I recently bought this 6j1 tube preamp/headphone amp
Amazon.com: 12V DIY Preamplifier Kit 6J1 Preamp Tube Board Preamplifier 3.5MM Headphone Amplifier Replacement: Electronics
I like how it sounds through the headphones, and would like to use the preamp outputs to drive a class D power amp board.
Does anyone know how to find the gain at the preamp outputs? A buffer stage or does it actually amplify the signal? (I could not find any schematics online on this specific model)
Thank you
Amazon.com: 12V DIY Preamplifier Kit 6J1 Preamp Tube Board Preamplifier 3.5MM Headphone Amplifier Replacement: Electronics
I like how it sounds through the headphones, and would like to use the preamp outputs to drive a class D power amp board.
Does anyone know how to find the gain at the preamp outputs? A buffer stage or does it actually amplify the signal? (I could not find any schematics online on this specific model)
Thank you
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The 6J1 preamp that is everywhere is this one: Fever 6j1 diy kit resistors polarity? : diytubes
This does indeed have gain as the 6J1 is configured as a common cathode amplifier. Gain is approximately 8-10 (+18-20dB). The exact amount depends on if the resistor values and powersupply voltages are the same as the above schematic and also how closely the tubes match the datasheet.
Your amplifier seems to have an opamp added, which is probably just buffering the output of the 6J1, since the 6J1 doesn't provide enough current to drive most headphones. This way you still get the tubey sound and have enough current to drive the headphones. If you run the tubes with unity gain (cathode follower amplifier), you will get very little tube sound (distortion) imparted as the feedback needed to bring the gain to unity will linearise the amplifier.
To know exactly what you have bought you should trace the connections from the opamp and the 6J1 socket. Just noting the values of the resistors connected to the 6J1 and opamp (and which pins) will give us a fair idea of how things are configured, without having to trace the entire board.
Alternatively you could supply the amp a test tone (~1khz) and probe the input and output with a multimeter set to AC volts.
This does indeed have gain as the 6J1 is configured as a common cathode amplifier. Gain is approximately 8-10 (+18-20dB). The exact amount depends on if the resistor values and powersupply voltages are the same as the above schematic and also how closely the tubes match the datasheet.
Your amplifier seems to have an opamp added, which is probably just buffering the output of the 6J1, since the 6J1 doesn't provide enough current to drive most headphones. This way you still get the tubey sound and have enough current to drive the headphones. If you run the tubes with unity gain (cathode follower amplifier), you will get very little tube sound (distortion) imparted as the feedback needed to bring the gain to unity will linearise the amplifier.
To know exactly what you have bought you should trace the connections from the opamp and the 6J1 socket. Just noting the values of the resistors connected to the 6J1 and opamp (and which pins) will give us a fair idea of how things are configured, without having to trace the entire board.
Alternatively you could supply the amp a test tone (~1khz) and probe the input and output with a multimeter set to AC volts.
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Thanks TMM, for your suggestions.
I measured the AC voltage at the outputs using a 1 kHz test tone and 2V RMS input from my DAC.
With the volume halfway output is 2V and with the volume at max output is 5V.
I assume this is an 8 db gain?
I just found that another member drew the schematic for this board, and it looks like the pre-outs are before the op-amps
6J1\EF95 Hybrid Tube Preamp, Headphone Amp Teardown and Schematic
I measured the AC voltage at the outputs using a 1 kHz test tone and 2V RMS input from my DAC.
With the volume halfway output is 2V and with the volume at max output is 5V.
I assume this is an 8 db gain?
I just found that another member drew the schematic for this board, and it looks like the pre-outs are before the op-amps
6J1\EF95 Hybrid Tube Preamp, Headphone Amp Teardown and Schematic
Yes about 8dB. That sounds about right for that schematic. The gain is lower because the tube has a high output impedance and it is being loaded down by the opamp circuit input impedance (1kohm). The 8-10x gain from the tube is achieved with 100k load - if desired you could remove R24/R25 or C14/C15 and use the preout only.
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I am using the op-amps with the headphones and I like what I hear.
I also want to use the pre-outs to power a small class D board for desktop speakers.
I'm leaning towards this board
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The board is set at 26 db gain, 20 kohm input impedance, and I was mostly afraid not to overload with the additional pre-amp gain.
My dac provides 2V rms output, and I may need to lower that?
I also want to use the pre-outs to power a small class D board for desktop speakers.
I'm leaning towards this board
Access Denied
The board is set at 26 db gain, 20 kohm input impedance, and I was mostly afraid not to overload with the additional pre-amp gain.
My dac provides 2V rms output, and I may need to lower that?
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