BrownDog Adapters

George S.

Veteran and General Yakker
Joined
Feb 18, 2020
Messages
2,042
#24
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.
 
Last edited:

WOPL Sniffer

Veteran and General Yakker
Joined
Aug 10, 2015
Messages
8,275
Location
Minnie-Soda
Tagline
Screw it
#26
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.
 

George S.

Veteran and General Yakker
Joined
Feb 18, 2020
Messages
2,042
#27
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
Joined
Jun 24, 2011
Messages
2,684
Location
Jacksonville, FL
#28
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.
 

George S.

Veteran and General Yakker
Joined
Feb 18, 2020
Messages
2,042
#29
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
Joined
Aug 13, 2014
Messages
2,163
Location
Vancouver
Tagline
---
#30
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.
 

George S.

Veteran and General Yakker
Joined
Feb 18, 2020
Messages
2,042
#31
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
Joined
Aug 10, 2015
Messages
8,275
Location
Minnie-Soda
Tagline
Screw it
#32
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.

Glen, did you mean RC4136?
 

mlucitt

Veteran and General Yakker
Joined
Jun 24, 2011
Messages
2,684
Location
Jacksonville, FL
#33
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.
 
Last edited:

George S.

Veteran and General Yakker
Joined
Feb 18, 2020
Messages
2,042
#34
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 OPAMO 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.
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 OPAMO 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.
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.
 

George S.

Veteran and General Yakker
Joined
Feb 18, 2020
Messages
2,042
#36
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!
 

Attachments

George S.

Veteran and General Yakker
Joined
Feb 18, 2020
Messages
2,042
#38
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!
 

Gepetto

Administrator
Staff member
Joined
May 15, 2011
Messages
11,067
Location
Sterling, MA
Tagline
Old 'Arn Enthusiast
#40
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!
They used electrolytics because they were cheap, the bean counters ran PL :)
 
Top