First ever Yamaha amp

Hi all,

Today I got an AX-550 RS for what (I believed) a reasonable price of 60 EUR (it was priced 65, but the guy left it for 60).

It's my fisrt Yamaha. I have a Sansui AU-317 (recapped here) that cost me 25 EUR, and an Onkyo TX-84 receiver (20 EUR).

It's in really good condition and quite clean also inside. The previous owner left it in the closet for about 2 years as he got a Sony TA-FA3ES since then.

I was always curious to try an Yamaha unit and this just came across as we are some 200m "neighbours".

Anyway, I took the unit inside, opened it to see if everything was ok. I discovered that one of the pins of the left main power cap (12,000uF) had a broken solder point. Quickly I heat the iron and fix it and did another overview, everything looked nice.



Turn it on, waited some 15 minutes before start checking for bias adjustments (10mV). It was 4.6mV in one channel and 14,3mV in the other. After some 15 mins. I put the values according to the MS to the 10mV.



I noticed the values rised up to roughly 10.4mV every 5 minutes. Waited about half an hour and adjusted it again to 9.9mV both channels and waited another 10 minutes. Reached the 10mV and stayed there. Unit closed.

I liked the way it is made, not messy at all, no flexy cables across the board, seems pretty easy to service. And the parts, even for an average unit like this, seem well selected. This is an amplifier manufactured between 1991 and 1993, so maybe more than 20 years ago. Street price in the EU countries seemed to be around $420.00 in 1992.



The AX-550 RS presents good numbers: 85Wpc RMS, 0.005% of THD, 110dB S/N ratio, higher than the 100dB S/N the Sansui AU-317 has and more powerful.

However...

... the Sansui sounds much better to my ears. Maybe I have to get used to the Natural (flat?) Sound of Yamaha amps. Or maybe the full recap I did on the AU-317 is making some difference, I don't know... But I expected more from this unit... After one hour of listening, the amp appears tired, lifeless, without any dynamics and... not clear at all!
Seems even showing some little distortion, but I'm not sure...

Even the Onkyo TX-84 receiver sounds better than the AX-550 RS...

I'll leave running for a few days to see if I change perception of its sound...

Ok, I think I'll drop some Panasonic FM/FR across the boards of this amp to see if it gets more vivid...

Just one question if you recommend: can the 9-pin 4558S opamp (IC101) be replaced with something better? Since it has 1V/uS and seems to operate at 3MHz, I was thinking to put something a bit faster, but I couldn't find anything suitable. Reading few threads over here, some people recommend the uPC4570, but others don't it. And the its 9-pin version (uPC4570HA) can't be found easily. Such an opamp like this one would be ideal: 7V/uS is enough I guess...

Any suggestions?

There is no loudness switch on those Yammie. It bothers me. I know, I know,
the variable loudness inherent to Yamahas has many audiophile '' turned on ''

But, for my part, I think that, there lies the lack of life from those amp.

I had an AX400 once. Flipped it.

I still have my old CA-44 ( 20 watters ) WITH a loudness switch and that thing has a '' soul ''... and meters !!

OMG and dust too !

Oh, thanks for the input! And nice one that CA-44...

Yeah, this AX-550RS has good numbers... on paper. But in real life it's being so far kind of "well, I don't know..."

It's a +20 years old amp, I could drop some fresh electrolycs inside it to see what happens...

Does that opamp worth the job to be replaced?

Cheers.

Karl vd Berg said:

Oh, thanks for the input! And nice one that CA-44...

Yeah, this AX-550RS has good numbers... on paper. But in real life it's being so far kind of "well, I don't know..."

It's a +20 years old amp, I could drop some fresh electrolycs inside it to see what happens...

That Variable Loudness is really weird (for me). Denon also did the same, but seemed that it never impressed anyone that much...

Does that opamp worth the job to be replaced?

Cheers.

Click to expand...

Sorry there Karl, but with that opamp, i'm not qualified.

Good luck

Hmmm....an OPAMP?

In the signal path in an integrated amplifier?

Red flag.

belgianbrain said:

Hmmm....an OPAMP?

In the signal path in an integrated amplifier?

Red flag.

Click to expand...

Hi belgianbrain,

Schematics suggest an IC101 NJM4558S..

Maybe it cannot be replaced with anything else?

Link: http://www.littlediode.com/datasheets/pdf/Datasheets-NJM/NJM4558S.PDF

..

What I'm saying is that the Sansui sounds better for a reason.

OPAMPs are not the preferred method of audio amplification, but more of a low cost trade-off.

I wouldn't spend any money on that Yamaha. Use it for what it is.

If you're really interested in something Yamaha, I'd recommend an A-700 or A-1000. The A-700 I have susprises the heck out of me for what it is. It even sounds better than the CA-2010 I have. It's only a little bit embarrassed by my M2 power amp.

belgianbrain said:

Hmmm....an OPAMP?

In the signal path in an integrated amplifier?

Red flag.

Click to expand...

Bull shit..

avionic said:

Bull shit..

Click to expand...

Ah well, it has a nice look !

belgianbrain said:

What I'm saying is that the Sansui sounds better for a reason.

OPAMPs are not the preferred method of audio amplification, but more of a low cost trade-off.

I wouldn't spend any money on that Yamaha. Use it for what it is.

If you're really interested in something Yamaha, I'd recommend an A-700 or A-1000. The A-700 I have susprises the heck out of me for what it is. It even sounds better than the CA-2010 I have. It's only a little bit embarrassed by my M2 power amp.

Click to expand...

I was totally unaware of this unit. Just giving a try.

I believe this unit can do more with a little upgrade, sort of 20 euros (which is less than a round of beers in Leidseplein)...

An A-700 can't be found for that money. I'll keep this unit...

Thanks. :thmbsp:

avionic said:

Bull shit..

Click to expand...

This is a controversial subject, so opinions vary.

In my opinion (and from what I've heard), it's a reasonable rule of thumb to follow, especially for older equipment. It's easier for many designers to drop in an opamp (often of unknown quality), than to try and design a good quality pre-amplifier stage on their own.

Now, there are some very high grade opamps out there today that sound good. I doubt you'll find them anywhere but in expensive equipment. So, there are exceptions. I have an OPPO BD-83 Bluray player that is filled with surface mount components and opamps for the amplifier stage that sounds mighty fine. But any of my discrete component based DACs still kill it.

This can be debated forever...but to be more specific: I'd look at it like this: Finding an opamp in a low to moderately priced integrated amplifier from 20+ years ago is probably a sign that it won't be hard to beat.

belgianbrain said:

This is a controversial subject, so opinions vary.

In my opinion (and from what I've heard), it's a reasonable rule of thumb to follow, especially for older equipment. It's easier for many designers to drop in an opamp (often of unknown quality), than to try and design a good quality pre-amplifier stage on their own.

Now, there are some very high grade opamps out there today that sound good. I doubt you'll find them anywhere but in expensive equipment. So, there are exceptions. I have an OPPO BD-83 Bluray player that is filled with surface mount components and opamps for the amplifier stage that sounds mighty fine. But any of my discrete component based DACs still kill it.

This can be debated forever...but to be more specific: I'd look at it like this: Finding an opamp in a low to moderately priced integrated amplifier from 20+ years ago is probably a sign that it won't be hard to beat.

Click to expand...

Not all op amps are created equal and the quality doesn't necessarily correlate with the price tag. See:

http://nwavguy.blogspot.ca/2011/08/op-amps-myths-facts.html
http://nwavguy.blogspot.ca/2011/08/op-amp-measurements.html

The 4558 op amp is an obsolete design now and was/is a relatively poor performer wrt bandwidth, distortion and noise when compared to its contemporary discrete designs. But modern op amps can be much better; I did an op amp swap in a preamp using the data in the aforementioned links as a guide (see http://www.audiokarma.org/forums/showthread.php?p=6563913) and the results were well worth the effort.

Question for the OP is the 4588S in the AX-550S in the signal path or is it possibly being used in a DC servo circuit?

Karl vd Berg said:

Reading few threads over here, some people recommend the uPC4570, but others don't it. And the its 9-pin version (uPC4570HA) can't be found easily. Such an opamp like this one would be ideal: 7V/uS is enough I guess...

Any suggestions?

Click to expand...

Found this on line: http://www.mcmelectronics.com/product/UPC4570HA

Here I am again.

Today I found a 75Wpc AX-470 (same time of the AX-550, I believe) and paid 25 EUR for it. To give a try...

The worst amp I ever had! Just unbelievable how this series came out so bad!! I even put two new Vishays at the power supply section to see if the two 6800uF were "weak" or "dry" or whaterver and if the amp could push a bit more... but nothing to do. Like the AX-550, the sound is crappy, flat. There's NO bass!





The sound can be beaten by ANY other amplifier. Any plastic Samsung mini system can perform better.

Don't know what happen with some models from this series (1991-1993) but previous series sounded much better.

I used to have AX-596, which I bought in 1998. It was a descent performer. I sold it after 10 years of service, and it was still sounding good by then. But it was mostly discreet design, and sounded best with tone control bypassed (which was one of its features).

for_p1 said:

I used to have AX-596, which I bought in 1998. It was a descent performer. I sold it after 10 years of service, and it was still sounding good by then. But it was mostly discreet design, and sounded best with tone control bypassed (which was one of its features).

Click to expand...

That series is much better. I listened to an AX-496 and it blew my previous AX-550 away.