Following on....Well i still have abit to go on this one. I think i'll need to add a pre-amp with volumn control in front of the signal, match the impedance correctly. A soft start circuit maybe, anything else?
I have a little Topping T amp TP20, if matched the impendance from the high level output to the signal input of the chip amp with a couple resistors i could use that TP20 as a preamp, right? but i'll need to measure and calculate and balance loads, and this i'm not too familiar with.
Soft start circuits, fairly straight foward i'd think, but should that be on the primary side of the transformer, or the secondary?
I have a little Topping T amp TP20, if matched the impendance from the high level output to the signal input of the chip amp with a couple resistors i could use that TP20 as a preamp, right? but i'll need to measure and calculate and balance loads, and this i'm not too familiar with.
Soft start circuits, fairly straight foward i'd think, but should that be on the primary side of the transformer, or the secondary?
I'm not familiar with the TP20 you mention. But an LME49710 with a motorized pot in front would make a killer preamp. Just add remote control...
The soft start circuit should go on the primary side.
~Tom
Ok, i was thinking it would have been alright to use the TP20 with a large value resistors on the high levels to bring it to a low level. The main reason for this idea is to add a volume control, and knowing the chip amp may need some pre gain on the signal to make full use of it's power.
Whats your theory with the 10K Log potentiometer Andrew?
Whats your theory with the 10K Log potentiometer Andrew?
determine from your source/s the max voltage swing and it's output driving impedance and calculate the chip amp gain needed to drive full swing at the chip amps output depending on its power rails. you want to keep the source level maxed to keep a good S/N ratio and use a variable pot at the chip amp input. Depending on the source impedance and pot value you may have some gain reduction to contend with. In most cases a preamp with gain is unnecessary.
example / with a source output of 2 Volts p-p, a chip amp with 32 Vdc rails will need a gain of about 20log(1+29) note 60 Vpp using 2V of overhead for each rail before clipping into very light loads. if the source is 1K into a 10K pot you will lose 20log 10K/(1K+10K) or a little less than 1dB
example / with a source output of 2 Volts p-p, a chip amp with 32 Vdc rails will need a gain of about 20log(1+29) note 60 Vpp using 2V of overhead for each rail before clipping into very light loads. if the source is 1K into a 10K pot you will lose 20log 10K/(1K+10K) or a little less than 1dB
Last edited:
So basicaly i may not need any pre amplification for as long as the source signal is strong enough, thats a no brainer. And a potentiometer on the input side for impendance matching and volume control) between the source and and amp. Is this correct what i'm saying?
I mean at the end of the day the source signal may well be my laptop sound card, the laptop may have the control of, and volume to drive the amp, no?
I mean at the end of the day the source signal may well be my laptop sound card, the laptop may have the control of, and volume to drive the amp, no?
I must add i am a beginner to the math and building of amps, so alot of this i can interpret, but may not be correctly. So please bare with me.
Hi Richard...
Worry about preamps and gain when the power amp is all done.
As Andrew mentions, a simple pot may well be all that is needed, certainly for any modern source.
If using a laptop etc then it's possible best sound will be with the laptop turned up and use a pot for volume rather than just using the laptop itself. It's also "safer" in that the inputs to the amp aren't "open" and so the potential for speaker damage etc is less when inadvertently connecting/disconnecting leads etc.
Measuring AC (music/noise) on a DVM won't work as infinia says. Pick a sine wave tone of say 100 to 400 hz which falls within any DVM's range. Measure that and that is an RMS voltage.
e.g. A cd player at 0db (max level on disc) would output approx 2 volts RMS. As a "peak" value that is 2vrm times root 2 or 2 *1.414 which is 2.828 volts pk. The peak to peak is 2.828 times 2 or 5.656 volts. From "top to bottom" in other words. Any source be it laptop or CD player etc won't be loaded noticeably by the power amp or a 10k pot.
Worry about preamps and gain when the power amp is all done.
As Andrew mentions, a simple pot may well be all that is needed, certainly for any modern source.
If using a laptop etc then it's possible best sound will be with the laptop turned up and use a pot for volume rather than just using the laptop itself. It's also "safer" in that the inputs to the amp aren't "open" and so the potential for speaker damage etc is less when inadvertently connecting/disconnecting leads etc.
Measuring AC (music/noise) on a DVM won't work as infinia says. Pick a sine wave tone of say 100 to 400 hz which falls within any DVM's range. Measure that and that is an RMS voltage.
e.g. A cd player at 0db (max level on disc) would output approx 2 volts RMS. As a "peak" value that is 2vrm times root 2 or 2 *1.414 which is 2.828 volts pk. The peak to peak is 2.828 times 2 or 5.656 volts. From "top to bottom" in other words. Any source be it laptop or CD player etc won't be loaded noticeably by the power amp or a 10k pot.
Just to clarify why the DVM won't work on music. It's because the DVM "averages" the reading over time and has a very very slow response. Music and pink noise is full of transients and these happen (as far as the DVM is concerned) so fast that they just don't register at all.
That 0.15vac you measured. If you looked at that on an oscillosope it could well be nearer 3 to 6 volts peak to peak.
That 0.15vac you measured. If you looked at that on an oscillosope it could well be nearer 3 to 6 volts peak to peak.
Allright got the toroidal tranny today, tested the AC voltage from it and got 27VAC *2 close 37VDC after the rectifier circuit. I hooked it all up correctly double checked, then double checked again, got the heat sinks on, and IT WORKS, and i must say these chip amps sound nice.. So i'm happy for the time being, and i'll be posting up in the next week with questions relating to this project, and further add-ons, protection circuits, soft start, pre-amp(maybe needed it this point???), and enclosures available within Australia, or available to Australia. I'll be looking around for some ideas on enclosures, i may build one, maybe. Thanks to everyone for the guidance and help, i learned some new things this last week. cheers!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.