When using the ECC82, the total heater current is only 900mA.
this transformer could fit: https://aliexpress.com/item/1005001496708765.html
The 8V~ (after rectification and charging of the electrolytic capacitor higher!) are sufficient for regulation to 6.3V.
unfortunately high shipping costs,
so I would prefer a 2-transformer solution!
For a 2-transformer solution, the HV transformer looks like this:
https://www.amazon.de/Pikatron-Isolating-Transformer-0-208-230V-230V-23VA/ dp/B01AC1YR8W/
https://www.ebay.com/itm/182856482350
this transformer could fit: https://aliexpress.com/item/1005001496708765.html
The 8V~ (after rectification and charging of the electrolytic capacitor higher!) are sufficient for regulation to 6.3V.
unfortunately high shipping costs,
so I would prefer a 2-transformer solution!For a 2-transformer solution, the HV transformer looks like this:
https://www.amazon.de/Pikatron-Isolating-Transformer-0-208-230V-230V-23VA/ dp/B01AC1YR8W/
https://www.ebay.com/itm/182856482350
This one is close, apart from the heater ...
Toroidy TSTA 0040/001
Around €55. In the past I have found Toroidy to be very amenable to altering windings at a reasonable additional charge. So it would be possible to specify a 4.5V-0-4.5V heater winding, or 0-6.3V-9V perhaps?
Maybe with a guaranteed order of so many units they would make a batch for the standard price?
Toroidy TSTA 0040/001
| Nominal power | 40VA |
| Input voltage | 230V or 2x115V |
| Secondary SEC I | 235V / 75mA |
| Secondary SEC II | 3,15 - 0 - 3,15V / 3A |
Around €55. In the past I have found Toroidy to be very amenable to altering windings at a reasonable additional charge. So it would be possible to specify a 4.5V-0-4.5V heater winding, or 0-6.3V-9V perhaps?
Maybe with a guaranteed order of so many units they would make a batch for the standard price?
Depending on the country, add 23-29€ shipping costs and then with a heating system that doesn't fit, no thanks
for 30 € including shipping there is the transformer from aliexpress and the heating voltage also fits
https://aliexpress.com/item/1005001496708765.html
for 30 € including shipping there is the transformer from aliexpress and the heating voltage also fits
https://aliexpress.com/item/1005001496708765.html
The Chinese also have nice R-Core transformers (similar to toroid), I just haven't found one with the right 9V 1.5A for heating, but I asked if they had contact with the manufacturer about a custom-made product!?
https://aliexpress.com/item/32803653126.html
I also found many choke coils there, which inductance would fit?
https://aliexpress.com/item/1005005353091622.html
https://aliexpress.com/item/1005002991562285.html
https://aliexpress.com/item/1005003353757646.html
https://aliexpress.com/item/1005004194990852.html
https://aliexpress.com/item/4001211975781.html
https://aliexpress.com/item/4001099030116.html --->2 pieces, a pair !
https://aliexpress.com/item/32803653126.html
I also found many choke coils there, which inductance would fit?
https://aliexpress.com/item/1005005353091622.html
https://aliexpress.com/item/1005002991562285.html
https://aliexpress.com/item/1005003353757646.html
https://aliexpress.com/item/1005004194990852.html
https://aliexpress.com/item/4001211975781.html
https://aliexpress.com/item/4001099030116.html --->2 pieces, a pair !
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Just looking at what I have in my spare parts box - if I was to use a transformer with a 6,3V winding, then in theory I could get DC for the PC900, but have to use AC for the ECC82. Is that a compromise too far? I have no experience of anything that handles a signal smaller that typical line input (1V RMS). I suppose I can only try!
You can use https://octopart.com to search for, actually Mouser, Arrow , Digikey have the parts in stock. Original schematic report instead FQPF2N60C and che be found on ebay or aliexpress .
Even a lowly IRF710 would work fine here. Crss = 6.3pF. Not the very lowest, but low enough.
https://www.mouser.com/ProductDetail/Vishay-Semiconductors/IRF710PBF?qs=cvaI6Thkwxuk0gB7iIUQ%2Bg==
Crss of FQPF2N60C was 5,6pF, which is pretty much the same as IRF710.
IRF710 Vds max is 400V, though, compared to 600V for FQPF2N60C.
https://www.mouser.com/ProductDetail/Vishay-Semiconductors/IRF710PBF?qs=cvaI6Thkwxuk0gB7iIUQ%2Bg==
Crss of FQPF2N60C was 5,6pF, which is pretty much the same as IRF710.
IRF710 Vds max is 400V, though, compared to 600V for FQPF2N60C.
The Baby Huey thread mentioned these ones ... STF2N80K5 STU9HN65M2 STF7N60M2, and all are available from Mouser.
STF2N80K5 has 0.5pF Crss, STU9HN65M2 has 0.85pF and STF7N60M2 0.68pF, that is if I am reading the datasheets correctly.
I will probably go for the first one mentioned.
I am wondering what type of capacitor would be best for the critical RIAA filter. The part number in Marc's BOM for the 3.3nF one is PME271YA4330MR30, which is a Kemet paper protection capacitor, 300VAC. What is a good choice for these (C3 10nF, C4 3.3nF, C5 82pF)? Do they need to be reasonable tolerance, 1% or 5%?
STF2N80K5 has 0.5pF Crss, STU9HN65M2 has 0.85pF and STF7N60M2 0.68pF, that is if I am reading the datasheets correctly.
I will probably go for the first one mentioned.
I am wondering what type of capacitor would be best for the critical RIAA filter. The part number in Marc's BOM for the 3.3nF one is PME271YA4330MR30, which is a Kemet paper protection capacitor, 300VAC. What is a good choice for these (C3 10nF, C4 3.3nF, C5 82pF)? Do they need to be reasonable tolerance, 1% or 5%?
Do you have a capacitance tester?
1) For channel balance, you want the capacitors to be matched in value channel-to-channel as closely as possible.
If the capacitors you have for C3 measure 3350pF (3.35nF), then it's best to make sure the C3 in each channel is the same value. Let's say the left channel is 3346pF and the right channel is 3351pF. That's within less than 1%, so those would be considered to be 'perfectly' matched side-to-side, but they're more than 1% off the target value of 3300pF.
2) For flattest frequency response, you want the capacitors to be as close to the target value as possible.
If you can get a pair of capacitors for C3 that are nearly exactly 3300pF (3.3nF) then that's best. Let's say the left channel C3 is 3298pF and the right channel C3 is 3308pF. Those are also within 1%, both of each other and of the target value,
Capacitor types?
Many will argue long and hard about what is the best capacitor type for this application.
Generally speaking, polystyrene film and foil capacitors (PS) are the best for use in precision filters, but they're becoming obsolete.
Polypropylene film and foil (FKP) are very close to as good (technically speaking) and are the preferred choice these days.
Some people will argue that silvered mica capacitors are the best for use in RIAA filter networks.
The most readily available capacitors will be metalized polypropylene (MKP). These are inferior to the above types in some ways, but they're considered to be more than good enough for this use.
Let the Great Capacitor Debate begin! (Again....)
1) For channel balance, you want the capacitors to be matched in value channel-to-channel as closely as possible.
If the capacitors you have for C3 measure 3350pF (3.35nF), then it's best to make sure the C3 in each channel is the same value. Let's say the left channel is 3346pF and the right channel is 3351pF. That's within less than 1%, so those would be considered to be 'perfectly' matched side-to-side, but they're more than 1% off the target value of 3300pF.
2) For flattest frequency response, you want the capacitors to be as close to the target value as possible.
If you can get a pair of capacitors for C3 that are nearly exactly 3300pF (3.3nF) then that's best. Let's say the left channel C3 is 3298pF and the right channel C3 is 3308pF. Those are also within 1%, both of each other and of the target value,
Capacitor types?
Many will argue long and hard about what is the best capacitor type for this application.
Generally speaking, polystyrene film and foil capacitors (PS) are the best for use in precision filters, but they're becoming obsolete.
Polypropylene film and foil (FKP) are very close to as good (technically speaking) and are the preferred choice these days.
Some people will argue that silvered mica capacitors are the best for use in RIAA filter networks.
The most readily available capacitors will be metalized polypropylene (MKP). These are inferior to the above types in some ways, but they're considered to be more than good enough for this use.
Let the Great Capacitor Debate begin! (Again....)
Generally speaking, the higher the voltage rating of the capacitor, the better it will perform (thicker film = better capacitor performance). However, the higher the voltage rating of the capacitor, the physically bigger it will be. You may not be able to fit 1000V rated caps on the PCB. Everything is a compromise.
The circuit on the PCB has a DC blocking cap right after the plate of V1, so you don't have to use very high voltage caps for C3, C4, C5. You could use 63Vdc rated parts for those. Just make sure C2 is rated for 400Vdc or higher.
The circuit on the PCB has a DC blocking cap right after the plate of V1, so you don't have to use very high voltage caps for C3, C4, C5. You could use 63Vdc rated parts for those. Just make sure C2 is rated for 400Vdc or higher.
Wima FKP2 is real easy choice in Mouser / Digi-key.
The Soviet K71-7, 1-2,5% stacked Polystyrene can still be found in 3,300pF value on ebay & S+M KS orange box polystyrene ( these are the best ).
Farnell had LCR axial polystyrene but that should be looked for - don't know if they still have them.
The Soviet K71-7, 1-2,5% stacked Polystyrene can still be found in 3,300pF value on ebay & S+M KS orange box polystyrene ( these are the best ).
Farnell had LCR axial polystyrene but that should be looked for - don't know if they still have them.
Could not see a 82pF in Wima FKP2.
Also looking at capacitors, and influenced by this article ...
Selecting Capacitors to Minimize Distortion in Audio Applications
MLCC C0G (NP0) get the nod, along with film (polypropylene and polystyrene). The main issue I think is the allocated space on the board.
Are these contenders?
Multilayer Ceramic Capacitors MLCC - Leaded 200V 0.01uF C0G 2% LS=5.08mm
Multilayer Ceramic Capacitors MLCC - Leaded 200V 3300pF C0G 2% LS=5.08mm
Multilayer Ceramic Capacitors MLCC - Leaded 200V 82pF C0G 5% LS=5.08mm
Also looking at capacitors, and influenced by this article ...
Selecting Capacitors to Minimize Distortion in Audio Applications
MLCC C0G (NP0) get the nod, along with film (polypropylene and polystyrene). The main issue I think is the allocated space on the board.
Are these contenders?
Multilayer Ceramic Capacitors MLCC - Leaded 200V 0.01uF C0G 2% LS=5.08mm
Multilayer Ceramic Capacitors MLCC - Leaded 200V 3300pF C0G 2% LS=5.08mm
Multilayer Ceramic Capacitors MLCC - Leaded 200V 82pF C0G 5% LS=5.08mm
Going down the Wima FKP2 route, then a 33pF and 47pF in parallel is an option, but there is only a 1000Vdc rated part. Lead spacing is 5mm, so it ought to be possible to squeeze them in in some way. 82pf is available as a mica, a mixture of mica and film is a possibility. 3300pF and 10nF as FKP2 400Vdc or 630Vdc are not a problem and should fit.
The 100V 5W zener, 1N5378B was unavailable on Mouser. I suppose a couple of 50V would work instead? Otherwise I have to start to split the order.
The 100V 5W zener, 1N5378B was unavailable on Mouser. I suppose a couple of 50V would work instead? Otherwise I have to start to split the order.
The zener seems to be available on mouser :
https://www.mouser.it/ProductDetail/Diotec-Semiconductor/1N5378B?qs=OlC7AqGiEDlofoZ/UT9GZg==
https://www.mouser.it/ProductDetail/Diotec-Semiconductor/1N5378B?qs=OlC7AqGiEDlofoZ/UT9GZg==
I'd call it a hybrid preamp, what with that MOSFET source follower in there.I have been very interested by Merlin book on Tube Preamps and I decided to build the RIAA amplifier, however I decided to replace the cathode follower in the output stage by a MOSFET source follower (I already used this solution in a Baby Huey amplifier with a very good result) to save one tube and because I wanted to avoid the big voltage difference between the heater and the cathode of the output tube...
As I don't like point to point soldering, I have started to design a PCB. If someone has any suggestion about this project, please let me know.
Do you know if the PC900 can also be a good device for this project ? The pin-out is not compatible however
Cheers,
Marc
