Need Help which parts to upgrade?

[audioholik]

Hi,
i own an old car audio amps and i want to upgrade it.
but i dont know which parts should i go first..
so i need help to decide which parts should i upgrade
some component inside it still use cheap caps and IC.

i post some pics of the component inside.

for more detail parts
http://i12.photobucket.com/albums/a219/imoet/123IMG_7450.jpg
http://i12.photobucket.com/albums/a219/imoet/123IMG_7452.jpg
http://i12.photobucket.com/albums/a219/imoet/123IMG_7459.jpg
http://i12.photobucket.com/albums/a219/imoet/123IMG_74516.jpg

thanks for the help

 

[Sonusthree]

Hi audioholik and welcome to the forum.

You should post this in the car audio section together with details of which manufacturer, model number and age. More details are always helpful. You should get more help there

Cheers,
Martin.

 

[audioholik]

hi sonusthree,

sorry about my post.. how can i move my post to car audio section?

anyway its type Orion XTR 200 dual mono block rated @ 2x100watts
2 channel amps, Class AB,from design maybe its push pull tecnology
it uses MJL1302/3281

Date manufacture around '97s

thanks

 

[Perry Babin]

There's not much you can do. That amp uses some of the best parts available. There's almost no chance of making it better by using different parts and there's a really good chance that you'll do nothing except reduce the value of the amp.


I know this isn't what you want to hear but if it's in good working order, leave it alone.

 

[1moreamp]

I agree with Perry. Unless you want to rewind the power transformer your pretty much maxxed out as is. To get more out you must put more in, and that starts with the power transformer in the main supply.

Please don't ask me how to rewind your toroid, I don't do this even for myself

 

[audioholik]

thanks for the reply

my other amps got DC offset so i need to change the opamps.
can i just replace standart opamp with let say OPA2134 and NE 5534 with OPA 627?
i read somewhere in this forum changing opamps can really improve sound quality if its properly implemented..

and this amp use balanced/XLR for input. since i dont have balanced output. i jumper DIN input to make RCA conection.
is there better way to make unbalanced input with this amps?

thanks

 

[Perry Babin]

Don't believe the hype about changing op-amps and getting significant improvements. Although it's possible, I think most people want to believe that there was an improvement because they don't want to admit that they did it for nothing. Many times, the 'high-end' op-amps are less stable (oscillate easier) than the workhorse type op-amps that are commonly used. If you don't have an oscilloscope, I would avoid changing op-amps (use identical replacements if you need to replace defective components). Also, some of the op-amps used in amps are high-speed devices that allow the amp to be used in class B mode. If slower, high-end opamps are used, distortion may be a problem because the slew rate of the new op-amps isn't high enough.

To get a balanced input, you either need to build an op-amp inverter (for the negative half of the balanced signal) or you need to use a transformer to float the signal. A ground loop isolator may work to convert the unbalanced signal to a balanced signal. Don't ground the wires that connect to the output side of the GLI's shield ground. That will defeat the purpose of having the transformer. Since I've never used a transformer with that amp, I can't say that it will work properly. Try it at your own risk.

If the amp is working well with an unbalanced input and isn't causing problems (engine noise...). leave is as it is.

 

[audioholik]

well, my friend have osilloscope. so i can try changing different opamp and see if it will oscilate or not.

if i change it with better opamp do i need to change the value of bypass caps or something?
some people say that i should add a 22-100uf from -V to +V or from ground to -V so the opamp wills sound better.

 

[1moreamp]

well, my friend have osilloscope. so i can try changing different opamp and see if it will oscilate or not.

if i change it with better opamp do i need to change the value of bypass caps or something?
some people say that i should add a 22-100uf from -V to +V or from ground to -V so the opamp wills sound better.

The caps your adding just bypass noise and hash from the power supply, most op-amps have wonderful PSRR ( power supply Rejection ratio) and so it really won't inprove much. Its easier to clean up the + - 15 prior to using it at the chip. But I think that will have only a very small effect on your overall SQ.

If your seriously going to try the upgrade, then heres some advice:

Find and compare the "unity gain" specs for the op-amps your thinking about using. against the ones you plan on installing. Most exotic op-amps like the ones Perry was talking about will have poor to terrible "unity gain" specs.

And no matter what chip you pick for the upgrade, certain spec's must stay the same to keep the circuitry stabile. "unity gain" is one of those specs. ( my opinion, No flaming Please)

Also, there are two most basic types of op-amps, the Bi-polar kind, and the Mosfet kind. Find the type of op-amp your replacing and try and stay in the same family type for that device, (just a suggestion).

Also look out for Hybrids. Bi-polars with J-fet or Mosfet inputs. these offer some really fantastic specs, but you just altered the input circuitry to the op-amp in a hugh way. These impedence mismatchs can cause issues, like Perry mentioned.

I myself use only Burr-Brown and Analog Devices chips. I stock Mosfet, Bi-polar, and Hybrids. Some of these op-amps can run you upwards of 6 to 10 dollars each. But they do alter the sound of a amp, each in its own way.
Some reduce the DC offsets at the output. Some alter the bandwidth and slew rate (speed) of the amp.
And all I have tried change the sound of a amp. Some more than others. And the changes range from the bassline through out the band to the ultrasonic (inaudiable).
You see the output change on the O-scope for those differences.

There are a couple web-sites dedicated just to this sort of upgrade. try searching for them with Goggle. i've seen them out there and browsed a few in the past.

It all ends up at your ears and their hearing abilities. You after all, are the one searching for a better sound to your ears.

there is a whole lot more to look at and investigate before just popping in some chips. I recommend some very carefull thought on your part, unless you got time to kill trying hunt down ghosts later on after something ugly has reared up its head and shut your music down.

Good luck, and best sound to your efforts


P.S. some of the side effects won't show up till you overload the inputs on some op-amps. Like the TLO series, they can reverse phase on the output signal on overload. you will not see this until you push the device too far in the wrong direction ( a tricky scenario at best). take care

 

[Perry Babin]

The op-amps are already heavily bypassed in that amp. More capacitance is not likely to do anything.

If the amp has DC offset, you need to use the original part number replacements. If you use a substitute and the sub also causes problems (possibly different problems), you could waste a lot of time chasing problems that are not there. When you get the amp working properly, you can then start changing op-amps.

If you change any op-amps, you need to check for stability against oscillation. You should know that some amplifiers will destroy outputs if driven to clipping with high frequency signals. If this amp oscillates for as little as a couple of seconds, it may blow the output transistors.

If you change the NE5534 on that's used to drive the power amplifier section, you need to check for stability into various loads. Connect a 0.1uf film capacitor across the speaker leads with no load, with a resistive load (large 4 ohm resistor) and with a speaker. If the amp plays cleanly (on the scope, the oscillation won't be audible in most cases) with the 0.1uf cap across the speaker leads (connected as close to the amp as possible), then the amp is stable.

Again, in my opinion, you should restore the amp to proper working order with the original components. This is a nice amp. Modifying it will only reduce its value. There is almost no way to make this amp better by changing the op-amps.

 

[audioholik]

thanks for ur concern.

after reading ur statement.. i dediced not to change it.
ill stick with ne5532/34 as you say so.
is there a diff between ceramic and plastic opamps?
i can find NE5532AFE with ceramic die cast..

and 1 problem this amps got a pop up noise when it on/off, is there a way to fix this problem?

 

[Perry Babin]

There should be no functional difference in the ceramic vs plastic DIPs in audio amplifiers.

Does the amp pop with no audio input signal source connected?

What is the DC voltage across the speaker output terminals (measure each channels separately) after the amp is on for a few seconds?

 

[audioholik]

There should be no functional difference in the ceramic vs plastic DIPs in audio amplifiers.

Does the amp pop with no audio input signal source connected?

What is the DC voltage across the speaker output terminals (measure each channels separately) after the amp is on for a few seconds?

yes, the amp pop even with no input signal conected.

if im not wrong DC offset around 0.2v

 

[Perry Babin]

A DC offset of only 0.2v shouldn't cause a loud pop (more like a moderately loud click) but it's much more than it should be.

Is the DC offset the same on both channels?

Do both channels pop?

 

[audioholik]

yes, this amps has dc offset around 0,2v at both channels.
strange thing after poping it has "pssstt" sound for 1 sec around 5 times when it turns on or off.

it really doesnt matter at all for me as long its ok and not damaging my whole audio systems.

btw, my friend make a list for me which parts should be changed
1. replacing old gain pot with better one like ALPS blue
2. replacing all the caps in PSU section with fresh and better caps. because its already 10years old. maybe with nichicon KG or Elna black
3. replacing all the caps in signal path with elna silmic. (that little 10uf/50v caps)

well, thats about everything for now..
i hope it will sound better
any comments are welcome.
thanks

 

[markk02474]

Try the new LM4562 dual opamps!

I used to find most opamps sounded fairly alike such that swapping them wasn't worth the effort.

The LM4562 changed my mind. Besides amazing specs, it sounds dramatically more open, dynamic, and clear than any opamp I've heard. The bad news is they're brand new and Digikey doesn't have stock of the 8-pin dip yet. I've had to get samples from National 3 at a time. National also plans single and quad versions after the new year.

My preference for electrolytic caps in the signal path are Black Gate N types. The 6.3v ones work well for DC-blocking caps size-wise and price-wise. Price is much higher than Elna, but quality is better too.

I spotted some ceramic caps in the front end which I generally dislike, though they have their applications - NPO (C0G) when necessary in signal paths, MLC (multi-layer) types as power supply bypasses in digital circuits. I prefer film/foil or metalized polypropylene when there is room.

Do a search on this site for the LM4562. Using them in the front end I think will make the biggest improvement in your amp. I was floored by how much better they sounded than OP249's in my CD player. I'm going to use them in a sound card, DVD player, and surround sound decoder now that availability has improved.

In your amp, there might be a dc-servo which: a. is less critical to use a top opamp, and b. could be the source of your dc-offset.