GHXAMP 3A5 Tube Preamplifier SRPP Circuit For Power Amplifier Board Enhance Sound Quality Home Audio DIY DC150V 1PCS|Amplifier| - AliExpress
Aliexpress claims they have a SRPP curcuit with 3A5.
So is it possible?
Aliexpress claims they have a SRPP curcuit with 3A5.
So is it possible?
On the page it says: "This circuit adopts 3A5 parallel mode,...". That seems to indicate a mono board with each 3A5 parallel connected?
A matching power supply is also mentioned on the page. I didn't search for it, although I am curious how they arrange for the two seperate filament supplies. I would think that they both have to float.
A matching power supply is also mentioned on the page. I didn't search for it, although I am curious how they arrange for the two seperate filament supplies. I would think that they both have to float.
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With the views given, you can see the component values except the caps next to the 10uF MKTs. You could probably generate an accurate schematic based on the pictures.
No, this is not SRPP, I have worked on this board, schematic is here. Some things to note:
The circuit is 3a5 with both triodes paralleled.
The PCB has no heater input - you must wire to pins 1/4/7 and you can run it with heaters in parallel or series 1.4/2.8V operation
You need a dedicated filament supply. Some batteries will be fine to try it out. A regular regulated/adjustable supply will give you hum but you can at least hear it working.
I am using it as the IV converter after a DAC, and ended up using Rod Coleman filament boards, and Ale Moglia gyrators for the plate load in a filament bias set, exactly as per Bartola valves. It sounds wonderful in this arrangement. I mean seriously good, the realism and soundstage is just fantastic. Beware these valves are microphonic, so you will need to sit the board on some foam or something.
The page on Ale's site is here.
The circuit is 3a5 with both triodes paralleled.
The PCB has no heater input - you must wire to pins 1/4/7 and you can run it with heaters in parallel or series 1.4/2.8V operation
You need a dedicated filament supply. Some batteries will be fine to try it out. A regular regulated/adjustable supply will give you hum but you can at least hear it working.
I am using it as the IV converter after a DAC, and ended up using Rod Coleman filament boards, and Ale Moglia gyrators for the plate load in a filament bias set, exactly as per Bartola valves. It sounds wonderful in this arrangement. I mean seriously good, the realism and soundstage is just fantastic. Beware these valves are microphonic, so you will need to sit the board on some foam or something.
The page on Ale's site is here.
Do you remember what values the R4,R6,R7 and R8 has on the Gyrator?
And on the schema:
How did you connect the Coleman regulator?
Did you use the pin 4 to the 680 ohm resistor or?
Yes. Just two 30's or 1H4G's, filaments heated by rechargeable AA cells. And the usual R's & C's to make it happen. All done.🙂
Oh, & a DPST switch for the filament supplies when not in use.😀
Oh, & a DPST switch for the filament supplies when not in use.😀
In reverse order:
The Coleman regulator connection: join pins 1 and 7 together on the valve socket. Remove all the cathode components from the schematic above - C2, R5, R6. Fit 10R resistor between the junction of pin 1/7 and ground. Then positive of Coleman supply goes to pin 4, negative of his supply goes to ground (bottom of the 10R resistor). Then you need to adjust current on the Coleman to get 1.4V across pin 1/7 to pin 4. If you are using the bartola schematic, you will end up with about 3.6v or so at pin 4, 2.2V or so at pin 1/7 above ground.
I'll have to pull out the Gyrator to look at the values you mention, but its all covered in the PDF that Ale will send you when you order the boards.
fran
The Coleman regulator connection: join pins 1 and 7 together on the valve socket. Remove all the cathode components from the schematic above - C2, R5, R6. Fit 10R resistor between the junction of pin 1/7 and ground. Then positive of Coleman supply goes to pin 4, negative of his supply goes to ground (bottom of the 10R resistor). Then you need to adjust current on the Coleman to get 1.4V across pin 1/7 to pin 4. If you are using the bartola schematic, you will end up with about 3.6v or so at pin 4, 2.2V or so at pin 1/7 above ground.
I'll have to pull out the Gyrator to look at the values you mention, but its all covered in the PDF that Ale will send you when you order the boards.
fran
A transformer that puts out 9-12V should be fine (if you are using the schematic with gyrator etc from Bartola). My recommendation would be to use different transformers for the filament regs and the B+. The current is not high for either, so some nice r-core transformers would fit the bill nicely.
Also, if you are building your own raw DC supply (ie not using Rods raw DC kit) then don't use a 317 type regulator - I had buzz when I used one. Just a simple rectifier - 10,000uF cap-10r-10,000uf cap will do nicely. I used a common mode choke on another build and it worked nicely too, but I don't know if it actually made it any quieter. Rod recommends 10,000uF but I know I have used 6800uF and they seem fine.
The challenge here is getting it all quiet enough.
Also, if you are building your own raw DC supply (ie not using Rods raw DC kit) then don't use a 317 type regulator - I had buzz when I used one. Just a simple rectifier - 10,000uF cap-10r-10,000uf cap will do nicely. I used a common mode choke on another build and it worked nicely too, but I don't know if it actually made it any quieter. Rod recommends 10,000uF but I know I have used 6800uF and they seem fine.
The challenge here is getting it all quiet enough.
The challenge here is getting it all quiet enough.
That is why a rechargeable battery for the filament supply is the better way with this kind of tube, What mysterious quality makes the 3A5 better than some other battery operated tube that uses less filament current? The 3A5 was built to run for a short life as Class C oscillator in a balloon launched Radiosonde.🙂
That is why a rechargeable battery for the filament supply is the better way with this kind of tube, What mysterious quality makes the 3A5 better than some other battery operated tube that uses less filament current? The 3A5 was built to run for a short life as Class C oscillator in a balloon launched Radiosonde.🙂
There are lots of choices for different valves for sure!!
I can say that using this circuit, as an output stage for an AD1862 dac really sounds wonderful. Would other DHT (and IDHT, and solid state circuits) sounds great - yep, I think they would. But like any project, I took a chance on the board from Aliexpress (not needed really, its simple enough to do it on perfboard) and with the help I mention up further in the thread, managed to get it running well enough to sound really good.
Batteries on the filaments will be dead quiet - if you use rechargeables and a relay system for recharging then you will have quiet filaments. I know I used a d-cell to test and it worked perfectly - but I can't comment on how it sounds compared to the Coleman filament supply, I haven't done that test.
Fran
I can say that using this circuit, as an output stage for an AD1862 dac really sounds wonderful. Would other DHT (and IDHT, and solid state circuits) sounds great - yep, I think they would. But like any project, I took a chance on the board from Aliexpress (not needed really, its simple enough to do it on perfboard) and with the help I mention up further in the thread, managed to get it running well enough to sound really good.
Batteries on the filaments will be dead quiet - if you use rechargeables and a relay system for recharging then you will have quiet filaments. I know I used a d-cell to test and it worked perfectly - but I can't comment on how it sounds compared to the Coleman filament supply, I haven't done that test.
Fran