OK I will try scoping the amp output before the speaker protection board. The board came with used Omron relays, maybe they have some resistance.
I have made some big mistakes on this build and generated a whole lot of discussion based on these - big apology to the forum (especially John who kindly retested his kit)
The shitty leads connecting the speaker terminal to the load dropped a lot of voltage so the DSO was off by 2-3V.
New results:
One channel driven with 1khz signal output into the 8.3 ohm load. Output voltage at the amp board terminals (before the speaker protection circuit) = 16.0 Vrms measured with true RMS DMM. 15.8Vrms at the speaker cable terminal.
Power available to drive speakers before clipping now 30.5W
Happy days. Wonder how this amp would compare with the old by highly regarded NAD 2030 that I once had?
I held my breath while shorting the outputs at the amp board and the chips survived.
I have another pair of LM1875 chips bought from an reputable electronics shop and the only difference I can detect is much crisper screen printing.
The shitty leads connecting the speaker terminal to the load dropped a lot of voltage so the DSO was off by 2-3V.
New results:
One channel driven with 1khz signal output into the 8.3 ohm load. Output voltage at the amp board terminals (before the speaker protection circuit) = 16.0 Vrms measured with true RMS DMM. 15.8Vrms at the speaker cable terminal.
Power available to drive speakers before clipping now 30.5W
Happy days. Wonder how this amp would compare with the old by highly regarded NAD 2030 that I once had?
I held my breath while shorting the outputs at the amp board and the chips survived.
I have another pair of LM1875 chips bought from an reputable electronics shop and the only difference I can detect is much crisper screen printing.
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Glad you have this sorted! People helping others. This is what the forum is all about.
As far as what the amplifier sounds like depends on a few things: The frequency response and distortion across the audio spectrum and from low to high power. Also the damping factor and the nature of the load connected to its output. Fortunately the LM1875 is a well behaved IC when the circuit is properly laid out (these little single chip boards are nicely done).
The LM1875's current limit kicks in at 3 amps rms. It is not sudden but a gradual application. It also utilizes a SOA (safe operating area) circuit for its output transistors. When operating these ICs close to their current limits with reactive loud speaker loads, there is some concern that these limiter circuits can affect the sound. One should make an impedance graph of the speakers to be used with the amp to be sure that there isn't a large dip at some frequency which would indicate the speaker might be a challenging load.
A lot of ICs and discrete amplifier current limiter circuits misbehave badly when activated by a reactive load. It can cause the output to slam to the opposite rail which makes a loud pop sound. The TDA2050 is guilty of this. The LM1875 has a more sophisticated circuit and seems to be immune to this, even when driving a transformer. Still, the activation of the current limiter can reduce the bass "punch".
As far as what the amplifier sounds like depends on a few things: The frequency response and distortion across the audio spectrum and from low to high power. Also the damping factor and the nature of the load connected to its output. Fortunately the LM1875 is a well behaved IC when the circuit is properly laid out (these little single chip boards are nicely done).
The LM1875's current limit kicks in at 3 amps rms. It is not sudden but a gradual application. It also utilizes a SOA (safe operating area) circuit for its output transistors. When operating these ICs close to their current limits with reactive loud speaker loads, there is some concern that these limiter circuits can affect the sound. One should make an impedance graph of the speakers to be used with the amp to be sure that there isn't a large dip at some frequency which would indicate the speaker might be a challenging load.
A lot of ICs and discrete amplifier current limiter circuits misbehave badly when activated by a reactive load. It can cause the output to slam to the opposite rail which makes a loud pop sound. The TDA2050 is guilty of this. The LM1875 has a more sophisticated circuit and seems to be immune to this, even when driving a transformer. Still, the activation of the current limiter can reduce the bass "punch".
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What does it sound like?
My 1875 (recently completed) using the blue boards and ALL replaced bits ie; Genuine 1875, Elna and Fg caps, even fresh resistors.
It sounds pretty good.. to be honest.
It is however of lesser Sq than my lm 3886 amp. ie; it has less bass power/depth, fewer sparkly highs... a reduced soundstage.
But at least there is one, I've had several amps that couldn't manage that.... grr.
That said; the lm 3886 was a ~200+$ amp adventure, the 1875 a ~50$ one.
However this 1875 amp is 'just fine' for it's intended Computer speaker usage.
I'd be hesitant to rely on it as a main system though.
As digression.. my Firstwatt (25watts) seriously outperforms my lm 3886 in ever possible way... despite being less than half it's 'power'.
It relegated it to storage years ago
Firstwatt is proving a lifelong 'keeper' .
All amps compared on the same Tannoy gold speakers
My 1875 (recently completed) using the blue boards and ALL replaced bits ie; Genuine 1875, Elna and Fg caps, even fresh resistors.
It sounds pretty good.. to be honest.
It is however of lesser Sq than my lm 3886 amp. ie; it has less bass power/depth, fewer sparkly highs... a reduced soundstage.
But at least there is one, I've had several amps that couldn't manage that.... grr.
That said; the lm 3886 was a ~200+$ amp adventure, the 1875 a ~50$ one.
However this 1875 amp is 'just fine' for it's intended Computer speaker usage.
I'd be hesitant to rely on it as a main system though.
As digression.. my Firstwatt (25watts) seriously outperforms my lm 3886 in ever possible way... despite being less than half it's 'power'.
It relegated it to storage years ago
Firstwatt is proving a lifelong 'keeper' .
All amps compared on the same Tannoy gold speakers
How does it sound?
Pretty good ‘cos I made it
Seriously, I don’t really know how to critically judge one amp from another. I can hear the difference between speakers! An MP3 Singing Beasts Crying Winds sound pretty good to me.
I think the amp will be best for near field listening (what I would call enthusiastic listening)- not a lot of watts for a party with a pair of low efficiency 86dB bookshelf speakers, but plenty for a medium sized room if needed. I may or may not use it with a DIY preamp depending on the source. I will be conscious of avoiding clipping (wish I had a clipping indicator to rely on).
Why did I make it?
Well I got caught up in John’s amplifier videos, had a desire to learn more electronics, had a basic electronics lab ready to output a substantial project, just built some speakers and needed a low power amp, like my music, love DIY.
Waiting for a new DAP to see what FLAC files will sound like. Just re-ripped all my favourite CDs ready to go when it arrives.
Just to wrap it up: one very solid but plain looking Chinese chassis kit (AU$70), two Chinese blue LM1875 mono amplifier boards with all supplied components replaced except ceramic caps and the chip amp (Dale resistors, Panasonic caps, also changed the signal input coupling cap)(maybe about AU$10-15 each). 120VA toroidal transformer (AU$50), Chinese DC power supply (AU$13), independent power supply for Chinese speaker protection board (AU$22+10), one possibly fake Alps pot (AU$12), some fuse holders and fuses for a grand total of about AU$210.
On to the next project.
Thanks again everyone!
Pretty good ‘cos I made it
Seriously, I don’t really know how to critically judge one amp from another. I can hear the difference between speakers! An MP3 Singing Beasts Crying Winds sound pretty good to me.
I think the amp will be best for near field listening (what I would call enthusiastic listening)- not a lot of watts for a party with a pair of low efficiency 86dB bookshelf speakers, but plenty for a medium sized room if needed. I may or may not use it with a DIY preamp depending on the source. I will be conscious of avoiding clipping (wish I had a clipping indicator to rely on).
Why did I make it?
Well I got caught up in John’s amplifier videos, had a desire to learn more electronics, had a basic electronics lab ready to output a substantial project, just built some speakers and needed a low power amp, like my music, love DIY.
Waiting for a new DAP to see what FLAC files will sound like. Just re-ripped all my favourite CDs ready to go when it arrives.
Just to wrap it up: one very solid but plain looking Chinese chassis kit (AU$70), two Chinese blue LM1875 mono amplifier boards with all supplied components replaced except ceramic caps and the chip amp (Dale resistors, Panasonic caps, also changed the signal input coupling cap)(maybe about AU$10-15 each). 120VA toroidal transformer (AU$50), Chinese DC power supply (AU$13), independent power supply for Chinese speaker protection board (AU$22+10), one possibly fake Alps pot (AU$12), some fuse holders and fuses for a grand total of about AU$210.
On to the next project.
Thanks again everyone!
One more test I want to do.
I have noticed that some music appears to have off centre vocals (Dire Straits CD).
Now considering I built the amp and the speakers, and that the music may have been recorded this way, I would like investigate but need some advice on measuring channel balance.
I know that I can do differential probing of the two channel outputs with a sine wave source signal to detect any L/R channel imbalance. How critical is it that the wires and resistive loads on the amplifier outputs have identical impedences? Is there a “best” setup for this? And if there is a difference, how is it corrected?
Cheers
I have noticed that some music appears to have off centre vocals (Dire Straits CD).
Now considering I built the amp and the speakers, and that the music may have been recorded this way, I would like investigate but need some advice on measuring channel balance.
I know that I can do differential probing of the two channel outputs with a sine wave source signal to detect any L/R channel imbalance. How critical is it that the wires and resistive loads on the amplifier outputs have identical impedences? Is there a “best” setup for this? And if there is a difference, how is it corrected?
Cheers
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As with any measurement, the more precise your methods, the better the results. As measured on the amp board, the damping factor of the the circuit is very high which would make the influence of any slight difference in the load impedance less critical.
Feed each channel the same signal using a Y splitter cable. This insures the exact same signal is on the inputs. Connect load resistors to the outputs and a speaker across the +L and +R output. Ideally, there will be no sound from the speaker, however, expect a small amount of signal to show.
Volume controls are the worst offenders of imbalance as they may not track perfectly.
Sorry to bring this post back to life but I have another questions about this amp’s capability.
I measured ~30w continuous clean power with one channel driven (with a 1khz sine wave (IIRC). I recall that this was achieved at about 80% dial rotation.
At this level does the amp have any dynamic headroom capacity? If not, how can I determine maximum volume setting?
I measured ~30w continuous clean power with one channel driven (with a 1khz sine wave (IIRC). I recall that this was achieved at about 80% dial rotation.
At this level does the amp have any dynamic headroom capacity? If not, how can I determine maximum volume setting?
Hi Dunk02
please look into the datasheet - you are at the max of this chip into 8R.
Figure 5 (1% THD - nobody wants to listen to this) and figure10 show you that with a 30W you are at the max!
please remember that a continuous signal is luckily not the music signal. music is more dynamic and therefore we have more pause - this is called crest factor --> this helps the amp to survive better.
If you really "need" 30W continuous power e.g. bad efficiency of the speakers or a very big room - you have to use a other chip for that.
chris
please look into the datasheet - you are at the max of this chip into 8R.
Figure 5 (1% THD - nobody wants to listen to this) and figure10 show you that with a 30W you are at the max!
please remember that a continuous signal is luckily not the music signal. music is more dynamic and therefore we have more pause - this is called crest factor --> this helps the amp to survive better
.If you really "need" 30W continuous power e.g. bad efficiency of the speakers or a very big room - you have to use a other chip for that.
chris
Play music through it in your system and environment and only worry if you find you're pushing it into distortion.
In normal rooms with normal speakers at normal listening volumes, power requirements rarely exceed 1 watt, which still leaves you 14dB of headroom if the amplifier can deliver 30W
In normal rooms with normal speakers at normal listening volumes, power requirements rarely exceed 1 watt, which still leaves you 14dB of headroom if the amplifier can deliver 30W
Hi Dunk02
please look into the datasheet - you are at the max of this chip into 8R.
Figure 5 (1% THD - nobody wants to listen to this) and figure10 show you that with a 30W you are at the max!
please remember that a continuous signal is luckily not the music signal. music is more dynamic and therefore we have more pause - this is called crest factor --> this helps the amp to survive better
If you really "need" 30W continuous power e.g. bad efficiency of the speakers or a very big room - you have to use a other chip for that.
chris
Hi Chis
Thanks for reminding me of some of the chip parameters.
I forgot to mention that I control volume with an NE5532 preamp and have been using the integrated amp as a power amp. Sometimes my source signal is low, and this adds a little extra volume. The speaker drivers are only rated at 30W (Dayton ND91-4) in the current setup, but not sure what the actual power handling capability will be (slightly more I expect as the crossover resistors etc will consume some watts).
I want to determine a suitable set and forget volume setting, presumably well within the LM1874 amps amplification linear range but at a point where I can expect sufficient dynamic headroom current to be available.
Is there a way to determine this?
If at 80% a signal at 0dB is clipping your volume range is about right, IMO.
Beyond that, music is recorded at different levels, speakers and rooms have varying efficiency, sources have varying output levels, listeners have varying volume preferences etc.
You're over thinking this. Put some music on and enjoy it!
Beyond that, music is recorded at different levels, speakers and rooms have varying efficiency, sources have varying output levels, listeners have varying volume preferences etc.
You're over thinking this. Put some music on and enjoy it!
Thanks Uber
I recently experienced some distortion from my FLAC player after dropping it (only a few inches) onto my desk, and I also think I detected bass loss when using some very light gauge speaker wire (now using 16AWG, 2m long). Both issues now fixed.
With nearly all the components in my system being DIY (including cables), trouble shooting these types of issues is tricky when I am not entirely sure how the amp performs.
No clipping indicator lights in either amp’s circuit!
Am I over thinking it?