue with it is R1, which is dissipating more than it ought to. I have a choke to go there anyway, so it's no biggie.

[neonthecat]

Originally Posted by bigjppop

......cut...... Any of you original builders have any "long term" reviews you want to post on this amp? I'd love to hear some more thoughts/experiences/debate on this project.

Well, yeah, my SP-P has been running flawlessly, almost everyday now for nearly a year. It worked perfectly the minute I first turned it on. It sounds very, very good. I found it does not need ultra sensitive speakers to play loudly (enough) for me. It seems to output more watts than George claims it was designed to. As a matter of fact, it seems to have more dynamic "punch" than my Millett DCPP, although the Millett offers somewhat more detail to my ears.

The only thing that was an issue, was the mild red-plating of the Electro-Harmonix EL84's I first used. SP-P builder and beta tester, Russ, discovered this early on. I subbed JJ EL84 and Russian (Reflector) Military-issue equivalents, and they all worked without red-plate distress. Later on I installed a different Edcor power xfmr, that lowered the B+ by 30-40 volts. The EH tubes no longer red-plated at this lower voltage. I could detect no differences in the sound quality with the lower B+.
Don't know what the problem is with the EH tubes. They look almost identical inside to the Reflector mil-spec Russians.

The larger wattage resistors on the board do seem to get pretty hot. I ended up mounting a very small (and silent) fan to the bottom chassis plate, just to be safe. It blows upward on the board. The amp has played for over 12 hours at a time, and now the case and xfmrs are always cool to the touch.

A great design that's ridiculously easy to build, and gives results that probably exceed many commercially built products.

[Ian444]

I feel it is a very good amp that is overlooked. Some people seem to build it and go into some sort of audio nirvana...and don't report back much. I guess if you are a happy camper, then there is no need to report back It has the most detail of my 3 amps, the other 2 use 6V6, but have had other output tubes 6L6, EL34, the other amp originally had 6P1P (6AQ5). I would not hesitate to recommend the SPP to anyone for 2 simple reasons, (1) it is an easy build (2) it sounds fantastic, very quiet, excellent detail. I believe that George has a real talent not only for tube circuits but also a major talent in PCB layout to create an amp that is vey quiet. The stereo seperation is also very good, much better than my other amps. As someone else said recently, something like, a modest circuit that can produce scary sounds. It does do that. Scary in that, is that sound coming from outside the house or from the speakers? I'm talking real life sounds like a car horn, birds, a dog barking, like on old Pink Floyd perhaps. That happened to me a lot in the early days with this amp.

My other 2 amps, I tried to make them sound as good as the SPP. In one I tried at least 6 different topologies and in the other I can't remember, but it went through many stages. I never succeeded, but I learnt a lot. Both of those amps I like a lot, they have their own character, but they have a lot of parts in them, CCS's, mosfet source followers, one has regulated screen voltages, four of them, one for each output tube... The SPP is still the cleanest most detailed amp of the three. I did do a small mod (LED bias) but I think that's just more for my taste in sound, it sounded really nice straight out of the box too. Just a wonderful amp IMO.

[bigjppop]

Glad to see a couple of the original builders chiming in. I am very close to ordering the parts for one of these, but one thing holds me back... I REALLY hate board mounted tube sockets. I have no issue with PCB designs, in fact I really like them; I just hate not having chassis mounted tube sockets. I know I probably won't, but I always feel like I'm going to break something when I'm rolling tubes into board mounted sockets. I know some people have wired chassis mounted sockets to a PCB, which I guess is an option, but that really makes it difficult to work on the board after its wired up. I'm tempted to try this point to point, but I've never done that and I'm a little afraid of messing up the layout and getting a noisy amp.

Decisions, decisions.

[neonthecat]

I'm not crazy about board-mounted sockets either, but I've swapped tubes in-n-out several times now and the SP-P board is no worse off. And, Ian makes a good point about the quietness of George's PCB designs. Both my SSE and the SP-P are totally hum, hiss and buzz free. I don't subscribe to the theory that P-T-P-wired stuff always sounds better. The only thing I really like about it is the ease of replacing parts. My first and only tubed P-T-P projects were a preamp and Cathode Follower amp designed by Bruce Rozenblit. They turned out okay, and I recommend them as first time P-T-P projects.

[rknize]

George's boards are good quality. As long as the PCB is properly mounted and the soldeing job is good, you don't need to worry. I haven't tube rolled the SPP much because I only have one set of output tubes that can handle the B+. I tube roll the SSE constantly and have never had a single problem with the sockets.

[chrisb]

Originally Posted by bigjppop

Glad to see a couple of the original builders chiming in. I am very close to ordering the parts for one of these, but one thing holds me back... I REALLY hate board mounted tube sockets. I have no issue with PCB designs, in fact I really like them; I just hate not having chassis mounted tube sockets. I know I probably won't, but I always feel like I'm going to break something when I'm rolling tubes into board mounted sockets. I know some people have wired chassis mounted sockets to a PCB, which I guess is an option, but that really makes it difficult to work on the board after its wired up. I'm tempted to try this point to point, but I've never done that and I'm a little afraid of messing up the layout and getting a noisy amp.

Decisions, decisions.

well then, use chassis mount sockets and short flying leads to the boards, and see if you could hear the difference - I'd bet that selected quality of certain caps or the tube types would have far more impact