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Old 20th February 2010, 06:43 PM   #101
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Quote:
Originally Posted by wahab View Post
surely, the difference in basses is due to input capacitance being too low in the 1558Q schematic from phillips.

personally, i did double the value, although, as you mention it, its somewhat useless considering the kind of speakers that are used with it..
just waiting for your 8561Q investigations, i m dead curious about it. Hope it will be successful, as this chip seems to be a good replacement of its helder brother...
Sorry, its going to take a bit of time. Work has set in for now, so it will be some days before there's a "head to head" comparison of the two amps.

For TDA1554Q, the power circuit used is 100nF//47uF at the amp chip, cabled out to 3300uF at the size M jack, and these caps are signal grade high quality models. You can, of course, substitute nearby values. The power supply is an SMPS.

STK test, head to head against STK459 running on capacitive multiplier power supply, is an old amplifier which is the prior "gold standard" of decent quality mid-fi (for comparison), shows TDA1554 giving at approximately this quality of performance.

Any handbuilt amp should be able to pass this test before its considered a worthwhile project to repeat. The TDA1554 does pass this test and thus shows that it can provide some entertaining music replay, and its Not likely to be discarded. The TDA1554 isn't hifi, but it is a worthwhile project, due to price versus performance ratio. In comparison, most amplifiers in retail stores cannot pass this test, regardless of their terribly higher prices.

In addition, you can pre-set the bass-n-treble by your choice of input cap size for bass and your choice of bypass cap (smaller cap parallel with input cap) for treble. This allows you to match it somewhat to your speakers without having to use an eq or tone control.

Not bad for less than $20 and a bit of of soldering!

Soon (when work lets up) we'll check out 8561Q and see if that one can do better resolution, such as hi-fi. I'm hoping. . .

Last edited by danielwritesbac; 20th February 2010 at 06:47 PM.
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Old 20th February 2010, 06:52 PM   #102
paulb is offline paulb  Canada
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Quote:
Originally Posted by danielwritesbac View Post
In addition, you can pre-set the bass-n-treble by your choice of input cap size for bass and your choice of bypass cap (smaller cap parallel with input cap) for treble. This allows you to match it somewhat to your speakers without having to use an eq or tone control.
Still misleading the general public, eh?
Changing input capacitance values will only affect the bass response. You would need a low-pass filter to affect the treble, and a capacitor in series running to a resistive load is a high-pass filter.
If your thinking is that low frequencies go through the big cap, and high frequencies through (just) the small cap, this is incorrect.

Last edited by paulb; 20th February 2010 at 06:54 PM.
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Old 20th February 2010, 08:24 PM   #103
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Quote:
Originally Posted by paulb View Post
Still misleading the general public, eh?
Changing input capacitance values will only affect the bass response. You would need a low-pass filter to affect the treble, and a capacitor in series running to a resistive load is a high-pass filter.
The smaller cap affects signal in its passband, which is treble.
This method is not helpful all of the time; however, it can be noticeable in conditions where gain is applied.

If you haven't explored this yet, then now might be a good time.
Input filter cap + tiny bypass cap in parallel with it is a fantastic method to combine two cheap caps to approximate the performance of a single spendy cap. Therefore, I do believe that the common technique is appropriate for this low budget amplifier.

Clearly put:
No, a bypass cap will not make a large difference in treble.
No, a bypass cap cannot compete with the effectiveness of a baxandall (bass-n-treble) circuit.
Yes, a bypass cap will potentially make a slight boost in treble response.
Yes, if all you needed was a slight treble boost then a bypass cap can help you avoid the overall signal quality reduction of using a baxandall/eq.
And, unfortunately, a System with TDA1554Q cannot withstand a further reduction in quality, so we really do need to omit the equalizer.

Hopefully there will be better luck with the newer model, which is TDA8561Q (not yet interviewed). . .

P.S.
I don't wish to explore input cap tomfoolery any farther than the simple, common and classic methods; because, almost all other areas of the amplifier are much more important. Please do let this be the end of it, because when "getting close is still off the mark" then we need to explore a different car chip amp.
P.P.S.
Information: LA4628 is already recommendable on both fidelity and ease of use (put speaker zobels onto nearby speaker jacks), but it comes with the caveats (trouble) of needing a larger heatsink, stronger power (laptop cord will do fine) and a few more components than its competitors from Philips.
My reason to play with the Philips parts is fascination over the fairly dramatic decrease in price due to its high efficiency costing less for power and heatsinks.

Last edited by danielwritesbac; 20th February 2010 at 08:31 PM.
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Old 10th March 2010, 01:01 AM   #104
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Any news Daniel?

It's almost spring break so I will be able to work on this project now. Any advice on the new build?
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Old 10th March 2010, 01:09 PM   #105
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Originally Posted by irishpatrick33 View Post
Any news Daniel?

It's almost spring break so I will be able to work on this project now. Any advice on the new build?
Sure.

The chip you already have will maximize a 12vdc power supply, it really must have a potentiometer, and it probably should have a metal box. That deal is a bit noisy, but it can be used with compact speakers, which are inefficient and thus more difficult to hear noise (and everything). Its an odd chip, because whatever isn't noise is hifi. lol! weird, but fun! Check DC offset before connecting speakers--larger size input caps cause greater DC offset, so use at or close to spec (from the datasheet).

For the 15vdc econo laptop supply: TDA8561Q/TDA1554Q also run cool and will heatsink easily onto available metal scrap or direct-mount to a metal enclosure. Oddly enough, it will take the Philips TDA1554Q about two weeks of use or more before its transistors run smooth (you'll hear a bit of "grit" when the amp is new, but mine smoothed out).

For the 15vdc econo laptop supply:
LA4628 is the premium option, but needs a higher amperage 15vdc~16.5vdc laptop cord, such as the one that I've got listed here in your thread (earlier), and LA4628 needs a Real heatsink. The "extra parts" of LA4628 are simply speaker output zobel, and those may be mounted onto the speaker jack itself.

All of these chips are designed for unit ground, and thus Ground, Signal Ground, and NC are all ground. You can easily re-bend the chip (pins bend about 3x before losing integrity) so that the power pins are all closest to the chip's face, the ground bus pins are in the middle and the audio pins are at the bottom. This is like "3 rows across" and the spacing in-between rows is about the same as the pin spacing of a capacitor. Holding at maximum 100uF size parts, these amps have no need of a circuit board.
On-amp power circuit has 100uF//100nF with additional capacitance a short distance away (dc input jack of enclosure) via cable.*
A bit of 4 conductor zip wire from the auto parts store has the exact spacing of the Philips chip's speaker output pins, and this cable can keep the pins from touching.
Input filter capacitors go between potentiometer and amplifier; however, these are tiny caps and may be mounted upon the potentiometer itself. For amps that take output zobel, those parts can be mounted upon the speaker jack.

*If the power supply is weak, it may not be able to deal with a bass beat, and for this reason, I put a larger capacity cap (1500uF~3300uF) in parallel with my DC input jack. I found this cap(s) on an old computer motherboard and simply recycled it.

Voltage and clipping:
The 15vdc econo laptop cord will make less clipping than a 12vdc wall plug. Higher voltage makes for less clipping because it makes for a more powerful amplifier. Most automotive chips top out at 15.5vdc soa.
Caveat: Using higher than 12vdc requires a regulated power supply in order to insure expected voltages and resistance to surges.

Output versus clipping (Speakers are the output):
Generally, you could use the 12vdc supply if your speakers are 4 ohm; or you could use the 15vdc supply if your speakers are 8 ohm. A possible combination of 15vdc with 4 ohm speakers needs good quality heatsinking because that combination is absolute maximum power (and heat!). Consider that some 90db 8 ohm speakers will play as loud as some 87db 4 ohm speakers; however, any 8 ohm speakers will make Much less heat in the amplifier.
Interesting research: See Parts Express website and have a look at woofers that have a generally flat response (less crossover losses that way) and high efficiency too, because this sort is ideal for speakers that work well with small amplifiers. Edit: The exception is that if your particular model of car chip amp is stuck at excessively high gain then that one is best used with commonplace inefficient speakers in order to decrease noise floor output; but that just further reinforces the idea that speakers are the output.

Other thoughts: These low voltage technologies work best in small rooms, probably because that is decently close to expected usage. The low voltage car chip amp brings with it the high availability of inexpensive regulated power supplies, and even though the datasheet figures of the amplifier itself may be inferior to hi-fi amps, use of small regulated power supplies (with their considerably cleaner power) may help the little car chips compete with a hi-fi amplifier. The expected performance of this combination (handbuilt car chip amp on regulated power) exceeds the quality of products available at Best Buy and other mass production black-box retail audio vendors. So, its probably worth your time to play with the car chip amps.

Last edited by danielwritesbac; 10th March 2010 at 01:13 PM.
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Old 10th March 2010, 01:37 PM   #106
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Default Efficiency exploration

Given a larger enclosure with an AC mains power switch to cut off the APFC switchmode power supply and. . .
A circuit that would exchange the speaker load for a 120 ohm load and simultaneously operate the mute/standby function upon detection that no music has played for a few minutes; and, also given an additional circuit that would power down the amp if it was forgotten left on, then the Philips products could qualify for and exceed the Class IV energy efficiency rating, which is the current highest standard.

So if you want an amp to "leave on" but don't want the nonstop treble output, extraneous complexities and durability issues of Class-D, then try out the Philips class A-B instead. One thing is for sure, the heatsink ratio is much cheaper than average for a Class A-B linear amplifier.

At this time, my Philips has been left on, and without the additional circuits to force energy efficiency. The 3"x3"x1" heatsink ($1.80) is approximately room temperature despite the 4 ohm load which is connected to a linear amplifier (how the heck?). Given a switch to disconnect the power supply from the AC side, this amplifier could probably still qualify for an energy efficiency rating.
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Old 10th March 2010, 05:37 PM   #107
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Sorry to hear that. I was hoping the 8561Q was a better performer than the previous attempts.
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Old 13th March 2010, 08:04 AM   #108
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Quote:
Originally Posted by irishpatrick33 View Post
Sorry to hear that. I was hoping the 8561Q was a better performer than the previous attempts.
I have not yet had time to optimize support circuit for this one. My apologies.

Its best performance has not yet been observed--no evaluation on it at this time.
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Old 13th March 2010, 08:06 AM   #109
wahab is offline wahab  Algeria
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Great work, daniel..
But seems that there s some pessimism by there.
I ll order a 8561Q soon for verification purposes.

Anyway, those chips are in need of an input potentiometer,
as they were designed to be used this way.
A direct connection to a laptop would be catastrophic,
whatever the amp used.
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Old 21st March 2010, 05:20 AM   #110
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Default TDA1554Q Lengthy testing complete.

I wondered what it would be like living with TDA1554Q and have run it as my only system for some time now.

Like most of the car amps, its tonality beats most gainclones, quite easily (but that is mostly due to the regulated power supply).

Oddly enough, it sounded like "transistor grit" for some days but has since smoothed that out completely and then the amp got more powerful. Break-in takes an so long that the timeframe isn't plausible. But, I can definitely confirm that it got more powerful after being left on for a week.

To power my big 8 ohm speakers, I used a 15vdc regulated high-efficiency Toshiba laptop supply (vendor listed earlier in this thread). At 12v, the amp was disappointing. At 15 it works fine. For reference, my car would have powered it to 14.4~14.8vdc with the car running.

The expectation for this amplifier was, at long last, met when it exceeded the performance of the reference headphones because of assisting in extrapolating a compressed audio file. The effect is not strong; however playback of WMA@48kbits (flat soundfield--very boring) demonstrated a large soundfield and thus this amp can amplify more than just voltage. It can amplify music. For that, it has earned itself an enclosure.

I do think that more is possible; however, TDA1554 is a good amp, once past its lengthy break-in(!), and then fine tuned a bit.

Summary:
A pleasant tone for lengthy listening
Easy assembly--high probability of success
Runs well with 15vdc cheap ebay laptop cord
Very inexpensive
Extreme high efficiency!!!

P.S.
This amp wasn't sufficient with the 12vdc wall plug (I'm running 8 ohm speakers). Sorry about that. Will try again later. Perhaps there's another model that will run well under-volted?
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