John Curl's Blowtorch preamplifier part II

[john curl]

No, todays really good phono stages weigh up to 90lb, and the size of a small refrigerator.

 

[john curl]

Like this Chris? The schematic will have to be updated since it is about 44 years old. '-)

 

[SY]

Not important are strong words.

But accurate. A quick run of the numbers puts this effect somewhere in the residual background noise of the Big Bang.

 

[Kindhornman]

Why can't more people draw a nice drawing like that these days John? A resistor looks like a resistor symbol and a transistor the same and it is so nice and easy to follow the circuit. Nice pencil drawing work there even if it is 40 years old.......

 

[Chris Hornbeck]

Like this Chris? The schematic will have to be updated since it is about 44 years old. '-)

Perzactly!

Thanks, as always,
Chris

 

[31697B]

But accurate. A quick run of the numbers puts this effect somewhere in the residual background noise of the Big Bang.

Thats a really, really, really tiny amount of noise. But since the void is limited is size, there might be some big reflections coming back.... echos and in these circuits, there are equivelents -- residuals too --

There are other bennies of cascoding besides lowering distortion.... and the two transistor (differential) also has added beneifits in rejecting common-mode and other undesirables etc. BUT did we already say the differential has the two devices in series for noise increase? So to get every benifit possible a complimentary differential arrangement works well... keeps the noise and the distortions low and rejections high. The best of all worlds.

If you dont have to worry about common-mode noise in your short cable runs nor RFI, nor psr issues, then a simpler compl. push-pull works and the two transistors are in parallel for inherently lower noise with a minimum of parts.

Thx-RNMarsh

 

[SY]

ns high. The best of all worlds.

If you dont have to worry about c-mode noise in your short cable runs nor RFI, nor psr issues, then a simpler compl. push-pull works and the two transistors are in parallel for inherently lower noise with a minimum of parts. etc etc etc.

But this is the one part of the audio chain where balanced really DOES offer an advantage. I can actually touch a pin of my cartridge and not get hum and I don't have to take heroic shielding measures in the interconnects. The 3dB noise disadvantage is real, though- one can either design the stage so that the 3dB is unimportant (i.e., a stage with noise well below the cartridge's Johnson noise) or use a transformer (my own preferred solution). Or live with the extra noise, as many tube aficionados do, but not this tube aficionado!

 

[31697B]

yes, there are good apps for balanced inputs... esp for very low level signals. Like a phono preamp. When I had a MC cart, I used a Denon MC step-up transformer and then later I tried my hand at a compl push-pull pre-pre. i never had noise problems with either approach IF I didnt touch the pins of the cartridge(!).

Thx-RNMarsh [BTW - compl push-pull can be easily configured to do balanced duty]

 

[john curl]

My single input preamp doesn't hum. I must be doing something wrong! '-)

 

[jan.didden]

My single input preamp doesn't hum.

Maybe it doesn't know the tune

jan

 

[john curl]

Maybe I know what I am doing. '-)

 

[Kindhornman]

John,
Since you are up so late here is a question. What would you change on the phono stage that you say you would need to update, is that because some of the components are no longer available or because you could replace something with something newer and better?

 

[SY]

Maybe I know what I am doing. '-)

You're designing for compatibility with mass-market standards, a restriction diyers don't have but commercial designers do. We can go "no compromise" without worrying that it will affect sales because the average buyer won't want to redo his turntable wiring.

 

[Pano]

Indeed! And designing for the pro market can be even worse. It amazes me how good the designs can actually be, considering the constraints.

 

[jacco vermeulen]

mass-market standards

Maybe it's because the standards are wrong.

[me all-balanced from TT/CDT(AES) to loudspeaker in/out, aka including the LSP cables]

 

[SY]

If I hate QWERTY, I can remap my own keyboard. If I'm designing a keyboard to actually sell, it's not likely that my remapped version will succeed, even if I can argue that QWERTY is "wrong." The market has a lot of inertia!

 

[jacco vermeulen]

If the egg turns out a square nut, don't blame the chicken for not having his AES rewired.

Not Mr Curl's fault that he's forged to poop out a less than perfect omelet, because the customer's key-menu top doesn't read Quail.

 

[gpapag]

Makes me wonder if a 2013 MC phono design could include a phantom powered head amp up near the phono cartridge. Would remove the desire for differential inputs, but would need to work with existing two-coax signal cables (only).
Thanks,
Chris

Salas has one here
http://www.diyaudio.com/forums/analogue-source/188730-2sk170-bl-mc-step-up-amp.html#post2567139

Joachim has shown more than many circuits.
I saw his latest one (balanced to single ended) here
http://www.diyaudio.com/forums/analogue-source/226508-openamp1-mm-phono-preamp-open-project.html#post3301025

I am planning to try it without the servo with AD620 instr amp (one ic per channel) I have. AD8221 has better specs, if one wants to try this approach. Being balanced input / single out, I don’t find it beneficial to mount it on the cartridge shell.
For balanced in/ balanced out, AD8222 fits in there with the same minimal construction complexity.

George

 

[SY]

Not Mr Curl's fault that he's forged to poop out a less than perfect omelet, because the customer's key-menu top doesn't read Quail.

100% agreed. Fortunately, we diyers can have square rectums if we so desire.

 

[gpapag]

100% agreed. Fortunately, we diyers can have square rectums if we so desire.

The octagonal would fit better to the “nut” description.

George