If you wanted to you could use the same voltage divider network on both grids of the 6SN7s. The bias divider network has a resistor going to ground. Assuming that when things are perfectly balanced the servo output will be at zero volts, you could then drive one of those resistors. In that way if the circuit were perfectly balanced, the servo output would be at 0 volts and the bias point on each grid would be -1.7V.
The build begins
Well, it's been a few weeks, but I have now started the build of the MP-3 clone
The signal circuitry is similar to the last schematic that was posted here, but has had a few mods and tweaks, thanks to some help from over this side of the pond. Unfortunately, I cannot therefore post the final schematic as I am not sure how close it now is to an actual MP-3 and I have no intention of compromising Ralph's generous assistance and IP.
2 boards have been made using the press n peel system, printed from Express PCB.
The power supply board is basically a collection of circuits off the internet. The front end uses an ECC81 regulated 250V supply, the output 6SN7's are powered from 4 simple CRC supplies, and the -ve bias voltage is taken from a circuit in Morgan Jones book. There are also a couple of LM317 regulated circuits for tube heaters etc.
Due to work commitments etc, the build will take some while, but I'll post a few pics as I go.
Cheers,
Steve.
Well, it's been a few weeks, but I have now started the build of the MP-3 clone
The signal circuitry is similar to the last schematic that was posted here, but has had a few mods and tweaks, thanks to some help from over this side of the pond. Unfortunately, I cannot therefore post the final schematic as I am not sure how close it now is to an actual MP-3 and I have no intention of compromising Ralph's generous assistance and IP.
2 boards have been made using the press n peel system, printed from Express PCB.
The power supply board is basically a collection of circuits off the internet. The front end uses an ECC81 regulated 250V supply, the output 6SN7's are powered from 4 simple CRC supplies, and the -ve bias voltage is taken from a circuit in Morgan Jones book. There are also a couple of LM317 regulated circuits for tube heaters etc.
Due to work commitments etc, the build will take some while, but I'll post a few pics as I go.
Cheers,
Steve.
Attachments
Hello Valvemaniacuk...
Have you finished assembling this pre amp?
Can you tell if it worked well?
I imagine the db gain of this pre amp is pretty high.
As the atma m-60 needs 3 volts to provide its maximum power, would using only the first valve of your pre-set would be enough to have a good operation?
Considering that I intend to use a device that plays cd (for now). I believe this cd has a 250 mv output.
Sorry for the questions...
Have you finished assembling this pre amp?
Can you tell if it worked well?
I imagine the db gain of this pre amp is pretty high.
As the atma m-60 needs 3 volts to provide its maximum power, would using only the first valve of your pre-set would be enough to have a good operation?
Considering that I intend to use a device that plays cd (for now). I believe this cd has a 250 mv output.
Sorry for the questions...
I found the cascade (in my case 12bh7a) can be tuned to deliver anything from 2-3Vpp to 100Vpp. However it needs a high impedance next stage as cascode S don’t deliver much power by before it impacts the waveform. That’s why there the cathode follow driver for paralleled output tubes of the OTL.
In that CD player is 250mV it sounds like that’s RMS as the peak is close to 316mV which is -10dBv consumer line level.
Ralph's MP-3.3 recently converted me to balanced circuits (ref. page 4 of this thread.) Atma-Sphere MP-3 vs. my DIY 5842 Line Preamp, Balanced vs. Unbalanced In My System.
I own a DIY 5842 line preamp > Magnequest OPTs, tube rectified OPS. My 5842 outperformed a nice commercial 300B line preamp and ditto a nice commercial 6SN7 preamp (all 3 prior described preamps are unbalanced.) In the system described below the MP-3.3 outperformed my 5842 by twice the margin of my 5842 over the two preamps it beat. It wasn’t subtle. The MP-3.3 was probably the biggest revelation in my long audio history. I still think about daily (someone else auditions my MP-3.3 now.)
System: L is a friend/full time pro network systems engineer. Summer of 2021 L built my huge custom dedicated computer, a streamer/server running the most advanced HQ Player settings. One outboard NUC runs Roon library function only, no Roon processing. I named the computer Big Daddy or BD for short. I can’t explain much about BD except to say it’s audio/musical performance appears to be without reproach.
BD feeds the DAC high OS rates of either PCM or DSD selected in HQ Player. Filter and demodulator selections are legion (I generally use whatever L suggests.) Renderer USB > Holo Audio May KTE DAC in “NOS” (non-oversample) mode.
All Clarity Cable including their best "Natural" balanced and unbalanced IC from May DAC to MP-3.3 (both DAC outputs function simultaneously.)
Ralph’s MP-3.3 w/V-Caps unbalanced output > mid-90s 140W Nelson Pass designed AB stereo power amp AKA Adcom GFA-545, 2021 resto-mod: PCBs stripped/cleaned and loaded w/all new high end parts including higher voltage Toshiba output devices, Hoppe’s Brain PS board, dual mono PS transformers replaced single, IEC jack, Cardas binding posts.
Speakers: AudioKinesis Gina main speaker parallel wired with discrete high-impedance Space Generator reverberant field system. Two kilowatt sub amps in Dr. David Greisinger’s phase quad tuning > four AK Tall Subs in distributed array. Large, symmetrical, dead quiet, lightly treated, moderately lively room.
Switching between balanced and unbalanced required only flipping an MP-3.3 toggle switch. IMO the balanced IC was 20% better. In this application balanced was better throughout, esp. blacker silence between notes, more explosive, natural, transparent, etc. with no downside/all upside. No way I would voluntarily return to unbalanced after this test.
Someone borrows my primary amps, balanced input mono blocks: $5200/pr Atma-Sphere new patented class D GaN. In earlier tests with my inferior 5842 preamp the Class D outperformed my Adcom GFA-545 backup amp by huge margin.
I can only presume the class D amps shall magnify the balanced IC benefit in my AB test. And further, the balanced IC would magnify the class D margin over my Adcom.
Prior to hearing MP-3.3 I wrongly thought balanced circuits were mediocre to bad value. Now I’m a total believer. My room has till now been generally void of noise/RF problems.
If your DIY MP-3.3 gets a good portion of it's performance prepare to fall in love with your system again, more so if the source and amps are balanced.
I own a DIY 5842 line preamp > Magnequest OPTs, tube rectified OPS. My 5842 outperformed a nice commercial 300B line preamp and ditto a nice commercial 6SN7 preamp (all 3 prior described preamps are unbalanced.) In the system described below the MP-3.3 outperformed my 5842 by twice the margin of my 5842 over the two preamps it beat. It wasn’t subtle. The MP-3.3 was probably the biggest revelation in my long audio history. I still think about daily (someone else auditions my MP-3.3 now.)
System: L is a friend/full time pro network systems engineer. Summer of 2021 L built my huge custom dedicated computer, a streamer/server running the most advanced HQ Player settings. One outboard NUC runs Roon library function only, no Roon processing. I named the computer Big Daddy or BD for short. I can’t explain much about BD except to say it’s audio/musical performance appears to be without reproach.
BD feeds the DAC high OS rates of either PCM or DSD selected in HQ Player. Filter and demodulator selections are legion (I generally use whatever L suggests.) Renderer USB > Holo Audio May KTE DAC in “NOS” (non-oversample) mode.
All Clarity Cable including their best "Natural" balanced and unbalanced IC from May DAC to MP-3.3 (both DAC outputs function simultaneously.)
Ralph’s MP-3.3 w/V-Caps unbalanced output > mid-90s 140W Nelson Pass designed AB stereo power amp AKA Adcom GFA-545, 2021 resto-mod: PCBs stripped/cleaned and loaded w/all new high end parts including higher voltage Toshiba output devices, Hoppe’s Brain PS board, dual mono PS transformers replaced single, IEC jack, Cardas binding posts.
Speakers: AudioKinesis Gina main speaker parallel wired with discrete high-impedance Space Generator reverberant field system. Two kilowatt sub amps in Dr. David Greisinger’s phase quad tuning > four AK Tall Subs in distributed array. Large, symmetrical, dead quiet, lightly treated, moderately lively room.
Switching between balanced and unbalanced required only flipping an MP-3.3 toggle switch. IMO the balanced IC was 20% better. In this application balanced was better throughout, esp. blacker silence between notes, more explosive, natural, transparent, etc. with no downside/all upside. No way I would voluntarily return to unbalanced after this test.
Someone borrows my primary amps, balanced input mono blocks: $5200/pr Atma-Sphere new patented class D GaN. In earlier tests with my inferior 5842 preamp the Class D outperformed my Adcom GFA-545 backup amp by huge margin.
I can only presume the class D amps shall magnify the balanced IC benefit in my AB test. And further, the balanced IC would magnify the class D margin over my Adcom.
Prior to hearing MP-3.3 I wrongly thought balanced circuits were mediocre to bad value. Now I’m a total believer. My room has till now been generally void of noise/RF problems.
If your DIY MP-3.3 gets a good portion of it's performance prepare to fall in love with your system again, more so if the source and amps are balanced.
Yes and no,
I collected almost all the needed parts including chassis and an alternative multideck volume-pot.
It has been on hold due to lack of time, combined with absolutely no shortage of projects. Eventually a very rare offer to buy one "locally" popped up and I seized the opportunity.
It is a fantastic Pre-amp
After some fiddling with running the Phono balanced - I also have to chime in and wonder why it was ever thought to be a good idea to run the pick-up output unbalanced.
I collected almost all the needed parts including chassis and an alternative multideck volume-pot.
It has been on hold due to lack of time, combined with absolutely no shortage of projects. Eventually a very rare offer to buy one "locally" popped up and I seized the opportunity.
It is a fantastic Pre-amp
After some fiddling with running the Phono balanced - I also have to chime in and wonder why it was ever thought to be a good idea to run the pick-up output unbalanced.
I do, but also must admit that for this I never got to create a project container. I might still have a go at making a mock-up for the line-stage. But no pcb's and the like , so not much help there I'm afraid