This circuit is my momentary whim, want to quickly hear its sound, even in the case of the schematic draw this test board. The circuit prototype is the famous Matisse circuit, but in the output of this one, I changed to the op amp, this benefit is to make the line more easily match the power amp. The use of positive and negative power supply, easier to find the power transformer.
Practical debugging output level adjustment does not enlarge the voltage state, so that the coloration of the op amp to minimize, by adding a small amount of feedback from the output to the tube, to prevent high frequency interference. This is also because I'm using is 6J1, because its features are vulnerable to outside interference. If a friend is to use other low magnification tube, you can cancel the feedback resistor.
This circuit is successfully installed, anti-jamming capability had the desired effect, relative to the first pure OP level, the sound of the tube can be well reflected. The positioning of the sound field but also because of the added feedback rather than a single tube so lax. However, too much feedback I do not like the dynamic of the sound will be compressed. Voice in the use of different op amp will be slightly different, and this to me when debugging a lot of fun, I am sure you like DIY friends can experience the feelings of which.
I like the sound of 6J1 with OPA2604, bile taste good, strong high-frequency detailed grainy, IF, like a silky smooth, low frequency is not an exaggeration, a little Microsoft points, but also acceptable.
6J1 with NE5532's voice, slightly fuzzy contrast to 2604 high-frequency point, not grainy, IF sound is very thick and full, the IF is best to listen to this test. Low-frequency part of the powerful but slightly mixed points, more suitable for listening to human voice.
6J1 with the voice of the BA4560, very neutral, unhurried, without exaggeration, the IF is the most realistic, like HIFI friends may like the sound. Unfortunately, the low frequency is too soft.
6J1 with the sound of TL072, this combination is very good, high-frequency and intermediate frequency is relatively bright, low-frequency strong without exaggeration, my friends and I found that this is a classic American sound. Dynamic well, the shortage of high-frequency detailed combination of better than OPA2604.
6J1 with LF353, rough voice, although I LF353 has been a soft spot, but this test is not the old version of NS LF353, but TI's, Texas, LF353, the sound quality is absolutely not the same grades.