Help me find the right amplifier

audioguru said:

Many years ago when I was a kid I had a soldering gun. It damaged everything I used it on because it could get red hot which is way too hot for soldering. I got my temperature controlled soldering iron when I got my first job many years ago and it still works perfectly and is still sold.

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Well.many years ago, I had a dual heat Weller gun which I still have. I didn't damage much because most of what i worked on was tube stuff. A 10-15 YO kid. Tube stuff. the HV anode always bothered me then, I built a 3 kV DC supply for a biology science fair project. I grew up and worked on 15 kV at 1.5A and 100 kV at 0.1A power supplies. I bet there haven;t been any problems since I rebuilt both of them.
Strange was a a resistor around 1-5 Meg ohms and 200 Watts as a bleeder resistor and keys to access.

then I bought a 40 W Iron.

I also bought a Master Appliance butane soldering iron which I really love. It has to get re-built every so often.

Then I got a Circuit specialists, hot air, iron and de-solder tool. You can't use solder and de-solder at the same time. If i was doing more activities, I'd buy an integrated de-solder tool.

Metcal, the RF soldering tool is probably the iron to emulate.

audioguru: I agree about it being luck. Remember that other 2x25W i used before, TDA7492. If i connect that to TCP115 speaker, it will clip badly at max volume, music stopping all the time, i guess amp isnt able to deliver the power. That is why i like this 2x50W amplifier so much, because it is cheap and delivers to my expectations. On 4 ohms it is outputing about 55W per channel, while the TCP115 is 45W speaker. So i was thinking, what if i just lower the pot until i see that 45W per channel ? The other thing is, a while ago u said there is a way to measure resistance of receiver so i can then make sure i set that resistance with resistor/pot. How do i do that ?

rjenkinsgb: This is the amp from the same brand, i actualy had this one at home a while ago. The problem is, at 4 ohms it delivers the same 50W per channel. So after i lower the pot and combine the L and R, i am at the same position i am with this existing 2x50W amp. Or am i missing something ?

Half the power or double the power is only a little less volume or more volume because the sensitivity of our hearing is logarithmic and is why volume controls are logarithmic.
If the Bluetooth receiver has an output resistance if 4.7k ohms and you load it with a 4.7k ohms mixing resistor and if it is able to drive it then the output voltage is half, resulting in the output current to also be half and then the output power is 1/4 which is noticefully less.

How do i measure the receiver output resistance ? Btw i decided i will just set the pot to 1K ohms and if it breaks, i will just replace it and set higher resistance

Also, i know double power is only 3dB and thats 23% perceived loudness, i read a lot about this. But if i set it at 100% volume and then at 77% ... the problem is that i KNOW what 100% sounds like, i just heard it and i certanly noticed the difference. But i agree, if someone limited my speaker to 77% without telling me, maybe i wouldn't even notice that it is playing less loud than it did the last week

The Bluetooth receiver does not produce enough output power to damage itself or a pot but if its load is too low for it then it produces severe distortion on all the loud peaks.
Solder together the middle wipers of the pot to make mono and set it to halfway, then turn it up slowly while listening for distorting loud peaks. Then turn it down a little for no distortion. Glue the pot.
If the user's phone is not as loud as your phone then it will not be loud enough.

I don't think my phone is anything special, its Samsung A3 2017 that i got second hand for 60€, im a really minimalistic type of guy and only ever buy something when there is absolute life necesity for it. I guess that is why i am 1 of the few who stores hot glue and solder leftovers in pots for (potential) future use. When i was going to college and had about 20.000€ in savings .. when i bought the coffe in college, i brought the plastic cup home because i couldn't stand to throw it away knowing that i could use it at home for this or that reason. Silly, i know, but thats how i live.

Anyway back to important stuff, please correct me where i am wrong. Let's say i bridge left and right channel together without any resistors and pots. I thought that the main danger doing that is because .. lets say part of the song is blasting at max volume on left channel and playing nothing on right channel. And in that situation, the voltage difference would drive the current from left channel into the right channel of the receiver and damage it (for the sake of argument lets say left channel is blasting at 16V and right channel is dead silent at 0V). And if we add a resistor, then its harder for current to flow into the 0V channel and easier to flow into the amplifier. Am i right in assuming this ? Because otherwise ... i mean, what if i put pot to 100% (0 ohms) and bridge the channels and put it to 100% and not notice any distortion, would that mean that there is minimal risk for receiver/amp to break down ?

My phone is a Sony and I always have it at max volume so I cannot turn it up high enough to hear when the sound level is low.

The maximum output current from a line-level Bluetooth receiver output is low so there might be no damage when one output tries to blast at max volume and is directly connected to the other channel that tries to have no output. Each output will produce half of the output voltage at a low current, but maybe with severe distortion. Resistors are added as a mixer to reduce the current. If the resistances are too high then the total volume is reduced.

Alright. So maybe i will go with about 1K for this speaker since my friend isnt so much about absolute max SPL as i am. And for my next speaker maybe i will test the stereo->mono with some minimal resistance or maybe even no resistance and then i can test how this amplifier handles it. Another test is distortion but i always like to leave a little headroom, because distortion is very different at different songs. Some songs are just quiet and in that case that extra SPL comes into play. There are certain songs that will slightly distort on my speaker and others who wont. Truth be told, when we listen to the speaker we are right next to it. And the loudness is such that we probably do not even notice the distortion. Not to mention .. u have to take the context .. i listen to rachmaninoff at home with my nice speakers. When i use BT speaker i usualy have a few beers and crank some silly songs from my youth, music of no quality and no one cares much about distortion as long as it is not to much. I really did a mistake when i started building this type of speakers not telling outright the context. On another forum people refused to even help me since they said TCP115 is to low quality to be worth words. Well, it might be, but if it is doing its job well for what me and friends use it for, then i think its just ok.

I made an amplifier and two speakers for my TV. I never play the amplifier loud enough to produce clipping distortion but when my son comes over for a visit he plays it loud and very distorted. I asked if he hears the distortion and he said no.

So I built a "clipping indicator" circuit that lights an LED when the amplifier is clipping and now when my son sees it he turns down the loudness.

I think some things also you have to learn to hear. For instance if i hear some speakers play, i can tell you nothing about the sound. I can only tell you if i like it or not, nothing more. An expert will say, ok, it has good thing, bad this, u can hear this, etc.

I had an argument with my friend who owns JBL extreme 1. After we measured that my speaker is louder and goes lower in bass, he pulled the stereo argument out, maybe defending his speaker or trying to annoy me. And i said, if i thought stereo was an issue, i would implement it in my speaker obviously, but i dont notice a difference so i didnt. And i said also, that talking about stereo in such a small enclosure where left and right speaker is right next to eachother is, well, kind of silly. And he said " nooo, r u crazy ? I can hear stereo and it is awesome". Now again, i dont know if he really notices it so much or he was just trying to defend his speaker or trash mine, but, i played probably 100 or 200 songs on speaker and only noticed it twice for like 5 seconds. And i have an extreme case of woofer on left and tweeter on right. If i secretely mixed his stereo JBL extreme 1 into mono ... well it would be fun to test if he noticed a difference. I certanly wouldnt, but maybe he would.

Btw to defend my friend and everyone else .. i have perfect pitch. 1 side effect of this is that when i hear someone playing a violin, or singing ... even if he misses the frequency for even 0.1Hz, it physicaly hurts me, i swear. And it was like this all my life when i was in music school, even some teachers didnt notice it. So its even more funny that small distortion doesn't bother me, i bet that if u were listening to my speaker when i crank it up, u would notice huge dirtortion and i would be like, what, where ??

SentinelAeon said:

rjenkinsgb: This is the amp from the same brand, i actualy had this one at home a while ago. The problem is, at 4 ohms it delivers the same 50W per channel. So after i lower the pot and combine the L and R, i am at the same position i am with this existing 2x50W amp. Or am i missing something

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I suggest that one because it uses an amp IC that you can get the data for, so it may be easier to reconfigure.

eg. It has gain setting pin; it's it not at maximum gain as supplied, changing a resistor could increase the gain to make up for the mixing loss.
It's just more versatile if you can follow the circuit and know what it's doing.

Hi SentinelAeon, thanks for reminding me. I haven't tested whether I have Perfect Pitch for months. Last night I asked Google to play musical A at 440Hz and now I thought of its pitch and got it exactly right.
If I know what something is supposed to sound like (maybe an acoustic guitar) then when it is played with distortion I hear the extra distortion, but since acid rock and electric geetars are full of distortion then I do not listen to them.

I hate to hear "singers" like Drake using Autotune that sounds fake and obvious. The first time I heard Cher sing Believe with Autotune I wondered how they played her voice pitch changes on a keyboard. They say 99% of singers today use Autotune to get the pitch perfectly in tune.

I have a simple question. When i am designing a box, i have to include volume of my speaker (everything from the speaker, so magnet, etc.). Where would i find such information for TCP115 ?

From the partsexpress.com product page...

I don't think you understood my question. I am designing the box in winisd. And after i calculate the port and enclosure size to get the satisfying F3 .. now i have to make that enclosure a big bigger to account for port volume, batteries volume, amplifier volume and also for volume that the speakers themselves take, since they are inside the box. I measured the volume of all components except the speakers themselves.

SentinelAeon said:

I don't think you understood my question. I am designing the box in winisd. And after i calculate the port and enclosure size to get the satisfying F3 .. now i have to make that enclosure a big bigger to account for port volume, batteries volume, amplifier volume and also for volume that the speakers themselves take, since they are inside the box. I measured the volume of all components except the speakers themselves.

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Ok i calculated it. Could someone verify it for me please ? Its around 0.17L or 170cm^3 which is about 10 cubic inches

Your enclosure volume is about 10 times larger than the recommended 0.06 cubic feet. It might cause the cone excursion to hit the magnet structure at high power and low frequencies.

0.06 cubic feet is 1.6L. My speaker is about 3.5L ...

I have another question that is not directly related to my current project. But as soon as i have time i will have to asemble that big 15L speaker for that guy who only cares about maximum SPL. I will be using a big 6" SB speaker. I calculated it, gives me decent F3 and a whooping 10dB more than my small speaker in which i have TCP115 which is 4" speaker. Now here is the thing, both speakers are rated at 40W, both speakers will use the same 2x50W amplifier. Now all this data is pointing that their power usage should be the same, or at least close, since i am using same amplifier, same batteries, same voltage. But since the bigger speaker will be so much larger, 6" vs 4", for some reason i am having difficulty accepting that they will consume similar amount of energy. Whats more - The bigger speaker has a much bigger sensitivity which means that for the same amount of SPL in dB, it will consume less energy. The reason i am asking is because i will only put 6 batteries into the speaker. For my small TCP115 speaker, i can drive it at max with those batteries for many many many many many hours, much more than i can stand drinking. So can you just confirm that it should be fine meaning it will consume similar amount of juice ?