[kcaesthete]

Hi all,

I had posted this within a thread in amplification and got nobody to respond. I'm about to order a Larocco Pocket Reference and need some info on opamp replacement should the stock one prove to be too bright for my Ety 4p+s's.

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I went to Digi-Key.com to see how much an opamp would be. I searched for LT1122, and multiple results came up, some of which had "DIP" in the description and others had "SOIC." How do I know which one of the four to get?

See choices below:
LT1122DCN8 IC OP-AMP JFET FAST-SETTLNG 8DIP
LT1122DS8 IC OP-AMP JFET FASTSETTLNG 8SOIC
LT1122CCN8 IC OP-AMP JFET FAST-SETTLNG 8DIP Linear Technology
LT1122CS8 IC OP-AMP JFET FASTSETTLNG 8SOIC

For the AD8065, there was only one in stock:
AD8065AR IC VOLT-FDBK AMP SNGL HS 8-SOIC

Thanks in advance for your help. I'm a fairly savvy electronics user & audiophile, but am a babe in the woods "under the hood."

 

[Pars]

Judging from Larocco's site, the Pocket Reference appears to use an AD8620, which AFAIK is only available in an SOIC package, which is surface mount. Unless you are comfortable soldering and desoldering SMT devices, opamp rolling in this isn't going to be easy. You might contact Larocco and see if they have any suggestions. The AD8620 is a good chip... I have no experience with ETYs, so not much help there in terms of whether it might be too bright or not.

 

[kcaesthete]

Thanks Pars. I definitely don't have the skills necessary to desolder/install/solder. I did email Phil at Larocco Audio and he said that the opamps are socketed. I got the idea from xtreme4099 who suggested in this thread that I try the two opamps mentioned earlier. I don't know if this helps, but here's the Pocket Reference page on the Larocco site.

Any further comments would be helpful.

 

[Pars]

kcaesthete,

Thanks for the link to Larocco, although I had looked at it quickly before I replied previously. Yeah, in looking more closely (DUH!), there is definitely a socket (8 pin DIP) there, so going with the opamps that are available in a DIP package should not be a problem, and I would think that with the 8620 in there stock, that as long as you don't go really nuts with a really fast opamp with bipolar input such as an LM6172, etc. you should be OK in terms of oscillation. Opamps that are only available in an SOIC package would have to be mounted on an adapter (i.e., soldered... I know Tangent supplies a couple that way).

One thing that Tangent has pointed out in a couple of threads where people have had oscillation problems is a somewhat reoccuring comment by the listener that they reach a point increasing the volume where the sound thru the cans goes "click" and starts to sound ****ty. He has told them to put a DMM on it and measure the current draw, and they have invariably reported back that when the "click" occurs, the current draw of the amp spikes (as in double or so from what it had previously been). This is where the oscillation begins to occur. So just be aware of that as a possible alert that something ungood is happening. If the opamp is oscillating immediately, it will sound bad also, and the chip will tend to get hot. If you have a DMM, to measure the amps current draw, the DMM has to be placed in ampere mode and put in series with the battery or PSU to measure it.

Otherwise, as far as I know, all the dual opamps are pin for pin compatible, but double check the spec sheets to make sure. Good luck, and enjoy.

Chris

 

[kcaesthete]

Thanks for the info, Pars. Once I get my PR, I'll start experimenting.