I would look into getting a Step Up Transformer (SUT) for your cart to install between the cart and the phono preamp. This will step up the voltage from 0.3mv to about 3 to 5mv that your phono preamp can handle. Right now your phono preamp is maxed out and your hearing what happens to all but the best and most expensive ones.
Check around to see what folks are using with your cart as far as a SUT goes. They need to be matched. Tell us what the output impedance is. It's measured in ohms.
BillWojo
|
thanks for your reply. Output impedance for the cartridge is 5 ohms. I'll have to look into step up transformers to educate myself a bit. When you say it's maxed out and I'm hearing what happens to all but the best, are you talking about the background noise when the volume is cranked?
|
+1 for a SUT! I have several, including. a Bellari. This is an excellent USA-made SUT at a reasonable price! |
Low output mc cartridges sound best with a good SUT. High gain phono stages suffer from too much noise when used with a cartridge putting out 1 millivolt or less! Since a SUT is a passive device it adds NO noise - unlike any active gain stage. |
It still sounds good, but on the occasion I do crank the volume to near max (50-60 out of 60) What is 60? 50-60% out of 100% ? 58db Gain should be enough for 0.3mV cartridge. On one of my phono stages I use 60db gain for lower output (0.25 mV) cartridges. The volume control on my passive preamp is about 50%. I have another phono stage Gold Note PH-10 with higher gain (optional gain settings) and I want to tell you that you have to use the lower possible gain if you satisfied with the sound. I do not use higher gain settings even if I can. SUT is not necessary better, probably you don’t need it, but you can try. 0.3mV is not so low output for MC, I have cartridges with 0.15 mV and even lower. You could check the tubes in your amp, there are just 2 tubes, you could change the tubes (it can be huge upgrade if you will find the best 12AU7 tubes) Specs for your preamp: - Tube complement: 2 x 12AU7/ECC82 tubes
- Frequency response: 1Hz – 75KHz +/- 1 dB
- THD: <0.1%
- Gain line stage: 7 dB
- Rated output: 1V
- Output impedance: 750 Ohms
- Gain phono stage: 43dB, 58dB
- RIAA accuracy: +/- 0.1 dB
- Phono overload: 40mV
- Headphone amp: 1W (32 ohms)
- Power consumption off <1W
- Power consumption on: 23W
- Dimensions: 15.25 ”W X 14.5 ”D X 3.2” H
- Weight 16 pounds
- Shipping weight 20 pounds
- Power requirements 115V – 50/60Hz
- Power requirements 220/230/240V – 50/60Hz
|
|
There is no advantage to using a high gain stage with a lomc cartridge because all such active stages add noise - something to be avoided! Properly amplified a lomc cartridge has a significantly lower noise floor than any mm or mi cartridge. A transformer is the best way to convert the high current of a lomc to the higher voltage required by a phono stage - all without adding more noise! |
The only caveats regarding an SUT is that it must be grounded to the tonearm/TT AND the phono stage/preamp. 2: The IC from the SUT to the phono stage/preamp should be kept as short as possible. This is to avoid high frequency roll-off due to capacitive loading between the transformer secondary winding and the connecting cable. The interconnect cable between the lomc cartridge and SUT can be any reasonable length. A meter or two or three doesn't have any deleterious effect. |
To be honest, a high gain phono stage for 0.3 mV cartridge is not necessary, a high gain phono stage is required for 0.05 mV or 0.15 mV cartridges and those very low output carts can be problematic even with SUT, Headamp or phono stage.
Personally I use all methods including current-injection type of the phono stage for low impedance cartridges.
I can’t categorically say that SUT is the best!
But MM/MI carts are dead quiet almost with every good phono stage, the MC are not.
|
Despite the many self-assured responses you received, no one can really analyze the phono gain inherent in your system without also knowing something about your amplifier and speakers. First, the SPLs coming from your system depend not only upon the output from your preamp but also on the input sensitivity of your amplifier. Input sensitivity is defined as the signal voltage required to drive your amp to its full output. Typically that is anywhere from 0.5V to 2.0V, somewhere in there. After that, we need to know the efficiency of your speakers and the size of your listening room.
But we can say that a cartridge that puts out 0.3mV into a phono stage with 58db of gain will result in a signal voltage of around 0.24V at the output of the phono section. Bear in mind that the figure of 0.3mV is published by the manufacturer for a stylus velocity of either 3.54 or 5.0 cm/sec. Most music will actually push the stylus around a bit faster than the standard velocity; thus usually the rated output is a bit pessimistic as far as the actual overall gain you get. Then that signal will go through the linestage of your preamplifier, which according to data posted by Chakster, adds 7db of gain, for a total signal voltage of about 0.5V. Depending upon the input sensitivity of your amplifier, that might be close to enough if not quite enough to make your listening experience a happy one. (To make these conversions of db to V, I use calculators available to anyone on-line. You should learn to use them too.)
I don't at all agree with the insistence of a few that a SUT is always superior to a high gain phono stage, but if you do choose a SUT, you MUST connect it to the MM input of your phono stage, which we know yields 43db of gain. The difference between your high and low gain inputs is therefore 15db. 15db of gain is equivalent to a voltage gain difference of 5.6X. You want a SUT that adds more voltage gain than that, because you already know (pending further info about your amp and speakers) that 58db is not enough. Your cartridge, which has an internal resistance of 5 ohms, according to someone, will work fine with a SUT that has a 1:20 turns ratio (a voltage gain of 20X). That combo of 43db gain from your MM stage plus a SUT with a 1:20 turns ratio should put you in a safe area for total gain. 1:10 might work too (voltage gain 10X).
I think why many others think 58db should be "enough" is because most linestage sections add more than 7db of gain on top of the output of the phono section, more typically 10 to 20db. That may be why the consensus is you should have enough gain already. Plus we don't know about your amplifier.
|
Many cool ideas here to consider. To help clarify, my equipment:
Rega P2 with Dynavector 20x2L
Bluesound NODE 2021
Rogue RP-1 preamp
Rogue Stereo 100 Power amp
Fyne Audio F301 bookshelf speakers
Polk Audio powered sub
Blue jean cabling
Room is 12’w x 18’d x 9’h
I also want to say I’m not dissatisfied with the sound coming from the TT rig, just wonder if it can be improved with a couple more db. Perhaps 60db or 61db etc. I do not ALWAYS crank the volume. Volume goes to 60 on the Rogue RP-1 and its usually set to 45+, when I get to the upper settings is where I hear a faint background noise. It’s manageable.
Some additional specs for equipment:
Stereo 100
100 wpc
input sens. 1.0 V rms
RP-1
gain 9.5 db (The gain on the post above was incorrect or revised in according to the manual that came with my new unit 2021)
output impedance 725 ohms
phono gain 43db, 58db
phono overload 45 mv
Speakers
89db
8 ohm
Right now I have the Pre phono gain set at 58db and resistive loading set at 1K ohms.
Really appreciate your input, learn a lot on this forum! I wonder if I am splitting hairs here, but then again look at the hoppy we are in ...lol
What would you do??
|
Oh, and I tried to use a couple of the online calculators. Kinda steep learning curve for me right now but I believe the KAB calculator suggested 61db gain. Am I missing anything with a 58db to 61 db difference? I’m sure some of you more seasoned audiophiles have been down this road before!
If someone with more knowledge than me can help me out with the math: With my set up, is my TT plus Pre producing enough input V to the power amp? Do I have to crank the volume because there's not enough input? |
I thought I covered this in my earlier post. We mentioned that 58db of gain applied to the 0.3mV output of your cartridge would yield a ~0.24V output from your phono stage. Adding to that the 9.5db gain of your linestage would result in a net signal voltage output from your whole preamplifier of ~3 X 0.24V = 0.72V. (9.5db translates to about 3X voltage gain.) The calculation gave a different result the first time, because I was working with a putative 7db gain from your linestage, as opposed to 9,5db. Given that we now know the sensitivity of your amplifier is 1V and also given that you disclosed the fact you use powered subwoofers, which presumably relieves your main amplifiers of the power demands required for deep bass response, I would say you ought not to be suffering from lack of gain adequate to drive your speakers. "Faint background noise" can be what is known as "tube rush". Sometimes that happens when you crank the gain on your tube preamp, which you are not really doing. Maybe your tubes are going weak. Also, was Chakster correct in stating that your phono stage uses two 12AU7 tubes, only? If so, there has to be either a SUT built into the MC input stage OR there are solid state devices adding gain. You cannot derive 58db of gain from two 12AU7s alone. Below is a useful website. http://www.sengpielaudio.com/calculator-gainloss.htmhttp:// |
@lewm
Thanks for breaking that down for me! So sounds like everything from the cartridge through to the power amp matches up well. Could there be any improvement by getting closer to the full 1 volt rating? By the way, I use a powered sub, but the mains are still running full range off the power amp. The sub is being fed by the preamp. You probably already realize this just wanted to point it out. It's my understanding that to relieve the mains of the work of producing deep bass you need to add a crossover or filter? Again, still learning all the different setups. If I remember correctly the RP1 uses a tube output stage, the phono stage may be solid state, I'll have to look into that. |
I assumed that if you are using powered subs, usually those products have built-in electronic crossovers. I guess I also assumed that the crossover is also driving the main amplifier you use for upper frequencies. That's very worth doing if you don't mind spending the money. As it is, then of course your main amplifier is working full range and the power demands on it are greater than I thought. What you say about the RP1, which I know zero about and which I cannot even find on the internet (albeit I did not look very hard), makes more sense, if the phono section is solid state. Technically, I think you should be OK so far as driving your amplifier to power the speakers, but the proof of the pudding is in your listening. The symptoms you describe do fit the description of a lack of adequate gain somewhere in your chain. Maybe try to borrow a preamplifier with more overall gain from phono input to linestage output, and see what that gets you. Or borrow a 1:20 SUT.
|
If you try using a SUT to solve your problem, keep in mind that you need to attach it to the moving magnet inputs of your phono stage, not the MC inputs..
|
@lewm, I think the OP can kill two birds with one stone by getting an active two way crossover for his subwoofers. It will cut the bass to his main speakers and add some more gain to the preamps output.
jin78, check out MiniDSP I do believe they make such a crossover. It will improve your system performance quite a bit with less distortion in your main speakers, better subwoofer integration and more gain.
As for as your phono stage is concerned the real limiting factor is the signal to noise ratio. If you are hearing noise I consider that to be a problem. I think it is unacceptable to hear any noise at the listening position at the highest levels you listen. If you hear noise then the solution is a quieter phono stage or a cartridge with higher output.
Low output in a moving coil cartridge is an advantage because the coils are lighter (fewer turns) which gives better tracking and a higher resonance frequency pushing the high frequency response of the cartridge up higher. The problem is having to use a phono stage with high gain and a very low signal to noise ratio. These are obviously expensive. Moving Iron cartridges like the Grados and Soundsmiths have no such problem. With phono stages that have gain below 60 dB they are the superior choice IMHO. The are now some excellent moving magnet cartridges from Audio Technica, Clearaudio, and Goldring that have performance comparable to many moving coil cartridges if not better in some ways. I have never heard a moving coil cartridge as dynamic as the Charisma from Clearaudio. I think any of these would be a better match for your system. IMHO moving coil cartridges are over rated and over priced. The ones that I really like are $5k and over, a lot of money for a perishable item. If you check out my system you will see that it is pretty serious stuff and I am more than happy with cartridges made by any of the above, so much so that I have sold all my moving coil cartridges! |
Yeah, well it’s always easy to tell someone to invest $$$ to solve a specific problem. I did suggest that an electronic crossover with a high pass filter would help, no doubt. So would a different preamp with more total gain. So would a cartridge with higher output. And so would a SUT. |
