Topic: My DIY tube amplifier and preamplifiers

[wufei]

I like the kit master kaso parang mas ok talaga sa akin yung DIY kahit mas mahal. yung latest na 12AX7 12AU7 preamp ko I learned so much from it and still learning.  Challenging ang pre-amp kesa power amp. for me madali gawin ang power amp pero yung pre-amp it requires careful thinking, lalo yung phono stage, konting careless mo sa ground loop you will be met by oscillation. hum is another, little by little nagiging prototype yung 12ax7 na pre-amp ko, experiment which will make it better then when im satisfied gagawa na ko ng final product.

my latest preamp, the pics that posted, magkaiba ng konti, below is the latest circuit




this one is the early circuit. with baxandall feedback type bass mid treble tone control.  maganda naman yung kinalabasan kaya lang yung extra controls like mid and treble wala pala ako use. so I resorted to the low pass filter na lang.

[remington]

nice bro pahiram ulit ako nyan nang marinig sa AN hehehe!

[dana]

nice & solid looking builds,Wufei.
about your phono stage pre-amp, musta ang gain level nya sir  (ilan dB, estimate...) ...
have you tried taking its frequency response curve behaviour...maganda sana, makuhanan ...

[wufei]

Thank you sir.  the estimated output gain is at around 13db.  I still havent taken any measurement regarding frequency response though, maybe pag sinipag mag hook up ng noise generator I will post some measurements.  Remington and I tested it with several vinyl, I personally liked the result (not that I build it, if it sounded trash it wont be posted here anyway ), sound good to me on PAX20G speakers with some bottom. We even compare it with my solid state german phono preamp and there are some details present on the tube that are not audible on the solid state.
 When I added some LF the bottom end sings, its not boomy but a bass that you can actually feel (maybe I can save money by not purchasing AN anymore).  I log a couple of hours pa lang with the preamp so it will take a while bago lumabas yung tunay na tunog. but so far im happy, mas malakas nga lang yung phono stage kesa sa line preamp, i might put attenuator on the phono stage

nice & solid looking builds,Wufei.
about your phono stage pre-amp, musta ang gain level nya sir  (ilan dB, estimate...) ...
have you tried taking its frequency response curve behaviour...maganda sana, makuhanan ...

[wufei]

oo bro punta ako dyan sa inyo.  gusto ko na nga marinig tong preamp na to sa AN mo.  oo para makapausap din tayo

nice bro pahiram ulit ako nyan nang marinig sa AN hehehe!

[remington]

Nice bro! SMS mo lang ako kung kelan.

[wufei]

@remington - oo para mabigay ko din sayo list ng pamalengke.

@master tony - punta ako ulit sa inyo master, dalhin ko yung print out ng circuit. I really wanted to discuss it with you and get your thorough opinion.

Eto master yung schematics

[tony]

Joey, you can play around with the value of R11A/R11B, increasing the value increase gain and vice versa.

[wufei]

@master tony - master I havent implemented the circuit.  Im still planning to build this one.  its a line amplifier base from jadis circuit.  I used different circuit.

[tony]

i have seen many implementations of this topology,
high open loop gains, and low closed loop gains utilizing GNFB,
the design goal that i can see why they come up with such
a line amp is consistency from unit to unit, stable gains even
as the tube ages, lowering total harmonic distortions....
the circuit is adequately immune to tube variations,
but tube rollers will not stop at this...
some audiophiles scoff at global negative feedback..
for me even the simple common cathode sounds nice..

[dana]

Thank you sir.  the estimated output gain is at around 13db.  I still havent taken any measurement regarding frequency response though, maybe pag sinipag mag hook up ng noise generator I will post some measurements.  Remington and I tested it with several vinyl, I personally liked the result (not that I build it, if it sounded trash it wont be posted here anyway ), sound good to me on PAX20G speakers with some bottom. We even compare it with my solid state german phono preamp and there are some details present on the tube that are not audible on the solid state.
 When I added some LF the bottom end sings, its not boomy but a bass that you can actually feel (maybe I can save money by not purchasing AN anymore).  I log a couple of hours pa lang with the preamp so it will take a while bago lumabas yung tunay na tunog. but so far im happy, mas malakas nga lang yung phono stage kesa sa line preamp, i might put attenuator on the phono stage

say, for a 2mV MM cartridge output level , it needs around 42~48dB gain, to bring it to typical line level of 250~500mV. acceptable level difference of +/-  6db as compared with other sources, para di nakakagulat when switching with other source for a given volume setting.
kung MC cartridge naman, which has a lowish output of typical 0.1~0.3mV (1/10th of MM...), needs higher gain more to bring about to line level signal. kaya mas masalimuot ang design, else lahat ng basura sa  signal, kasama sa ma-aamplify...
am sure it is still ongoing fine tuning...pag medyo ok ok na, hopefully mapakinggan rin yang creations mo...
goodluck, wufei

[wufei]

Hi Dana, medyo malakas yung phono preamp, pero I think pag nilagayan ko ng attenuator para mag level ang volume level nya sa line mas hihina pa ang ang noise.  ngayon ok ang signal to noise ratio nya, pag full volume lahat may noticeable hum pero sa full volume lang.  I think hindi matatapos tong pre-amp nato kasi parang sya naging test bed ko. kanina hindi na naman napigil mga kamay ko hahaha.

say, for a 2mV MM cartridge output level , it needs around 42~48dB gain, to bring it to typical line level of 250~500mV. acceptable level difference of +/-  6db as compared with other sources, para di nakakagulat when switching with other source for a given volume setting.
kung MC cartridge naman, which has a lowish output of typical 0.1~0.3mV (1/10th of MM...), needs higher gain more to bring about to line level signal. kaya mas masalimuot ang design, else lahat ng basura sa  signal, kasama sa ma-aamplify...
am sure it is still ongoing fine tuning...pag medyo ok ok na, hopefully mapakinggan rin yang creations mo...
goodluck, wufei

[tony]

Joey, yun bang phoono stage mo yung sa RCA handbook?

[wufei]

Hi Master Tony

Sorry ngayon lang ako naka reply dito. Got so very very busy from work and traveling abroad.  No master
Tony it was a design I been toying around since the late 80s.  its a normal high gain mic circuit but I modified the RIAA eq following a design from a discreet transistorized version I had a long time ago. I like how the transistorized version sounds so I figured maybe by adopting the EQ of it to the Mic Preamp I have it will transform and lo! it sounds very very satisfactory.. Low Mid and High are all equal to my untrained ears though

Joey, yun bang phoono stage mo yung sa RCA handbook?

[tony]

Hi Master Tony

Sorry ngayon lang ako naka reply dito. Got so very very busy from work and traveling abroad.  No master
Tony it was a design I been toying around since the late 80s.  its a normal high gain mic circuit but I modified the RIAA eq following a design from a discreet transistorized version I had a long time ago. I like how the transistorized version sounds so I figured maybe by adopting the EQ of it to the Mic Preamp I have it will transform and lo! it sounds very very satisfactory.. Low Mid and High are all equal to my untrained ears though

your circuit is a feedback type...you may also want to try passive type phono equalizers...
you paralleled tube sections for higher gains and lower source impedance...
nowadays you will find tubes that can get you higher gains and lower source impedance
without resorting to paralleled sections...
the D3a(russian 6J52) triode connected for example has a mu of 70(12at7 like) and lowish plate resistance of the 6dj8 family of tubes...



this is the very much cloned preamp, the Marantz 7, i have many requests to make this types..


notice the striking similarity of the Marantz7 with the AR SP3( well liked by the Malabon Boys)

[wufei]

Thats a very very interesting circuit master tony thanks.  yup im using a feedback type RIAA. I havent tried the passive eq but I read it somewhere passive is easily affected by the input impedance, I dont know if its really true.  I just like the simple circuit that I have now, though I will build soon an adjustable input impedance dedicated preamp, I missd the opportunity to buy a lundahl input and output transformer when I was in japan though, but I was able to get a Toei opt in akihabara and planning to build a 6v6 SE amp.

your circuit is a feedback type...you may also want to try passive type phono equalizers...
you paralleled tube sections for higher gains and lower source impedance...
nowadays you will find tubes that can get you higher gains and lower source impedance
without resorting to paralleled sections...
the D3a(russian 6J52) triode connected for example has a mu of 70(12at7 like) and lowish plate resistance of the 6dj8 family of tubes...



this is the very much cloned preamp, the Marantz 7, i have many requests to make this types..


notice the striking similarity of the Marantz7 with the AR SP3( well liked by the Malabon Boys)