TDV amplifier adventures - replacing the STTH6110 rectifiers with prasi's board for the LT4320 is worthwhile and something new builders should consider using from the start.
I replaced the LUNDAHL LL2733 choke in the CLC power supply filter with the HAMMOND 195T5 since the LUINDAHLs, even with a piece of I beam aluminum as a heatsink, would get too warm - I thought they were getting too warm. Hot is more like it. The much larger in size HAMMONDs do not get hot at all. I suspect this is a trade off - the LUNDAHLs superior construction versus the mass of the HAMMOND - I think it is a wash sonically.
Now that I will have these extra LL2733s, in combination with the fact that those used to load the THF51 get pretty hot, too, even though they are attached to the same heatsink as the THF51, - as an aside the top of the LL2733 is much hotter than the area where the choke is bolted to the heatsink - one wonders if using two in parallel would lessen the heat soaking?
What about connecting two in parallel with each of the chokes having the coils in series? You would have twice as much inductance while resistance would stay the same. Would the extra mass of using two ameliorate the heating any or is the fact that the resistance would be the same guarantee they would both get to the same temperature as the single?
Are there other considerations to using two chokes in parallel in this part of the circuit?
All counsel is appreciated.
Take care,
I replaced the LUNDAHL LL2733 choke in the CLC power supply filter with the HAMMOND 195T5 since the LUINDAHLs, even with a piece of I beam aluminum as a heatsink, would get too warm - I thought they were getting too warm. Hot is more like it. The much larger in size HAMMONDs do not get hot at all. I suspect this is a trade off - the LUNDAHLs superior construction versus the mass of the HAMMOND - I think it is a wash sonically.
Now that I will have these extra LL2733s, in combination with the fact that those used to load the THF51 get pretty hot, too, even though they are attached to the same heatsink as the THF51, - as an aside the top of the LL2733 is much hotter than the area where the choke is bolted to the heatsink - one wonders if using two in parallel would lessen the heat soaking?
What about connecting two in parallel with each of the chokes having the coils in series? You would have twice as much inductance while resistance would stay the same. Would the extra mass of using two ameliorate the heating any or is the fact that the resistance would be the same guarantee they would both get to the same temperature as the single?
Are there other considerations to using two chokes in parallel in this part of the circuit?
All counsel is appreciated.
Take care,
Hi Codyt,
there has not been much action (at least discussion) in the choked SIT amplifier front lately but I am planning one and I would like to ask if you ever tried the THF-51S in your amp, which I will be using. I do not need that much power and I found your operating point preference of 1.8A really interesting. I want to try a fancy custom made choke and I might specify current capability around 2.5A and a higher DCR around 1.2-1.5. I have curve matched THF51.
If you have tired the THF-51S, what operating point was your preference? Have you used a choke in your PSU?
There are two other amps with the THF-51s that I have interested in, the Scryer you also built and the SIT-4.
Hi Swak -
Unfortunately I never got around to trying the thf51 in this follower circuit, though I’m hoping to use it or another large SIT in a choke loaded common source amp soon. Research on that front points to something like 32v B+ and around 3A for Iq. Not sure if those operating points are comparable for CD, but I’m sure someone who’s tried it will make some suggestions. Zen Mod or Ben Mah come to mind as people who’d be a good resource.
Unfortunately I never got around to trying the thf51 in this follower circuit, though I’m hoping to use it or another large SIT in a choke loaded common source amp soon. Research on that front points to something like 32v B+ and around 3A for Iq. Not sure if those operating points are comparable for CD, but I’m sure someone who’s tried it will make some suggestions. Zen Mod or Ben Mah come to mind as people who’d be a good resource.
Which schematic are you referring to? C1 is the input cap and it forms a high pass filter with the 10k resistor to ground. 4.7 uf with 10k gives a -3db point of 3.4 Hz. Good enough for me. Bigger cap will push that point lower. Smaller cap will push it higher. Check it out here:
https://www.digikey.com/en/resource...sion-calculator-low-pass-and-high-pass-filter
If your VFET ends up needing a lower value resistor for stable bias, you might need a bigger cap. Say 5k resistor with 4.7 uF gives a corner of 6.8 Hz.
https://www.digikey.com/en/resource...sion-calculator-low-pass-and-high-pass-filter
If your VFET ends up needing a lower value resistor for stable bias, you might need a bigger cap. Say 5k resistor with 4.7 uF gives a corner of 6.8 Hz.
I have one of those questions - plus this thread deserves to be noticed again.
How does this amplifier behave with a 4 Ohms load? What nominal load does it prefer? Is four ohms too low?
I am using one of the amps to drive two 4 ohms woofers in series and wonder if there is anything to be gained in using two 16 ohms woofers in parallel.
Would two 8 ohms woofers in parallel be OK?
How does this amplifier behave with a 4 Ohms load? What nominal load does it prefer? Is four ohms too low?
I am using one of the amps to drive two 4 ohms woofers in series and wonder if there is anything to be gained in using two 16 ohms woofers in parallel.
Would two 8 ohms woofers in parallel be OK?
It will drive them but probably not well. Output impedance is low but not very low. I haven’t done the math on SPL, efficiency, and voltage swing. You might still come out ahead in certain aspects. You could give it a try.
Is it one of those topologies that produces more power with high impedances like the SIT-1? If so, that would settle it.
Good evening, gentlemen
Where can I buy 2SK2087C transistors?
Thank you in advance for your answers.
Where can I buy 2SK2087C transistors?
Thank you in advance for your answers.
Hi
Unfortunately you won’t find any, there’s a few vendors on AliExpress but it’s probably all fakes.
Each 2SK2087C has a unique serial number near the bottom of the die so I always ask for a picture of 4 of them next to each other. They never want to….
If you find a reliable source or a 2SK2087C hoarder decides to let go of some please let me know. It’s best to buy THF-51S or similar SIT while the 2SK2087C isn’t available
Bonne chance
Eric
Unfortunately you won’t find any, there’s a few vendors on AliExpress but it’s probably all fakes.
Each 2SK2087C has a unique serial number near the bottom of the die so I always ask for a picture of 4 of them next to each other. They never want to….
If you find a reliable source or a 2SK2087C hoarder decides to let go of some please let me know. It’s best to buy THF-51S or similar SIT while the 2SK2087C isn’t available
Bonne chance
Eric
Gentlemen
In this setup, if I use a THF-51S with a Hammond 193 V what voltage and current should I choose?
Thank you for your future responses.
In this setup, if I use a THF-51S with a Hammond 193 V what voltage and current should I choose?
Thank you for your future responses.
I am not sure of the answer. Perhaps it should be tested. In a single-ended design, such as this one, the max output current swing is the standing current. With P = I^2 x R, if you double the R, you’d get twice the power. But P is also equal to V^2/R, and so for a given power, you need higher voltage swing with higher R. How all this holds up in practice, I have not measured. But try it out, Rick, if it is easily done.
Those are beasts. You could easily start with 50W dissipation per device and go from there. Something like 25-30V and 2 amps.
Thinking about inductor quality with these circuits I was wondering if one could use a big inductor - like the Hammond 100mF/5 amps inductor in series with a smaller inductor in the same way one might use a smaller capacitor in parallel a large capacitor for better high frequency response. Looking at the HAMMOND 159ZL - 2.5 mH and 10 A which could be mounted close the the THF51 and far enough away from the big one to minimize interaction.
The question is could this make any difference in sound quality versus using the big choke by itself? Of course, I know one never knows until they try but I am curious if there is any chance of this doing any good?
The question is could this make any difference in sound quality versus using the big choke by itself? Of course, I know one never knows until they try but I am curious if there is any chance of this doing any good?
I don’t know if it would make a difference. Could be simmed in LTSpice. But if you have the parts 😉
Good evening, gentlemen,
1:In case the THF-51S is used for this assembly, is it reasonable to use a resistance of 220 Ohms/4W instead of 1 KOhms/4W?
2:If a negative power supply is used, so GND side +,the resistance R1 of 10 k goes towards the V- of the power supply?
I am a handyman!
Thank you in advance for your answers.
Toto 34
1:In case the THF-51S is used for this assembly, is it reasonable to use a resistance of 220 Ohms/4W instead of 1 KOhms/4W?
2:If a negative power supply is used, so GND side +,the resistance R1 of 10 k goes towards the V- of the power supply?
I am a handyman!
Thank you in advance for your answers.
Toto 34