Anyone substitue a dual op amp with twin singles?

[billbillw]

My preamp has just one dual channel op amp for the headphone output (NJM5532D). I was thinking about using a browndog adapter to implement twin AD797 op amps. Anyone ever do something like this?

If so, did it give you what you were looking for? More power? Cleaner?
I know the ultimate power output of the circuit is limited by the rail voltage and capacitance in the headphone circuit.

Right now, there are a pair of 100uF/25V filter caps for each channel in the headphone circuit. I'd like to double or tripple the size of them if there is room on the circuit. I'm not worried about drawing down the voltage rails because the main supply is huge and has over 20000uf of capacitance. That should provide plenty of headroom.

 

[Jahn]

way back when i had two AD8610 chips browndogged on a cmoy that i could opamp roll with a AD8620. Didn't seem to make any kind of SQ or battery drain diff, at least to me. But then, that was just for a cmoy, ymmv for a better amp.

 

[FallenAngel]

Simply switching from a dual opamp to 2 singles will not have any results if you're changing the exactly same opamps (ie 2 AD8610 vs AD8620). There is definitely a difference when switching opamps. The NJM5532D is a 68 cent chip, and I think you'll get better performance with a better chip. I haven't heard the NJM5532D or AD797 so I can't comment on them, my favorite chip is the OPA2107 because at $15 it's not too pricey for a dual opamp and it I think it sounds great.

 

[billbillw]

I knew the NJM5532D was a cheapie. I have a pair of AD797 laying around here and the browndog adaptor is only $3. Pretty cheap to try it out. I also have several dual channel parts (LM4562, OPA2132 and the TI NE5532) to try out as well. I'll probably put sockets in the headphone board as well as the browndog adaptor so I can try out other single channel models if the AD797 doesn't suit me.

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Simply switching from a dual opamp to 2 singles will not have any results if you're changing the exactly same opamps (ie 2 AD8610 vs AD8620). There is definitely a difference when switching opamps. The NJM5532D is a 68 cent chip, and I think you'll get better performance with a better chip. I haven't heard the NJM5532D or AD797 so I can't comment on them, my favorite chip is the OPA2107 because at $15 it's not too pricey for a dual opamp and it I think it sounds great.

 

[FallenAngel]

Definitely socket it and get rolling

 

[Filburt]

Be careful when using the AD797. It's very sensitive to rail impedance in my experience (so make sure you have proper bypassing). Your circuit may not be suitable for its substitution without modification first. Additionally, a single-to-dual adaptor may end up being a problem as well. You could try adding some external compensation to improve the situation, though, but it can get a bit clunky.

You could also simply try swapping in the AD8599 for the NE5532, instead. It's the closer analog to it. The AD797 is the replacement for the 5534 whereas the 8599 is for the 5532. The difference between the chips as far as I can tell, other than one being single and one being dual, is internal compensation as opposed to some sort of greater circuit differences. I imagine this is, in the case of both the 5532 and the 8599, to make it easier to use the chip at unity gain.

 

[billbillw]

Quote:

Originally Posted by Filburt /img/forum/go_quote.gif You could also simply try swapping in the AD8599 for the NE5532, instead. It's the closer analog to it. The AD797 is the replacement for the 5534 whereas the 8599 is for the 5532. The difference between the chips as far as I can tell, other than one being single and one being dual, is internal compensation as opposed to some sort of greater circuit differences. I imagine this is, in the case of both the 5532 and the 8599, to make it easier to use the chip at unity gain.

I'd like to stay away from surface mount chips. I can solder through holes ok, but I'm not skilled enough for surface stuff.

Isn't the AD8599 nearly impossible to get right now anyway?

 

[d-cee]

no idea what you're using it in, but the LM4562 is a fine dual channel op amp in my Zhaolu

 

[uzziah]

oh the mighty browndog; so versitile, so lovely

go at it

 

[uzziah]

oh the mighty browndog; so versitile, so lovely

go at it



btw: anybody can SMD; a pair of pliers is the trick, then put a little dab of solder on the trace, THEN put your chip in place, and heat that blob of solder; once you get one trace on (and have it lined up right) you're good

 

[joe_cool]

The LM4562 will give you great performance with a similar tone to the 5532. For a headphone amp I prefer something with wider open loop gain and stronger output drive. The AD825 is a single SO chip and will do a great job. It is designed for high slew rate and fast settling time and is OK happy with +-15 volts power supply.

These wideband amps must have a 0.1uF cap soldered across the rails (on the BD adapter if possible) or they will sound mushy or even oscillate. I used a pair of 0.47uF caps in series soldered to the PS rails on the BD with a center ground wire going to the power supply star ground about 3 inches away, and this was quite good.

You will also need a small resistor in series with the output but outside the feedback loop. This will make a big difference in the treble tone, smooth not strained. Most preamp headphone circuits will already have this but may be too large for your headphones, like 150+ ohms.

 

[Filburt]

Quote:

Originally Posted by billbillw /img/forum/go_quote.gif I'd like to stay away from surface mount chips. I can solder through holes ok, but I'm not skilled enough for surface stuff. Isn't the AD8599 nearly impossible to get right now anyway?

You could try ordering samples. For soldering surface mount, just pick up some 0.015" solder such as what Radio Shack sells and use a smallish tip for your iron. Get a pair of curved tip tweezers to help orient the chip on the pads. I stick the tips between the centremost pins on the chip to get a good grip on it, put a little bit of solder on one of the pads, heat the pad and then slide the chip in place. Then I solder the other pins. Personally, given the choice between through hole and SMD, I'd take SMD almost any day of the week. I can usually get better performance out of it unless I'm needing high output power (not something to really be concerned with in this application) or swappability.

Like joe, I tend to prefer wideband op-amps. The AD8058 is probably the most extreme example of wide open loop bandwidth, though the 8056 used to be wider by a factor of 4. There are some fantastic op-amps that lack this characteristic, but probably the best of them manages its performance through unusual topology (OPA2365) and is limited to 6V max. Proper bypassing of the rails is almost always a good idea, so make sure to do that.

The LM4562 is a reasonable suggestion for replacing the NE5532 as well. I actually don't think the NE5532 is necessarily a poor performing chip, so I'd advise you to not start swapping op-amps with the assumption that you will obtain better performance outright, and don't confuse different sound with better sound

. The price of a chip doesn't necessarily indicate its quality or performance; mostly, it indicates the cost of manufacture. OPA627 is expensive because it's expensive to make due to the di-fet process. NE5532 is cheap because it's a well known design and relatively old design that is now easy to manufacture at low cost. Most of my favourite op-amps only cost a few dollars a piece.

 

[peranders]

Quote:

Originally Posted by billbillw /img/forum/go_quote.gif My preamp has just one dual channel op amp for the headphone output (NJM5532D). I was thinking about using a browndog adapter to implement twin AD797 op amps. Anyone ever do something like this?

Have you seen this high end adapter?
http://www.svalander.se/shoppen/smdadapter.htm

English text here.

Documentation here.

Notice that the adapters are made of 1 mm pcb, not 1.6 mm as in the picture.

 

[billbillw]

Cool. Thanks for all the suggestions. I've got to place an order to Digikey and to Partsconnexion sometime in the next week or two. The headphone circuit mods are down the list for me right now. First I've got to do some work on my Mirage's crossover network, then I'm going to replace all the coupling caps throughout my preamp with Blackgate N series, and I'm going to make some changes to my phono board (socket for opamp, bigger filter caps, etc). After that, I'll dig into the headphone circuit.

 

[Filburt]

Quote:

Originally Posted by peranders /img/forum/go_quote.gif Have you seen this high end adapter? http://www.svalander.se/shoppen/smdadapter.htm English text here. Documentation here. Notice that the adapters are made of 1 mm pcb, not 1.6 mm as in the picture.

Heh, I wish I could get some of those here in the states