Yes, the hum (which is of course 50 Hz, my bad) goes away with only one input connected. But I also have only one ground connection from psu to amp pcb (per channel). Chassis ground and system ground are (well, should be) only connected through the ground lift.
I measured for continuity between the grounds of my inputs and outputs and the chassis, and after a couple of seconds there is, but at 9 Ohm so through the resistor of the ground lift I guess. There is another thing: every time I switch on the amp with sources connected and running, there is a 'shivering' going through the chassis and I hear mechanical hum from the (800 VA) transformer. Then after a little while I hear the hum through my speakers (and no more mechanical hum). Could this have to do with my problem?
The shudder at initial power-on is probably magentisation current and is not related to electrical hum in most cases.
I see you've used fairly thick unshielded twisted pair for the input signal, I've not had much success with anything but screened pair with a grounded screen.
Do you have access to a portable source (not connected to mains)?
I see you've used fairly thick unshielded twisted pair for the input signal, I've not had much success with anything but screened pair with a grounded screen.
Do you have access to a portable source (not connected to mains)?
It is actually thin silver plated copper wire in a pvc sleeve. I connected my cell phone to the amp and played a song: the hum was still there (maybe only just a little bit less loud).
I might have found the cause of the problem: the right pcb gets the correct voltage (63 V between + and -), but the left almost nothing (a couple of mV), both with a not insignificant ac part that I'm not being able to measure with my dmm. I used solid core copper wire for the connections between the psu en the pcb's, and that has underwent quite some stress during the build. I suspect one or more of the wires to the left pcb is (almost completely) broken..
...... never use solid core for power routing
- you can, if soldering points are fixed in space and time, but in our most often used arrangements, that's rare case
- just see difference in approach, between what's most often here in Papaland and tube amp made in point to point fashion
- you can, if soldering points are fixed in space and time, but in our most often used arrangements, that's rare case
- just see difference in approach, between what's most often here in Papaland and tube amp made in point to point fashion
I was thinking that might be it, or else "measure your psu voltage before setting bias". I see the wisdom of this moral. Wires will be replaced with flexible ones. Any suggestion for a good quality make/brand?
I replaced all solid core power cable with flexible ones and the input wires with microphone (asymmetrical) cable, but alas: the hum is still there 🙁
Albeit more prominent in the right than in the left channel (???)
Albeit more prominent in the right than in the left channel (???)
Can the F5 Turbo V3 be built with a 650VA 2x39V (over sized) toroidal transformer per mono block? I remain with a empty Aleph X amplifier case (about 10kg heatsink / channel just got comfortably warm with the X). I want to put that amplifier case to a good use! I have 2Pc of the mentioned toroidal transformer for this project in case if would be OK. I do not want to rebuild the Aleph X (still have all the parts), rather build something new with a different sound. I believe the Turbo V3 have a fixed bias, so I thought to ask if my transformers adequate or way too undersized. I see some DIY-ers used 1000VA / channel.
Thank you
Thank you
Sure!
You can bias the amp to whatever you want.
Make sure you use the cascode transistors and properly rated capacitors. Avoid using the “turbo” diodes, just omit them altogether. The fab that made the diodes when F5T was designed doesn’t make them anymore, and the new ones do not have the same tempco that the “turbo” effect was relying on, so to make a stable operating amp just omit the diodes and keep everyting else as designed. Will work great.
🙂
You can bias the amp to whatever you want.
Make sure you use the cascode transistors and properly rated capacitors. Avoid using the “turbo” diodes, just omit them altogether. The fab that made the diodes when F5T was designed doesn’t make them anymore, and the new ones do not have the same tempco that the “turbo” effect was relying on, so to make a stable operating amp just omit the diodes and keep everyting else as designed. Will work great.
🙂
Thanks for your reply!
The original diodes was produced by Vishay? MUR3020WT.
If I can buy (order from Europe) or eBay still better build without the diodes??
To be honest I would love to build based on (original) Mr Pass published schematic how it was published (maybe set up the bias according to the existing power transformers rating if that possible, [with that I may need some help]) Too bad looks like I am late to this party 😢 😢 .
The original diodes was produced by Vishay? MUR3020WT.
If I can buy (order from Europe) or eBay still better build without the diodes??
To be honest I would love to build based on (original) Mr Pass published schematic how it was published (maybe set up the bias according to the existing power transformers rating if that possible, [with that I may need some help]) Too bad looks like I am late to this party 😢 😢 .
Hello gaborbela,
your plan to build a F5T is a cool (more a hot) project. I love my F5T-monoblocks. They have a crystal clear and powerful sound.
You want to use your transformer with a secondary voltage of 2x39 V AC. If I assume the voltage after the
bridgerectifiers and the crc(rc)-filter, then I use a factor of 1.3 to 1.4. This means, that your railvoltages after
the psu will be anywhere around +-50.7 V DC (x1.3) to +- 54.6 V DC (x1.4).
My monoblocks are running on +-42.7 V DC railvoltages. I couldn`t bias higher than 330mV over each biasresistor. You will have to manage the heat. Lots of heatsink / material will be necessary.
Don't forget to use the cascode transistors (protection from high railvoltages for the Jfets) and perhaps 2 pairs of JFets in the frontend (depends on how many Mosfets you wanna drive in the outputstage). Adjust some resistor values in the frontend.
Formula is in the buildguide.
Have fun!
Cheers
Dirk 🙂
your plan to build a F5T is a cool (more a hot) project. I love my F5T-monoblocks. They have a crystal clear and powerful sound.
You want to use your transformer with a secondary voltage of 2x39 V AC. If I assume the voltage after the
bridgerectifiers and the crc(rc)-filter, then I use a factor of 1.3 to 1.4. This means, that your railvoltages after
the psu will be anywhere around +-50.7 V DC (x1.3) to +- 54.6 V DC (x1.4).
My monoblocks are running on +-42.7 V DC railvoltages. I couldn`t bias higher than 330mV over each biasresistor. You will have to manage the heat. Lots of heatsink / material will be necessary.
Don't forget to use the cascode transistors (protection from high railvoltages for the Jfets) and perhaps 2 pairs of JFets in the frontend (depends on how many Mosfets you wanna drive in the outputstage). Adjust some resistor values in the frontend.
Formula is in the buildguide.
Have fun!
Cheers
Dirk 🙂
Yes, it will be a class AB amp but a lot of people love AB amps. Some even more than class A. That seems to really come down to the speaker though.
Just ordered some parts from Parts Connexion.
I decided to scale back the project from Turbo V3 to Turbo V2.
100 plus Watts in Class A just gives up a tremendous amount of heat and will be only useful at winter.
50 Watts power plenty enough to drive my speakers!
Previously I owned some low power amplifiers like the Hiraga Le Monstre 8 Watt or SEWA (8 to 10 Watt) and they "almost" was enough to drive my speakers with most of the music I listen!
Right now I use an F5 variant with Toshiba power mosfets without any preamplifier. The power just enough!
I will upgrade the F5 to Turbo 2 V, that is more than enough heat and power!
The reason I dismantled my Aleph X because of the too much heat (!) and did not fall in love with her sound as much to keep it!
I decided to scale back the project from Turbo V3 to Turbo V2.
100 plus Watts in Class A just gives up a tremendous amount of heat and will be only useful at winter.
50 Watts power plenty enough to drive my speakers!
Previously I owned some low power amplifiers like the Hiraga Le Monstre 8 Watt or SEWA (8 to 10 Watt) and they "almost" was enough to drive my speakers with most of the music I listen!
Right now I use an F5 variant with Toshiba power mosfets without any preamplifier. The power just enough!
I will upgrade the F5 to Turbo 2 V, that is more than enough heat and power!
The reason I dismantled my Aleph X because of the too much heat (!) and did not fall in love with her sound as much to keep it!
I'm not very good at interpreting datasheets. I ran across this diode that makes me wonder if it might be suitable for the "Turbo" diodes. Vishay VS-C5PH6006LHN3. The forward voltage is apparently a little higher than the MUR3020WT, and the tempco looks a bit better. The datasheets seem to be a bit of apples to oranges with regard to the temperature vs. forward voltage vs. forward current graphs. What are your thoughts?
Suitable, but for all diode builds a small amount of negative tempco is probably a good idea, maybe a 0.1 ohm resistor in series with the diode to help prevent bias runaway that everyone seems to suffer from at some point. This restricts the maximum current a bit, but 0.1 ohm (divided by number of pairs) is probably small enough to allow prodigious amounts of power. 0.1 is not an absolute value, I'm just eyeballing it.
Just ordered 10Pc 4.7k thermistors marked 472.
My problem they all measure only 3.3 to 3.5 K Ohms with my DMM.
Can I use those or must order from other source?
It is so annoying to order a couple Dollar value parts and pay 4-5 X as much for the shipping cost and who knows second times they measure the same!
Please guys let me know.
Thank you!
If someone has at home some extra I would like to buy it and send it in an envelope.
Big companies does not ship in envelope, right now I do not need other parts.
My problem they all measure only 3.3 to 3.5 K Ohms with my DMM.
Can I use those or must order from other source?
It is so annoying to order a couple Dollar value parts and pay 4-5 X as much for the shipping cost and who knows second times they measure the same!
Please guys let me know.
Thank you!
If someone has at home some extra I would like to buy it and send it in an envelope.
Big companies does not ship in envelope, right now I do not need other parts.
