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回覆 (27): Beer and gals
Hello folks, I met 師父this afternoon! Awesome! More on that later ... Tomorrow, evening, do you guys have a great place to get together to drink heavily around 金鐘, I fly out 7am next day .... But can meet if to are as motivated as I am ... After that will be back a week later, stay a nite and then off to japan ..... Busy vacation lor :-)
Cadiver
13-11-25
20:17:25
回覆 (26): Beer and gals
I keep hearing more Lam song on TV ads recently. Have you not? This one is my all time hit. I will be rushing home soon to hear it in 33/1/3 from my newly acquired Denon 103pro. Ah Ah!........ Ah!  
 
Amp? Single ended Mazda pp4/500 and Lowther more than good enough la for vocal? Right?  
 
bobui
13-11-25
19:17:15
回覆 (25): Beer and gals
Cadiver, please email, apps, twit or use your latest gadgets and make contact with me, Kong or whoever you know from 1pk once you got this announcement. The gang want to meet you for beer and gals.  
 
bobui
13-11-25
17:32:46
回覆 (56): DIY Valve - Best of Godfather
Drill, spray and solder for a 1pk high hand. The highly regarded UTC LS-10X mc transformer.  
 
bobui
13-11-21
16:35:56
回覆 (55): DIY Valve - Best of Godfather
Cadiver, being subtle and discreet is...... to some, a virtue. I am totally with you lor! The music is marvellous!
bobui
13-11-17
20:18:44
回覆 (54): DIY Valve - Best of Godfather
 
Like, grazie ...
Cadiver
13-11-16
06:53:00
回覆 (53): DIY Valve - Best of Godfather
look at her face when she said "grazie" at 1:15 and her smile at 1:55  
 
You like?  
 
bobui
13-11-16
00:28:13
回覆 (52): DIY Valve - Why dB
Oh, I mean horn la! Not horm! What an amature!
bobui
13-11-14
11:33:17
回覆 (51): DIY Valve - Why dB
Wrong!  
 
Is a horm speaker. Offical made from Lowther UK.
bobui
13-11-14
11:28:53
回覆 (50): DIY Valve - Why dB
An antique cupboard?
bobui
13-11-14
11:26:04
回覆 (49): DIY Valve - Why dB
All I want to share is the limitation on dB and the benefit if you look into voltage when it comes to gain. Tell me how wrong lor!  
--------  
yes! very wrong.
drwkng
13-11-14
10:42:53
回覆 (50): DIY Valve - Why dB
 
Mdlover, BTW, I have this new toy for you to try out this Sat., you may like it! ;-)  
 
 
thekong
13-11-14
09:51:50
回覆 (49): DIY Valve - Why dB
 
I stand corrected! I always thought dB was mainly a sound pressure unit which was applied to electrical signal for the convenience of calculating the final sound level!  
 
Just found out from Wikipedia (which is not always correct, I know) that dB is actually “ a logarithmic unit used to express the ratio between two values of a physical quantity (usually measured in units of power or intensity).”, which has a wide range of applications!  
 
Learn something new everyday!  
 
thekong
13-11-14
09:08:10
回覆 (48): DIY Valve - Why dB
Come on guys, if this thread is not about blow water and info exchange. What else you want it to be? Personal attack? Never lor! Surely not from me.  
 
WHAT DOES dBu MEAN? dBu is a voltage based decibel unit referred to 0.7746 Volts. 0 dBu = 0.7746 Volts, +10 dBu = 2.45 Volts, +20 dBu =7.746 V, +30 dBu = 24.49 Volts, +40 dBu = 77.46 Volts etc. dBu is numerically equal to dBm which is referenced to 1 mW into 600 ohms (= 0.7746 volts).  
 
Above is from Sowter and for the first time I am quoting it someone else. Ever ask where dB dervied from. When you design a phono or power amp. Do you use dB as the fundemental unit for calculation?  
 
All I want to share is the limitation on dB and the benefit if you look into voltage when it comes to gain. Tell me how wrong lor!  
 
bobui
13-11-13
22:21:16
回覆 (47): DIY Valve - Why dB
真夠朋友 -_-'
mdlover
13-11-13
21:12:59
回覆 (46): DIY Valve - Why dB
oh! my dear Kong, i gave up a few posts ago. how does one know where to begin when almost every sentence written so far is questionable?  
i will leave it to Mdlover^-^  
drwkng
13-11-13
18:27:34
回覆 (45): DIY Valve - Why dB
 
I give up, I will let experts like Dr King and Mdlover to follow-up!  
 
thekong
13-11-13
17:52:55
回覆 (44): DIY Valve - Why dB
You sure 3 db gain in preamp is equal to 3 dB louder in sound volume?  
 
Since when the input voltage is proportion to the output voltage. You guys keep saying 3dB. You cant gorget that sound is AC and AC is Voltage.
bobui
13-11-13
17:46:44
回覆 (43): DIY Valve - Why dB
I try to infavour to your wild guess. So, let say after some tweaks, you preamp output has inreased by 3db. And just assume you did find out your preamp was 1V output before the tweak. 3dB high equal to 1.41V. 3dB higher sound level from the speakers. Nice!  
 
Then,  
1. How did you get the calculation that the tweaks offer you 3dB?  
2. How do you know your power amp is driven to max after the 3 dB  
3. How do you measure the new output power of your power amp or even the preamp after the tweak. Do you get a dB measure to ensure the right and left channel is equal.?
bobui
13-11-13
17:43:25
回覆 (43): DIY Valve - Why dB
>And what is a 3dB increase in preamp output to a power amp. Does it mean if the power amp was not driven in full power. Now it can be driven to full power with the extra 3dB. <  
________________________________________  
 
I would think a 3db more gain in the preamp would result in a 3db more output in the poweramps (assuming it is within its power range), which in turn, would increase the sound level output of the speaker by 3db!  
 
As an end user, I really don't need to know what is the output of my power amp (in V or in power) in this situation, as long as it is within its power range. All I want to know is that I can have a 3db high sound level from my speaker!  
 
thekong
13-11-13
17:42:17
回覆 (42): DIY Valve - Why dB
And what is a 3dB increase in preamp output to a power amp. Does it mean if the power amp was not driven in full power. Now it can be driven to full power with the extra 3dB.  
 
dB is range only. It doesnt tell you where you start and if you dont know where you start, you cant tell if you have reach the end. You can only guess from experience. Its expression of how wide the range is not a number per unit.  
bobui
13-11-13
17:31:24
回覆 (42): DIY Valve - Why dB
 
>Educate me what good it is to HOME audio electronic when talk dB. I like to hear! <  
_________________________________________________________________  
 
Let me take a wild guess!  
 
The purpose of an audio system, whether pro or home use, is to reproduce sound! Sound level is measured in db, so all audio equipment use db as the measurement for gain, or noise!  
 
Just for the convenience, say if I increase the gain of my phono (or preamp, or power amp) by 3 db, everything else being equal, I can expect 3db higher sound level coming out from the speakers!  
 
You just can’t do the same with V !  
 
thekong
13-11-13
17:25:27
回覆 (41): DIY Valve - Why dB
Educate me what good it is to HOME audio electronic when talk dB. I like to hear!  
 
bobui
13-11-13
17:09:13
回覆 (40): DIY Valve - Why dB
That is the only real magic when using dB because you can disregard any source reference.  
-----------------------------------  
 
are you serious?
mdlover
13-11-13
16:59:34
回覆 (39): DIY Valve - Why dB
I try lor! If dB interests you. Allow me to put it in simple words for sharing.  
 
 
1. dB is decibels that show you the difference without the reference. You get that? Assume you have an equipment that offer 20db gain and gain is measured in voltage. First case, you try input 1V, you get 10V output. OK! Then second case, you input 10V, the voltage output become 100V. The dB remain unchanged in both cases as 20dB. But if you input 1V and get 100V. The dB become dB 40. The + or - in dB is just there to indicate if it is a gain or loss.  
 
2. That is the only real magic when using dB because you can disregard any source reference. It is this reason that its most suitable to express gain in power, voltage, current or sound level of a stand alone equipment or in studio.  
 
3. Studio like to use dB because of the many equipments they have in the chain of a recording. They couldnt care the input sensitivity of each equipment. Just not practical! Be it mic amp, equaliser, A to D processor, frequency multiplier, noise compresser etc. All they ever need to know is the overall gain required and as long as all their equipments have huge overload headroom and 600ohms or lower drive capability, they can then add on or take out any intermediate equipement. As long as the overall dB gain can match with or exceed their desire value.  
 
Click the link below which is a simple dB converter. dBV, dBuA, dBSPL dBW. All there for you.  
 
http://www.rapidtables.com/convert/electric/db-converter.htm  
 
In the link. Choose Voltage in the "Quantity type" as it is easier to understand and more related to our discussion.  
1. There is a "Reference" of 1 which you cant change.  
2. There is a "Level" you can type in your desire output or input. And then press convert. You will get the dB.  
bobui
13-11-13
14:16:21
回覆 (38): DIY Valve - mc phono noise problem
no eyes see!
drwkng
13-11-13
13:39:29
回覆 (37): DIY Valve - mc phono noise problem
Kong, you think too much la! Look, if you like dB, by all means. No one would stop you. OK  
 
1. Nearly all measurement is done on a particular frequency. You cant expect anyone tell you input sensitivity figures for each particular frequency. If you insist. You can look at the frequency response curve and thats what it is for. And no one would do measure with music.  
 
2. The mathmaticial unit for gain is Voltage. A repair man would take a fluke that measure a component to find out if there is anything wrong with it and measure it in term of unit of Voltage andn current. Not dB. Right? No need to think too much.  
 
3. Music intrument and the pitch in music is express in octave and frequency. Sound level is express in dBSPL.  
 
If dB gives you a better idea on gain. So be it. I was trying to tell you in any of my calculation when let say building a phono. dB is never needed. Its means nothing to me.
bobui
13-11-13
12:10:18
回覆 (36): DIY Valve - mc phono noise problem
Good questions  
 
Enlighten me here as I am a bit dense! When talking about S/N ratio, there has to be both signal and noise, right? So, if you short the input to ground, you only have noise but no signal; how could you get an S/N ratio?  
A: Signal short to ground means NO signal. Its a common practice for measures. Meaning if the manufactorer say a measurement is done at NO signal. It implies the signal is short to ground.  
 
 
I am assuming the background noise (in mv in this case) in a particular circuit, with a certain gain, is pretty much constant no matter what the input signal level is (assuming no overload), is that right?  
No, Noise is proportion to the gain. Thats what King tried to remind me! The higher the gain, the greater the noise you can and is porportional. Unlike distortion.  
 
 
If that is the case, then you need to reference to an input level (therefore also an output level after the specific gain of the circuit), to get the S/N ratio, right?  
Answer below  
 
Also, if the background noise is constant in a circuit, then the higher the input level (hence higher output level) , the higher the S/N ratio, right?  
The 1mv input from Pass Lab and IO from my estimation is that they both realise the unavoidable noise picked up from turntable, cartridge and tonearm wire. So they input a 1mv pink noise or what to replicate the hum noise. Just to be fair, I think.  
 
 
Have i answer all your queries? One pint if you not happy, Two pints if you pleased with my answers.
bobui
13-11-13
11:52:09
回覆 (36): DIY Valve - mc phono noise problem
>But if i say the preamp line input sensitivity is 2V to a full output of 3.5V. You know it can drive your power amp to full power if it's input sensitivity less than 3.5V. And you know precisely the margin you have. <  
________________________________________________________  
 
Actually, I think it is not that simple, as music is not static but constantly changing, ie there is a dynamic range, which is also expressed in db!  
 
So, if you need to check the margin of headroom in your equipment / system, you probably need to get back to the db format again!  
 
I suppose you have never heard people saying something like “this piece of music has a dynamic range of 100mV to 2V from my phono output”!  
 
 
thekong
13-11-13
11:52:03
回覆 (35): DIY Valve - mc phono noise problem
Actually, dB has been around for a very long time used amongst studio. Be it as a unit of sound level or conversion to dBWatts, dBV or dBuA etc. dB is simple and allow user to recongise the level of gain without reference to the source. Its most easy to make comparsion between equipment for gain only.  
 
As a DIYer, nearly all the time, we need to understanding in terms of its voltage gain in V, impdeance in ohms (resistance) and current in A etc. to bring the basic ohms law for even the most simple calculation. Sorry lor! dB never seems to be in the radar lor! And since, if the souce has already been clearly indentified. Its much more easy and accurate to refer to the basic parameters.  
 
For example: if you have a preamp line gain express in 18dB. Would you know if it can drive your power amp to full output? At most, you can only assume from EXPERIENCE. If you want precise figures, you still need to convert dB back to Voltage.  
 
But if i say the preamp line input sensitivity is 2V to a full output of 3.5V. You know it can drive your power amp to full power if it's input sensitivity less than 3.5V. And you know precisely the margin you have.  
 
Because for home audio, we always have a reference to refer to or compare. For studio and manufacterers. They dont know each of their customer applications. So they need to tell you in dB as well just in case. And 100% of the time, they would tell you the input sensitivity and output power in V anyway. So, why not use it?  
 
bobui
13-11-13
11:29:00
回覆 (34): DIY Valve - mc phono noise problem
>Wah! Confusing as ever lor when comparing different amps in db………..I am so bloodly old fashion lor.<  
________________________________________________________  
 
Wow….you must be really really old fashion if you have never used db! :-)  
 
Ever since I get into hifi, nearly all, if not all, of the specifications on gain and noise that I have even seen were in db! I see gain specifications of 10X, 20X etc., on MC transformers, but that is about it!  
 
Yes, it would be a lot easier for laymen like me to understand if all the gain specs are in Xs, but I suppose there are technical reasons why the whole industry has gone with db!  
 
 
 
>I never really understood how and what all these db really means when connected to the whole system. I tried a db / volt converter like 1mv hiss noise at 1V output level equal to -60dB but then i kind of think thats when the input is to short to ground, right? Like what Allnic is interpreting which I am not so sure lor! So, why IO and Pass Lab measured at 1mv input? <  
_______________________________________________________  
 
Enlighten me here as I am a bit dense! When talking about S/N ratio, there has to be both signal and noise, right? So, if you short the input to ground, you only have noise but no signal; how could you get an S/N ratio?  
 
I am assuming the background noise (in mv in this case) in a particular circuit, with a certain gain, is pretty much constant no matter what the input signal level is (assuming no overload), is that right?  
 
If that is the case, then you need to reference to an input level (therefore also an output level after the specific gain of the circuit), to get the S/N ratio, right?  
 
Also, if the background noise is constant in a circuit, then the higher the input level (hence higher output level) , the higher the S/N ratio, right?  
thekong
13-11-13
10:46:42
回覆 (36): DIY Valve - different type of RIAA valve phono?
Passive two splits type.
bobui
13-11-13
10:11:34
回覆 (35): DIY Valve - different type of RIAA valve phono?
Opss! Here is the LCR RIAA example
bobui
13-11-13
10:09:19
回覆 (34): DIY Valve - different type of RIAA valve phono?
Consider having one of each below. Well, no one stop you from having more than one lor! Four phonos.......minmium lar!  
 
1. Active feedback type  
Active overall feedback type such as the EAR, Marantz7. Most popular type of phono circuit from late 60s to 80s. The hey day of LPs. Mostly made up of 12AX7 and AU7 or AT7 triodes.  
Features: Smooth and silky sound. Open and natural. Very sweet sound.  
 
2. Passive two splits type  
Passive feedback two splits type such as ARC, CJ and a whole lot more. Commonly find in early 90s to current production phonos. Mostly made up of E88CC (6922), 5687, 417A, and high gm, low u triodes.  
Features: More accurate RIAA. More slam, dynamic and low level details.  
 
3. Mono  
Passive two splits or active feedback type Mono phono with at least 6 of the most common mono curves such as Decca FFSS, Columbia, EMI, 78s etc. Should be made up of larger voltage triodes such as 6SN7, 6J5, EF37 and 6SL7 for their airy sound and more vintage feel.  
Features: Hard to beat a good mono recording on solo piano, violin, cello and 60's Jazz.  
 
4. LCR RIAA  
LCR phono. RIAA handled by coils, caps and resistor. Just like how original recordings were done at the studio. Mostly accompany by high gm tubes for their low impedance drive and better noise performance.  
Features: Most accurate type of RIAA. What more do you want?  
 
Below is a typical passive two splits phono circuit. You can see resistors and caps to ground for RIAA located both after first valve and second valve. Hence two splits.  
 
The other picture is example of a LCR phono circuit. You dont see any RIAA caps of resistors. All you have is a box of LCR RIAA filter located in the middle of two gain stages. The LCR is made up of coils as well as caps and resistors of very unusal values. The use of coils enable the RIAA to be more accurate than any other types.
bobui
13-11-13
10:07:54
回覆 (33): DIY Valve - mc phono noise problem
more for you, Sir  
 
5. If the value of the feedback network is chosen very carefully, and the network does not impose too low a load on the tubes driving it at high frequency. The overall result can be very very good when compare to a two slits passive filter network.  
 
6. I like this circuit for its simple design. Most of the time, being simple is the essence of good sound! My current mm phono do not have a single SS regulator and is much more open sounding than even with only valve as regulators. It doesnt carry a cathode follower stage either which i remember reading Bruce Moore interview that he totally dislike it.  
 
bobui
13-11-12
17:53:18
回覆 (32): DIY Valve - mc phono noise problem
1. The RIAA is made up of three times constants. At 75us, 3130us and 318 us. Most of modern three stages RIAA de-emphasis filter work is done by two splits. First one immedate after the first gain stage for 75us. The second one after the second gain stage for the 3180 and 318us. An overall negative feedback from the output to the cathode of the first gain stage is far less accurate.  
 
2. The first 12AX7 input capacitance together with its high gain u=100 is high compare to more popular valve such as E88CC and together with wiring capacitance. Overall input capacitance can easily exceed 200 to 300pf which may even be more than an average mm cartridge desired loading of 200pf and a moving coil transformer generally require minmium shunt capacitance.  
 
3. The 12AX7 has a very high ra which doesnt help with noise performance. A low ra is a small proportion of the toal resistance that defines the 75us roll off which makes is far less sensitive to valve ageing and changes.  
 
4. Noise of the input stage is not only determined by the valve but also the loading Resistor RL. RL generate Thermal noise. With such high ra, the RL would be at least a few times of ra. Not ideal for nosie reduction. Too low a RL increase distortion.  
 
Despite in theory of the many drawbacks in using 12AX7s in an overall feedback phono. I must say that the final result from my own experience is not bad at all. I like ar! The hiss level is a little higher when compare to a typical three E88CC triodes phono but the sound is more relax and smooth.
bobui
13-11-12
17:27:42
回覆 (31): DIY Valve - mc phono noise problem
 
 
I've been using the cheap EAR phono amp for more than 10 years and it continues to give me great satisfaction on virtually every kind of music going through its simple circuitry.  
 
The circuit is almost Spartan in design without even the barest power regulation nor massive filtering banks. Three 12AX7 are used which ensure high gain as well as pretty low noise floor. What Tim has done, I guess, is to get back to the basics and have them done properly, nothing spectacular and nothing expensive.  
 
I presume this circuit is easy to diy but then the cost of a new unit is so low that it's hardly worth the hassle. bubui, please have me enlightened on the merits of this circuit, if any at all!  
 
 
 
limage
13-11-12
15:42:59
回覆 (30): DIY Valve - mc phono noise problem
CAS has no such hideous problem associate with noise, right? Lucky you!  
 
------------------------------------------------------------------------------  
 
I have seen phono circuits selectively compress noise by introducing some kind of filter into the circuit. Be it for hiss noise, hum from 50Hz live wire or low frequency rumble noise from pick up. Many of these are to me, might have negative impact to the sound.  
 
My humble sharing yesterday is mainly aim to illustrate the growing trend of full on valve mc phono in recent years. Many of these nicely made phonos acheive great or to some, an acceptable level of signal to noise ratio from the application of various techiques such as lower cost SS regulators, Cascode circuit, high gm tubes, seperate power supply etc. Some of these techiques or practices were not widely popular in the 80s or earlier but have now become norms in 21st century. And many of these techiques do have postive attribution in noise reduction.  
 
And since I have tried some of these techiques myself with good results or acceptable outcome. I just share with you lor! Not meaning I or others who have adpot these practices are Kings of problem solving such as noise or unwanted peaks in certain frequencies.  
 
bobui
13-11-12
15:05:54
回覆 (29): DIY Valve - mc phono noise problem
 
 
To be honest, I dont know what I am talking about. Do you?  
________________________________________________  
 
 
Usually we don't, but that doesn't matter. Noise floor is one thing and good sound is another.  
 
Believe it or not, sometimes noise may even enhance the atmosphere of analogue playback!  
 
 
limage
13-11-12
14:23:01
回覆 (28): DIY Valve - mc phono noise problem
Wah! Confusing as ever lor when comparing different amps in db. DIfferent level of gain means different db. One could be 78 dB gain and the other is 82dB. It doesnt mean much to me lor! Sorry sir! I am more familiar with miles and pounds. Tell me something in km or kg. I really have to think twice to get an idea lor!  
 
I am so bloodly old fashion lor. I look at gain in mv and V only. My current phono amp input 2mv gives you 2V. I know that is good enough because all my power amps have less than 2V input sensitivty for full power. Average CD ouput is 2V also. Some can be as high as 3V!  
 
I never really understood how and what all these db really means when connected to the whole system. I tried a db / volt converter like 1mv hiss noise at 1V output level equal to -60dB but then i kind of think thats when the input is to short to ground, right? Like what Allnic is interpreting which I am not so sure lor! So, why IO and Pass Lab measured at 1mv input?  
 
As a DIYer, I can tell you my normal practice is to measure output in mv with the volume on full swing. At speaker terminal, 100mv is is dead no noise with my 90db Leak 3090. A bit of hiss I can hear if connected to my over 100db Lowther.  
 
At phono output, I have the record of a measure on the noise level in my current 417A mm phono in mv when the volume is full on with an mc cartridge connected via an external mc transformer. but thats not how manufacturer measures with their phonos, right? The noise was something like 7mv at a 2V max output level. If short the input to ground, the noise become no more than 0.3mv. That would translate to -70db. Right?  
 
Ah, I think the 1mv input (Pass Lab and IO) is for the assumption that cables, cartridge and turntable always pick up some noise. Am I right?  
 
To be honest, I dont know what I am talking about. Do you?  
 
I hate dB!
bobui
13-11-12
12:40:52
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