They would be extremely difficult to measure without the appropriate equipment and typically would require a VHF network analyzer to do it. (Or a lot of other test equipment and a lot of work to vet and calibrate the test set up.)
Version 2 Questions
Hello all, it has been a long time since my last most and I want to get back into the two stage 6c45p lcr.
I have attached my latest design and it achieves 70dB gain before MC step up to output.
Question 1: I know all about MC step up core saturation and wanted to check if I did do a bias on sec of the Amorphous 1678 would it saturate the core? I have never seen anyone do it, but read its ok. but know that if even 1mA can saturate core.
Question 2: What is the proper way to calc transformer inductance and resistance for coils in specific configurations? I want to do 1:32 Alt:E for LL1678
I got 43.75mH for Pri and 88H for sec.
Question 3: Is there a way to simulate tube ageing and reduction in transductance? I want to see how the LCR behaves as tubes age?
Thank you all very much.
Hello all, it has been a long time since my last most and I want to get back into the two stage 6c45p lcr.
I have attached my latest design and it achieves 70dB gain before MC step up to output.
Question 1: I know all about MC step up core saturation and wanted to check if I did do a bias on sec of the Amorphous 1678 would it saturate the core? I have never seen anyone do it, but read its ok. but know that if even 1mA can saturate core.
Question 2: What is the proper way to calc transformer inductance and resistance for coils in specific configurations? I want to do 1:32 Alt:E for LL1678
I got 43.75mH for Pri and 88H for sec.
Question 3: Is there a way to simulate tube ageing and reduction in transductance? I want to see how the LCR behaves as tubes age?
Thank you all very much.
Attachments
As long as no significant grid current flows there is no problem in terms of saturating the transformer core.
Note that I use a very similar bias arrangement in the front end of my transformer coupled power amps, and I use very low noise references to generate the bias voltage. Here you should expect to need to low pass the bias supply to the transformer secondary to keep noise down. (Any noise on the bias supply will significantly degrade the pre-amps SNR)
Note that I use a very similar bias arrangement in the front end of my transformer coupled power amps, and I use very low noise references to generate the bias voltage. Here you should expect to need to low pass the bias supply to the transformer secondary to keep noise down. (Any noise on the bias supply will significantly degrade the pre-amps SNR)
Note you can also use a Laplace transform to generate the inverse RIAA at the input. There are examples in some of my muscovite threads.
With 1:32 step up ratio, 43.75 mH for the primary would give 0.04375 x 32² = 44.8 H for the secondary.
Be aware however this is theoretical; the real values will be different.
Thank you Pieter T, maybe I calculated it wrong. Why do you say theoretical? is there a way to cal it exact or is that based on load/source impedance what H you get?
kevinkr, thanks I will check out the muscovite threads. I will need to check what current the grid of the 6c45p draws and I guess that effects the saturation.
kevinkr, thanks I will check out the muscovite threads. I will need to check what current the grid of the 6c45p draws and I guess that effects the saturation.
Theoretically, inductance goes up/down with the square/root of the winding ratio.
Theory and practice meet in case of air coils; when coils have cores the formula does not apply exactly.
By the way, your L3 in 4:1 mode should have 35 and 2.19 H (instead of 8.75).
After hours and hours playing and simulating different LCR networks I have found that a 6k network works the best and isn't effected by the 6c45p aging. I think.....
I think I will not do the IT coupling and go with CCS since I will not need a step down or up. I have never done a CCS and wanted to check with everyone based on the schematic attached if I did it correctly and if the 10M45S is a good choice? I have also seen the IXYS IXTP08N100D2 but not sure how to implement that one.
Any help is appreciated.
I think I will not do the IT coupling and go with CCS since I will not need a step down or up. I have never done a CCS and wanted to check with everyone based on the schematic attached if I did it correctly and if the 10M45S is a good choice? I have also seen the IXYS IXTP08N100D2 but not sure how to implement that one.
Any help is appreciated.
Attachments
So after hours of tweaking and tweaking the RC CCS loaded 6c45p phono I am still not getting the quality I want out of ether the Caps or the RC network itself. Tubes are dead quite and all tests show very good linearity.
I want to go ahead and try a LCR RIAA at 600Ohm but want to stay with SE 6c45p. So to drive that hard load I will go with Transformer loaded. After searching the internet for a suitable transformer I came across the LL2765.
Anyone used this on a tube with 3:1 ratio? I will be running tubes at 28mA 150V 1.5V bias.
Its a headphone Transfomer with a 5.4K Pri @ 600ohm Sec.
I have way way too much gain. I use last 3 levels of the Preamp and thats over 1.1V output. I only need 67dB phono gain for full power so I am willing to live with the 3:1 step down. I have 76dB gain now.
Do yall think the LL2765 is better then the LL1671 with the 6c45p?
I want to go ahead and try a LCR RIAA at 600Ohm but want to stay with SE 6c45p. So to drive that hard load I will go with Transformer loaded. After searching the internet for a suitable transformer I came across the LL2765.
Anyone used this on a tube with 3:1 ratio? I will be running tubes at 28mA 150V 1.5V bias.
Its a headphone Transfomer with a 5.4K Pri @ 600ohm Sec.
I have way way too much gain. I use last 3 levels of the Preamp and thats over 1.1V output. I only need 67dB phono gain for full power so I am willing to live with the 3:1 step down. I have 76dB gain now.
Do yall think the LL2765 is better then the LL1671 with the 6c45p?
Attachments
So I removed the 2nd 1uF bypass caps, I tried this so instantaneous current would pass via a higher quality cap instead of the electrolytic 1000uF. Removing this idea improved the sound a little bit, some listening fatigue went away.
I then removed the 1000uF bypass altogether and left the 50ohm Cathode resistors on all tubes. OMG the sound is amazing!!!! I haven't stopped listening to the pre-amp. Rediscovering amazing sounds from all my LPs now. I cannot believe all the mods to the PSU and it ends up being the bypass caps. IF you use a 6c45p remove caps and it changes everything. Maybe its the linearity it brings to this critical stage of the effect of the cathode feedback but its glorious.
Now that removing bypass caps has such an amazing effect on the sound I thought why not remove the first coupling cap as well. So I ordered some LL1671 30mA Transformers and removed the CCS and CC from the initial gain stage before the RIAA.
Holy ****, the background is dead quite, and black, impact seems like its hitting my face, and the timber of instruments is move emotional, you can feel things in music that I didn't know existed with cap coupling. Time to remove all caps everywhere from all stages. I am sold on the Transformer coupling. Was a hater for years and thought caps were the only logical way but you have to hear it for your self and you will because a believer.
My 2cent.
I then removed the 1000uF bypass altogether and left the 50ohm Cathode resistors on all tubes. OMG the sound is amazing!!!! I haven't stopped listening to the pre-amp. Rediscovering amazing sounds from all my LPs now. I cannot believe all the mods to the PSU and it ends up being the bypass caps. IF you use a 6c45p remove caps and it changes everything. Maybe its the linearity it brings to this critical stage of the effect of the cathode feedback but its glorious.
Now that removing bypass caps has such an amazing effect on the sound I thought why not remove the first coupling cap as well. So I ordered some LL1671 30mA Transformers and removed the CCS and CC from the initial gain stage before the RIAA.
Holy ****, the background is dead quite, and black, impact seems like its hitting my face, and the timber of instruments is move emotional, you can feel things in music that I didn't know existed with cap coupling. Time to remove all caps everywhere from all stages. I am sold on the Transformer coupling. Was a hater for years and thought caps were the only logical way but you have to hear it for your self and you will because a believer.
My 2cent.
This is why I use LED or diode bias in the cathode or batteries to provide fixed bias, with transformers battery bias is pretty easy with some tubes.
Large electrolytics in low level cathode biased phono stages has proved to be a problem for me. (linearity issues)
I wouldn't be opposed to trying that. LED bias seems interesting. What value/brand do you recommend fro 50ohm (1.5v)? Can I source them from Mouser?
Mouser or Digi-Key. Look for ones with vf close to what you need. Some infrared LEDs will give you a vf of 1.2V or less, and reds run the range from 1.5 - 2.1V.. If possible choose ones with low dynamic impedance all other things being equal.
1.5V Alkaline AA batteries are good sources of bias in grid bias applications (with RC or transformer coupling)
1.5V Alkaline AA batteries are good sources of bias in grid bias applications (with RC or transformer coupling)
I intend to build an LCR phono preamp possibly with 6c45p tubes. I was interested to know what results you had with yours, and which circuit you finally chose.