Before pushing the project over the side, better find out what the source will be,
During the socalled 'Golden Age' of toob audio power amps were usually built to deliver full output from a One Volt Source.
But people don't use those kinds of things now, lets find out what the source will be. That should be a good indicator
of where this will or could go. 😀
During the socalled 'Golden Age' of toob audio power amps were usually built to deliver full output from a One Volt Source.
But people don't use those kinds of things now, lets find out what the source will be. That should be a good indicator
of where this will or could go. 😀
45: My speakers are of very high sensitivity, at 104 DB/W/M, and my source is normally a DAC of the usual 2 volt output. This thread has been useful to me as someone unfamiliar with push pull circuits, and especially with respect to the information on the use of input and other transformers as gain and phase splitters. Thanks for your contribution. I was hoping for a two stage amp, which is what I usually shoot for in my single ended amps, that has a DHT front end. Perhaps making it a three stage would be okay too. It would certainly make it easier. John’s most recent schematics in this thread seem to fit the bill by using two DHTs in the first stage. All of it is new territory for me, and it seems that new ideas and opinions keep popping up. Thanks for yours!
Yes decide what you want. However the more conditions, the less choices and/or trade-offs.
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I run my SE 2a3 amp straight from my DAC. 10Y driver stage, just 2 stage with a 1:4 step up in front.
My speakers are about 88db sensitive. Yours are much more. Why don't you just go SE?
Because I never draw schematics for fun. I find it boring, honestly. I am also lazy! I barely do it by hand for myself when I decide to do it. My boss at work also complains that I never take notes at meetings and I always reply I don't need them. I remember everything. Why waste my time?😛
Right now, I am going to watch some TV instead of drawing a schematic.🙂
I don't think that 12AY7 + 49 is something you will EVER find in the net or in ANY magazine. The only place where you might find something about the 49 is Ale's blog (bartola.co.uk) because I "introduced it" to him and he immediately curve-traced one used tube to build a Spice model. We are good friends. Otherwise, I have never seen one. You show me if you have.
Adding one DC coupled stage to what you have done so far, Sun-Audio style, is nothing complicated. Why don't you do it?
One more anode resistor, one more bypassed cathode resistor and one more triode per branch of the differential. Only difference respect to 49 alone is that the input 12AY7 takes 90-100V of supply (and can use very high anode resistor or higher anode current than usual) so the next DC coupled stage with 49 will have 300V "only". At 20V bias +140V anode voltage for 7 mA anode current it means that you can use 20K anode resistor. With 220K next stage it's 18K load. It's an anode load that is still more than 5 times the plate resistance.
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I have one from the 1960s, and built a stage at 150V; it seemed too microphonic, even with soft mountings. I don't think they are worth £30 (€35).
I have used the LP2/CV1166 in my filament bias line amp for five years now and in my humble opinion it is a very good sounding valve. What first caught my attention with this valve was the high amplification factor for a DHT (15) combined with a comparatively low Rp (4 KOhm). When I first put them in they were very microphonic. They soon quietened down however and nowadays I can’t hear any microphonic artefacts at all. Highly recommended, even at 30 GBP.
I have mostly gone SE in the past, and it has been my preference so far, but I have a pair of push-pull, Menno van der Veen designed, Plitron toroidal output transformers that I would like to put to use. I may end up going for a more conventional IDHT front end into DHT power tubes, but I thought it would be interesting to explore a DHT front end into push-pull triode connected pentodes. I want to use the Plitron output transformers because they are supposed to be very good. I'm in the midst of building a 45/46 single ended amp with a EL84 front end based on the Thorsten Loesch Legacy 300B amp, albeit with a choke input power supply, so I do continue to build single ended amps.
@tizman, if you want 2 stages only then there is not much choice for a PP amp with one DHT gain stage. One gain stage is enough only if it doesn't have to swing much voltage because of its limited gain. So I would settle for lower output power (5-10W) and use the EL84 (or similar) in place of the EL34 (and similar). If is not enough, then look at step-up input transformer making sure you DAC can drive it. I would consider it in such order.
Your Plitron has the right specs for the EL84 except is oversized but this is not a problem or a compromise except for weight.
Your Plitron has the right specs for the EL84 except is oversized but this is not a problem or a compromise except for weight.
If yours is usable in a line stage, I imagine it's constructed very differently from the sample I have.
If it's a CV1166, is there some other letters on the marking? Is it ST-shape?
My CV1166 was unused (NOS), but the microphony is too bad, even for a driver; a linestage would be impossible. I'll take a picture when I get a chance.
Maybe I missed it, but does anyone know of a transformer solution that combines a step-up like the Hammond 1140-LN-C (1:4 step-up or similar) with a phase inverter? I guess it would be called a 1: 4 + 4 or something?
If not, @45 is suggesting that a configuration that uses a Hammond 1140-LN-C at the input, a pair of DHTs in a phase inverter stage and a pair of easy to drive output tubes (like EL84s) would be a feasible alternative.
@Rod Coleman seems to imply that microphonics are sometimes not as problematic when the tube is used as a driver. Would a pair of tubes used in a phase inverter stage be considered as drivers if the input stage is a step up transformer?
If not, @45 is suggesting that a configuration that uses a Hammond 1140-LN-C at the input, a pair of DHTs in a phase inverter stage and a pair of easy to drive output tubes (like EL84s) would be a feasible alternative.
@Rod Coleman seems to imply that microphonics are sometimes not as problematic when the tube is used as a driver. Would a pair of tubes used in a phase inverter stage be considered as drivers if the input stage is a step up transformer?
The noise signal from the microphonic susceptibility is always the same, for a given mechanical knock, or vibration. But the music signal is much smaller, in a tube used for a line stage, so the effect is more noticeable than a driver stage, where the music signal is larger.
The microphonic noise might still be a problem, if the tube has very bad microphony; or if the loudspeakers are very sensitive.
If the first stage of the amplifier has a step-up, the tubes can be thought of as drivers, if the phase inverter is the last stage before the power tubes, yes.
Or . . . showing my ignorance here . . . many vintage amps use pentode / triode tubes such as the 7199 / 6U8 / 6GH8 etc as phase inverters.
Would there be any possible advantage to using a DHP and DHT in combination for phase inversion duty?
Would there be any possible advantage to using a DHP and DHT in combination for phase inversion duty?
I mentioned this in post # 92. The secondary of any transformer can be a phase splitter as they ALL have two wires for the two phases. You are thinking split windings with two wires tied together to form a center tap. But that's not necessary if you use two loading resistors (also acting as grid leak resistors), matching the secondary impedance, to form a virtual center tap and tie to ground and you have yourself a phase splitter.
Here's an example and look at the way Jensen does it:
https://www.jensen-transformers.com/wp-content/uploads/2014/08/as088.pdf
Thanks. So the Hammond 1140-LN-C could be wired the same way to provide both a 1:4 step up and phase inversion. Then a pair of DHT tubes that have additional gain and are not microphonic enough to cause problems.
If the output tubes require more drive than common DHTs can provide, would it be feasible to use DHPs that have more gain? If the output tubes are common pentodes then some NFB will be necessary, of course. So, depending on the FB method, it seems like the increased gain of a DHP might be advantageous.
Or is there a flaw(s) in my reasoning? I am definitely not a designer.
The 1140-LN-C version in step-up mode will have 2.2K input impedance and miller capacitance of the DHT stage multiplied by 16. If the DAC can drive that without issues, fine. Otherwise such step-up is not a good idea.
I would personally go for the 1140-LN-A which is 1:1.41 step up and 10K impedance. The EL84 at 300V and 8K plate-to-plate will require some 20V rms grid-to-grid. So DHTs with mu around 8-10 can be used.
You can use DHP's for more gain (as pentodes, as triodes they generally have gain around 5-10, at least those that I know). I would look at all glass types for sure.
I would personally go for the 1140-LN-A which is 1:1.41 step up and 10K impedance. The EL84 at 300V and 8K plate-to-plate will require some 20V rms grid-to-grid. So DHTs with mu around 8-10 can be used.
You can use DHP's for more gain (as pentodes, as triodes they generally have gain around 5-10, at least those that I know). I would look at all glass types for sure.
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I appreciate all the answers / clarification. Apologies to @tizman if I've gone off on a tangent. He is the one who will likely be building something like this relatively soon. I'm interested, but I won't be able to jump on it in the near term.
Are the drive requirements you mention for triode or pentode? He seems to be interested in running PP EL84s in triode. I was the one who mentioned pentode as I was thinking the increased power output might be nice to have.
As for the impedance match between DAC and the step-up, I'm using Loxjie D30 DACs (the first version without MQA) in my main systems. I assume it's output impedance is similar to the newest version, whose RCA outputs have an impedance of 100 ohms.
In my breadboard setup I'm streaming to an old Apple Airport Express and running analog outputs from it. Output impedance? I don't know but it sounds fine. I use these in a variety of systems. My computer streams to them via Wi-Fi at CD quality. They have a built in DAC that outputs analog or they can also output digital via optical to an external DAC, like the Loxjie.
I'm afraid I'm not well versed in the affect of Miller capacitance.