WOPL Sniffer
Veteran and General Yakker
Damn, you guys woke up a 2016 thread???? You must be bored
BrownDog Adapters
- Thread starter AZG
- Start date
WOPL Sniffer
Veteran and General Yakker
Careful where you use them. We did a bunch of testing in this old shit. It will cause issues if used just anywhere.
Yeah, I read your thread where I think you were doing a PL4000 that I guess uses a dozen or more. Only 1 RC4136 and 2 RC4739 in the PL2000, going to give it a shot. Getting parts together to do 2 preamps even though I only have 1 now.
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WOPL Sniffer
Veteran and General Yakker
Joe design them into his new stuff. That's ok, used in the old junk, bypass caps and such need to be used. Good luck.
WOPL Sniffer
Veteran and General Yakker
I need to put up the dozens I have sitting here. I won't use them. Neither single OR doubles. The new TI 4136's are equal or better.
Got the RC4739 Browndogs with NE5532A opamps and the RC4136 Browndogs with duel OPA2134 opamps ordered. I know it's a gamble, but going for it. I have sockets installed on the board. I'll replace them one at a time, but how do I check for oscillation without test equipment? I only have a multimeter. I do have a approximately 40 WPC power amp hooked up to old Pioneer speakers. Use them to test the results of each opamp swap? I imagine "oscillation" is high pitched squealing or is it DC out the preamps outputs?
mlucitt
Veteran and General Yakker
Oscillation (AC waveforms such as sawtooth, square wave or sine wave) which is not common, comes from the newer, high speed OPAMPs that are not configured for vintage circuitry and typically occurs well beyond the capability of human hearing. Sometimes it can reach the RF spectrum, (30kHz to 300kHz). The biggest problem with this type of oscillation is the heat generated in the components. A simple blocking capacitor can prevent this if you know the right value and the best place to insert it. If you have a IR thermometer, you might be able to see the heat after operating for long time.
Thanks Mark, yeah have a IR temp gun. What would be the proper test equipment, thinking a signal generator and oscilloscope. My father has a huge test bench with that equipment, but it's all very old and out of spec. Maybe I'll run it over and see what he thinks. Thanks.
grapplesaw
Veteran and General Yakker
I have used the brown dog dual opa2134 on the phono board and main output driver chip in the c4000 and 4000t. I add caps to both + and - rail as close each ic socket as possible. Have very good results. As Perry points out populating all the ic’s with them may cause issues so choose where you use them. I agree with Perry that the new RC4937 work just as well so why bother Upgrading other than to say you did.
That's good to know. I'm willing to play with it and learn as I go. To me it sounds excellent with the 3 stock opamps. I'm just curious and want to see if it can be improved. Time probably better spent at other pursuits. I'll update results. Thanks.
WOPL Sniffer
Veteran and General Yakker
mlucitt
Veteran and General Yakker
George,
Do you have the PL1000 Service Manual? If you are doing the PL2000 Series I or II, there are three OPAMPs to deal with. Z1 is a RC4739 Dual OPAMP and only amplifies the Phono input to the rest of the circuit. Z2 is also a RC4739 and only amplifies the Rear Channel outputs of the PL2000. The key OPAMP is Z3, which is a RC4136 Quad OPAMP, as you know.
All you need is an oscilloscope to see the high frequency oscillations. Just put it on the Main outputs with nothing on the inputs at first. If you see oscillations as you change the time base, with the voltage set very low (millivolts scale), then you can check the output of each OPAMP to find the offender. If no oscillations appear with no input signal, try a 2kHz sinewave signal at 200mV (not the Phono input, that one only needs 2mV). Adjust the scope to magnify the sine wave to look for "ringing" on top of the sinewave signal (it will look like fuzz).
The fix is to install one grounded 100nF capacitor on each rail near the DIP socket (+pin 14 and -pin 7 for the RC4739 and +pin 11 and -pin 7 for the RC4136) as Glen suggested, but the PL2000 OPAMP rails are short, so there is not much chance to pick up oscillations from rail loops.
Do you have the PL1000 Service Manual? If you are doing the PL2000 Series I or II, there are three OPAMPs to deal with. Z1 is a RC4739 Dual OPAMP and only amplifies the Phono input to the rest of the circuit. Z2 is also a RC4739 and only amplifies the Rear Channel outputs of the PL2000. The key OPAMP is Z3, which is a RC4136 Quad OPAMP, as you know.
All you need is an oscilloscope to see the high frequency oscillations. Just put it on the Main outputs with nothing on the inputs at first. If you see oscillations as you change the time base, with the voltage set very low (millivolts scale), then you can check the output of each OPAMP to find the offender. If no oscillations appear with no input signal, try a 2kHz sinewave signal at 200mV (not the Phono input, that one only needs 2mV). Adjust the scope to magnify the sine wave to look for "ringing" on top of the sinewave signal (it will look like fuzz).
The fix is to install one grounded 100nF capacitor on each rail near the DIP socket (+pin 14 and -pin 7 for the RC4739 and +pin 11 and -pin 7 for the RC4136) as Glen suggested, but the PL2000 OPAMP rails are short, so there is not much chance to pick up oscillations from rail loops.
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Mark, fantastic information. Now I understand. Pretty sure my father's antique test equipment can handle this easily. You've come through again. Thank you! I'll try to get everything documented to help the next guy.
grapplesaw
Veteran and General Yakker
Yes! my bad
So, found the preamp had some issues to fix before even embarking on installing Browndogs.
Q1 location had a TIS97 installed, Q2 had a GES97. According to the schematic, they should be reversed. I did so and that's when my trouble started.
B+ and B- shot up from 17 VDC to 18.5 VDC taking out the Z3 opamp and GES97 now in Q1.
The TIS97 now in Q2 still worked, but shortly quit rendering the LED inop.
Luckily Lee was working on the DChristie preamp with Joe's help so I got some good info. Luckily I had parts, except for the big film caps that had to be ordered. And Joe solved my LED not working in the PL2000 LED driver thread.
So to bring the B+ and B- down to 15 volts, I installed a 1W 121ohm Dale metal film resistor in series with each of the two red secondary wires at the pcb.
A new TIS97 was installed at Q1.
A new TI Rc4136N opamp was installed at Z3.
Q2 transistor was removed and a jumper installed.
The 2.2k resistor in the Q2 LED driver circuit was increased to 2.7k.
Two big 4.7uF Panasonic film caps replace the 4 axial electrolytic dc protect caps at the preamps outputs.
Removed the resistor across the power switch lugs and replaced the two capacitors.
Just want to say Thanks to Joe, Lee, and Mark for their help. Thank you Gentlemen!
Q1 location had a TIS97 installed, Q2 had a GES97. According to the schematic, they should be reversed. I did so and that's when my trouble started.
B+ and B- shot up from 17 VDC to 18.5 VDC taking out the Z3 opamp and GES97 now in Q1.
The TIS97 now in Q2 still worked, but shortly quit rendering the LED inop.
Luckily Lee was working on the DChristie preamp with Joe's help so I got some good info. Luckily I had parts, except for the big film caps that had to be ordered. And Joe solved my LED not working in the PL2000 LED driver thread.
So to bring the B+ and B- down to 15 volts, I installed a 1W 121ohm Dale metal film resistor in series with each of the two red secondary wires at the pcb.
A new TIS97 was installed at Q1.
A new TI Rc4136N opamp was installed at Z3.
Q2 transistor was removed and a jumper installed.
The 2.2k resistor in the Q2 LED driver circuit was increased to 2.7k.
Two big 4.7uF Panasonic film caps replace the 4 axial electrolytic dc protect caps at the preamps outputs.
Removed the resistor across the power switch lugs and replaced the two capacitors.
Just want to say Thanks to Joe, Lee, and Mark for their help. Thank you Gentlemen!
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mlucitt
Veteran and General Yakker
Nice work, those new resistors look sweet!
It sounds great. Somehow FM broadcasts sound slightly less compressed with those big film caps installed and I'm pretty sure it's just not just psychological. Spoke with my father about them, and he said that when this equipment was designed, film caps like them weren't available so they had to use electrolytics.
It's so nice knowing the B+ and B- voltages are on the money and how to manipulate them for various opamps. I've learned a lot in a short time without damaging anything beyond repair. I'm going to wade into deeper water and try to learn more. Thanks!
WOPL Sniffer
Veteran and General Yakker
Yeah, sweet resistors......... HUH?
