Philip,
you are a busy man
For a scratch-built phono stage, and if simplicity is a major point, then it is really difficult to beat the old RCA Ortho stage. It gives over 40 dB of gain and if the RIAA filter (passive EQ, the very best kind is done well, you'll get a very good match to the RIAA curve. It doesn't attempt to get the final LF pole as on the IEC standard, but that anomaly is nearly inaudible (if you are using a decent turntable with low rumble) and it requires an extra tube sstage to get it. Few traditional (good) phono stages bothered with it. Oh, yes, that extra tube stage will be a cathode follower and there is a *lot* of opinion out there that no CF really sounds good.
Having said that, i'll aver that the Ortho stage can be made a good bit better by modifying the EQ values to match the characteristics of a different tube, specifically, the 12AY7/6072. If this interests you , I have a schematic with all this worked out. The 12AY7 is not as easy to get as the 12AX7, but it is worth the trouble to buy a couple plus an extra set as spares, and you'll be set for life, no matter if the price of these tubes goes through the roof during your long life
Now, I'll go one step further and say that the Wright phono stage is substantially better than the Ortho, but it is a *great deal* more work to build. I would not recommend it as a first attempt unless you are a very determined lad and have a fair bit of money to throw at it. It *does* immplement the IEC LF pole and it *does* have CF that you can't hear. All you hear with the Wright is a ridiculously black background, no noise, and superb dynamics. Oh, yes, exceptional compliance to the RIAA and IEC standards. Don't build it... yet
Another point, build the PSU on a separate chassis and make sure it has enough grunt to run your line stage as well. You'll need about 38 mA if your line stage is a 6AH4, which it *should be*. So, make sue your transformer and choke are capable of at least 80mA. This should be easy. Make it a choke input and use the finest caps you can get; motor run (not motor start) or NOS oil caps are the best, but you'll need a separate PSU chassis and a big one. I'd make it at least LCLC. Using Hammond iron it will not be too expensive. use a vacuum tube rectifier if you wish, but a SS FW suing low noise diodes, snubbed, can sound just as good. Go over to the Bottlehead Forum on Audio Asylum and snoop around to gind information of good SS rectifier systems. I can't do all your work for you; you've got to do some digging for yourself
I'd also recommend that you make your phono preamp chassis large enough to hold a line stage (which, did I say, should be a 6AH4??? switching, and volume controls, as well as 4 or so pairs of inut jacks. The reason for this is to simplify the cabling from the PSU.
Now, you'll have to watch the input and output impedances from the phono preamp to the Darling. However, if you use the 12AY7, it will drive a 100K volume pot if you use a 100K buildout resistor in front of the pot.
Nowk with all that said (assuming you are going to buils the modified Ortho) I'd recommend going ahead and building the line stage. the schematic is so simple that it is ridiculous. The most difficult part is mechanical, providing the input jacks, the volume pots, and the switching. Leave it for later if you wish.
OK, there are my thoughts. They are entirely correct, no matter what the hundreds of objectors say. but it is likely that their ideas and schematics are corect also Listen and make your choices, as *you* are the one you have to please!!!
Cheers/Fader
WHEW!!!!
you are a busy man
For a scratch-built phono stage, and if simplicity is a major point, then it is really difficult to beat the old RCA Ortho stage. It gives over 40 dB of gain and if the RIAA filter (passive EQ, the very best kind
is done well, you'll get a very good match to the RIAA curve. It doesn't attempt to get the final LF pole as on the IEC standard, but that anomaly is nearly inaudible (if you are using a decent turntable with low rumble) and it requires an extra tube sstage to get it. Few traditional (good) phono stages bothered with it. Oh, yes, that extra tube stage will be a cathode follower and there is a *lot* of opinion out there that no CF really sounds good.Having said that, i'll aver that the Ortho stage can be made a good bit better by modifying the EQ values to match the characteristics of a different tube, specifically, the 12AY7/6072. If this interests you , I have a schematic with all this worked out. The 12AY7 is not as easy to get as the 12AX7, but it is worth the trouble to buy a couple plus an extra set as spares, and you'll be set for life, no matter if the price of these tubes goes through the roof during your long life
Now, I'll go one step further and say that the Wright phono stage is substantially better than the Ortho, but it is a *great deal* more work to build. I would not recommend it as a first attempt unless you are a very determined lad and have a fair bit of money to throw at it. It *does* immplement the IEC LF pole and it *does* have CF that you can't hear. All you hear with the Wright is a ridiculously black background, no noise, and superb dynamics. Oh, yes, exceptional compliance to the RIAA and IEC standards. Don't build it... yet
Another point, build the PSU on a separate chassis and make sure it has enough grunt to run your line stage as well. You'll need about 38 mA if your line stage is a 6AH4, which it *should be*. So, make sue your transformer and choke are capable of at least 80mA. This should be easy. Make it a choke input and use the finest caps you can get; motor run (not motor start) or NOS oil caps are the best, but you'll need a separate PSU chassis and a big one. I'd make it at least LCLC. Using Hammond iron it will not be too expensive. use a vacuum tube rectifier if you wish, but a SS FW suing low noise diodes, snubbed, can sound just as good. Go over to the Bottlehead Forum on Audio Asylum and snoop around to gind information of good SS rectifier systems. I can't do all your work for you; you've got to do some digging for yourself
I'd also recommend that you make your phono preamp chassis large enough to hold a line stage (which, did I say, should be a 6AH4???
switching, and volume controls, as well as 4 or so pairs of inut jacks. The reason for this is to simplify the cabling from the PSU.Now, you'll have to watch the input and output impedances from the phono preamp to the Darling. However, if you use the 12AY7, it will drive a 100K volume pot if you use a 100K buildout resistor in front of the pot.
Nowk with all that said (assuming you are going to buils the modified Ortho) I'd recommend going ahead and building the line stage. the schematic is so simple that it is ridiculous. The most difficult part is mechanical, providing the input jacks, the volume pots, and the switching. Leave it for later if you wish.
OK, there are my thoughts. They are entirely correct, no matter what the hundreds of objectors say. but it is likely that their ideas and schematics are corect also
Listen and make your choices, as *you* are the one you have to please!!!Cheers/Fader
WHEW!!!!
Easy
Suoerb, and nowhere near as complicated to build as it looks. And it will walk all over the RCA in resolution.
John has already given the PS details in para 4 above, except that a 6AX4 or similar damper diode will do extremely well, is cheap as dirt and quieter than any SS rectified system I've ever tried. Plug'n'play.
Run DC to the heaters from a seperate tx.
An externally hosted image should be here but it was not working when we last tested it.
Suoerb, and nowhere near as complicated to build as it looks. And it will walk all over the RCA in resolution.
John has already given the PS details in para 4 above, except that a 6AX4 or similar damper diode will do extremely well, is cheap as dirt and quieter than any SS rectified system I've ever tried. Plug'n'play.
Run DC to the heaters from a seperate tx.
Konnichiwa,
You may find this thread usefull:
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
At the end are several experiences from people who actually build the darn thing.
Sayonara
philipbarrett said:
You may find this thread usefull:
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
At the end are several experiences from people who actually build the darn thing.
Sayonara
Although it's hardly a simple design, I've always wondered why there was so little love for JC Morrison's Siren Song. It seems few people have commented on it - perhaps because few built it?? I just did a forum search expecting more info, especially since an updated version appeared in AudioXpress last year, but there is hardly anything.
Hi,
That's a balanced preamp using a 6SL7, right?
From what I remember of it it should work great, very musical but RIAA correction could be bettered.
Note that those are just my "gut" comments as I recall them from merely looking at the circuit many years ago.
A common problem with 6SL7s in such high gain places is a tendency towards microphony and probably a little too high in noise levels too.
Cheers,
That's a balanced preamp using a 6SL7, right?
From what I remember of it it should work great, very musical but RIAA correction could be bettered.
Note that those are just my "gut" comments as I recall them from merely looking at the circuit many years ago.
A common problem with 6SL7s in such high gain places is a tendency towards microphony and probably a little too high in noise levels too.
Cheers,
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