I have added the caps, and used the floating ground as a reference for the feedback divider and the input.
I see the point of the 3,9k now. Without it voltage will drift with no speaker connected.
I cheated and did not change the input circuit for now (exept C2 removed), but I see no issues when powering it up and feeding a sine wave, or even disconnecting the input. The voltage of the floating ground can be adjusted by the offset trimmer perfectly, and it seems to stay there.
What values would be reasonable limits to adjust the 8,2k for Q4 current?
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As you are using 19v instead of 27 the value of 8.2k can be 5.6k to 56k for 3ma to 0.3ma extra current for the input transistor . As you noticed you can tune the sound with it . The 3.3k resistor on the base of the driver was for 3055 , now you chose another transistor you may also adjust it for higher value , always with ears . All at the end , readjust the sweat spot point for the outputs . The input capacitor 100uf , remember the + is towards the input . How long is the cable of 19v laptop supply?
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Ok! I will try it as it is first, to check if I hear improvement in the bass from the floating ground. Input capacitor is still standard too.
I liked it very much (except bass) in the beginning, after I just replaced the output transistors (and got the 2A Iq), so I would like to try it like that, only with added floating ground too..
The cable from the laptop supply is maybe 15cm long. I also have connection between 230V gnd and 19V gnd on that one, I have to remember to disconnect that before I try it..
I liked it very much (except bass) in the beginning, after I just replaced the output transistors (and got the 2A Iq), so I would like to try it like that, only with added floating ground too..
The cable from the laptop supply is maybe 15cm long. I also have connection between 230V gnd and 19V gnd on that one, I have to remember to disconnect that before I try it..
I have a problem.. With both channels connected to the same supply, and then the floating grounds of each channel is connected via the ground of the input at the source. This is picking up a lot of noise, and who knows what happens then both channels are loaded with stereo signals, and currents start flowing through the input ground between the amplifiers through my sound card..
I could see already with only one channel powered (only + disconnected on the other), the led was on without + supply because of supply through the gnd of the input..I guess with this concept there should be two separate supplies, one will not work?
I could see already with only one channel powered (only + disconnected on the other), the led was on without + supply because of supply through the gnd of the input..I guess with this concept there should be two separate supplies, one will not work?
Yes, I will have to get some connectors before I can hook up two supplies. I think it's actually stated somewhere in the beginning of the thread, I just forgot about it.
I did a measurement/adjustment on them. Current was up to near 2A again, and IMD was lower again, same levels as I measured & posted before when I had only replaced the outputs and had the same Iq.
An externally hosted image should be here but it was not working when we last tested it.
Sublimed JLH 1969-2.JPG - Google Drive
Qb Q3 have nearly the same current adjusted by Ra 8.2k . Q4 have half of R4 determined by the bias current / by Hfe of the output lower transistor.
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The input capacitor does the filter , you can apply only small value less than 1uf or else it may go motorboating .
This amplifier is conceived for 8 ohms load . I suppose you are using 4 ohms . The damping factor is not enough. To higher it you must increase the open loop gain by R1. Cut it and listen if the bass reflex of your speaker works . If the amp oscillates, than a zobel on the output or few picofarad capacitor from output to the base of Q3 can help. Apply then 22k adjust instead of R1 temporarily and by listening find the best equilibrium between the bass and the tweeter.
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Now I have done a little listening with the floating ground. Bass is better, but I don't hear a massive improvement on the speakers I'm listening to. This is compared to when I had double capacitance on the output cap, and 15mF on the supply. I think the speakers are a pretty easy load, and do not play very low. I would say the bass is up to the same level as with my favorite for 8ohm bass, LJM MX50SE.
However, I don't like the sound after the CCS modification. The treble is too forward for my taste, not blending with the rest. It sounds like I lost some with and depth to the sound. I will try some adjustment on that part.
Below is a picture of my test setup. I used the power bricks and the base for my PNP JLH to get the dual supply for floating ground. Capacitors are 15mF.
However, I don't like the sound after the CCS modification. The treble is too forward for my taste, not blending with the rest. It sounds like I lost some with and depth to the sound. I will try some adjustment on that part.
Below is a picture of my test setup. I used the power bricks and the base for my PNP JLH to get the dual supply for floating ground. Capacitors are 15mF.
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I know, the supply cable got longer because I temporarily used the supplies from another amplifier. I don't want the supplies really close to the boards either, thinking they radiate some noise that might be picked up in the amps.
The capacitors are something I had from before, but the ESR measures good at least up to 10kHz (limit of the meter), so I figured they would be good enough.
After listening more last night (different music), I heard more improvements in the bass department. I'm happy with the bass performance, I only want to tweak the brightness.
The capacitors are something I had from before, but the ESR measures good at least up to 10kHz (limit of the meter), so I figured they would be good enough.
After listening more last night (different music), I heard more improvements in the bass department. I'm happy with the bass performance, I only want to tweak the brightness.
Adjust the 8.2k pull up current mirrors resistor , my power supply is few centimeters away with no problem .
I will be off line from tomorrow until 11 dec.
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Ok, thank you for the input! I forgot to thank you for all the help so far!
I will look in to that later, will see what kind of case and arrangement it ends up in when I'm finished playing around with it. Still have to try a bigger input cap etc.. At the moment I'm enjoying listening to it
Sound is crisp and clear with a good balance to it, and no headache so far. I played around with the CCS with a trimmer, but it ended up in the minimum current position. I can see on the FFT that this 'spices up' the 2nd harmonic when the current is increased.
FFT is really clean too, low IMD and THD and noise, since I've played around with the trimmers and resistors a bit. Iq is abt 1,5A at the moment. It's a bit sensitive on the adjustments, since everything drifts a little bit with temperature, so I tried to dial in the 'sweet spot' when it was up to working temperature.
I still have to do some referencing on the bass with some other amp, and I should try it with some better speakers too.
I will look in to that later, will see what kind of case and arrangement it ends up in when I'm finished playing around with it. Still have to try a bigger input cap etc.. At the moment I'm enjoying listening to it
Sound is crisp and clear with a good balance to it, and no headache so far. I played around with the CCS with a trimmer, but it ended up in the minimum current position. I can see on the FFT that this 'spices up' the 2nd harmonic when the current is increased.
FFT is really clean too, low IMD and THD and noise, since I've played around with the trimmers and resistors a bit. Iq is abt 1,5A at the moment. It's a bit sensitive on the adjustments, since everything drifts a little bit with temperature, so I tried to dial in the 'sweet spot' when it was up to working temperature.
I still have to do some referencing on the bass with some other amp, and I should try it with some better speakers too.
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