It is not used as preamp. It is used to replace an opamp output stage in a DAC so without volume control directly to a CS43198 DAC chip (that is as usual 2V rms capable) that officially requires a symmetric output stage for best performance.
DAC chips of the last 4 decades are 2V rms capable so every possible device/opamp stage/tube stage connected should be able to cope with 2V rms and for sure those without volume control at their inputs. The DAC output circuits are adjusted to a standardized 2V rms output level by means of feedback/design etc.
But in this case the non-global feedback output stage can output at least a maximum of 15V rms. Probably more in practice. It is implemented at random. That is where attention should go to as it may be detrimental to anything adhering to normal standards. This misunderstanding happens quite often and such constructions usually have too high gain and way higher output levels than normal which results in best sonical results according those that do so. The cause is the word “TUBE” flashing in neon and not “calculate and then implement”.
DAC chips of the last 4 decades are 2V rms capable so every possible device/opamp stage/tube stage connected should be able to cope with 2V rms and for sure those without volume control at their inputs. The DAC output circuits are adjusted to a standardized 2V rms output level by means of feedback/design etc.
But in this case the non-global feedback output stage can output at least a maximum of 15V rms. Probably more in practice. It is implemented at random. That is where attention should go to as it may be detrimental to anything adhering to normal standards. This misunderstanding happens quite often and such constructions usually have too high gain and way higher output levels than normal which results in best sonical results according those that do so. The cause is the word “TUBE” flashing in neon and not “calculate and then implement”.
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Even the original schematic can handle the CS43198 DAC chip output of up to 2V RMS, without going into grid current. That was may point. Is it the best schematic for the job? I don't think so. Does it work? Yes.
As expected, not pretty. Current through output triodes reaching zero with 1V RMS input, 1khz, 5.8 mW onto 600 ohm load.
But then it will be a preamp turned to multifunctional output stage/HPA. Likely a jack of all trades but master at none. It will work in a way though 🙂 Many things work. A laundry dryer also can work to dry peoples hair in a way.
Also for use as HPA volume control seems mandatory.
It seems a choice must be made to use it either as preamp with fixed gain turned to output stage or as preamp with fixed gain turned to HPA with volume control and not both.
Also for use as HPA volume control seems mandatory.
It seems a choice must be made to use it either as preamp with fixed gain turned to output stage or as preamp with fixed gain turned to HPA with volume control and not both.
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I'd say that, taking into account the DAC output capabilities, a proper HPA could be also used as pre-amp.
But yes, circuits designed for a specific purpose will always perform better.
But yes, circuits designed for a specific purpose will always perform better.
Guys I'm not insisting on this pre being able to drive headphones. I love it's sonics on the double CS43198 DAC and it sounds much better than anything I bought or tried so far. Wiim Ultra isn't remotely in the same league. Same goes for SMSL DL200 with Sparkos SS2590 output stage which is a stepp above Wiim Ultra but still not nearly as analog sounding and real.
Would have been nice if I could just plug my Sennheisers into it but it's not a big deal since I rarely listen to headphones.
My amp is not in its final housing yet and has quite some hum when wide open on its input but it's much better when its volume pot is on low. I thought I could give the pre more gain to minimize the hum issue until I get to work on the amp again.
Once I solve the hum issue I'm sure it will work out fine on my amp/speaker setup.
I actually bought two of the Cary SLP 90 clone boards to be able to test a balanced configuration into my various D-Amps skipping any opamps.
Klaus
Would have been nice if I could just plug my Sennheisers into it but it's not a big deal since I rarely listen to headphones.
My amp is not in its final housing yet and has quite some hum when wide open on its input but it's much better when its volume pot is on low. I thought I could give the pre more gain to minimize the hum issue until I get to work on the amp again.
Once I solve the hum issue I'm sure it will work out fine on my amp/speaker setup.
I actually bought two of the Cary SLP 90 clone boards to be able to test a balanced configuration into my various D-Amps skipping any opamps.
Klaus
Sometimes that heater coupling to the grid of the first stage or running the heater on AC - try a battery as a test just for that one. You can always make the pot 10K log. Keep the first stage and the input cables away from magnetic fields of the mains transformers. If you want more gain just bypass the first cathode resistor. with a smaller resistor and cap in series. The pre-amp might be good enough into headphones if you increase the output cap a bit currently you have a 40Hz rolloff so maybe 22uF
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Classic. The too high gain amplifies everything too much so also hum and hiss.
If everybody keeps calling it a pre things don’t get much clearer. I think you mean the DACs output stage.
With even more gain things will not improve. As said earlier: with a wire all this would likely not occur. There is no gain at all needed in fact. The device is inserted because of its desired sonical manipulation with insufficient care for right specifications. IMHO you need a buffer so no gain. Or a wire.
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