Beefing up a SimpleSE Power Supply

[tunertom]

Hi Folks - I'm building SSE and TSE amps to biamp my speakers.

The SimpleSE will use Tungsol 6550s and Hammond 1628SEA OPTs to put out some ka-wump to drive the woofers. The TubelabSE will use 45's and cheapy edcor OPTs to handle frequencies above 1800Hz.

I have a 400-0-400 200ma PT for the SSE and will use all off-board 440vac motor run caps, and a couple of triad C-14x chokes to drop the voltage a bit. PSUD says I should end up with about 468volts with a CLCLC arrangement. I'll add CL80/CL90s to protect the 5AR4 during startup.

I've been reading Morgan Jones and trying to understand what demands a SE output tube puts on the power supply as it plays music.

It's not clear in my head whether it makes much difference to dynamics and channel separation to add more capacitance across the final stage of a SE amp since the tubes are pulling about the same current whether at idle or playing music.

In the interest of maximizing the dynamics and channel separation, I am thinking of separating the power supply after the initial CLC and giving each channel it's own final choke and cap (perhaps 200uF or so for each 6550). The 12AT7 CCS's could have their own final choke and cap. This adds under maybe $80 to the project using Triad chokes and ebay motor runs. (Yes, I know I might need to cut a trace on the PCB here and there and pay close attention to my wiring and grounds...)

So my question is: more capacitance and isolation the merrier, or is this a noobie's waste of time?!?

Another noobie question: I need to save space on one of the amps for a volume control to balance the woofers and tweeters. The tweeters are about 3dB more sensitive than the woofers. Obviously the 6550/1628SEA SSE amp running UL and CFB is going to outpower the 45 TSE, but doesn't the input sensitivity/gain (rather than power wattage) of each amp determine which one will need the volume control? I'm fuzzy on this. Anybody have any insight for me?

Many thanks to George and all the wonderful contributors on this forum!!

Tom

[tubelab.com]

So my question is: more capacitance and isolation the merrier, or is this a noobie's waste of time?!?

More capacitance beyond a 200 uF or so won't help if they are all electrolytics. In fact too many electrolytics can cause problems. No capacitor is perfect, and each type has its deficiencies. Electrolytics do a great job storing energy, but they can't release it all quickly (ESR and ESL) and some gets lost in the dielectric (dielectric absorption and DF). A small film cam can't store much energy but it responds quickly. Each type may also have inherent resonances and other issues. Some builders attempt to install several types of capacitors in parallel to "get everything". This shotgun approach often works, but it is possible that a random combination of capacitors can have a resonance in or just above the audio band leading to really ugly sound. The trick that works well with the Simple SE is to use the 47 uF electrolytic that is on the board for the first cap. Then use the 120 uF electrolytic that is on board for the second cap AND a polypropelyne motor run cap in parallel for the second cap. The motor run cap is a film cap that complements the elertrolytic well and improves the dynamics. Some builders omit the second electrolytic using only the film cap with good results. I haven't tried this. One builder succesfully built a Simple SE without any electrolytics at all. Search these forums.

I have a 400-0-400 200ma PT for the SSE

A 400-0-400 volt transformer will result in a rather high B+ voltage. I tried an Antek 4T400 on mine and got over 500 volts. This would require using higher than 500 volt caps in the power supply. I haven't found any 630 volt electrolytics that will fit the PC board. If you try this you will probably need to use off board capacitors and reduce the value of the first cap to far less than 47 uF to avoid blowing the 5AR4. If you run 500 volts of B+ use 63 volt caps for the cathode bypass caps on the output tubes. You will need to increast the cathode resistors to avoid overdissipation in the output tubes, and you will be near 50 volts on the cathodes.

I am thinking of separating the power supply after the initial CLC and giving each channel it's own final choke and cap...The 12AT7 CCS's could have their own final choke and cap.

There is no reason to isolate the 12AT7 supply since the CCS chips provide more isolation than you can get from caps and chokes. Isolating the supplies to each output tubes may provide some benefit. It can be done without modification to the PC board. Build the board as per instructions (sxcept for higher voltage caps as required. Wire the board for using a suplemental motor run cap. Run one wire from each additional choke to the positive terminal on the supplemental cap. Run the other wire from each choke to the positive terminal of each isolation cap. Connect the negative terminals of each cap to the same ground terminal on the PC board as the supplemental cap. Connect the red wire from each OPT to its respective isolation cap.

Obviously the 6550/1628SEA SSE amp running UL and CFB is going to outpower the 45 TSE, but doesn't the input sensitivity/gain (rather than power wattage) of each amp determine which one will need the volume control?

Yes. The Simple SE is a bit more sensitive than the Tubelab SE. When I wired the two together I needed the volume control on the Simple SE (set at about half throttle). I assume that you will be using an active crossover of some sort. It should have level controls.

[tunertom]

George - thanks for your help!

[Ty_Bower]

Originally Posted by tunertom

The SimpleSE will... put out some ka-wump to drive the woofers.

If you want ka-wump, you might want to consider foregoing the vacuum rectifier and go with the solid state Fairchild ISL9R8120P2 diode. And as George noted, your high voltage secondary winding is going to give an awful lot of B+. I'd think you'll be happier if you had something closer to a 320-0-320, especially if you go with SS rectification.