BrownDog Adapters

Gepetto

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#41
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!
Did you replace the RC4136 devices with your Brown Dogs?
 

George S.

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#42
Did you replace the RC4136 devices with your Brown Dogs?
Not yet. Working on getting real test equipment first, learning how to use it, and establishing a base line for the preamp with the original opamps.
Have them sitting on the bench in antistatic bags, so no hurry.
Been eyeing test equipment for years. Have 3 Dell XPS desktops being unused that I need to scope the power supplies. They shut down randomly and I need to determine if it's the power supplies or caps on the motherboards by the heatsinks(probably bad caps in the supplies and on the boards).
My father's test equipment is just too old to trust, so been looking at Picoscopes, Siglent oscilloscopes and signal generators and others. Still deciding what to get, just doing research, want to buy new.
 

mlucitt

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#45
My father's test equipment is just too old to trust
Sometimes you only need a trace to look at. If the time base is slightly out of calibration, you might count 1005 Hz instead of 1000 Hz or the voltage level display might show 55.2 VDC but in reality you are measuring 55 VDC. If it is a quality scope, it likely is still fairly accurate. Often we use qualitative measurements (voltage vs no voltage or a clean sine wave instead of a fuzzy sine wave - noise) and not quantitative measurements.
 

George S.

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#46
Sometimes you only need a trace to look at. If the time base is slightly out of calibration, you might count 1005 Hz instead of 1000 Hz or the voltage level display might show 55.2 VDC but in reality you are measuring 55 VDC. If it is a quality scope, it likely is still fairly accurate. Often we use qualitative measurements (voltage vs no voltage or a clean sine wave instead of a fuzzy sine wave - noise) and not quantitative measurements.
That makes perfect sense. I'm glad you stated the value of qualitative measurement.
For many years I've wanted a scope, I've wanted to "see" that electrical signal to better understand it and not guess.
I also have about eight 10 and 11 meter mobil ham radios that need alignment.
One of my other interests is SDR (software defined radio), I've built two of the Softrock Ensemble receivers and listen to shortwave broadcasts during the cold winter months.
I also do all my own auto repair and help the neighbors, been times I could have used a scope to look at crank or cam sensor output.
So, I'm going to get at least a scope and signal generator. Probably just order "Amazon's Choice" or a 100 MHz Picoscope. Want new not used, probably just go with Amazon, just hate to buy Chinese after the virus. Picoscope is English, but probably also China product.
 

George S.

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#47
Have spent many days over the last many weeks swapping the opamps in and out. Have looked for ringing on the scope at x10 magnification, haven't seen any. Looked for ringing on the graphs that REW produced, haven't seen any. Been doing lots of comparing the opamps. Simply cut power to the preamp, swap opamp, restore power to preamp, no changes to test equipment or preamp settings.
And, I see no difference other than lower THD with the OPA2134 in place of the RC4136.
Granted, doing distortion testing using a sound card and REW isn't optimum. Have also swapped opamps with the preamp in the system and replayed very high quality FLAC tracks. I really can't tell any difference, but then my hearing isn't as good as it once was.
So, for me and my amateur test equipment, I conclude the Browndogs are a suitable sub if the original opamps can't be sourced. So I put the originals back in.
Was it worth the trouble? Yup, learned a little bit more.
 

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Gepetto

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#48
Have spent many days over the last many weeks swapping the opamps in and out. Have looked for ringing on the scope at x10 magnification, haven't seen any. Looked for ringing on the graphs that REW produced, haven't seen any. Been doing lots of comparing the opamps. Simply cut power to the preamp, swap opamp, restore power to preamp, no changes to test equipment or preamp settings.
And, I see no difference other than lower THD with the OPA2134 in place of the RC4136.
Granted, doing distortion testing using a sound card and REW isn't optimum. Have also swapped opamps with the preamp in the system and replayed very high quality FLAC tracks. I really can't tell any difference, but then my hearing isn't as good as it once was.
So, for me and my amateur test equipment, I conclude the Browndogs are a suitable sub if the original opamps can't be sourced. So I put the originals back in.
Was it worth the trouble? Yup, learned a little bit more.
I would not expect any oscillation George, both amps are unity gain stable.

You likely cannot measure it but the noise floor will be lower with the OPA2134 amps in play, they are fully specified for noise versus the targeted noise spec for the RC4136, especially with a Rs of 100 ohms which is impractical in most preamp circuits. The specs for the 2134 are not reliant on the source resistance.
 

George S.

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#49
I would not expect any oscillation George, both amps are unity gain stable.

You likely cannot measure it but the noise floor will be lower with the OPA2134 amps in play, they are fully specified for noise versus the targeted noise spec for the RC4136, especially with a Rs of 100 ohms which is impractical in most preamp circuits. The specs for the 2134 are not reliant on the source resistance.
Thanks Joe, going to reread this many times, and do some research and reading. Your posts often lead me down a rabbit hole! I'm going to learn more about this.
 

mlucitt

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#50
The RC4136 is a dinosaur, compared to the latest version of the Texas Instruments, Burr Brown Division, OPAx134. The earliest reference I have found to the OPAx134 is the first datasheet, with a copywrite date of 1997. I like the fact that the OPAx134 is designed to swing the output voltage to within 1V of the rail supply voltage, which gives these devices outstanding headroom; something OPAMPs are not famous for.
 

George S.

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#51
The RC4136 is a dinosaur, compared to the latest version of the Texas Instruments, Burr Brown Division, OPAx134. The earliest reference I have found to the OPAx134 is the first datasheet, with a copywrite date of 1997. I like the fact that the OPAx134 is designed to swing the output voltage to within 1V of the rail supply voltage, which gives these devices outstanding headroom; something OPAMPs are not famous for.
Now that is interesting. Going to pop the OPA 2134 back in and give it some more critical listening.
Any experience with the Browndog RC4739 adapter that uses the NE5532?
Saw one old post where I think Lee stated that there is no replacement for the RC4739 due to issues with phase angles or something. I looked the NE5532 up before ordering, seemed to have good reviews and specs. Seems to work perfect as a replacement, at least from what I saw on my limited equipment.
The biggest issue I ran into using REW and a sound card was the noise floor. Using a USB sound card helped by getting it out of the computer, but noise was still high.
Replacing all three original opamps with Browndogs cut the THD in half, but the noise was high. So THD+N was high regardless. Wish I had kept some of the numbers, but didn't as I had little faith they were accurate. However, the numbers were repeatable time after time, so it was good for comparisons, just not quantifying.
 
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George S.

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#52
Swapped out all three. Listening to BTO (Bachman Turner Overdrive) discography, FLAC, it's fairly dynamic music. Even replaced all the cheap cables I've been using with the Monoprice Monolith cables I've had sitting here unused. Definitely sounds very good, really does. I'm just hesitant to say the Browndogs make a big difference. Perhaps they do, I don't know. I just don't want to fall for the psychological trap that the mind plays when trying upgrades. I'm going to roll with it as is for a while, and ponder what Joe said. Thanks guys, your a big help. MAGNETOSTRICTION.
 

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Gepetto

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#53
Swapped out all three. Listening to BTO (Bachman Turner Overdrive) discography, FLAC, it's fairly dynamic music. Even replaced all the cheap cables I've been using with the Monoprice Monolith cables I've had sitting here unused. Definitely sounds very good, really does. I'm just hesitant to say the Browndogs make a big difference. Perhaps they do, I don't know. I just don't want to fall for the psychological trap that the mind plays when trying upgrades. I'm going to roll with it as is for a while, and ponder what Joe said. Thanks guys, your a big help. MAGNETOSTRICTION.
You will never notice a big difference. As I mentioned earlier, you likely cannot measure an improvement in noise floor unless you have very good test equipment in a very controlled environment. A 1.6V/usec to 15V/usec slew rate difference appears rather large on the spec sheets but I doubt you will hear that except for subtle differences due to feedback involved. 15V/usec is overkill for sure but will come through as slight improvements in clarity for example.
 

mlucitt

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#55
Saw one old post where I think Lee stated that there is no replacement for the RC4739
The issue with the RC4739 (and Lee knows about this) is that the pinout is unique. Perhaps Raytheon thought they would set the standard but that was not the case. For one thing, the RC4739 is a dual OPAMP in a 14-pin DIP. Most other 14-pin DIPs, such as the RC4136 are quad OPAMPs.
Browndog makes an adapter, #1025G, that uses an OPA2134 but switches the pinout to correspond to the unique pinout of the RC4739. I think it costs $11.50 with the chip installed.
 

George S.

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#56
The issue with the RC4739 (and Lee knows about this) is that the pinout is unique. Perhaps Raytheon thought they would set the standard but that was not the case. For one thing, the RC4739 is a dual OPAMP in a 14-pin DIP. Most other 14-pin DIPs, such as the RC4136 are quad OPAMPs.
Browndog makes an adapter, #1025G, that uses an OPA2134 but switches the pinout to correspond to the unique pinout of the RC4739. I think it costs $11.50 with the chip installed.
Good info to know. Thanks.
 

George S.

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#57
Did some more critical listening, and I can tell a difference between the original and new opamps on the Phono circuit, not so much on the Aux which I use for input from a Lenovo S30 Work Station. Started thinking "why", then "oh crap!", the preamp is no longer the weak link in the system. It's now the sound card! So I've been using the on board "Azalia HD Audio" feeding the Modi 3 DAC digital via USB. Swapped in my only USB soundcard, a old Asus Xonar U7 Mkii to feed the Modi 3 over cable, and, a big improvement! Now, the U7 is mostly a gaming soundcard, and running loopback testing on REW showed it doesn't have a flat response. There is a emphasis on bass in the 50 Hz range.
So, I need to get a good USB sound card to feed my Modi 3. Any suggestions on models to look at?
Also, ordered some of the RC4736 Browndogs with the OPA2134. When I looked at the Cimmeron Tech site, they weren't shown. Emailed them, they said "oh yes, we have them". Boom! They put them back up on site.
 
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George S.

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#58
Wait a minute, do I even need a sound card with the Modi 3???? Think I don't unless I want headphones at the computer or soundcard. If I just want digital out, can't I bypass the Azalia and not use a soundcard at all. Pretty sure it was Azalia digital out over the USB and Xonar digital out because that's where the cable to the Modi was plugged into. Going to have to play with Windows Sound settings and find out.
 
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George S.

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#59
D'oh, wow was I ever confused. Had my Schiit Modi 3 DAC connected to the desktops Azalia on board digital usb output. All good now, piping the digital direct to the DAC now. Well, first stand-alone DAC I've had. Definitely sounds a little better. I can tell the noise level is lower. Live and learn, or maybe read the directions, naw!
 
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