TU-8500 with Sparkos Labs Discreet Voltages Regulators
I was talking to one of my good friends recently, and when we got on the subject of our current audio projects he told me how he had significantly lowered the noise in his diy phono amp by switching over to discreet voltage regulators. specifically, regulators made by Sparkos Labs.
This got me thinking about my TU-8500, The Phono section is probably one of the quietest I've ever heard, Especially with some Burr Brown OP AMP, This gear is just spectacular. Even with my HD800's can I barely hear the Phono hiss.
When I switched to an ART-7 MC pickup last year I finally got to make use of my AT-1000T SUT (only 1,000 were ever made). But even with this SUT, the gain was just half of my previous pickup, a VM750SH MM, who's output sits at 4.0mV. The ART-7 in the other hand has a super low output at 0.12mV (2.2mV with loss after the SUT).
This required a bit more gain from the TU-8500, but even with the knob turned up a bit more. the phono hiss, although a bit more audible, still sat very low. and after the conversation with my friend I decided to order two discreet Voltage regulators from Sparkos Labs, a +12V regulator and a -12V regulator.
I just got them in today, and honestly I wasn't expecting any audible differences, they are only voltage regulators after all. I carefully removed the original LM2940C, and LM2990 regulators. The Sparkos labs regulators, although bigger, fit perfectly on the board. After placing everything back together I did some voltage checks on the provided test points on the TU-8500, everything was more or less the same except the +12V and -12V points. With the original regulators +12 sat at 11.6V and -12 measured at -11.74. The Sparkos labs regulators+12, measured 12.0, right on the money! and -12 now at -11.98.
Again, when I got this back into my chain, I wasn't expecting anything, they are just voltage regulators, how much of a difference can they really make anyways to the over all sound? After flipping the switch and putting on my HD800 over my ears I stood there waiting for the 8500 to power on, just watching the blue LED blink on and off until it finally just stayed solid.. And what I heard next was nothing.. I looked at the amp, and made sure I had adjusted the volume pot to my marked sweet spot, that I had it set to 3x gain, and that I had set the input to phono, everything was correct. And still, I heard nothing. normally I would hear a faint hiss.
I don't have the gear to measure noise or anything like that but my ears. The phono hiss is gone at the same volume setting and 3x gain. As Im writing this im Listing to Max Richter's "The Blue Notebook, and it sounds just a little bit louder than before. I normally have the volume knob at 12 O clock on my TU-8600, I've had to back down a little bit.
I decided to figure out what happened to the hiss. without a scope on hand I'll have to use my ears. With the stock regulators my Volume knob on the 8500 was set to about 2 O-clock, this was the ideal spot, just a little hiss but enough gain. With the Sparkos Labs regulators, I can push the knob to about 3:00 and I can start to hear the faintest of hiss, moving on to 4 o clock and I can hear the same amount of hiss that I did before on the stock regulators.
With the Sparkos labs regulators I can get more gain with far less noise trade off. I don't know why, I really wish I had a scope. As far as sound stage goes I hear no difference through my KEF R300, or HD800.. The only difference I hear is noise. Maybe the Sparkos regulators provide a cleaner power source for the phono section of the TU-8500. It would be worth looking into for those with a scope!
Interesting. Thanks for the info. Less than a nice pair of NOS tubes.
So you have two options, I tested both methods and I tied both methods. And I just got my O scope delivered this morning so I have pictures to share.
First option as recommended by Andrew of Sparkos labs. He recommended to bypass the zener, Its "ZD2" on the schematic. this is on the ground leg of the +12V regulator. He explained that the point of this Zener was to up up voltage to make up for the losses in the diod networks, but this zener could probably restrict the output capacitor on the discreet regulator from discharging properly. But, once the zener is bypassed C26 then takes over ias being the output capacitor. he said this capacitor is ok to use. obviously this is just from looking at the schematic .
I went ahead and verified this. with the stock +12V regulator, Zener ZD2 in place, and measuring on the +12V test point. voltage was at +11.6V. Same test conditions but this time with the zener bypassed, voltage read at +10.7V.
When I recieved my discreet regulators, the +12V and -12V, I tested having the Zener in place and bypassed. Audibly, there was no difference having it bypassed or in place. The discreet regulator does have less of a voltage drop without it as you will see in the pictures, it only drops to +11.5V without the zener.
Second option is to leave everything in place and just swap out the regulators.
Using a scope this morning I see no difference in the traces from having the zener bypassed or leaving it place, aside from the voltage drop. I had to zoom all the way down to 100mV per division and 5.00nS to try to find a difference, and it just wasn't there.
To tie all of this up. If your going to bypass the Zener , which Andrew recommends order a +12.6V 78XX regulator and a -12V 79XX regulator. I ordered the +12.9V if I chose to bypass the zener permanently.
If you are going to leave everything in place as is. order a +12.0V 78XX, and a -12.0V 79XX. This is what i'm sticking with after the scope readings.
first picture with +12.3V is with the Zener in place
second picture with +11.5V is with Zener bypassed
Third picture is just the -11.9V trace
And the last picture is the test point I used
Thanks for the additional info & pic's.
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