I have been working on this preamp for a while now, it has a dual gain stage, the potentiometer sits in the middle of the two gain stages and is a 10k pot. The second stage has a switch, which can be used to turn the gain on of off. When the switch is in the off position, the switch is out of the circuit and the second gain stage acts as a buffer.
The default gain is 1.5x for the first stage and unity gain for the second stage (gain switch =off). For low voltage sources like portable devices, the second stage has a gain of about 4.2x, giving a total gain of about 6x. You can configure it as a buffer-pot-buffer also by skipping a resistor in the first gain stage.
There are some SMD 1206 components in this.
I am using dual 16.5v supply with this. Depending upon the opamp used and your output voltage requirements, you can also power it with 2 or 4 9v batteries.
The two channels are completely independent. They only share the pcb, you can use these for monoblock operation also.
I have omitted both input and output caps from the build as my amp has a 2.2uf input cap.
I tested it with quite a few opamps, with both using the scope and music. I checked the waveforms at 20hz, 1khz, 20khz. The load was 10k resistor and 3300pf capacitor. There are no oscillations with 200Mhz bandwidth setting of the scope.
I tested with the following opamps: LM6172, LME49725, NE5532, OPA1642, OPA2134, OPA2107, OPA2227, AD8599. Yeah, even the dreaded LM6172 is absolutely stable, in my opinion, it probably sounded best of the lot.
I have a few more opamps that I have that I wish to test with, these require a lower supply (max 15v), so I would modify the supply and test these out and post here. I also might have a few good ones in existing equipment, will check and test if some opamp looks worth it.
I tested a lot with familiar music, familiar speakers. These are a bunch of very good opamps and there are only minor differences. You can try with any of these with this PCB and you wont be disappointed. Its going to be more of which one suits your current system more.
I initially used panasonic fc 470/25v caps for onboard supply. These sounded fine, later I changed these to elna silmic 47uf/35v. There was a significant change, sound cleared up a lot. These caps do require some burn in time. Initially these sounded a little harsh and bright, but only after a few hours it improved a lot. I also want to try a panny FM here.
I did a lot of testing with single channel (the smd ones, I ran out of opamp adaptors), so the sound stage related observations arent there. I used foobar plugin for stereo to mono for this. Once I get more adaptors and find time, will post more info about stereo tests.
Here is the Link with detailed documentation like build guide, schematic, images, BOM etc. Click on the additional information tab once you goto the page.
The name is of course blues based, Blues Before Sunrise.
PIcs:
Schematic
The default gain is 1.5x for the first stage and unity gain for the second stage (gain switch =off). For low voltage sources like portable devices, the second stage has a gain of about 4.2x, giving a total gain of about 6x. You can configure it as a buffer-pot-buffer also by skipping a resistor in the first gain stage.
There are some SMD 1206 components in this.
I am using dual 16.5v supply with this. Depending upon the opamp used and your output voltage requirements, you can also power it with 2 or 4 9v batteries.
The two channels are completely independent. They only share the pcb, you can use these for monoblock operation also.
I have omitted both input and output caps from the build as my amp has a 2.2uf input cap.
I tested it with quite a few opamps, with both using the scope and music. I checked the waveforms at 20hz, 1khz, 20khz. The load was 10k resistor and 3300pf capacitor. There are no oscillations with 200Mhz bandwidth setting of the scope.
I tested with the following opamps: LM6172, LME49725, NE5532, OPA1642, OPA2134, OPA2107, OPA2227, AD8599. Yeah, even the dreaded LM6172 is absolutely stable, in my opinion, it probably sounded best of the lot.
I have a few more opamps that I have that I wish to test with, these require a lower supply (max 15v), so I would modify the supply and test these out and post here. I also might have a few good ones in existing equipment, will check and test if some opamp looks worth it.
I tested a lot with familiar music, familiar speakers. These are a bunch of very good opamps and there are only minor differences. You can try with any of these with this PCB and you wont be disappointed. Its going to be more of which one suits your current system more.
I initially used panasonic fc 470/25v caps for onboard supply. These sounded fine, later I changed these to elna silmic 47uf/35v. There was a significant change, sound cleared up a lot. These caps do require some burn in time. Initially these sounded a little harsh and bright, but only after a few hours it improved a lot. I also want to try a panny FM here.
I did a lot of testing with single channel (the smd ones, I ran out of opamp adaptors), so the sound stage related observations arent there. I used foobar plugin for stereo to mono for this. Once I get more adaptors and find time, will post more info about stereo tests.
Here is the Link with detailed documentation like build guide, schematic, images, BOM etc. Click on the additional information tab once you goto the page.
The name is of course blues based, Blues Before Sunrise.
PIcs:
Schematic
hyeah
