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Hello!
Here is the phono circuit of the Marantz Model 1 which I found sounds better than the Marantz 7 but not enough gain for some cartridge.
I'm thinking about using either choke or CCS loaded to overcome this issue.
Which way would you prefer?
Thanks!
CCS should draw more current than a choke :-)
If choke loaded is recommended, what inductance it should use?
What about 160H/10mA with DCR 1160R? I have one pair made by Tango and bought years ago.
Follow Ups:
The two CCSs shown would not be ideal at the low bias current in a 12AX7 type tube. Those depletion mode MOSFETs do not perform well at low currents. I consider 8mA-10mAs the bare minimum. I would look in Morgan Jones 4th ed. for more appropriate examples. I designed a CCS load for a 12AX7 using two PNP BJTs in cascode with a decently large emitter resister to yield a high AC impedance. This will require a couple of resistors and either an LED or voltage reference to provide the base voltages for the two transistors, an emitter resistor and a low voltage high hfe BJT and a high voltage BJT. Morgan Jones has a table of suitable PNP BJTs and some examples. The greater the difference in the top BJT's ( the bottom of the cascode, PNP transistors can be confusing ) base voltage and the B+ the higher resistance emitter resistor and the greater impedance of the CCS.
As an aside, I didn't need a gain of 100; what I was looking for was eliminating Rp in the gain equation. Went with a half mu stage which eliminates the effect of Rp with a gain of 50 and only needs a dual triode and 2 resistors to implement.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
It might have too much gain with CCS.
Refer to the description, it has low current version.
"I have three versions of the CCS:
JFET lower device, current adjustment range 0.2mA to 5mA
Depletion MOSFET lower device, current adjustment range 2mA to 15mA
Depletion MOSFET lower device, current adjustment range 5mA to 50mA"
For a choke load, you're going to need at least 2000 henries; when Magnequest made one - I believe it was from a Freed design - it was rated > 4000H at 1mA. They are now very hard to find.
But a choke will (approximately) double the plate voltage and current, which would call for adjusting the other resistors and capacitors. Plus, any choke not double-mumetal shielded against magnetic fields would likely pick up hum if used in the first stage.
The gain is set by the feedback network, not the stage gains, so current source loads would increase the feedback, not the gain.
The posted circuit appears to have voltages indicated, but the values are illegible so I can't offer much more. And the feedback network is partially cut off, so it's hard to guess the feedback-adjusted gain.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
But it should be no problem to use CCS or plate choke for the line section circuit to replace the 270K and 100K, right?
http://www.pmillett.com/current_source.htm
Choke loads will have the same issues, more or less. CCS would be the way to go, in my opinion.
I'm recently working on very similar thing. Here's my friend suggestion.
" was talking about a resistor ACROSS the inductor! so the low DCR of the inductor will be used!!!
THAT shunting offers a real need, sets the impedance of the inductor to its value
Using a choke (inductor) as plate load and shunting it with a plate load resistor, will offer more plate voltage to the tube used. due to the plate load resistor will be the load impedance, not the DCR,
The choke will be maybe 50 ohms or so......"
Frankly, I don't know how to do that.
Is this approach okay 🙂
Paul,
After talking to my friend and he reminds me the CCS will make the linestage has too much of gain. And it required some change of feedback.
And he suggests I put a 400H plate choke with 3000 ohm DCR in series with, let's, say 267K resistor; so it ends up 270K for the plate load of the first ECC83.
And I can do the same thing to the second tube (same choke with 97K resistor).
What do you think?
If you are building a linestage, why use an ECC83 in the first place?
But it should be no problem to use CCS or plate choke for the line section circuit to replace the 270K and 100K, right?
http://www.pmillett.com/current_source.htm
.
Have Fun and Enjoy the Music
"Still Working the Problem"
I have 2 cartridges, one is MI and the other is MM, output is 3mV and 4.5mV respectively.
You would need about 40-50db of gain total including the line stage.Has anyone measured the gain of the stock preamp?
I just looked at this schematic. That thing should have plenty of gain.
Or are you only using the phono stage? If so, do you have a line stage following it? If so there should be plenty of gain.
Maybe there is something not working right with the stock unit?
Edit, I found this "The phono preamp section is more than adequate; it has enough gain and low enough noise, too, to handle very low-output cartridges without transformers"
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/05/25
although I never noticed enough additional gain using a CCS I could be wrong. Same with a choke load.
How much voltage gain do you need?
The higher the load impedance on a triode the more horizontal the load line will be. With a CCS in the plate circuit, the plate load impedance becomes the value of the grid resistor in the next stage and that would make a load line that is very close to horizontal.As horizontal load line on a triode gives the most gain and the least harmonic distortion.
In the example above we see that the voltage swing with a 8 volt peak to peak input signal is larger with better symmetry comparing the plate voltage change from the red idle point to the green (horizontal high impedance load line) vs. blue (lower plate load impedance load line).
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/05/25 02/05/25
I was tempted to think it would do just that, give me more vgain. But it's not a tube!
It wasn't enough, although it should have been. Graphs are not applicable in this case. My K&K CCS, although dated V09/02 years old, came with instructions and I followed them without mistake. At least 4 times or more. It was still not enough gain and put them away, still have them, worth a try but didn't particularly care for the sound.
Looking at the circuit he's reading, maybe he should try it anyway and see if it's suitable for his purposes although I doubt it.
Maybe you should explain it to HIM, NOT ME with some helpful advice.
Good luck you 'all
"I was tempted to think it would do just that, give me more vgain. But it's not a tube!"What is not a tube?
CCS aside, the gain of a triode tube stage goes up as the plate resistor is increased. That is a direct result of the load line becoming more horizontal. That is just a fact and if you are not getting that result then you are doing something wrong.
BTW the theoretical max gain of a stage is the mu of the tube in use. That can never be reached but with a CCS plate load and a high 'following stage' grid resistor value you can get really close.
P.S. I may have mis-read your post. If you got more gain but not enough more gain then I would use a different tube, one with a higher mu.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/05/25 02/05/25
you must have read my reply wrong, or I was just wrong answering this guys question and should not have as you mistakenly done so. My Brain damage from a fall works sporadically now, but getting better. I used to be far, far more succinct at one time.
I stand by my statements however, the query in the beginning of thread asks for CCS or Choke, and I say it will not be enough. Maybe a tube stage will do. Besides he never asked how much gain he needs.
If you've tried to get me off this forum, you've done a good job. I'll give you a 'B' grade. I will never GIVE UP. Doctors advice.
I have never tried to get you off of this forum.
I don't understand why you would have that impression?
Audio electronics is all just science. Opinions (especially mine) should never be taken personally. I only state what I believe to be the science. None was meant as a personal attack.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
it said it was a 'B' grade, and I will keep trying under MY circumstances.
Now please ask the OP what he wants, what he's looking for. Thank you Tre'
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