Monkeyboi Posted October 16, 2020 Share Posted October 16, 2020 Okay, I've checked out the innards of this phono pre-amp. It's a very simple design that uses three 2SC945 NPN silicon transistors per channel running from a single ended 12v supply that uses no internal voltage regulation. The power input uses a 1N4007 diode for reverse voltage protection, one 220uF electrolytic + 100nF ceramic disc + one 1000uF capacitor as additional filtering over and above what the external power supply can offer. IMHO running this from a pure battery supply with the implication that a battery would be a superior power source would be like casting pearl before swine. No offence intended, it's just a fact of life in this case. Any half decent regulated linear 12v power supply would be more than ample. The current consumption would in my estimation be about 100mA absolute maximum, so the manufacturer's 500mA supply is more than adequate. If you really want to improve the sound of this phono pre-amp, forget about battery operation and change 4 of the coupling electrolytic capacitors in the signal path with Wima film capacitors. Cheers, Alan R. 1 Link to comment Share on other sites More sharing options...
Spider27 Posted October 16, 2020 Author Share Posted October 16, 2020 4 minutes ago, Monkeyboi said: Okay, I've checked out the innards of this phono pre-amp. It's a very simple design that uses three 2SC945 NPN silicon transistors per channel running from a single ended 12v supply that uses no internal voltage regulation. The power input uses a 1N4007 diode for reverse voltage protection, one 220uF electrolytic + 100nF ceramic disc + one 1000uF capacitor as additional filtering over and above what the external power supply can offer. IMHO running this from a pure battery supply with the implication that a battery would be a superior power source would be like casting pearl before swine. No offence intended, it's just a fact of life in this case. Any half decent regulated linear 12v power supply would be more than ample. The current consumption would in my estimation be about 100mA absolute maximum, so the manufacturer's 500mA supply is more than adequate. If you really want to improve the sound of this phono pre-amp, forget about battery operation and change 4 of the coupling electrolytic capacitors in the signal path with Wima film capacitors. Cheers, Alan R. Thank you again for the suggestion. My one must be modified one because it looks a bit different to stock one that you featured. Link to comment Share on other sites More sharing options...
Spider27 Posted October 16, 2020 Author Share Posted October 16, 2020 My board has 1uJ63 from WIMA (red ones) in 2 spots on 10U/50 and 2 spots on 4U7/50. And, no caps on 2 spots on 220U/16. Link to comment Share on other sites More sharing options...
Monkeyboi Posted October 16, 2020 Share Posted October 16, 2020 3 minutes ago, Spider27 said: Thank you again for the suggestion. My one must be modified one because it looks a bit different to stock one that you featured. Yes, your's has the 4 coupling capacitors replaces with film capacitors, albeit with different capacitance values. 1uF units replacing 4.7uF and 10uF ??? The power supply section has the reverse polarity protection diode replaced by a wire link which isn't good if someone accidentally connects a power adapter with a reversed polarity to the power input jack. The filtering capacitors in the power supply have been also removed Possibly not that important as the manufacturer's PSU is supposed to be regulated and well filtered,however if it was me I'd be fitting the missing electrolytics if only to provide adequate on-board local PSU decoupling. The 220uF / 16VW capacitors specified on the silk screen overlay would be adequate for the job. The two loading capacitors, each of 220pF have been removed from the input stage. Whilst this isn't really an issue I guess you have to ask why as most MM cartridges require some shunt capacitance loading to optimise the frequency response especially in the upper audio frequency range. This shunting capacitance should be in accordance with the cartridge manufacturer's recommendations and is made up of the capacitance of the tonearm leads, turntable / interconnect leads to the phono pre-amp inputs and the input capacitance of the phono stage itself. May I ask what cartridge are you using with this phono pre-amp? Cheers, Alan R. Link to comment Share on other sites More sharing options...
Batty Posted October 16, 2020 Share Posted October 16, 2020 Jim Hagerman uses 1mH inductors on the rails to eliminate SMPS noise in his Bugle phono stages Link to comment Share on other sites More sharing options...
Spider27 Posted October 16, 2020 Author Share Posted October 16, 2020 38 minutes ago, Monkeyboi said: Yes, your's has the 4 coupling capacitors replaces with film capacitors, albeit with different capacitance values. 1uF units replacing 4.7uF and 10uF ??? Yes, it is weird why same 1uf for all 4 spots. I might need to replace them to correct value of WIMA caps. And, when I check all of caps with ERS meters, i found that 2 caps on 100u/16v spot are out of spec. I will change them with 100uf 25v caps that I currently have. Hope it is ok. 38 minutes ago, Monkeyboi said: The power supply section has the reverse polarity protection diode replaced by a wire link which isn't good if someone accidentally connects a power adapter with a reversed polarity to the power input jack. The filtering capacitors in the power supply have been also removed Possibly not that important as the manufacturer's PSU is supposed to be regulated and well filtered,however if it was me I'd be fitting the missing electrolytics if only to provide adequate on-board local PSU decoupling. The 220uF / 16VW capacitors specified on the silk screen overlay would be adequate for the job. The two loading capacitors, each of 220pF have been removed from the input stage. Whilst this isn't really an issue I guess you have to ask why as most MM cartridges require some shunt capacitance loading to optimise the frequency response especially in the upper audio frequency range. This shunting capacitance should be in accordance with the cartridge manufacturer's recommendations and is made up of the capacitance of the tonearm leads, turntable / interconnect leads to the phono pre-amp inputs and the input capacitance of the phono stage itself. I have spare 220uf 50v caps at hand so can use these new caps in those 2 empty spots. 38 minutes ago, Monkeyboi said: May I ask what cartridge are you using with this phono pre-amp? Cheers, Alan R. I am planning to use Nagaoka MP-110 cart on this pre. I have not tested this pre as yet because I lost power supply and cannot locate it but if my memory serves me correctly, this one had an issue with one channel distorted (not sure if it was left or right). Link to comment Share on other sites More sharing options...
Monkeyboi Posted October 16, 2020 Share Posted October 16, 2020 (edited) 29 minutes ago, Spider27 said: Yes, it is weird why same 1uf for all 4 spots. I might need to replace them to correct value of WIMA caps. That would be a good idea. You can get those Wima film caps in tall skinny configuration which should fit neatly in the spots provided. any in their 50 or 63v range is more than adequate. Here's an Australian supplier (not endorsing them, but they carry both values you require. https://www.pedalpartsaustralia.com/index.php?main_page=index&cPath=82_86 29 minutes ago, Spider27 said: And, when I check all of caps with ERS meters, i found that 2 caps on 100u/16v spot are out of spec. I will change them with 100uf 25v caps that I currently have. Hope it is ok. Electrolytic capacitors have a working lifespan. An increase in ESR isn't anything unusual unfortunately. Going slightly higher in working voltage isn't an issue. 29 minutes ago, Spider27 said: I have spare 220uf 50v caps at hand so can use these new caps in those 2 empty spots. Sweet. 29 minutes ago, Spider27 said: I am planning to use Nagaoka MP-110 cart on this pre. That cartridge's optimum load is 47k || 100pF. Most of that shunting capacitance is most likely to be in your T/T leads so no need to refit the missing two 220pF caps. You can verify the capacitance of your T/T cables using your capacitance meter. 29 minutes ago, Spider27 said: I have not tested this pre as yet because I lost power supply and cannot locate it but if my memory serves me correctly, this one had an issue with one channel distorted (not sure if it was left or right). You may find that a faulty cap may be contributing to the distortion issue. Anyhow, get it going and post back here how you went. Cheers, Alan R. Edited October 16, 2020 by Monkeyboi 1 Link to comment Share on other sites More sharing options...
Nada Posted October 17, 2020 Share Posted October 17, 2020 For a phono amp clean regulated power is indicated that has regulated 12V DC, not over-voltage from a "12V" lead battery no switch noise as from a lithium "battery" no recharging hassles eg TeraDak 12V power - search on ebay Internals: https://www.teradak.com/products/89.html 1 Link to comment Share on other sites More sharing options...
andyr Posted October 17, 2020 Share Posted October 17, 2020 Don't quite understand you, Nada? 12 hours ago, Nada said: For a phono amp clean regulated power is indicated that has regulated 12V DC, not over-voltage from a "12V" lead battery Are you suggesting the full charge voltage on a 12v SLA - which can exceed 13v - is dangerous to a phono stage? I don't see how it can - the minimum rating of any electros used will be 25v 12 hours ago, Nada said: no switch noise as from a lithium "battery" Are you saying that a lithium battery has 'switch noise'? What noise is this? 12 hours ago, Nada said: no recharging hassles I agree this is an advantage of using a LPS! Andy Link to comment Share on other sites More sharing options...
aussievintage Posted October 17, 2020 Share Posted October 17, 2020 (edited) 59 minutes ago, andyr said: Are you suggesting the full charge voltage on a 12v SLA - which can exceed 13v - is dangerous to a phono stage? I don't see how it can - the minimum rating of any electros used will be 25v There are other reasons a circuit might be limited to the max voltage that it should be operated at, not just electros. Operating points of transistors etc will shift, regulators will run hotter, etc but it's hard to imagine a small difference will matter. 59 minutes ago, andyr said: Are you saying that a lithium battery has 'switch noise'? What noise is this? I was going to ask the same thing. The battery itself won't, but some batteries have built in management circuitry, maybe this. Edited October 17, 2020 by aussievintage Link to comment Share on other sites More sharing options...
Nada Posted October 18, 2020 Share Posted October 18, 2020 (edited) Lithium 12v supplies like will need regulation to put out a steady 12.0V. Switching regulators can be small, efficient and cool for DC/DC voltage regulation. So the idea a lithium 12v battery pack yields clean battery power at 12.0V without switching noise might be a false assumption. Depends on the quality of the electronics. As long as it sounds good... Edited October 18, 2020 by Nada Link to comment Share on other sites More sharing options...
aussievintage Posted October 18, 2020 Share Posted October 18, 2020 (edited) 36 minutes ago, Nada said: Lithium 12v supplies like will need regulation to put out a steady 12.0V. Switching regulators can be small, efficient and cool for DC/DC voltage regulation. So the idea a lithium 12v battery pack yields clean battery power at 12.0V without switching noise might be a false assumption. Depends on the quality of the electronics. As long as it sounds good... I was thinking of something like Which does not need any regulation really. It's discharge curve is flat enough Edited October 18, 2020 by aussievintage 1 Link to comment Share on other sites More sharing options...
andyr Posted October 18, 2020 Share Posted October 18, 2020 2 hours ago, aussievintage said: There are other reasons a circuit might be limited to the max voltage that it should be operated at, not just electros. Operating points of transistors etc will shift, regulators will run hotter, etc but it's hard to imagine a small difference will matter. That may well be, av - but those other reasons pale into insignificance beside the issue of trying to power a phono stage from +12vDC! +/-12v DC - certainly! Or +24v DC, for a SE circuit like I use in my 'Muse'. But 12v simply doesn't provide sufficient headroom for good transient response. Do the maths: Input is 5mV, peak to peak Coming off the groove, HFs are boosted by up to 20dB (10x) So HFs come into the phono stage at up to 50mV, ptp 1st gain stage has, say, 30x gain So the signal exits the 1st gain stage at 1.5V ptp Even if transients are only 10x .. that gives 15v ptp! (Some people say transients rise even more). Regards, Andy Link to comment Share on other sites More sharing options...
aussievintage Posted October 18, 2020 Share Posted October 18, 2020 10 minutes ago, andyr said: That may well be, av - but those other reasons pale into insignificance beside the issue of trying to power a phono stage from +12vDC! +/-12v DC - certainly! Or +24v DC, for a SE circuit like I use in my 'Muse'. But 12v simply doesn't provide sufficient headroom for good transient response. Do the maths: Input is 5mV, peak to peak Coming off the groove, HFs are boosted by up to 20dB (10x) So HFs come into the phono stage at up to 50mV, ptp 1st gain stage has, say, 30x gain So the signal exits the 1st gain stage at 1.5V ptp Even if transients are only 10x .. that gives 15v ptp! (Some people say transients rise even more). Regards, Andy You were querying if 13V is dangerous to a phonostage that normally runs off 12V Nothing to do with the new issue you are now raising. Link to comment Share on other sites More sharing options...
andyr Posted October 18, 2020 Share Posted October 18, 2020 1 hour ago, aussievintage said: You were querying if 13V is dangerous to a phonostage that normally runs off 12V Nothing to do with the new issue you are now raising. Not so, av - I was suggesting that 13v was absolutely fine. My subsequent post was to suggest that 13v vs. 12v was unimportant - as the vital issue was the too-low voltage rail. Andy Link to comment Share on other sites More sharing options...
aussievintage Posted October 18, 2020 Share Posted October 18, 2020 26 minutes ago, andyr said: Not so, av - I was suggesting that 13v was absolutely fine. My subsequent post was to suggest that 13v vs. 12v was unimportant - as the vital issue was the too-low voltage rail. Andy Wow, yes exactly. You were query his fear that it wouldn't be. That's what I get for trying to agree with you, saying... 5 hours ago, aussievintage said: it's hard to imagine a small difference will matter. The too low voltage rail was a new problem you threw in at the end. Link to comment Share on other sites More sharing options...
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