Need help assessing a discrete voltage regulator
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heiney9
Posts: 25,080
I am considering changing out the I/C chip type regulators w/discrete Dexa regulators in my Mini Max Dac Plus.
The regulator for the tube filament circuit is -13v (7813). Dexa makes a -12v or -15v discrete regulator, but not the exact voltage.
Can I get by with the -12v discrete regulator without an issue. I am assuming the -15v is too much, but not sure how that would affect the tube filament?
I am replacing the op-amp regulators with the exact upgrade. 7815 and 7915.
This is what I found on 'net from Wayne Boulder in regards to the DAC PLUS
The DAC Plus uses two transformers, but the second transformer is just for the tube HV and filament. They are placed very close together and there may be some coupling going on. When the current load is removed from the transformer by removing the tube, some of that coupling is also gone. The regulator used in the tube filament circuit is a 7813. They can be a bit noisy. That might also have an influence on the sonic difference.
There is no problem with turning on the DAC with the tube circuit selected. All that switch does is open or close a relay to switch between where the signal is coming from. With the tube out, no signal, no voltage or current will flow into the relay. No damage can happen
The current draw by the 5534 op-amp is rather small but you are looking at 7815 and 7915 regulators supplying the op-amps. On the DAC Plus they are running off the same transformer that supplies the DAC chip.
Thanks for any advice
H9
The regulator for the tube filament circuit is -13v (7813). Dexa makes a -12v or -15v discrete regulator, but not the exact voltage.
Can I get by with the -12v discrete regulator without an issue. I am assuming the -15v is too much, but not sure how that would affect the tube filament?
I am replacing the op-amp regulators with the exact upgrade. 7815 and 7915.
This is what I found on 'net from Wayne Boulder in regards to the DAC PLUS
The DAC Plus uses two transformers, but the second transformer is just for the tube HV and filament. They are placed very close together and there may be some coupling going on. When the current load is removed from the transformer by removing the tube, some of that coupling is also gone. The regulator used in the tube filament circuit is a 7813. They can be a bit noisy. That might also have an influence on the sonic difference.
There is no problem with turning on the DAC with the tube circuit selected. All that switch does is open or close a relay to switch between where the signal is coming from. With the tube out, no signal, no voltage or current will flow into the relay. No damage can happen
The current draw by the 5534 op-amp is rather small but you are looking at 7815 and 7915 regulators supplying the op-amps. On the DAC Plus they are running off the same transformer that supplies the DAC chip.
Thanks for any advice
H9
"Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
Comments
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The tube is a 12AU7? They call for 12.6v, 150mA. Wondering if 12v might start to affect output in a negative way, or change qualities you are used to? Tubes can start to lose SQ when fed power lower than spec.Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ * Signature Series Sonore Music Server w/Deux PS * Roon * Gustard R26 DAC / Singxer SU-6 DDC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *
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According to Morgan Jones, in his book, "Valve Amplifiers", a vacuum tube's plate characteristics are critically dependent on cathode temperatures, which are related to heater power. It has been found that a 25% drop in heater voltage doubled the noise power. However, operating oxide-coated cathodes at higher heater voltages dramatically shortens life because it increases evaporation of the emissive material, so it's recommended for heater voltages to be less than 105% of recommended settings. So, long life, low noise and stable plate characteristics should have the correct heater supply.
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Thanks for the input Rich and Ken. I decided to leave it be for now. I did purchase a pair of Dexa New Class D discrete regulators for the solid state portion of the dac. Parts Connexion has a 50% off sale on upgrades for the 7815 and 7915 regulators. Also picked up a pair of the Special Edition single channel discrete op-amps for 50% off.
H9"Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul! -
It's probably just typing errors...but if I read it as written above, the regulator numbers are wrong. The "-13v 7813" was what jumped at me.
78XX are positive and 79XX series are the negative. Just sayin' ta say it for the magic smoke escapes....
CJA so called science type proudly says... "I do realize that I would fool myself all the time, about listening conclusions and many other observations, if I did listen before buying. That’s why I don’t, I bought all of my current gear based on technical parameters alone, such as specs and measurements." -
Yes, it is a typo.
The regulator for the tube filament circuit is -13v (7813). Dexa makes a -12v or -15v discrete regulator, but not the exact voltage.
The -13v above should be +13v. Doesn't matter as DEXA doesn't offer a 13v discrete regulator, just +/- 12v or +/- 15v
H9
"Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul! -
When I built the power supply for my preamp I made the filament section have a slow warm up and adjustable, gradually bringing the voltage up and then switched on the B+ so there wouldn't be any possibility of cathode stripping. The filament supply is the complete front of the board, the B+ is the rear board plus the large filter caps.
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