normH
Where's the goat.
Ok, let’s see what the electronic hoodspa is here. I have a Smokey Poly amp. I really don’t like the distortion it has. I don’t mind the speaker break up, but the distortion is to strong two soon. I could reduce the gain a lot and clean it up for the most part. If I were to add negative feedback to lower the distortion roll on, I would still have the problem of low input impedance dragging the pups down. If I were to add a fet input buffer, ala the Ruby or the Noisy Cricket, I would have to add even more negative feedback and would have to find a balance between the clipping of the fet and the clipping of the JRC386.
Instead of fighting these issues, I decided to design a different circuit. I like the warmth of a tube amp. A tube amp has three main things going for it, a slow slew rate of about 2 volt/microsecond, a tube follows a 3/2 law, and the transformer helps suppress the second harmonic.
I decided to attempt to overcome the 3/2 law by using a FET buffered input biased into the 3/2 point. I am attempting to slow the slew rate and approach the harmonic issues by using an inductive coupling to the op amp driver and inductive coupling output. The tough part is attempting a 3/2 bias of the op amp, I don’t know if it can be done with a bifet. I could use a cmos op amp and achieve the desired bias, but the sound would be brittle.
So this is a FET buffered input that has a 3 Meg ohm input. Inductively coupled to a bifet low power audio/video IC that is slew controlled and inductively coupled to the output. The op amp is a coupled class A summing amplifier. The output should drive either a 4 or 8 ohm speaker or cabinet. The amp is designed for use with two 9 volt batteries wired in a positive/negative configuration for a total of an 18 volt supply rail. The total voltage gain is six for about a 6.75 decibel gain. The input buffer can be driven into a soft clipping typical of a tube amp and that circuit is designed to emulate a 12AXJ tube. I am deliberately using poor quality Radio Shack transformers with a constant low voltage through them to more easily saturate the transformers. The entire amp is designed to fit into a Smokey Poly enclosure.
Give me some feedback on whether you think this amp would work as outlined, any design defects there might be, and if you have them, any circuit alterations you might think would be called for.
Below is attached a penciled schematic for the amp. Yes, some of us old goats still use paper and pencil although both are getting hard to find. Now where on this computer have I hidden Maple 13 and Maple Sims?
Note schematic component correction:
R8 = 60k; R9 = 60k; R10 = 30k
Instead of fighting these issues, I decided to design a different circuit. I like the warmth of a tube amp. A tube amp has three main things going for it, a slow slew rate of about 2 volt/microsecond, a tube follows a 3/2 law, and the transformer helps suppress the second harmonic.
I decided to attempt to overcome the 3/2 law by using a FET buffered input biased into the 3/2 point. I am attempting to slow the slew rate and approach the harmonic issues by using an inductive coupling to the op amp driver and inductive coupling output. The tough part is attempting a 3/2 bias of the op amp, I don’t know if it can be done with a bifet. I could use a cmos op amp and achieve the desired bias, but the sound would be brittle.
So this is a FET buffered input that has a 3 Meg ohm input. Inductively coupled to a bifet low power audio/video IC that is slew controlled and inductively coupled to the output. The op amp is a coupled class A summing amplifier. The output should drive either a 4 or 8 ohm speaker or cabinet. The amp is designed for use with two 9 volt batteries wired in a positive/negative configuration for a total of an 18 volt supply rail. The total voltage gain is six for about a 6.75 decibel gain. The input buffer can be driven into a soft clipping typical of a tube amp and that circuit is designed to emulate a 12AXJ tube. I am deliberately using poor quality Radio Shack transformers with a constant low voltage through them to more easily saturate the transformers. The entire amp is designed to fit into a Smokey Poly enclosure.
Give me some feedback on whether you think this amp would work as outlined, any design defects there might be, and if you have them, any circuit alterations you might think would be called for.
Below is attached a penciled schematic for the amp. Yes, some of us old goats still use paper and pencil although both are getting hard to find. Now where on this computer have I hidden Maple 13 and Maple Sims?
Note schematic component correction:
R8 = 60k; R9 = 60k; R10 = 30k
