[nickchen]

I got two of these superior 4562 DIP dual opamps yesterday.

One drives my cheap BTech SS, the other works in my selfbuilt portable Cmoy/RA1 clone. All the rave about this opamp seems to be more than justified, as it sounds absolutely superb and moreover provides a mentionable soundstage, which was almost nonexisting with both amps before.

However, there seems to be a price to pay - the Cmoy -dead silent with the 2132- hisses with the 4562.

The problem vanishes if I use a 100 ohm resistor in the output, and it also doesn't occur with high ohm fons. But that doesn't help as the amp is simply not loud enough in these cases.

I think about triggering the gain to get enough juice to work with a permanent 100 ohm resistor in the output. But I've no clue which other resistor values have to be changed to achieve this goal.

My Cmoy is designed with the standard RA1 configuration - each channel with a 100K, 120K and 470K resistor.

Thoughts?

 

[balou]

hm... the national website is mentioning that the lm4562 can drive a 600 ohm load without problem. could that mean that they will not drive any lower loads? and the the values of your resistors also seems a bit high.. maybe the lm4562 is also more suspectible to resistor noise?

and yeah, opa2132 sucks - no soundstage at all

 

[NelsonVandal]

1. Congratulations to a better sounding amp. Those OPA2132/4's should be banned! If we wanted mono, we would push the mono-button.

2. Why use these high resistor values? I'm surprised you didn't experience noise with the other opamps. Go for the standard CMOY-values R2 100k, R3 1k, but use a lower gain than 10, try 2 - 4 k for R4.

3. In my experience the LM4562 can be cranky and oscillate (I had noise and clicking). Try to cure it with 1. R5 10 Ohm (inside the feedback loop before the output like in the CMOY schematic) 2. a good decoupling (0,1 uF ceramics from V+ and V- to ground) 3. 10 pF ceramic cap in parrallel with R4. My problem was solved by 1 & 2.

4. I experienced a lower noise from LM4562 than OPA2132/4, but not as low as AD8620 wich was remarkable in that area.

5. Enjoy!

 

[AudioCats]

It is kind of strange that the RA-1, which has a bi-polar input opamp (usually have high input current noise), will use such high value resistors. Maybe try the 10k, 12K, and 47K combo and see? This will give you the same gain and balance but 10x less Johnson noise.

Since you have two 4562, what happen if you install the other chip?

and what phones are you using? 4562 only have a output capability of 26mA and that is with +/-15V supplies. for dual 9V the output is even less, I'd guess around 20mA. Not enough for Grado and Koss for sure. The lowest it can handle without a buffer is probably 120 ohms (which takes about 22mA to make 60mW).....

Trouble shooting is fun!

 

[AudioCats]

the standard Cmoy value is for FET input chips, might not work for the bi-polar chips like 4562. If you do so you will likely get DC offset voltage in output.

 

[nickchen]

Thanks for all kind replies, I'll enter the local parts dealer right away when I drive home from work. I'll organize all mentioned components and start fumbling. Not sure if I will be able to try all suggestion 1:1 - the scheme I used doesn't provide R4 and R5, only R1-3 and R10.

Quote:

Originally Posted by NelsonVandal a good decoupling (0,1 uF ceramics from V+ and V- to ground)

Good idea. Also implemented that already with my BTech months ago.
Quote:

Originally Posted by AudioCats and what phones are you using?

It's only intended to be used with my Alessandros (32 Ohm) and the K81 (70ish).
Quote:

Originally Posted by AudioCats the standard Cmoy value is for FET input chips, might not work for the bi-polar chips like 4562. If you do so you will likely get DC offset voltage in output.

Guess you mean I am in danger to roast my fon's drivers. Hm...that would be bad...looks I have to organize myself a reasonable voltmeter. The cheap 9€ thingy I've got won't work to measure this properly.

 

[majkel]

I assume 100k is on inputs, 120k and 470k in the feedback loop? If so,
120k - use 1.2k
470k - use 4.7k

High resistances in feeback produce the noise. 12k & 47k is still to high to have inaudible hiss.

 

[NelsonVandal]

Quote:

Originally Posted by AudioCats /img/forum/go_quote.gif the standard Cmoy value is for FET input chips, might not work for the bi-polar chips like 4562. If you do so you will likely get DC offset voltage in output.

The offset is 0.7 mV left and 0.4 mV right channel. I'm using R3=1.2k R4=2.7k R2=100k pot=10k input resistor=1k. Try to find an amp with lower offset than that! It's dead quiet.

It drives my 300 Ohm HD650 with ease. With my 32 Ohm Philips it lacks some bass and sound congested. Used in a 3 channel configuration it plays the 32 Ohm cans with authority. I use LMH6654 as ground channel amp. If you don't want to complicate things with buffers, try this 3 channel configuration à la PINT (like I do). It's not very hard to add an active ground channel.

 

[NelsonVandal]

It's not very hard to add some buffers either. The cheapest would be to make a pair of Sijosae buffers, and they sound quite good too. But a ground channel is recommended either way.

 

[nickchen]

I also have no problems with offset with the current RA1 configuration so far. I've heard that more than 100 mV would be critical, but it actually had just 0.7 mV - same as NelsonVandal.

I've organized lots of resistors meanwhile and will be going to play with them tomorrow. Meanwhile, I am quite optimistic to get the hissing killed, I'll keep you informed.

And if not - I still regard the 4562 to be the opamp of my choice, even with hissing. The phrase Quote:

Those OPA2132/4's should be banned! If we wanted mono, we would push the mono-button.

was quite a good laugh. BTW, the stock 5532 in the BTech was even worse, imagine a 2132 covered with a towel...

 

[NelsonVandal]

Quote:

Originally Posted by nickchen /img/forum/go_quote.gif BTW, the stock 5532 in the BTech was even worse, imagine a 2132 covered with a towel...

Double LOL

!

 

[balou]

I wonder what my cdp will sound like after I replace the two ne5532 with two ad8066 and the two electrolytic caps with polypropylenes.. I really can't imagine, because the player already sounds quite good
an opa2132 with a towel... wow... that does sound like quite a bad chip

 

[nickchen]

The 5532 isn't that bad. It has a quite warm & smooth sound signature, is a bit boomy and has little resolution and soundscape. The 4562 is brutally detailed, fast and icy cold in comparison. Not an opamp for Sennheiser fanboys for sure.

 

[NelsonVandal]

Quote:

Originally Posted by nickchen /img/forum/go_quote.gif The 4562 is brutally detailed, fast and icy cold in comparison. Not an opamp for Sennheiser fanboys for sure.

I agree. It's sterile. The treble is really nice, but it's just life-less all in all. The problem is there's no opamp that's for this Sennheiser fanboy. Maybe AD744 is as good as they say. If it's so I'll have to make a public apology. I'm also about to build an AD8099/8045 amp, I have great hopes for those chips. I hope I can order it sometime next week.

I once again experienced the crankiness of LM4562. I tried to use one channel of it in a closed loop with a buffer as active ground. Very very noisy, must be oscillating like hell even though used in a multiloop configuration, with a small cap and resistor in the local feedback loop, and with decoupling caps. Tremendous better sound than the OPA2134 I use. I'm waiting for AD744 to use in this position, or LT1363. My favourite in this position was LMH6654, before I remembered it was only spec'd to 12V and I use 18 - 24. Lucky I didn't blow it, and strangely there was no problems at all.

 

[nickchen]

Being electronicahead, the sterility of the 4562 suits me quite well. And I still have the mighty Millet in reserve for the "other" moods.

I always was a bit greedy about the famous AD227. These are said to be as good as the 4562 turned out to be, but with more warmth & musicality. The price is a bit steep for these thingies and they are awfully powerhungry, so I keep away from getting them.