My First Phase Linear Restore- New Guy to the Forum

[mjstriker]

So does this mean the new OP AMP is fried? I was looking over the unit and it looks like there are two jumper wires providing B+ and B- to the new OP AMP. I figure this could be a spot to introduce something to lower the voltage the OP AMP sees.

In lowering the voltage is it better to use a diode or resistors? Based on my reading I found that diodes appear to be better at maintaining consistent voltage.

This would also leave the other OP AMP's exposed to the higher voltage. One has two resistors running B+/- so I figure those could be changed but the OP AMP closest to the transformer has a direct trace providing the
+/- so I can't really see how I can reduce that one unless I can change the diodes in the bridge rectifier to provide a voltage closer to 15V.

 

[laatsch55]

Jeez, can't keep my op-amps straight..

So Joe, how hard would it be to design a no frills , gain capable pre consisting of a single board and user supplied enclosure?? One that would match the gain-bandwidth specs of the amps now?? I know there are quite a few capable pre's out there now but man they're getting ridiculous ...see what a Spec 1 in restored condition is going for now??

 

[Gepetto]

So does this mean the new OP AMP is fried? I was looking over the unit and it looks like there are two jumper wires providing B+ and B- to the new OP AMP. I figure this could be a spot to introduce something to lower the voltage the OP AMP sees.

In lowering the voltage is it better to use a diode or resistors? Based on my reading I found that diodes appear to be better at maintaining consistent voltage.

This would also leave the other OP AMP's exposed to the higher voltage. One has two resistors running B+/- so I figure those could be changed but the OP AMP closest to the transformer has a direct trace providing the
+/- so I can't really see how I can reduce that one unless I can change the diodes in the bridge rectifier to provide a voltage closer to 15V.

What is the pre model #? The PL2000?

 

[Gepetto]

So does this mean the new OP AMP is fried? I was looking over the unit and it looks like there are two jumper wires providing B+ and B- to the new OP AMP. I figure this could be a spot to introduce something to lower the voltage the OP AMP sees.

In lowering the voltage is it better to use a diode or resistors? Based on my reading I found that diodes appear to be better at maintaining consistent voltage.

This would also leave the other OP AMP's exposed to the higher voltage. One has two resistors running B+/- so I figure those could be changed but the OP AMP closest to the transformer has a direct trace providing the
+/- so I can't really see how I can reduce that one unless I can change the diodes in the bridge rectifier to provide a voltage closer to 15V.

Lets just see if we can drop the entire pre voltage, as we did with Jer's preamp.

 

[Gepetto]

Lets just see if we can drop the entire pre voltage, as we did with Jer's preamp.

Looks like most of it is just a few op amps in the 2000. The simplest way is to put a large zener in the leg of each of the bridge outputs. The bridge is discrete and consists of 4 diodes mounted on the board.

 

[mjstriker]

It's the 2000 series I. I found a thread I thinking talking about Jer restoring a 3000 but I couldn't find anything in it about dropping the voltage down. Maybe the wrong thread?

And yes the it only has 3 OP AMPS and I see where the 4 diodes are that act as the bridge. How would I go about calculating what Zener I would need to bring down the voltage? From what I am reading I would just need a ~4V Zener to bring it down to 15V (19V-4V) depending on current. Or would it be better to redo the 4 diode bridge entirely?

 

[Gepetto]

It's the 2000 series I. I found a thread I thinking talking about Jer restoring a 3000 but I couldn't find anything in it about dropping the voltage down. Maybe the wrong thread?

And yes the it only has 3 OP AMPS and I see where the 4 diodes are that act as the bridge. How would I go about calculating what Zener I would need to bring down the voltage? From what I am reading I would just need a ~4V Zener to bring it down to 15V (19V-4V) depending on current. Or would it be better to redo the 4 diode bridge entirely?

Use a 5W 3.6V zener, 863-1N5334BRLG

Lift the cathode end (band) of both D4 and D6 out of the PCB and stand them up, solder these cathode ends together along with the cathode end (band) of the 1N5334 zener. Then insert the anode (non-band) end of the 1N5334 zener into one of the PCB holes now left open from either D4 or D6.

Lift the anode end (non-band) of both D3 and D5 out of the PCB and stand them up, solder these anode ends together along with the anode end (non-band) of the 1N5334 zener. Then insert the cathode (band) end of the 1N5334 zener into one of the PCB holes now left open from either D3 or D5.

Clear?

 

[Gepetto]

Use a 5W 3.6V zener, 863-1N5334BRLG

Lift the cathode end (band) of both D4 and D6 out of the PCB and stand them up, solder these cathode ends together along with the cathode end (band) of the 1N5334 zener. Then insert the anode (non-band) end of the 1N5334 zener into one of the PCB holes now left open from either D4 or D6.

Lift the anode end (non-band) of both D3 and D5 out of the PCB and stand them up, solder these anode ends together along with the anode end (non-band) of the 1N5334 zener. Then insert the cathode (band) end of the 1N5334 zener into one of the PCB holes now left open from either D3 or D5.

Clear?

And keep diode leads short. The diodes use the PCB trace for heat sinking.

 

[mjstriker]

Use a 5W 3.6V zener, 863-1N5334BRLG

Lift the cathode end (band) of both D4 and D6 out of the PCB and stand them up, solder these cathode ends together along with the cathode end (band) of the 1N5334 zener. Then insert the anode (non-band) end of the 1N5334 zener into one of the PCB holes now left open from either D4 or D6.

Lift the anode end (non-band) of both D3 and D5 out of the PCB and stand them up, solder these anode ends together along with the anode end (non-band) of the 1N5334 zener. Then insert the cathode (band) end of the 1N5334 zener into one of the PCB holes now left open from either D3 or D5.

Clear?

The description makes sense. As a learning point, why use the 3.6V? My experience is just a notch above zero so trying to take every opportunity to learn and not have to ask the same question

Just have to get my hands on some Zeners from Mouser and I should be back up and running. Is it likely I fried the OP AMP that is in there now?

 

[Gepetto]

Makes sense. Just have to get my hands on some Zeners and hopefully I will be back up and running. Is it likely I fried the OP AMP that is in there now?

Likely it is a walking wounded at this point Mike...

 

[mjstriker]

Likely it is a walking wounded at this point Mike...

Well then the old one is gonna have to do for a while. Is this most likely my source of DC at the outputs or should I be investigating further ?

Also I edited the above post:

As a learning point, why use the 3.6V? My experience is just a notch above zero so trying to take every opportunity to learn and not have to ask the same question?

Just want to make sure I am learning along the way rather than just following instructions.

Thanks

 

[Gepetto]

Well then the old one is gonna have to do for a while. Is this most likely my source of DC at the outputs or should I be investigating further ?

Also I edited the above post:

As a learning point, why use the 3.6V? My experience is just a notch above zero so trying to take every opportunity to learn and not have to ask the same question?

Just want to make sure I am learning along the way rather than just following instructions.

Thanks

2 reasons

Zeners tend to regulate on the high side of their nominal value so you will likely get these to zener at about 3.8V producing about 15.2V for you.

3.6V is a very common zener value

Remember this is a totally unregulated supply in this preamp so no matter what you put in there will not be deadly accurate. Why they did not regulate the supply is a mystery to me, likely just to save money but it produces a Preamp with less than stellar SNR as a result. Many preamps have multiple cascaded precision voltage regulators to get the best SNR possible.

 

[mjstriker]

2 reasons

Zeners tend to regulate on the high side of their nominal value so you will likely get these to zener at about 3.8V producing about 15.2V for you.

3.6V is a very common zener value

Remember this is a totally unregulated supply in this preamp so no matter what you put in there will not be deadly accurate. Why they did not regulate the supply is a mystery to me, likely just to save money but it produces a Preamp with less than stellar SNR as a result. Many preamps have multiple cascaded precision voltage regulators to get the best SNR possible.

So it is better to get close to the nominal voltage rather than undershooting it down to say 14V? Or would the OP AMP not perform well at that voltage?

 

[Gepetto]

So it is better to get close to the nominal voltage rather than undershooting it down to say 14V? Or would the OP AMP not perform well at that voltage?

The op amp will perform fine at that voltage Mike, just did not do an exhaustive review of what other things may not like lower than that is all.

 

[mjstriker]

The op amp will perform fine at that voltage Mike, just did not do an exhaustive review of what other things may not like lower than that is all.

As you can tell I can be a little narrow minded

Thanks for the explanations and your patience. Trying to wrap my head around understanding electronics as I enjoy working on the amps/preamps but would rather not make some many costly mistakes on future projects.

 

[mjstriker]

So was looking on Mouser at getting the replacement OP AMP as they sell the OPA2134 at a reasonable price, and I need to fill up my order to justify the shipping of a pack of diodes. At this point is there a different/better OP AMP I could substitute in there or should I stay with what I have?

 

[Gepetto]

So was looking on Mouser at getting the replacement OP AMP as they sell the OPA2134 at a reasonable price, and I need to fill up my order to justify the shipping of a pack of diodes. At this point is there a different/better OP AMP I could substitute in there or should I stay with what I have?

Personal preference Mike. The OPA2134 has the famous Burr Brown legacy. TI acquired them some years back as Burr Brown was the undisputed leader in precision op amps at the time of the acquisition. The 134 series is my personal preference as it does not sound strident at all.

TI has their own series of fine audio op amps as well. Those are Jer's personal preference. One of the dual versions is the LME49720.

No matter what you choose, it will be an order of magnitude better than the original RC4136 type amp that they originally used.

TI has an entire series that you can explore...

http://www.ti.com/lsds/ti/audio-ic/audio-operational-amplifier-product.page

 

[jbeckva]

Mike those LME's Joe spoke of really pair up NICE with the PL14 WOPL's inputs. Clean and clear.. tight and powerful bass, transparent mids, good stuff.

 

[mjstriker]

Mike those LME's Joe spoke of really pair up NICE with the PL14 WOPL's inputs. Clean and clear.. tight and powerful bass, transparent mids, good stuff.

Was gonna get both and give them a little test run as long as my soldering skills hold up on those tiny pins.

 

[laatsch55]

Solder in some sockets, takes the stress off the traces too. Get the good machined sockets...a cheap socket will be a frustration.