Aah, OK - then that is the problem! 🙁
If you're only getting 125x gain with the 1:20 SUTs included ... then your actual phono stage board would only output 590/20mV = 30, say - which is just over a 6x gain.
An MM phono stage - without the SUT - should have 100x gain. There would appear to be something wrong with the phono stage itself?
Andy
Can you be more specific about your phono-stage?
When the tubes are resistively loaded, a cascade will give some 34-35 dB of gain, like euro21 mentioned.
When however loading the tubes with CCS's or inductances, there will be at least 40 dB of gain.
40 dB of gain (quite normal for a phono pre amp) should bring a "normal" input of 5 mV up to 0.5 V, which would require a rather high but not uncommon input sensitivity of your power amp.
Off course, the 5 mV should be available after the 1:20 SUT.
You mean where you said that:
Eerrrrrhhh NO! A typical MM phono stage has 40-42dB gain.
If a "typical D3a+5687 phono has about 30..34 dB gain" ... then it is deficient.
Andy
Andy,
Don't confuse "the typical D3a+5687 phono stage" with "a typical MM phono stage".
The difference (34dB - 40dB) is just like that.
That's why I asked the TO how his phono stage exactly looks like (loading).
Don't confuse "the typical D3a+5687 phono stage" with "a typical MM phono stage".
The difference (34dB - 40dB) is just like that.
That's why I asked the TO how his phono stage exactly looks like (loading).
I'll post the schematic in a bit but, I have a friend close by who built this exact phono stage from the exact same schematic and his has PLENTY of volume with very, very similar gear. So I believe the problem may reside within my build and not with the design. Of course, I could be wrong.
I did not use all the boutique parts called out-just top quality stuff from Mouser and the like.
Thanks WntrMute2,
4k7 load resistor for the D3a is lowish; gain of that stage will be ~ x 40.
5687 is CCS loaded, so gain will be ~ 18 like mu.
Total gain 720, divided by 10 (the 20 dB loss of RIAA equalization), net gain of 72, which is 37 dB.
It should work well enough with a very sensitive power amp; an additional line amplifier ??
What MC cart (output voltage?).
Check your first power supply cap; 100 uF is normally too much for a 5R4 rectifier, unless your power supply transformer high voltage winding has sufficient DCR (checking Hammond data it is ~46 ohm which is too low....).
4k7 load resistor for the D3a is lowish; gain of that stage will be ~ x 40.
5687 is CCS loaded, so gain will be ~ 18 like mu.
Total gain 720, divided by 10 (the 20 dB loss of RIAA equalization), net gain of 72, which is 37 dB.
It should work well enough with a very sensitive power amp; an additional line amplifier ??
What MC cart (output voltage?).
Check your first power supply cap; 100 uF is normally too much for a 5R4 rectifier, unless your power supply transformer high voltage winding has sufficient DCR (checking Hammond data it is ~46 ohm which is too low....).
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The cartridge is a Per Winfield at 0.3mV. I am running an active linestage. Also a 1:20 SUT.
I know about the 100uf cap but the designer assured me it had been working for him for years and it has been working fine for me for over a year. The gain issue is separate I believe. Thanks for the help!
I know about the 100uf cap but the designer assured me it had been working for him for years and it has been working fine for me for over a year. The gain issue is separate I believe. Thanks for the help!
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So you've got 0.4 - 0.5 V to drive the power amp.
You should be able to relate this to amplifier - loudspeaker (sensitivity) combination to see if you can reach the desired SPL.
That is when the phono preamp works like it should.
You should be able to relate this to amplifier - loudspeaker (sensitivity) combination to see if you can reach the desired SPL.
That is when the phono preamp works like it should.
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Thanks for that. I got things figured out. The CCSs were hooked to the 5687 tubes wrong. They were not regulating at all. Luckily I had some other units I made up for a different project and they fixed the problem.
When I measured things without the SUTs, I got 38dB of gain as you simulated. With the SUTs switched in, things are much, much better. Thanks all!
When I measured things without the SUTs, I got 38dB of gain as you simulated. With the SUTs switched in, things are much, much better. Thanks all!