skewed upwards, a lot.
That may explain the comments about lack of bass.
4Hz to 100kHz is more normal.
A squarewave check may show up something of what is happening that causes that HF bump.
That may explain the comments about lack of bass.
4Hz to 100kHz is more normal.
A squarewave check may show up something of what is happening that causes that HF bump.
Output transistor bias current is set with pot VR12. It is measured across R7 or R8, divide voltage by .5 resistor value to get current.
Bass drivers take some energy and 20 W isn't going to do it on real speakers. (it would work okay on headphones) . Change the resistor values to AX8 and boost the power transformer to 50-60v, Same transistors, similar geometry. There you are, punchy bass. Remember transformer peak voltage is 1.4 times the nominal voltage, and these single supply amps I think they show the peak value on the print as the rail, not the nominal transformer value. I'm running AX6 at 70v regulated from 80v peak, with some resistor tweaks to center the idle voltage. My Q1 has higher gain than the simulated one, I think.
Remember you don't have to run a 60 W amp at 60W all the time. Only in EDM or house "music" is the volume constant. I listen at 1 vpp most of the time, but have ~35 v there available if Tchaikovsky asks the orchestra to fire a cannon for an emotional peak.
Remember Q3 mounts on the output transistor heat sink so that the spreader voltage collapses as the output transistors heat up. Use an insulator.
The Power Supply cap has something to do with bass response. Too small and the rail sags before a bass note is through 1/2 cycle. I'm using 4300 uf on the ST120 with one channel AX6 driver. 1000 uf preregulator, 3300 uf post regulator. My bass response is quite adequate on my 101 db@1W1m speakers 8 ohms.
These 1967 organs all sound like wet kazoos with no bass or treble until I replace the dried up PS caps, then the Hammond H100s will rattle the light fixture.
Bass drivers take some energy and 20 W isn't going to do it on real speakers. (it would work okay on headphones) . Change the resistor values to AX8 and boost the power transformer to 50-60v, Same transistors, similar geometry. There you are, punchy bass. Remember transformer peak voltage is 1.4 times the nominal voltage, and these single supply amps I think they show the peak value on the print as the rail, not the nominal transformer value. I'm running AX6 at 70v regulated from 80v peak, with some resistor tweaks to center the idle voltage. My Q1 has higher gain than the simulated one, I think.
Remember you don't have to run a 60 W amp at 60W all the time. Only in EDM or house "music" is the volume constant. I listen at 1 vpp most of the time, but have ~35 v there available if Tchaikovsky asks the orchestra to fire a cannon for an emotional peak.
Remember Q3 mounts on the output transistor heat sink so that the spreader voltage collapses as the output transistors heat up. Use an insulator.
The Power Supply cap has something to do with bass response. Too small and the rail sags before a bass note is through 1/2 cycle. I'm using 4300 uf on the ST120 with one channel AX6 driver. 1000 uf preregulator, 3300 uf post regulator. My bass response is quite adequate on my 101 db@1W1m speakers 8 ohms.
These 1967 organs all sound like wet kazoos with no bass or treble until I replace the dried up PS caps, then the Hammond H100s will rattle the light fixture.
Last edited:
That is terrible.
How bad will it get with a bit of capacitance added to the output?
There are 5 electrolytics that may be the bottlenecks to bass performance.
The plastic input capacitor @ 1uF will roll off the bass -1dB @ ~5Hz.
There is a much more severe roll off higher than that.
Moving the input cap up to 4u7F will change the input filter and pass even more LF to the NFB capacitor and output capacitor.
Last edited:
Attachments
Much better! Now the last try i ask you, remove c16 c17 and change r4 r6 from 1k to 1k8 and r18 from 2k7 to 2k2.
Can you do it for me??many many thanks
Can you do it for me??many many thanks
You want a ~25 watt Amp?
As an Easy DIY that requires a minimum of Parts and is arguably one of the Best performing/sounding Amps designed by Anyone .. anywhere??
Go to the Pass Forum and ask there...could even peruse the DIYAudio 'shop'
Seriously unlikely one can .. honestly.. do a better amp. 😉
Curiously you had a similar suggestion in the First post/answer.
Something about leading horses to water??
As an Easy DIY that requires a minimum of Parts and is arguably one of the Best performing/sounding Amps designed by Anyone .. anywhere??
Go to the Pass Forum and ask there...could even peruse the DIYAudio 'shop'
Seriously unlikely one can .. honestly.. do a better amp. 😉
Curiously you had a similar suggestion in the First post/answer.
Something about leading horses to water??
Last edited:
C16 and C17 are not conventional and tbh C16 in particular adds a 680pf cap directly across the amp output which is not always a good thing as it can provoke very high frequency instability, particularly with less than perfect layouts and grounding schemes. C17 is isolated slightly by the 0.1 ohm but I'm not sure its a good thing. It would be better to add series resistor to the caps, even if only around 4 or 5 ohms. Maybe Carlos has a different idea but that is how I see it.
Small capacitance of around 1nf (and C16 is 0.68nf) can be enough to provoke some designs into oscillating.
Maybe the reasoning was that the caps will shunt any RF picked up by the speaker leads and stop them contaminating the feedback take off point in the amp (the main output node) but if so then I think the method is a little suspect.
Small capacitance of around 1nf (and C16 is 0.68nf) can be enough to provoke some designs into oscillating.
Maybe the reasoning was that the caps will shunt any RF picked up by the speaker leads and stop them contaminating the feedback take off point in the amp (the main output node) but if so then I think the method is a little suspect.
- Status
- Not open for further replies.