DIY Audio Projects Forum

HI.

Sorry, wrong guess.

I know many are using lithium batteries in thier tube biasing. But I tied it in my phonostage tube bias, it sounds sterile & flat. I even tried a sand diode in series with a lithium battery (1.5V) to give the required 2.3V cathode bias. But it sound even worse.

So guess again what battery have I finally settled down with to give me rich & musical sound I love?

c-J

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"If the facts don't fit the theory, change the facts" quoted Albert Einstein.

A 1.2Gw Flux capacitor taken straight from the doc's DeLorean? Then just put your amp in the back of your car, drive at 88mph and poof you'll have perfect crystal clear sound

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that reminds me!

I'll have to try using Mr. Fusion for my next power supply! It will be awesome, and I can finally get rid of those old bananna peels and other trash I've been saving for it!

Right this is getting seriously off topic so sorry but anyway:

Sorry Rock4016 but your idea has already been taken



He clearly has made this GM70 triode amplifier and he uses a flux capacitor to power it, If the doc does it then...



Lewis

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ROFLMAO

I say Duracell!!!

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Stephen

Not to get back on topic, but, how is the GM70 amp going?

All parts are in, all stages are designed, and assembly has begun but it will be slow going. I'm hoping I'll have sound (or at least smoke) in 2 or 3 weeks.

I need to take my time on this and I'm adding some safety features just in case the tranny's fail. I'd prefer not to blow up my speakers or start a fire if they do.

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Stephen

I ran across this and wondered if anybody has ever tried it. The point is to reduce the voltage stress on the OT, especially from primary to secondary to reduce the possibility of the OT primary arcing to the secondary from the very high voltages used by the power tubes, in this case the GM70.



I only looked at it briefly but see no obvious reason it wouldn't work. It would limit the max voltage to ground to about half that of a single ended supply.

Any thoughts? Anybody ever try this? Ignore the component values and the transformer impedances, just look at the power supply. It looks like the same principle could be applied to an SIPP output stage using a CCS like the Oddwatt. I'm working on the circuit modifications and will post them once they're done. I really want to get my GM70 amp finished, but I keep finding new ideas for better circuit topologies. Thanks to everyone who has commented. The help I've received has been indispensible.

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Stephen

I couldn't find this thread earlier (it's been awhile since I worked on this) and posted a new topic "Split Supply for PP Amp" (merged and is now above this post - GM) i. Please ignore that one and use this example instead.

This GM70 thread won't die until I succeed or fail at building a push-pull GM70 stereo amp.

I have a new power scheme I ran across and I have drawn out my latest schematic for comments/criticism. Here's the latest:



I found someone who claims to have bread boarded a similar design that works. His didn't have the CCS on the cathodes and also used a transformer phase splitter. I don't want an interstage tranny and would prefer capacitive coupling. The phase splitter is at the input of the my amp design - the input is split and feeds one inverting audio op-amp and a second non-inverting op amp, at least one of which has adjustable gain to allow balancing the positive and negative driver stage gains. The op-amps will have a split supply with input and output at ground potential and there will be NO coupling cap between the op-amp outs (an OPA134) and the driver tubes as shown in the schematic - those are gone. So the entire amp will have only one cap in the signal path, and can be driven to full power (hoping for 75 watts / channel) with a 1 volt peak-peak signal.

Has anyone built an amp using a split supply like this or does anyone see a problem with why it won't work? The idea here is to reduce the voltage between the OT primary and secondary. Buy using +/-500 instead of +1000 volts the maximum voltage between the primary and secondary of the OTs will be about half what it would be with a single ended PS. The chance of failure (arcing from primary to secondary is my concern) of the Edcor OT I bought should be radically lower and it the amp should be susceptible to fewer of the problems associated with high voltages. At least that's the theory.

I'm excited about this. If this works it solves the final remaining problem that concerned me greatly. I can't take credit for it though. I found the idea on another website. The heater supplies need to float, and although the output stage isn't self inverting and the amp uses a phase splitter, hopefully the CCS will have the same effect as it does in the Oddwatt to help linearize the operation and reduce the distortion.

Did I screw something up or does this look OK? It's actually quite a simple design. A split supply is easy to build and it also eliminates the grid bias supply since the tubes are self biasing. I just hope that the 25 ohm pot works as well on GM70s as it does on the KT88s in the Oddwatt to balance the tubes.

Oh yeah, the drivers might be either SRPP stages or pentodes, probably an SRPP but I just drew triodes for simplicity.

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Stephen

After sleeping on this idea it still looks good to me today.

The problem here is that the Edcor OT may not like a 1200 volt B+ (I'll be using higher voltages than shown on the schematic). That's a lot of voltage and a potential safety hazard. If the primary arced to the secondary it could put lethal voltages on the secondary, not to mention blow up your speaker. It looks like splitting the supply solves this problem. Now instead of a 1200 volt supply I'll have the equivalent of two 600 volt supplys and the maximum peak potential difference between the primary and secondary of the OTs will be reduced by 600 volts. Somebody please tell me I'm right and haven't made a mistake here.

Where's Suncalc? If you have time to comment on this Matt I'd greatly appreciate your opinion. (Outstanding job on the 300B design BTW - I'm truly jealous of you and Mark! Coolest thread going by far right now IMHO. Mark is not going to want to give up the amp though!).

Talk about luck, assuming this works - I thought I would need to buy a new power tranny, but I just realized my toroidal power tranny has two 120 volt colis. Putting those in series will reduce the voltages by half on the secondary coils, which there are also two of, so I have the perfect voltages for my split supply with the power tranny I already bought.

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Stephen