Technical OPA2134 question

[Mandarine]

I swapped the stock IC3 for a Burr Brown the oher night. It took about 3 hours all said and done. What I have found is that the clean tones do open up quite a bit. There is a lot of "air" present that was stiffled before. However, it is apparent that the chip overdrives at a MUCH lower signal level. In order not to run into distortion (even on the cleanest of settings), I've either had to either lower the gain on the Rythym Yellow and Green by about half (from 5 .5 to 3), OR use a single coil pickup rather than humbuckers.

The initial soldering of the IC socket proved to be intermittent, (tapping on the PCB cut the signal in and out), so I re-soldered and the intermittent connection was resolved. The question that I hope someone might help me with is to those who are familiar with the nature of the chip and how it works. Does this early clipping sound like it could be a short or an open on any of the IC pin connections? Obviously, the bottom of the circuit board is easy to test and I can do a visual check for a clean solder joint. The component side of the circuit board is not so easy to diagnose as the IC socket sites on top of the PCB traces.

It would appear to me that the positive and negative supply voltages are connected (V+ and V-) or the IC wouldn't work at all, no? Perhaps an open feedback connection to the chip on OutA back to -InA or an open or short on other pins? I will get the old Ohmeter going on this to check for continuity, but was hoping someone might have some other insight as the disassembly of this box is a mini project in itself and knowing what one might look for would be a tremenous help.

I am also going to swap back in a TI TL072 to see if the OPA2134 does indeed clip early. From what I have researched on this subject however, the 2134 should have more, not less headroom.

Man.

 

[Mandarine]

Checked all connections with an Ohmeter with schematic in hand, and all test good. Tested voltage supply and it was dead-on. Perhaps a bad chip. Perhaps the OPA2134 just not a good match for the Triaxis. Will try another OPA2134PA as soon as can be ordered.

 

[Dead Moon Rising]

Did you take your measurements right at the pins of the chip, not on the bottom of the circuitboard? also how was removing the old chip? did you inspect the solder holes to make sure non were damaged?

 

[leadfootdriver]

What's your master set at when the clip happens?

I'd just run the OPA2604 anyway. It's more of what the 2134 has in a good way. I don't have a clipping problem with mine.

 

[disassembled]

I didn't have a clipping problem with the 2134. The 2134 was much better than the TL702 as far as headroom goes.

Maybe you just have a bad 2134. I ordered like 3 or 4 when I bought mine just incase. Maybe you should order some more.

Greg

 

[Mandarine]

Thanks for the replies guys. Appreciate it.

The testing measurements came from the top side of the newly installed IC socket with the IC removed.

The old chip was a ***** to remove. Cut the pins off the original chip and used a solder wick from both sides of the board to clean up the leftover solder. Put a socket in the IC's place and tinned the socket leads beofore installation. This helped in getting solder to the top PCB traces while soldering from the bottom. I used an IC socket with circular holes for the IC. There is also a socket available with rectangular holes for setting of the IC (tension spring-type IC connection), but there is no "standoff" on the pins of the socket. The circular holed IC socket mount has larger diameter pins halway down to the pin tip that allow it some space so the socket it doesn't sit right on top of the PCB making a better electrical connection possible on the top of the PCB.

There is also a thread on this forum somewhere about disassembling the triaxis which was very helpful as there are a LOT of screws and some are not obvious.

With the socket in place, a swap of the IC is very easy just by removing the top cover plate of the Triaxis.

The unit with this particular 2134 swap clips at Rythym Yellow and Green gain settings of 3 and a master setting at 3. Once the master setting goes beyond this setting, it starts to clip and sound like Lead1 Red! Before the IC swap the gain and master could be set at 5.5 or 6 with no audible distortion (running an ECC81 as the 3rd tube).

I just received 2 more 2134s today from Mousser electronics (Texas) and I will try that as a replacement. Also ordered a couple of TL072s from Mesa just in case. The Mousser ordered chips came in s static bag (nice touch), where the 2134 ordered from Indonesia came in a plastic tube with scotch tape. Maybe some static damage?

Leadfooter: What do you like about the 2604? I'm really trying to get a pristine, non-clipped clean. Not too low mid heavy. And I want the overdrives to be very "heavy", but with plenty of definition and punch.

Thanks guys.

 

[leadfootdriver]

Leadfooter: What do you like about the 2604? I'm really trying to get a pristine, non-clipped clean. Not too low mid heavy. And I want the overdrives to be very "heavy", but with plenty of definition and punch.

It's a little warmer and more dynamic than the 2134. It's not harsh sounding like the stock piece.

 

[Mandarine]

I swapped the IC3 back to the stock TL072 ordered from Mesa. Same difference with what seems early overdrive in the rythym modes. NOw I am confused. I am going to try an OPA2604 this evening.