Hi Shawn,
-Chris 😉
I think that was the highest performance IC they could get at the time. Remember that other companies jumped onto this chip at the same time. These were not poorly designed products.
That's the best reason to do this. I agree wholeheartedly with you on this.
-Chris 😉
ua739, take out the trash!
Am I oscilating yet? Do I need feed back and/or pull downs? Is it too simple to be true? Can this "new" op amp drive Q100 and Q200 which are MPSA93(-200V, Ic 500mA{max}, PD 625mW)
Edit: I removed a wire going to the stereo/bridge switch. We can add that function later.
Am I oscilating yet? Do I need feed back and/or pull downs? Is it too simple to be true? Can this "new" op amp drive Q100 and Q200 which are MPSA93(-200V, Ic 500mA{max}, PD 625mW)
Edit: I removed a wire going to the stereo/bridge switch. We can add that function later.
Attachments
Hi Shawn,
What I would do is make an adapter PCB and try this on the original board. Make sure it works with the original IC first. You may have to play with compensation. Some op amps may require a buffer.
-Chris
What I would do is make an adapter PCB and try this on the original board. Make sure it works with the original IC first. You may have to play with compensation. Some op amps may require a buffer.
-Chris
Hi Tomwaits,
go and download that tome.
It shows how to get extra voltage from the low output voltage of the ICopamp.
You need the voltage gain to drive the main section of the amplifier.
go and download that tome.
It shows how to get extra voltage from the low output voltage of the ICopamp.
You need the voltage gain to drive the main section of the amplifier.
anatech said:
I'm afraid I would need to buy another DC300 to perform that action. Or bench this one back together; I guess that could happen too. I need to purchase some new outputs (MJ21194) and rebuild the output PCBs first. Then I will try to finish the testing with driver boards. Actually, right now would be a good time to own two of these DC300A's, you know, one in pieces and the other to test on? It's a learning experience and I'm slowing gaining knowledge here.
If someone would lend me their old unused DC300A I could advance much faster and do comparison tests. Right now would be a good time to have three of these things!
Meanwhile, I hope some more folks jump in and critique this op amp circuit.
Shawn.
Hi Shawn,
Those are your external pull down resistors for the uA749. Not used with the uA739, so lose 'em with a standard op amp.
-Chris
Those are your external pull down resistors for the uA749. Not used with the uA739, so lose 'em with a standard op amp.
-Chris
Hi Shawn,
I don't think you need critiques on an old amplifier at this point. Most people don't know what they were like when they were working well. Most need work at this point in time.
Do try and grab another. Maybe ask at Steve's Music in their service department. Long & McQuaid's service may have some dead ones as well. You may get a better faceplate doing this.
-Chris
I don't think you need critiques on an old amplifier at this point. Most people don't know what they were like when they were working well. Most need work at this point in time.
Do try and grab another. Maybe ask at Steve's Music in their service department. Long & McQuaid's service may have some dead ones as well. You may get a better faceplate doing this.
-Chris
Re: R107/R207
Hi guys sorry been busy.......
The resistors around the 739 were associated with different value volume pots, some amps used 22k log some used 100k log as i remember,
one of the schematics has a little box with technical notes in it!
Is anyone interested in some UA739's? (£10 each inc pp), i have some of the fairchild ceramic versions (ua739dc), i have noticed the later plastic case ic's are a bit prone to failure, (the 10 volt zener and associated cap neads to be changed after decades of use)
(These ics can actually fail s/c leading to dc floating about amp)
The 6 transistors on the main board can be replaced with d40 and d44 transistors.......
There were so many different components used over the years its a bit of a mystery at times....not to mention special part numbers......
I dont know that much about dc300a's but im willing to try and help anyone...if i can. i have repaired a few over the years....
please dont hold that against me, i know im sick!
now weres that smoke gone?
TomWaits said:
Hi guys sorry been busy.......
The resistors around the 739 were associated with different value volume pots, some amps used 22k log some used 100k log as i remember,
one of the schematics has a little box with technical notes in it!
Is anyone interested in some UA739's? (£10 each inc pp), i have some of the fairchild ceramic versions (ua739dc), i have noticed the later plastic case ic's are a bit prone to failure, (the 10 volt zener and associated cap neads to be changed after decades of use)
(These ics can actually fail s/c leading to dc floating about amp)
The 6 transistors on the main board can be replaced with d40 and d44 transistors.......
There were so many different components used over the years its a bit of a mystery at times....not to mention special part numbers......
I dont know that much about dc300a's but im willing to try and help anyone...if i can. i have repaired a few over the years....
please dont hold that against me, i know im sick!
now weres that smoke gone?
UA739DC's
What are these D40 & D44 transistors that you speak of? My shipment of MJ21194's got lost in transit this past week so I am still waiting to get back into this project. Meanwhile I have been working on substitutions for the transistor so any extra input would be appreciated.
I will email about your ua739dc's! I'd love to get a few of those to experiment with.
Shawn.
krmaudio said:
Hi guys sorry been busy.......
The resistors around the 739 were associated with different value volume pots, some amps used 22k log some used 100k log as i remember,
one of the schematics has a little box with technical notes in it!
Is anyone interested in some UA739's? (£10 each inc pp), i have some of the fairchild ceramic versions (ua739dc), i have noticed the later plastic case ic's are a bit prone to failure, (the 10 volt zener and associated cap neads to be changed after decades of use)
(These ics can actually fail s/c leading to dc floating about amp)
The 6 transistors on the main board can be replaced with d40 and d44 transistors.......
There were so many different components used over the years its a bit of a mystery at times....not to mention special part numbers......
I dont know that much about dc300a's but im willing to try and help anyone...if i can. i have repaired a few over the years....
please dont hold that against me, i know im sick!
now weres that smoke gone?
What are these D40 & D44 transistors that you speak of? My shipment of MJ21194's got lost in transit this past week so I am still waiting to get back into this project. Meanwhile I have been working on substitutions for the transistor so any extra input would be appreciated.
I will email about your ua739dc's! I'd love to get a few of those to experiment with.
Shawn.
hi shawn,
The transitors in the corner of the main board were.....
ss7304 and rca 61061 these are fitted with small circular heatsinks..... they were changed several times and eventually relaced with d40 and d44 TO202 transistors (like a TO220 but with long tag, any help you need with transistor replacements, please let me know will try to help as much as i can , i need to alter my reg e mail address its now a different one, due to endless spam.... sure you know the problem
I have had success with MJ15024 transistors as outputs,
sounds like you have made a good choice in your ops......
The transitors in the corner of the main board were.....
ss7304 and rca 61061 these are fitted with small circular heatsinks..... they were changed several times and eventually relaced with d40 and d44 TO202 transistors (like a TO220 but with long tag, any help you need with transistor replacements, please let me know will try to help as much as i can , i need to alter my reg e mail address its now a different one, due to endless spam.... sure you know the problem
I have had success with MJ15024 transistors as outputs,
sounds like you have made a good choice in your ops......
UA739DC___DC300A
Thanks for the scoop
I'll be using the MJ21194 if they ever show up🙁
On my first pass I will stick to the orriginal design like glue. That means I'll try to pick up a few of your ceramic dip 739's. You have mail.
Thanks,
Shawn.
krmaudio said:
Thanks for the scoop
I'll be using the MJ21194 if they ever show up🙁
On my first pass I will stick to the orriginal design like glue. That means I'll try to pick up a few of your ceramic dip 739's. You have mail.
Thanks,
Shawn.
Hi Shawn,
Wise move.
Most of the ones I've ever had to replace in any design were the plastic ones. Curiously, the ceramic ones fail a lot in the Marantz preamps. I'll bet the supplies are close to max.
-Chris
Wise move.
Most of the ones I've ever had to replace in any design were the plastic ones. Curiously, the ceramic ones fail a lot in the Marantz preamps. I'll bet the supplies are close to max.
-Chris
uA739 power supply
I associate ceramic with industrial temp and increased durability. I think I'm going to order 2 ceramics from krmaudio.
Speaking of power supplies, the one that feeds this uA739 is wacky. Do you folks see any room for a few tweaks using existing PC board?
Shawn.
anatech said:
I associate ceramic with industrial temp and increased durability. I think I'm going to order 2 ceramics from krmaudio.
Speaking of power supplies, the one that feeds this uA739 is wacky. Do you folks see any room for a few tweaks using existing PC board?
Shawn.
Attachments
Hi Shawn,
Zener regulated supplies, nothing strange here. If you want you could go for an active shunt regulator. Possibly perched that with a CCS. That might give you more noise isolation.
Is it worth while? Don't know. You could test this by restoring it, then run the op amp from a different supply to see if the supply artifacts go away. A pair of fresh 9V batteries would do nicely.
-Chris
Zener regulated supplies, nothing strange here. If you want you could go for an active shunt regulator. Possibly perched that with a CCS. That might give you more noise isolation.
Is it worth while? Don't know. You could test this by restoring it, then run the op amp from a different supply to see if the supply artifacts go away. A pair of fresh 9V batteries would do nicely.
-Chris