Hello everyone,
I’m new to audio equipment development and would appreciate some recommendations and ideas. I’m currently working on a tube preamp project with the goal of achieving the warm sound characteristic of these devices. I’m implementing a +17V and -17V power supply, as well as a 48V phantom power.
I plan to use this voltage phatom power to bias a tube stage that I want to amplify to 60dB (equivalent to 1000 times gain). I’ve looked into the 12AX7, but I’ve heard it can present distortion at low voltages. I’m currently testing the 12AU7, which is said to have less noise, although its amplification factor is much lower.
I’m wondering how I could achieve the desired gain to get that "warm" sound. I was considering a dual amplification stage using the 12AU7 along with a FET. What recommendations would you have for tackling this issue?
Sorry if my question seems basic; I’m new to this. Thanks.
Here is a basic dual-stage preamp with a gain of 15 per stage, along with some curves I obtained from the 12AU7 in Multisim.
I’m new to audio equipment development and would appreciate some recommendations and ideas. I’m currently working on a tube preamp project with the goal of achieving the warm sound characteristic of these devices. I’m implementing a +17V and -17V power supply, as well as a 48V phantom power.
I plan to use this voltage phatom power to bias a tube stage that I want to amplify to 60dB (equivalent to 1000 times gain). I’ve looked into the 12AX7, but I’ve heard it can present distortion at low voltages. I’m currently testing the 12AU7, which is said to have less noise, although its amplification factor is much lower.
I’m wondering how I could achieve the desired gain to get that "warm" sound. I was considering a dual amplification stage using the 12AU7 along with a FET. What recommendations would you have for tackling this issue?
Sorry if my question seems basic; I’m new to this. Thanks.
Here is a basic dual-stage preamp with a gain of 15 per stage, along with some curves I obtained from the 12AU7 in Multisim.
Last edited:
What do you have so far i.e. a schematic?
For 60db i'd not be using tubes, at least not exclusively.
And what do you mean exactly by "warm"? Rolled off high frequencies, high thd, or something else? Tubes are no warmer than solid state this is a myth IMHO. It depends on the circuit.
For 60db i'd not be using tubes, at least not exclusively.
And what do you mean exactly by "warm"? Rolled off high frequencies, high thd, or something else? Tubes are no warmer than solid state this is a myth IMHO. It depends on the circuit.
By "warm sound," I mean the low-order harmonics that contribute to a rich and full sound. I'm aiming to build a preamp that emphasizes these harmonics, which is why I'm exploring designs using tubes, FETs, or a hybrid of both technologies. I would appreciate any recommendations for creating this type of circuit or suggestions on which FETs are best suited for audio applications. The 60 dB's is for trying to get an approach to some popular pre amps in the market 
You do not need tubes to achieve pure or predominant 2nd harmonic. With proper jfet hamptone can sound warm and tube like.
https://www.diyaudio.com/community/threads/hamptone.405097/
https://www.diyaudio.com/community/threads/hamptone.405097/
How much output swing do you need? Guitar or hifi? You need to clearly define your requirements. A 12au7 doesn't have enough gain in two stages so not sure how that became a starting point. 12at7 maybe? You will have issues getting tubes quiet enough without negative feedback but then your gain requires get even higher. What are some of these popular preamps? Tell us exactly what you are trying to accomplish.
Last edited:
I'm aiming to design a preamp inspired by the Universal Audio 710 Twin-Finity, but I plan to use lower supply voltages, around 48V.
Last edited:
Yeah there's nothing hifi about that. It seems.to be a mic pre. I'm not sure where you are coming from at this point. Good luck.
60dB is too much gain for an all tube circuit. The bass response is reduced below 100Hz with the cathode bypass capacitors used.
The first tube has no DC path for its grid, and no proper grid bias, so I don't see how the software can simulate properly.
The first tube has no DC path for its grid, and no proper grid bias, so I don't see how the software can simulate properly.
Read the specs. The 60dB is for a mic input.
Are you going to use such an input?
If not, forget about the 60dB, it is useless for normal audio sources.
Jan
Are you going to use such an input?
If not, forget about the 60dB, it is useless for normal audio sources.
Jan
But that's exactly what the OP wants, a circuit that adds low order harmonics. Basically something that distorts the input signal in a particular way.
The 60 dB gain is probably a misunderstanding.
It is not HiFi. The misunderstanding is that OP thinks "warm" sound is obtained with too much gain. It will distort. In a way that is right to the average tube pilot but it is far from HiFi. So as long as terms are misinterpreted the rest of the audio world will not understand. If one wants to add something/anything to a signal it can not be called HiFi. HiFi normally is amplifying signals to speakers with as least manipulation as possible.
What OP seems to want is what guitar players etc. need/want. Overdriven/distorted sound. We go into great lengths to have that overdriven/distorted sound as perfect as possible through our chain 😀
What OP seems to want is what guitar players etc. need/want. Overdriven/distorted sound. We go into great lengths to have that overdriven/distorted sound as perfect as possible through our chain 😀
Last edited:
I perfectly understand that. My point is that the OP does not mention Hi-Fi at all. He wants "warm sound". That usually means 2nd harmonic-rich sound.
Post #7 was edited. It was mentioned to be HiFi.
In order to keep to logic people react to written statements. It would not be logic to react to stuff that was not written.
In order to keep to logic people react to written statements. It would not be logic to react to stuff that was not written.
Last edited:
Guys, I might have misunderstood the term HiFi. In short, I just want to design a preamp that has harmonic rich sound that's pleasing to the human ear at a relatively low voltage, in this case, 48 volts(in case of using tubes), I only want to know some advices to commit this goal, technologies, similar circuits etc. Regarding the gain, it's just a reference I saw in commercial devices like the one I mentioned as a reference ._.' In the end, my idea is a preamp with high harmonic content for that warm sound.
A preamp to amplify what signals? Tuner, CD etc? That voltage is too low for most tubes. If you care about not being electrocuted you may use low voltage tubes designed for low voltages.
High Fidelity.....Alta Fidelidad....
Let's suppose you listened to a few audio setups with shrill sounding cheap stuff. You do not like that metallic sound, bleh, yuck. What about making a low gain neutral preamp (who needs gain these days?) and just try that out? Maybe you will enjoy that better and perceive it as warm sound.
High Fidelity.....Alta Fidelidad....
Let's suppose you listened to a few audio setups with shrill sounding cheap stuff. You do not like that metallic sound, bleh, yuck. What about making a low gain neutral preamp (who needs gain these days?) and just try that out? Maybe you will enjoy that better and perceive it as warm sound.
Last edited:
To amplify microphone and instrument signals, the reason for using low voltage is that I can't find transformers in my area for the high voltage levels that tubes operate with. It would be helpful if you know of any references or websites where I could purchase them. An alternative was to design it with low voltage, but focusing on those harmonics
Last edited:
Ha! Now it is clear. You do know that you can use 2 normal low voltage transformers piggybacked for 110V AC? So when only a few signal tubes are used for instance a 110:12V 10VA type to a same type but then 12:110V. That means the 12V secondary of the first used as primary of the second transformer. You will have about 150...160V DC then after rectification/filtering.
You may also want to include an input transformer both for safety and for sound.
This man has designed a nice and safe one that even drives 600 Ohm. Tried and tested and there are PCBs for it. Not cheap but safe and good.
http://www.pmillett.com/micpre.htm
Please do not underestimate the peligro of high DC voltages. Always have stuff checked by someone with experience and the best tip of all: always keep one hand in a pocket!
You may also want to include an input transformer both for safety and for sound.
This man has designed a nice and safe one that even drives 600 Ohm. Tried and tested and there are PCBs for it. Not cheap but safe and good.
http://www.pmillett.com/micpre.htm
Please do not underestimate the peligro of high DC voltages. Always have stuff checked by someone with experience and the best tip of all: always keep one hand in a pocket!
Last edited:
My aikido runs on 12VAC as only power supply. Yet any ac can be multiplied to any DC in the end.
