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回覆 (27): DIY Valve - mc phono noise problem
Well, as with many other discussions, I believe we need to define what is “acceptable”! What is acceptable to one may not be acceptable to others.  
 
Just some examples of different gain arrangements:  
 
The Aesthetix IO, with 80db all tubes gain stages, claims to have a S/N ratio of 70db minimum (ref to 1mv input).  
 
The Pass Labs XP25, with 76db SS gain, claims a 85db S/N ration (also ref. at 1mv input)  
 
The Allnic H3000 LCR phono, with 66db MC transformer / tubes gain, claims 85db S/N ratio at 1kHz (no ref to input level)  
 
The ARC Ref 2 SE phono, with 74db FET MC / tubes gain, claims 65db S/N ration (ref. at 0.1mv input). At 51db gain (just tube gain I suppose), 73db S/N ration (ref. at 1mv input).  
 
So, what should be considered as acceptable?  
 
 
thekong
13-11-12
11:32:06
回覆 (26): DIY Valve - mc phono noise problem
Below link about Scott Frankland on MFA MC reference cascode arrangement. When I had the big opportunity to exam an all tube mc phono, the IO not long along, I saw the tube arrangement in cascode too. Wish I can have the chance to be 100% certain!  
 
 
http://www.audioasylum.com/cgi/t.mpl?f=prophead&m=2898  
 
Re: Neither pentodes nor transistors - Scott Frankland 19:55:07 05/06/03 (2)  
 
In Reply to: Re: Neither pentodes nor transistors posted by mfc on May 06, 2003 at 19:34:55:  
 
I like the simile! The 6DJ8 was invented for use as a low-noise, wideband (Wallman-type) cascode in rf circuits. Fisher called their top-of-the-line tuner rf-input the "golden cascode". MFA used a cascode input in our MC Reference preamp. This circuit used a parallel bottom tube to reduce noise even further.  
bobui
13-11-12
11:18:03
回覆 (25): DIY Valve - mc phono noise problem
My humble sharing below is one of the two all valve mc phono circuit I have tried in the past. As I have mentioned earlier, I parallel two E88CC in cascode arrangement to reduce the noise by approximately root factor of 1.5.  
The upper section fo the cascode is purposely set to feed a lower than normal voltage to the three lower sections triodes to further reduce noise. The lower sections troides were running at 40V only! This arrangement is actually borrowed from old transistor phono to acheive a better than average noise floor.  
 
This cascode phono has a fairly good performance that only marginally noisier than my Morgan Jones 417A mm phono.  
 
The cascode arrangment can also be found in many well known all valve mc phono. Dont be surprise if you discovered it in the MFA Reference and IO!  
 
bobui
13-11-12
11:01:45
回覆 (24): DIY Valve - mc cartridge loading
Anyone ever measure noise (hum) of your phono. You can do a simple test like this. Switch off your power amp and preamp. Turn with phono volume to max and measure it with an AC volt meter.. You phono must be connect to a cartridge. If you happen to know the max output voltage. Then you have a fairly good idea of how noisy your phono amp is.  
 
If your volt meter happen to have a Hz meaure. You can also find out the frequency.
bobui
13-11-11
17:38:04
回覆 (23): DIY Valve - mc cartridge loading
noise is always relative to signal strength. when you are talking about 0.25mv, anything will be an issue.
drwkng
13-11-11
17:08:34
回覆 (22): DIY Valve - mc cartridge loading
I live in Discovery Bay, a very unusal part of planet Hong Kong! Ah!  
 
I did tried adding a gain stage on my existing phono a while ago with various medium amplification tubes. A single E88CC, a 12AU7, 5687, 5956 etc. Best result when I parallel two E88CC in one channel for first stage, the noise reduced to an acceptable level. Still a bit noisier compare with a transformer. A 417A/5842 is very ok but then the frequency response is not very flat across the entire band.  
 
bobui
13-11-11
16:29:20
回覆 (21): DIY Valve - mc cartridge loading
noise is not an issue! this is starting to read like a science fiction. it must be happening in another parallel universe.
drwkng
13-11-11
15:46:02
回覆 (20): DIY Valve - mc cartridge loading
noise has always been a major issue with high gain all tube phonos,  
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Not anymore! Noise and hum generally come from one or more of the below in high gain mc tube phono.  
 
Zener diode: To be found in B+ or faliment regulation circuits. Noisy in nature. If you can avoid using zener, you can elimiate one noise source. Some voltage regulator valves have even lower noise floor than zener diode!  
Ground layout: Sound easy to handle but very difficult to get it done proper but if I can handle it ok . Any other high hands can lor! For big brands, that should be just a piece of cake!  
Tube: Frame grid tube mid to low amplication triode tube such as E88CC can offer low noise as long as you can control the microphonic! High gm tube such as 417A is a good option as phono tube. Very low noise even when compare with some older SS.  
Power supply: With a good B+ and faliment regulations, not as difficult as one may think when you want lower noise.  
 
MC phono using SS/Fet is much lower in cost lor! Think about all the additional regulations, high voltage transformers, high voltage caps etc in a tube mc phono amp. A risky business lor!
bobui
13-11-11
13:45:14
回覆 (19): DIY Valve - mc cartridge loading
>To me, noise is not a major problem in building a tube mc phono. <  
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Really?!!! I believe noise has always been a major issue with high gain all tube phonos, say those above 65db gain!  
 
That’s why many of the high gain tube MC phono actually use SS / FET for the MC gain to get the noise down.  
 
With all tube MC phonos, the MFA MC Ref and the Bruce Moore, are very quiet!  
 
thekong
13-11-11
13:21:26
回覆 (18): DIY Valve - mc cartridge loading
we have power and better bandwidth, but noise can be a problem.  
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To me, noise is not a major problem in building a tube mc phono. Not when dc regulator is so easy to work and perform so well. I have tried two tube mc circuits in the past. Noise accpetable with my over 100db lowther.  
 
Is the many unwanted peaks between 20Hz to 20Khz when amplifying a 0.2mv to 4mv that shift my desire to transformer rather than active mc phono. Worst is when a tube or SS got run in, the frequency reponse curve changes too!
bobui
13-11-11
13:05:17
回覆 (17): DIY Valve - mc cartridge loading
I know it doesn’t reflect their sonic performance 100%, but what is the typical frequency response of these transformer based step-ups, vintage and modern?  
 
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Three modern transformer makers I am familiar:  
Sowter generally offer +- 0.5db from 5Hz to 100Khz  
Lundahl offer +-1 db from 10Hz to 90Khz depending on core materials and windings  
Tango MCt-999 offer +0, -1db from 10Hz to 50Khz  
 
For vintage transformer such as UTC 100X is +-1db 30Hz to 20Khz  
 
For any mc transformer, I would be looking at a spec of +-2db or better in the audio frequency range 20Hz to 20Khz. Many older measurement only measure up to 20Khz.  
 
bobui
13-11-11
12:45:29
回覆 (17): DIY Valve - mc cartridge loading
SUT, there isn't any increment in power/energy. They only raise the voltage at the expense of current. With a MC gain stage, we have power and better bandwidth, but noise can be a problem.
Derek2A3
13-11-11
12:31:26
回覆 (16): DIY Valve - mc cartridge loading
all failing the above, lets stick to MM or MONO 8^) !  
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I have an audio technica 3/LP mono cartridge. Sound special on FFSS and EMI mono violin ar! I like! My plan is to mate with the Lenco!
bobui
13-11-11
12:06:09
回覆 (16): DIY Valve - mc cartridge loading
 
I know it doesn’t reflect their sonic performance 100%, but what is the typical frequency response of these transformer based step-ups, vintage and modern?  
 
 
thekong
13-11-11
11:48:49
回覆 (15): DIY Valve - mc cartridge loading
Headroom is everything ! the difficulty is matching the MC cart with the right SUT. My views should be opposite way round, get a good Microphone SUT and make a cartridge that will match the Microphone SUT.  
 
So what's a good match for an old fashion Altec Peerless 4722 ?  
 
all failing the above, lets stick to MM or MONO 8^) !  
daiwok
13-11-11
11:37:57
回覆 (14): DIY Valve - mc cartridge loading
always been using active MC gain stages, SS or tubes  
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The increasing use of low noise, high gm tubes such as E88CC, 5687, 417A or even the 6H30 in mu follower and cascade circuits together with the possibility of lower cost dc voltage regulators, we began to see more high performance tube mc phono amp appeared in the market from the 90s. Things you can dream of before the 80s lor! I suppose the MFA MC reference aroudn the early 90s was one of most well known front runner in an all tubes mc phono, right?  
 
On the other hand, the technical advancement of mc or mike transformer has been rather slow in the last 30 to 40 years. In fact, it may be hard to claim if there may be any advancement at all. Many of today core materials and winding technique as I mentioned earlier have been around for many years. For example, Permalloy core was widely used in UTC 1955's transfromer brochure. Colbat core was a very average stuff used by many transformer makers and speakers magnet from early 60's such as Lowther. Multi-secions windings were the norms in the 60s for increase frequency response. In fact some of its technique has been lost in the 70s together with the fade out transformer brands such as UTC, partridge or Gardners.
bobui
13-11-11
11:30:52
回覆 (14): DIY Valve - mc cartridge loading
Talking about MC loading, some of the well-known cartridge and phono stage designers, including J Carr of Lyra, and Ralph Karsten of Atmasphere, share the view that modern MC cartridge really doesn't need the loading as electrical damping! The loading is more for the phono stage rather than the cartridge!  
 
They claim that the reason why you hear a considerable difference in loadings is that the phono stage is being overloaded by signals in the ultrasonic region, and the loading helps to cut those signals down.  
 
So, if your phono stage has the required headroom in the ultrasonic region, and therefore not overloaded by those signals, there should be no difference in performance between a loading of 100 ohm or 47K ohms!  
 
So, try it with your phonos! :-)  
 
thekong
13-11-11
11:24:55
回覆 (13): DIY Valve - mc cartridge loading
Plug and play! And see how you feel about the sound! Could never go too wrong lor! Right?  
 
In case a newly acquired transformer sound a bit thin, too bright or dull and lifeless. Try to adjust your phono amp loading switch and see if there is any improvement. Be it a low impedance transformer or high impedance one, primary load matching with a mc cartridge can always be altered to your desire value by adjusting the secondary/phono amp loading resistor. If a transformer is of the low impedance type. What it really means is that the ratio is of 1:20 or higher. A high impedance type normally come with a gain ratio between 1:8 to 1:12.  
 
In most circumstances, a 1:20 ratio transformer may just be a bit too high gain for most systems anyway!  
 
To me, the interesting part is the different sounding offer from various exotic core materials, shape and winding arrangement such as amorphous, mumetal and permalloy. Cut core, Uncut colbat, E shape, C core etc. Double primary layer winding......etc.  
 
bobui
13-11-11
10:39:19
回覆 (13): DIY Valve - mc cartridge loading
> all I know is that it’s trouble free and it has none of the colorations of most head amps. <  
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It is interesting to note that some audiophiles refused to use MC transformers due to their colorations / limitations!  
 
I tend to believe both MC transformers and head amps have their own sets of colorations / distortions, and one’s choice really depends on his system and preferences, much like SS vs tubes!  
 
Being said that, I suppose MC transformers are, in general, quieter (if you can avoid the hum) than tube MC gain stage!  
 
I have to admit that I have always been using active MC gain stages, SS or tubes, and don't have much experience on MC transformers. So, it is probably time for me to try them out!  
 
thekong
13-11-11
10:38:14
回覆 (12): DIY Valve - mc cartridge loading
I couldn’t care less about the technical merits and demerits.........  
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A romantic statement. The very essence of Conrad-johnson's logo "It just sounds right".
kris
13-11-11
09:24:46
回覆 (11): DIY Valve - mc cartridge loading
 
 
I couldn’t care the less about the technical merits and demerits of the step-up transformer against the head amp, all I know is that it’s trouble free and it has none of the colorations of most head amps.  
 
The Koetsu transformer has been working quietly for me over so many years that I almost forget its very existence.  
 
limage
13-11-10
20:02:52
回覆 (10): DIY Valve - mc cartridge loading
How to choose a mc transformer?  
 
Q I sometimes see transformer not giving details about the ratio but rather written something like this - primary 200 ohms, secondary 100K. So can I make the assumption that this transformer is no good as a mc transformer because its secondary is for 100K? The norms is 47K secondary for phono preamp, right?  
A. The answer is NO. Here is the catch. A transformer manufacturer has two ways to show you the spec of its transformer.  
1. To written clearly the ratio such as 1:10 or 1:20 and tell you the application purpose or.  
2. To indicate the application purpose by showing you the primary impedance when the secondary is of a particular value such as the above 200 ohms and 100k.  
Basically, either way is to let you know the ratio. A transformer has a primary of 200 ohms when secondary is 100k means the transformer has a ratio of 1:22.36 when is a possible candidate for mc transformer.  
 
The reason some transformers were written in ohms rather than ratio is because it provides an immediate and better understanding for the user to realise the purpose of its application. For example: For studio mic transformer, the secondary is commonly connected either to a 50K or 100K mic pre-amp input load. To enable the user to get a better picture what would be the value of the primary loading when the transformer is connected to a 100K ohms mic pre-amp. The transformer was written with the exact primary reflective load impedance (200 ohms) for convenience when matching with a microphone.  
 
If you change the secondary loading from 100k to let say 47K, the reflective primary load become 94 ohms which is a perfect fit for a 10 ohms mc cartridge.  
 
You can calculate it from the link below. Go to the bottom of the link.  
http://www.hagtech.com/loading.html  
Step-Up Transformers  
In the Phonostage. Type in 100k, Turn Ratio 1 : 22.36 Press calculate. You get a loading of 200 ohms  
Change it to 47K, Turn ratio remain at 22.36. Press calculate. You get 94 ohms.  
 
Important notes to remember:  
1. A transformer primary is determined by the secondary loading resistor and the transformer ratio. The ratio is usually a fixed 1:10 or 1:20. A change in the secondary loading resistor will alter the primary loading sees by the cartidge. Its call reflective load.  
2. A transformer is nothing more than two windings in a metal frame of E shape or C core or round shape. There is no problem to change the secondary loading to match with your cartridge. Most phono amp has this features anyway. There are limitations and bandwidth restriction but I wont be going into details here to avoid things gets too complicated. In general a mic preamp with a ratio between 1:10 to 1:30 is fine to connect as a mc transformer.  
The exact primary loading in ohms for a particular cartridge has to be final decided by the listener in his or her system. All of the above gives you the principle on how it works and where you should start.  
bobui
13-11-09
18:15:40
回覆 (9): DIY Valve - mc cartridge loading
At HH yesterday, a few of us touch upon a very hot topic - mc cartridge loading with mc transformer.  
 
1. This link offer easy to understand on cartridge loading  
http://www.reddiamondaudio.net/cartridge_impedance_loading_.html  
 
2. Go to the bottom of this link, it offers an auto calculate formula for you to find out the loading your cartridge sees when connected to a transformer  
http://www.hagtech.com/loading.html  
 
3. This link below tells you the basic principle of cartridge loading from no other than one of the most famous transformer maker, Sowter  
http://www.sowter.co.uk/phono-cartridge-transformers.php  
 
In general, you need to know your mc cartridge internal impedance which usually range from 5 ohms to 50 ohms. For example: Let assume the internal impedance of your mc cartridge is10 ohms. The rule of thumb is to connect a transformer that gives a reflective primary load of 10 times of the cartridge impedance which is 100 ohms in this case.  
This is only a ballpark. Not a precise number you must follow. Lower than 100 ohms offer a damping in the high frequency. You can try various loading to match with your system and personal taste. It primary load normally should not go less than 5 times of your cartridge internal impedance or the sound may become dull and lifeless.  
 
Q. How do I know what is the primary loading of my mc transformer?  
A. You can use link 2 above to calculate. Allow me to give you an example for better understanding. First you need to know the transformer ratio. Let assume is 1:20, OK! Then you need to know the secondary loading resistance which is normally set at 47K in most phono amp. A 47k secondary loading with a 1:20 transformer, the primary loading sees by the cartridge is 117.5 ohms which is about right for cartridge with an internal impedance of 10 ohms (remember is10 times, right).  
 
Q. Why my very expensive mc transformer offer three very low ohms connections, something like 2 ohms, 10 ohms and 40 ohms?  
A. These are not the primary loading values. The transformer itself DOES NOT give you a fixed primary loading for your cartridge. Its the secondary loading resistor (47K or lower) that determine the transformer primary loading value. Its call reflective load. The written values at the back of the transformer are likely to be for the user to realise if your cartridge internal impedance is around 10 ohms, then connect to the 10 ohms RCA socket for best result.  
 
Q. What is the most common ratio I get from a normal mc transformer?  
A. Standard step-up ratios are 1:10 (20dB), 1:20 (26dB), and 1:30 (30dB). Lundhal mc transformer mostly offer 1:8 or 1:16  
 
Q. I dont care all these tech stuff. I just want a good transformer. I dont mind trying the loading switches in my phono to discover what I like best but why go so deep into the theory? Is that a problem? If so, Just tell me in plain English what I need to look for when matching transformer to a cartridge or phono amp?  
A. If your phono amp loading resistor is set at the common 47K, then you are unlikely to encounter any major problem with transformer matching. Simply because as example show above. A 47K with a 1:20 transformer gives you 117.5 ohms primary loading which is about right for most mc cartridges. A high loading not likely a problem. If it sound thin, then you can try a lower than 47K. Most of the time is when the primary loading come too lower or too close to the cartridge internal impedance that you may have a problem of a dull sound.
bobui
13-11-09
12:11:36
回覆 (8): DIY Valve - preamp
1. Total 36 tubes in four chassis.  
 
2. Balanced as well as RCA outputs  
 
3. MM and MC inputs  
 
4. Fully hard wire  
 
French DIY!  
 
bobui
13-11-07
13:55:21
回覆 (7): DIY Valve - preamp
True dual mono power supply and amplifying units! Preamp include mm and MC phono. Below is the power supply for one channel only.
bobui
13-11-07
13:39:24
回覆 (6): DIY Valve - preamp
Four chassis - two power supply, two main preamp units.  
 
bobui
13-11-07
13:34:27
回覆 (5): DIY Valve Q&A
Thank you !
Cadiver
13-11-06
23:43:14
回覆 (4): DIY Valve Q&A
For new valve, I would hook it up to my AVO tester and test the mutual conductance (gm). The ideal gm is written in the valve spec. Let me know if you need one for 6C33. Can list it here at 1pk or send you a pdf.  
 
Assume you do not have an AVO valve tester or any otehr good tube testers, you can try to test it on your valve amp. But best if your valve amp is fixed bias and offer an adjustable grid voltage. You can then measure the change in cathode current when you adjust the grid voltage. For example: Valve A gives you 200ma at -50 grid voltage at 250V. Valve B read 195ma at -50 grid voltage at 250V. These two valves to me is OK match. If either valves fall or rise by more than 8 to 10% difference. I wouldn't regard it as well match. Better still, if you get a few measures at different grid voltages. This method is not very accurate and can only offer a ballpark because most amps dont have regulated B+ and the variable grid voltage only offer a very narrow range.  
 
If you have difficulty conducting any of the above tests, you can perhaps measure the DC working condition (voltage and current) with a volt meter and then hook up a signal generator to measure the AC output voltage for a given input AC wave form.  
 
For all of the above non-AVO tests. You need to be competent on basic valve amp working principle. You also need a good volt meter that can measure dc current. A dummy load, an RCA plug that short signal to ground and a signal generator.  
 
If you have non of the above, bring the valves to HK and I match them before you make your way back. OK!
bobui
13-11-06
21:04:56
回覆 (3): DIY Valve Q&A
@bobui  
 
Can you provide some guidance/instruction/advise on how to measure & match 6c33c tubes please.  
 
Cheers!  
-D
Cadiver
13-11-06
14:57:42
回覆 (2): DIY Valve Q&A
Direct heat triode such as 6C33 and 6080, 6336,  
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Sorry for the typo. Should be Indirect heat triode such as 6C33, 6080 and 6336
bobui
13-11-06
10:03:20
回覆 (1): DIY Valve Q&A
Hope below Q&A would stop Hi hand friends the needs to call for more answers and stop your worries regarding valve placement in amps. Dont hit me if not clearly explaining or answering your queries. Just say it!  
 
Q: Better for indirect Heater valve to be in vertical than horizontial?  
A: Horizontial positioning would not do any harm to the faliment of an indirect heat valve but for heat dissipation, I can only assume vertical position is a more effective option.  
 
Q: What would happen to the faliment of a direct heat output valve if it is position horizontial?  
A: Nothing immediate! I hope! But best to avoid for long term.  
 
Q: I am no bloody expert in valve and surely not a DIYer. Which type of valves or valve amp I should avoid having horizontial position output valves?  
A: I never seen a KT88 faliment break down caused by horizontial positioning. Have you? I dont remember seeing any vintage amp position a direct heat output valve in a horizontial fashion. Have you? The truth is, most of the time people pay attention to the wrong details and worry too much for unimportant matters! Have you not?  
 
Common indirect heat output valves  
Any KT family valves such as KT90, KT100, KT88, KT66, KT67.  
Most pentode such as EL34, EL33, EL84, EL95, EL37, 6L6G, EL156  
Direct heat triode such as 6C33 and 6080, 6336,  
 
Direct heat output valves  
845, 211, 811, 300B, 2A3, 6B4g, VT25, 45, 71A, PX4, PX25, DET25, DA60, PM24,  
 
bobui
13-11-06
09:53:41
DIY Valve
Output valve in horizontial?  
 
Yes - can ar!  
For indirect heat valve such as KT88, KT66, 6C33. Horizontial placement is not a problem to the heater/faliment and won't affect the performance of the valve. Below diagram shows you the internal construction of a typcial indirect heat triode. You can see from illustration A that the heater wire is contained tightly and firmly inside a box shape cathode. In reality, there is no room for the heater wire to swing around inside the cathode. The cathode itself is made up of metal sheet that dont change in shape in regard to heat from the heater wire.  
 
No - not a good practice!  
For direct heat valve such as 300B, 2A3, PX25, U52 (5U4G). Horizontial placement is not recommeded. In this type of valve, the cathode is the heater wire. Meaning there is no sheet metal box cathode and the heater is usually carry by a number of spring load from both ends. The heater is the cathode. It is repsonsible to provide heat as well as to release electron in respect to a positive anode.  
In this type of valve, best to place the valve vertical.  
 
Be gentle when hot!  
Some direct heat valve such as the 300B is constructed from an exceptionally long heater/faliment in W shape rather the usual one turn U or V shape you see from a 5U4G. The faliment is very easy to break once it is light up. Please be gentle lor when hot!  
 
 
bobui
13-11-05
13:33:17
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