You can add voltage shunt feedback which will affect (drop) your input impedance but will reduce voltage gain. Is that what you were looking for ?
Implementation will be typically an input resistor in the grid ( where the grid stopper usually is) and a resistor from the grid to the output past the output cap to prevent dc from going back to the input.
It isn't a trivial circuit and component values have to be chosen carefully.
While gain might be reduced it can hardly be expected to 'sound' like other tubes with similar lower gain ! Electrically too it can never be made to perform like 'other' tubes as their characteristics will be completely different.
Implementation will be typically an input resistor in the grid ( where the grid stopper usually is) and a resistor from the grid to the output past the output cap to prevent dc from going back to the input.
It isn't a trivial circuit and component values have to be chosen carefully.
While gain might be reduced it can hardly be expected to 'sound' like other tubes with similar lower gain ! Electrically too it can never be made to perform like 'other' tubes as their characteristics will be completely different.
It's been done: Anode Follower.
Of course, this won't help with the limited current sourcing capability, but will get the gain down to the 12AU7, 'AT7 level.
Of course, this won't help with the limited current sourcing capability, but will get the gain down to the 12AU7, 'AT7 level.
I have no idea what the end application is, but there is another way to do it.
See attachment for details. Note also that this was not intended for applications where the required voltage swing is more than a few volts rms. (It's a low cost line stage circuit.) Also the approach rather significantly increases the already high rp of the 12AX7A and the cathode follower shown as part of the implementation is not window dressing for that reason. Information provided is for personal use only...
See attachment for details. Note also that this was not intended for applications where the required voltage swing is more than a few volts rms. (It's a low cost line stage circuit.) Also the approach rather significantly increases the already high rp of the 12AX7A and the cathode follower shown as part of the implementation is not window dressing for that reason. Information provided is for personal use only...
Last edited:
Always remember that what sounds good to you is what you should keep/use.....no matter what the rest of the world thinks of your implementation. In this matter your ears are your God !
When somebody says that XYZ produces the most accurate sound on planet Earth, it doesn't mean too much to you if you don't know what the other persons references / preferences are . In all likelyhood you might not like the other persons 'Best system'! But that's perfectly OK as long as you understand it.
So try all things that are possible for you and build your system. Spend 80% of your time listening to "music" ! The main reason why you are meddling with all these things.
So , try out all the circuits that you can try and pick your choice. Then put up your feet and listen to the best music you have irrespective of what others feel about your choice of equipment/schemes. You do have the final say in such matters !
Cheers.
Edit: Just a pointer. Check out the threads on the 12B4A preamps. I've tried it. I LIKE it ! You might too. Key reason for using this tube is that you can use it in standard configuration and it has very low gain without resorting to negative feedback. Lots of other reasons you will see in those threads. There must be other NOS tubes that can do this also.
When somebody says that XYZ produces the most accurate sound on planet Earth, it doesn't mean too much to you if you don't know what the other persons references / preferences are . In all likelyhood you might not like the other persons 'Best system'! But that's perfectly OK as long as you understand it.
So try all things that are possible for you and build your system. Spend 80% of your time listening to "music" ! The main reason why you are meddling with all these things.
So , try out all the circuits that you can try and pick your choice. Then put up your feet and listen to the best music you have irrespective of what others feel about your choice of equipment/schemes. You do have the final say in such matters !
Cheers.
Edit: Just a pointer. Check out the threads on the 12B4A preamps. I've tried it. I LIKE it ! You might too. Key reason for using this tube is that you can use it in standard configuration and it has very low gain without resorting to negative feedback. Lots of other reasons you will see in those threads. There must be other NOS tubes that can do this also.
Last edited:
re: 'no idea what the end application is' - well, I did say it was idle speculation ... actually I was thinking that I had a shedfull of AX7s, and would maybe useful to be able to substitute them for others in the same family, in any application (although I was thinking of the driver in amps like the Red Light District).
As Miles says however, the limited current sourcing capability is likely to be the killer.
... actually I was thinking that I had a shedfull of AX7s, and would maybe useful to be able to substitute them for others in the same family, in any application (although I was thinking of the driver in amps like the Red Light District). As Miles says however, the limited current sourcing capability is likely to be the killer.
Well since it's a "speculative" post I dare to hijack it a little since I also have reducing gain related Q. Years ago I've got Audio Note kit4 6V6 PP stuffed board and some time ago a pair of old Dyna Z- 565 transformers. I heard kit and always liked it althoug my tube savy friends call it a "bad design". I put Z-565 instead of original AN OTO (8k primary) transformers and I have way too much gain with original 10dB feedback RC 6.8k/560pF network ,and overblown bass . My friend suggested getting rid of 6SN7 stage and driving 6V6 from paraphase splitter.What are my options with circuit intact .Increasing feedback (I'd like to lover it actually, loosing bypass caps on 6SN7 driver (counter productive since it'll inrease driver impedance and make this redundant stage according to my friend even more redundant). The circuit sounds quite natural and pleasing with good balance of resolution and natural detail. It doesn't image or project very well (little monophonic) but I can live with that.
, loosing bypass caps on 6SN7 driver (counter productive since it'll inrease driver impedance and make this redundant stage according to my friend even more redundant). The circuit sounds quite natural and pleasing with good balance of resolution and natural detail. It doesn't image or project very well (little monophonic) but I can live with that.Attachments
What's with the 'info for personal use only' and what's with all the weird component values??
Cheers
Ian
Oh.....! You want to put them to good use.
Maybe keep enough to experiment with ( 10....20 ?) and dump the rest ? That way it wouldn't bug you seeing so many 12AX7 tubes every time !
I'm not sure I get the "weird" component values question? They're all standard 1% metal film resistor values, and should be easily obtainable from any electronic component reseller like Farnell, Radio Spares, Allied, Digikey, Mouser etc..
The design comes right out of one of my project books, and rather than state the obvious that if someone wants to use this design commercially (and frankly I can't imagine why they would) that the information was not presented for commercial use.
Last edited:
They are weird because they are not on the E24 series. 221 ohms is not weird? It's a grid stopper; 220 ohms, a standard value will be fine. How on earth did you calculate a value of 221 ohms for a grid stopper and why did you not think is was possible the round it to the nearest E24 series value? 511K is not weird; it's only there to provide a dc path for the output coupling cap so its value is not crucial; a standard 470K would do or if you are pedantic about it use the E24 standard 510K.
It's pretty much the same for all the other values. E24 series will be perfectly adequate and a lot cheaper than the weird values you have come up with.
Why should it not be used commercially? Specifically what is it about this design that you think is uniquely yours? It cannot be the use a of CC followed by a CF, that's been done many many times, or doing it with a 12AX7, that's common enough too. I cannot be the operating points, they have been used many times also. Is it just your weird component values that make it 'special'?
Cheers
Ian
Geeze guy give it a rest. What have I done to set off this tirade, and what have I ever done to you? You're entitled to your opinion, but you're not entitled to insult me over it. Go grind your axe somewhere else and at someone else's expense.
I just happen to prefer metal film 1% resistor values and in this neck of the woods there is little if any difference in cost between discrete 1/2W resistors. It's a choice, OK? Clearly any value in the ball park is going to be perfectly suitable. Your nit picking is a waste of my and other peoples time.
There is nothing particularly unique about the design, but it happens to be my take on the approach, I spent significant effort and time developing and testing it. It is MY design, that others are similar is irrelevant. Apparently as un-novel as you may regard it to be it is also my IP. A concept you clearly have no respect for. Whether or not is it worth anything at all is a different matter. I'm generally quite open in sharing my designs, your comments make me not want to do that anymore.
Let's move on, and suffice it to say we apparently don't agree on anything. I'd really like to not have to put you on my ignore list.
I just happen to prefer metal film 1% resistor values and in this neck of the woods there is little if any difference in cost between discrete 1/2W resistors. It's a choice, OK? Clearly any value in the ball park is going to be perfectly suitable. Your nit picking is a waste of my and other peoples time.
There is nothing particularly unique about the design, but it happens to be my take on the approach, I spent significant effort and time developing and testing it. It is MY design, that others are similar is irrelevant. Apparently as un-novel as you may regard it to be it is also my IP. A concept you clearly have no respect for. Whether or not is it worth anything at all is a different matter. I'm generally quite open in sharing my designs, your comments make me not want to do that anymore.
Let's move on, and suffice it to say we apparently don't agree on anything. I'd really like to not have to put you on my ignore list.
Five cents for the values you spec'd in onesey-twoseys from Mouser. All in stock. 1.2 cents in thousand lots.
FWIW.
I was just curious as to how you came to those particular values. No insult was intended. I was just pointing out that in at least two instances there was no clear reason why those strange values were chosen. Please enlighten me.
I am fully conversant with the concept of IP and made a significant sum of money out of it - enough to be able to retire at the age of 50. Stop stop arm waving and explain just where in that design there is your IP. It is certainly not in the toplogy.
Cheers
Ian
There isn't an answer to any of the above questions that you would accept. I will hint that there is a significant amount of local feedback but you already knew that. Clearly I am not permitted to make my own possibly arbitrary design choices or make money from my design efforts. Therefore my end of the discussion is over.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.