Convert cartridge output voltage to db gain
More gain will get you more noise and you do not say that the output is too low, only noisier. What you need is higher output or a lower noise phono stage. Another consideration is the impedance matching of the cartridge to the input of the phono stage. Gain = 20xLog10(V1/V0), so you need to have two voltages to calculate it. Kal |
Thanks for the input so far. Well I assumed it was a gain issue because I have to turn the volume knob up to around 2 o'clock to get satisfactory listening levels. When I play CD's, the volume knob is around 10 o'clock for the same listening level. In my old preamp/amp setup, I did have to turn the phono up louder than the CDP, but it wasn't as drastic. Phono was about 11 o'clock, CD around 9 o'clock. FWIW, previous amp was 75 wpc, the amp section in my current integrated amp is listed as 80 wpc. Sidssp, the phono stage is solid state, and was not noisy in my old preamp/amp setup. It does seem like surface noise, but my cartridge, speakers, and phono stage have not changed. I sold my preamp and amp (both tubed), bought an integrated amp, then I noticed the change. CD's play with no noise issue. The integrated amp has a tube line stage and tube power amp sections. Kal, where would I find V1 and V0? Cheers, John |
My cartridge is low enough, about .35mV that to get it to sound the same as the CD player the volume has to be turned up. Paul Marks, the phono preamp creator said it was a matter of the gain of the phono preamp combined with the cartridge output that made it necessary. A slightly higher one, .65mV was mentioned, would obviate that necessity. So some part of it is the gain issue, but not the noise issue. |
Actually, the equation is: db = 20Log10(Av), where Av is the voltage gain (Vout/Vin). Vin is the input signal (your cartridge output of 0.24mv) to the phono stage. Ultimately you want a line level of 0.5 to 1.0v from the phono stage's output to match the same same level from the CD Player. If you are aiming for 0.5v output from the phono stage, Av = (0.5v / .24mv) = 2083.3 Plug this into the "db = " equation and you have a db value of 66db, needed by the phono stage to achieve that 0.5v signal into the line stage. |
So, by that calculation, he has adequate gain in the phono stage despite his protestations. As I said, it is the noise level, not the gain that needs to be addressed. Since he is turning up the gain (reducing attenuation) in the in the integrated amp to attain the same (subjective) output with the same phono stage, I suspect the input stage on the new integrated. Kal |
Ok, thank you for the responses. That does explain the volume difference to some extent. According to John's calculations, my phono stage has an output of 0.5V, while my CDP has an output of 2.5V. So, I'm guessing (since I can't find my old sceintific calculator) that I would need a cartridge with about a 2.0 mV output with 66 db of gain to make a closer match to the 2.5 V output of my CDP. Is this correct? Or as Kal suggest, I should try changing the preamp tubes in the integrated amp? (1 12AX7, 1 12AU7) Cheers, John |
A cartridge with 2.0mv output will need a higher input impedance than your .24mv cartridge, typically something from 10K-47K ohms. Can your phono stage provide that *without* switching to the MM inputs and reducing the gain you're trying to increase? Even if you can get a suitable impedance without losing gain, I'm not sure I'd replace the cartridge. The higher noise floor is in the new line stage, not the phono stage or cartridge, so address that. Your old (seperate) line stage had an acceptable noise floor with phono, the new (integrated) line stage does not. It's not really a gain issue, as already discussed. Any decent line stage should play with a similar noise floor at both 10 o'clock and 2 o'clock. Those are not extreme settings. It's worth trying different tubes. Which will work best depends on the circuit of course, but FWIW the best new production JJ 12AX7 and 12AU7 both have a low noise floor in my preamp, and they won't break the bank. If that doesn't help, the quality of the line stage circuit and/or the power supplies in this new integrated begin to become suspect. You haven't described just what this higher noise floor sounds like. That might help... |
Phono preamp gain computer at kabusa.com (click on phono preamps and scroll to the bottom of the page) shows you need 63 db of gain. I'm with Kal above; unless you are running a system with very low overall gain in your actual preamp further up the line (say a passive) or extremely low efficiency speakers you need less gain not more or, a lower output cartridge. Sounds like the integrated you are running has a bit more gain than the component(s) you replaced. Once you hit into low output MC's, getting the gain right is very critical. My guess is that the "higher noise floor" you are hearing is a result of too much gain and the noise and hiss being amplified as a result of that. You might also have a very slight hardening of the sound as a result of too much gain. Go higher gain and your problems will become even worse and your sound quality will deteriorate even more. |
Hi John, I second Doug's excellent comments, and I agree with him and Kal that the noise you are hearing is most likely being generated in the front end of the integrated amp. Re aiming for a 2mv cartridge to match the level of your cdp: The actual number is 1.25 mv. 66db corresponds to a voltage gain of exactly 2000 (20log2000 = 66). 2.5V/2000 = 1.25mv. However, that still may be high enough to unduly limit your selection of a new cartridge (if you can't resolve the problem via tube rolling), and might still lead to the kind of impedance matching issues with your phono stage that Doug referred to. 1.25mv is about 14db greater than 0.24mv. A 10db increase in level (which was your initial rough guess) would correspond approximately to a 0.75mv cartridge (20log(0.75/0.24)= 9.9db). Another thought altogether: Although the problem is most likely in the line stage section of the amp, I'm wondering if it might be noise coupling that involves the interconnect between phono stage and amp (assuming the interconnection is unbalanced; if it is balanced that is almost certainly not an issue). That may differ with the new amp compared to the old preamp + amp, due to differences in ac-related leakage paths. Are the ac power plugs of the phono stage and amp plugged into separate dedicated ac lines, or into separate outlets or separately filtered power conditioner outputs? If so, try plugging them into the same ac source (which will minimize differences in potential between the two chassis, which might otherwise result in extraneous inter-chassis noise currents flowing through the interconnect shields, in common with signal return currents). Also try unplugging the cdp completely, to make sure digital noise it may generate is not somehow coupling into the phono signal path. And consider whether there may be any nearby sources of rfi/emi, such as dimmer switches, that the new amp may be more sensitive to than its predecessor. Best regards, -- Al |
Thank you Doug, Kal and Al for your very informative replies. I think I have some ideas of were to head here. First let me make a few points of clarification. Kal, you are right, I looked it up, and the preamp stage in my integrated amp has 11 db more than the gain of my seperate preamp. So more gain may be a bad thing. Secondly,I have owned this integrated for over a year now, but due to personal reasons, have not listened to analog for about the last 8-9 months. As I recall, the last I listened to this setup regularly, the noise was more apparent than with my seperates, but not nearly as loud as the noise floor is now. Doug, the noise sounds like surface noise, steady hiss, easily audible from the listening chair when I turn the volume up to my normal listening levels (70-90 db). Also thanks for the JJ tube reco Doug, I may try that. Here are my current thoughts. First, my phono stage is the Walker Audio Signature. Walker recommends that the DC offset be adjusted monthly. When I had the rig running regularly, I checked it about every 3 months, no issues after the original adjustment. However, I have lost the manual, and can't recall how to adjust the DC offset using the supplied DMM. I sent Lloyd an e-mail yesterday and I'm awaiting a reply. I think I should check the DC offset before tube rolling. Second, once I have made sure the Walker phono preamp is in spec, if the issue still exists, change out the preamp tubes. As far as everyone has said, and I tend to agree, one of these two steps should solve my problem. I do not expect a $6500 integrated amp to be as quiet as $20K seperates, but I do remember it being enjoyable before, so I should be able to make it enjoyable again for much less than buying a new cartridge or phono stage. I'll keep you posted once I've heard Lloyd's reply. Thanks again for all of your help. Cheers, John BTW, all cabling is single ended, not balanced. |
"Kal, you are right, I looked it up, and the preamp stage in my integrated amp has 11 db more than the gain of my seperate preamp. So more gain may be a bad thing." Bingo. The key thing here. Your system in its new incarnation is amplifying the noise resulting from the slight mismatch (slightly too much gain) you have with the phono stage and cartridge. Get your gain on the phono stage into the 63 db area or get a cartridge with an output of .17 mV and your noise problem will disappear. Things will sound better as well. Getting the gain right will be much easier, less costly, and less time consuming than coming up with a new cartridge! |
Hdm, I respectfully disagree. Lowering the cartridge output will make things worse. It will result in the signal being lower relative to the level of noise that is being summed onto it, presumably in the preamp stages of the integrated amp. The lowered signal level will result in John setting the volume control at a higher setting than he is presently using, which will further boost the noise (assuming the noise is being introduced at a point in the system that is prior to the volume control, which appears to be the case). What is called signal-to-noise ratio (s/n or snr) is what is important, and what needs to be improved, either by raising the signal level prior to the point at which the noise is being introduced, or by reducing the amount of noise that is being introduced, or both. Too much gain or too little gain is only an issue if the volume control ends up being used near the top or bottom of its range, or if the input of a component is overloaded, neither of those situations being present here, or if the additional gain comes at the expense of degraded s/n ratio in the particular design (which may be the case here). Regards, -- Al |
Correction. The last paragraph of my previous post should have read: Too much gain is only an issue if the volume control ends up being used near the bottom of its range, or if the input of a component is overloaded, neither of those situations being present here, or if the additional gain comes at the expense of degraded s/n ratio in the particular design (which may be the case here). Regards, -- Al |
Al: In this case, lowering the cartridge output (or reducing the gain for that matter) would indeed result in John having to run the volume pot higher with phono, but as you point out in your last paragraph that is only an issue if he's running full out on the volume pot of the integrated and that is (and IMO won't be the case with a reduced gain of 3 db at the phono stage) not the case. IME, the noise or hiss that he describes is totally consistent with too much gain at the phono stage. In effect, the phono stage is either on the verge of being overloaded, or is being overloaded by the cartridge which has too much output for the amount of gain on tap. That manifests itself in the hiss which he's describing as well as a bit of hardening up in sound quality and a collapse of soundstage, particularly front to back. Not having enough gain can also create noise problems as well as totally squashing dynamics and giving the effect of listening through about 3 wet blankets. Particularly with low output MC's having outputs in the .15 to .35 mV range, dialing in the gain is critical. Get 3 db in either direction on the wrong side at the phonostage and you have problems, 4-5 db wrong or more and it's not worth listening to. And those problems cannot be rectified further on down the line than the phonostage. Changing tubes may indeed help. I don't have much experience with tubes to be candid. But I would expect that if that was to help that the tubes themselves might, in fact, be altering the overall gain that the phono stage is ultimately providing. I would be curious to hear what Lloyd Walker would recommend in this situation, but I do think it is a gain issue and that the phono stage has too much gain for the cartridge being used. |
Another factor to consider is that the .24 mV cartridge may in fact have an output slightly higher than this. Both of my 103R's, spec'd at .25 mV came with data sheets showing testing on the individual cartridges and outputs higher than .25 mV. The one that is closest at hand shows an output on one channel of .31 mV and .32 on the other. If this is the case with the OP's cartridge it would be an argument for possibly further reducing the gain in the phono stage. |
Hdm -- If the preamp section of the integrated amp is introducing a certain amount of noise into the signal path, how is reducing the signal level that is going into that amp going to help? Answer: It will not, it will make things worse, because the ratio of signal to noise will be degraded. The statement that the higher gain of the new amp is exacerbating noise resulting from a cartridge/phono stage mismatch makes no sense. The signal level, noise level, signal-to-noise ratio, and distortion level of what is being fed by the cartridge + phono stage into the new amp is the same as what was being fed into the prior preamp + amp. If the new amp provides higher gain than the prior preamp + amp, the volume control would be adjusted down correspondingly, with no difference in the resulting noise EXCEPT for the difference in s/n performance of the new amp compared to the prior preamp + amp. Regards, -- Al |
I'm sorry Kal, but I tend to agree with Al here. I'm already listening with the knob set at 2 o'clock on the VAC, I can't understand how lowering the cartridge voltage and/or phono stage gain would accomplish anything but make me turn the volume knob up to 4-5 o'clock. If the problem is the VAC preamp tubes this wouldn't seem to solve anything as far as I can understand. I've owned this cartridge/phono preamp combination for about 3 years now. It was dead quiet with my ARC Ref 3 preamp. It was slightly noiser when I switched to the VAC Avatar Super (possibly due to the extra 11 db of gain) which I've been using for the last 15 months or so. I didn't listen to any LP's for about a 8-9 month time frame, and now the noise floor is much higher with the same players. I still think it's probably either the DC offset in the phono stage or a bad tube in the preamp stage of the VAC. It's certainly easier and cheaper to fiddle with the phono preamp and the preamp tubes than to buy another cartridge or phono preamp. I guess as an answer to my original question, there is no table that shows how to convert cartridge output voltage in db gain, but you did show me a formula to use, and I thank you for that. Thanks again, and happy holidays to all. Cheers, John |
For anyone interested, here is an easy to use online voltage/dB gain calculator. |
Thank you Darkmoebius. Using this calculator, it looks like I would need a phono stage with 80 db of gain or a cartridge with a 1.25 mV output to match the 2.5 V output of my CDP in SPL. My guess was at least 10 db difference, but now I know that there is a 14 db difference, which explains the different settings on the volume control knob. Still awaiting Lloyd's reply. I guess with the holidays and all I shouldn't hold my breath. Cheers, John |
If you just want to match the output of the CD player to your phono, just use attenuators on the CD player inputs. It will be a lot easier. But it won't address your noise issue on the phono side. Plus a 1.2 mV cartridge with a phono stage delivering 80 db of gain is going to sound absolutely horrendous. |
Jmcgrogan2, there is something I don't understand about your total system gain. The Parsifal Encores are ~89dB efficient, so they aren't impossibly hard to drive. From your AudioAsylum system list(linked to in a power cable review you posted), you have the VAC Avatar SE integrated(25dB ultra-linear/23dB triode) and the Walker Signature phono preamp. If the Signature is like the Reference, it has adjustable gain from 40-66 dB. |
Actually, the specs on the Avatar SE indicate that its preamp section has a gain of 24db, and its power amp section has a gain of 25 dB ultra-linear and 23 dB triode mode. It also indicates "Maximum input signal: Infinite (attenuation precedes line stage)." So with the phono stage set for 66db gain, the 0.24mv cartridge output would result in 480mv into the preamp section, which certainly will not overload it (in addition to the quoted statement, additional evidence of that being the fact that it can handle the cdp cleanly). The 24db of available gain in the preamp section would boost the 480mv to 7.7 volts (into the power amp section) IF the volume control is turned all the way up. However, John indicated that the 2pm position provided a comfortable listening volume, as did the 10am position for the cdp. I don't see any problem in any of that; all of these numbers, and the volume control settings, seem very reasonable. I note, though, that the Avatar SE specs indicate 60W/channel, while John mentioned 80W/channel. John, can you clarify? Best regards, -- Al |
Kal, please note the word OR between 1.25 mV cartridge output and 80 db gain phono preamp in my previous post. Darkmoebius and Al, actually that link shows that my integrated amp is a VAC Avatar Super, NOT the SE version. Your specs are correct for the SE version, the Super is different. The only spec I can find on the Super is the 80 wpc output in ultra-liniear (no triode option). The Super does use different preamp tubes, different driver tubes, and different power tubes. So I don't think I can use the SE gain specs. My Walker Signature phono stage specs the same as the Reference, and is set for the max gain of 66 db. According to the calculator that Darkmoebius provided, my 0.24 mV cartridge with 66 db of gain outputs a signal of 0.48 V. That would explain the difference in my volume control knob positioning, since my CDP output is 2.5 V, over 5 times the output of the phono stage. Both signals pass through the same line stage and power stage, so I discounted the gain of the integrated amp. Does this help clarify things? Again, thanks for the help. Cheers, John |
Yeah, not a lot you can do about that, except as you've already concluded. 1.25mV cart or up, it seems. BTW, which cart are you currently using? And, I forgot say it before, but you've got an awesome system. Bet it's musical as all get-out! Here's the Avatar Super's manual(.pdf), which has the spec sheet on the 3rd to last page Have you ever had the chance to compare the Avatar Super's built in MM phono section with anything else? Obviously, at 42dB gain, it doesn't have enough for your current cart. |
Yes, there don't seem to be any published specs on the gain of the line stage or power amp section of the Avatar Super, but the manual does indicate, as with the SE, that "attenuation precedes line stage" and consequently there is no practical limit on input voltage. And if 2.5V from the cdp doesn't overload anything, 480mv from the phono stage certainly won't. BTW, John, if I may I thought I'd point out that Hdm, to whom you've addressed a couple of comments, is not Kal. Kal is Kr4. Best regards, -- Al |
Al, you are right, I misread Hdm's first reply when he said "I'm with Kal above", I read "I am Kal from above". I thought maybe Kal had two monikers. My mistake, I apologize to Kr4 and Hdm. No, 2.5V does not overload the VAC at all. Darkmoebius, thank you for the compliment on my system and yes it does sound pretty good, even after the downsizing of '08. Thanks also for the VAC manual link, but I do have the VAC manual, I just misplaced the Walker manual. The specs in the VAC Avatar Super manual do not give the line and amp section gain levels like the Avatar SE did. FWIW, the VAC replaced a stock ARC REF 3 preamp and a highly modified BAT VK-75SE by Bob Backert of RHB Dezigns running fully balanced. My cartridge is the low output version of the ZYX UNIverse S-SB, same as listed in my system at AA. I have tried the built in MM phono stage of the VAC using a cheap SUT with the same ZYX cartridge. The sound was pretty good, but not in the same league as the Walker phono stage. I would not expect the inboard phono stage of a $6500 integrated amp to beat a $6650 outboard phono stage though. I know, to be fair I probably should have tried the VAC with a better SUT, but I was nervous about spending big $$$ on a SUT without hearing it in my system first. Thanks again for that calculator, I saved it in my favorites. Thanks for all of your help too Al, you bring a wealth of knowledge to these forums that is very refreshing. I think I'll try to give Lloyd a phone call tommorrow. I still think I'm best to: a)check the DC offset in the Walker (no coupling caps, Lloyd believes the best cap is no cap). If that doesn't help then... b)change the line stage tubes in the VAC. Hopefully that will solve my problem, if not, then I will probably proceed to looking at higher output cartridges. Happy Holidays, John |
John, You should be aware that ZYX's output specs for their MC's is not based on the industry standard test record. I lost the reference (I think Nsgarch posted it here once), but from memory you need to multiply ZYX's stated output by ~1.4 to get a spec that's comparable to most other cartridge brands. For a .24mv UNIverse, the actual output using the industry standard test record would be around .35mv. FWIW... |
Thanks Doug, I don't know if that makes much difference though. It does increase the output voltage from my phono preamp from 0.48V to 0.58V, but that's a relatively small increase compared to the 2.5V that my CDP outputs. I have read about differences between the two industry standards (CBS and JVC???). I never really delved into it though because the difference seemed rather minor when you're considering the difference in a 0.24 mV output and a 1.25 mV output cartridge. If I do wind up looking for a new cartridge, I can't see considering one with less than a 1.0 mV output regardless of measuring standard. Cheers, John |
Hi Jmcgrogan2, I don't have time to run through some of the likely great responses you received on this thread. Holiday activities beckon (happy holidays to all). In case some of the above advice has you stumped, , I dleve into this issue in a thread on my forum (in the Electronics forum in the Setup and Tweaks section): http://www.galibierdesign.com/phpbb/viewtopic.php?f=13&t=35. There, you'll find a real-world example showing how to use an online dB calculator that I link to. The calculator allows you to go both ways - from dB to step-up ratio as well as the reverse. Hopefully, this isn't redundant, and if it is ... accept my apologies. Cheers, Thom @ Galibier |
Hi Jmcgrogan2, Yes, I hate to post redundant information. Frequently, calculations like this need a working example, and hence the cross-link. Now that I had the opportunity to go through the thread, it looks as if we have everything covered. The posters' names led me to expect this to be the case. As mentioned above, as well as in my forum thread, sometimes the numbers will show everything to be hunky-dory and yet the system sounds like utter drek - typically due to circuit noise somewhere in the amplification chain. Sometimes you have a noisy gain stage you can't bypass, and other times you have barely enough gain - a situation where a step-up transformer might bail you out - with some "noise free" gain in the first stage. The numbers (as usual) are only a starting point, but are(as usual) a useful one. Happy holidays to all ... Cheers, Thom @ Galibier |
Thanks to all for all of your help. The problem is solved, though I'm not exactly sure what the problem was, since I made several changes, but my guess would be the problem was using unshielded interconnects. First, I finally got in touch with Lloyd, and checked the DC offset in my Walker phono stage, it checked out fine. Then, I noticed that I had moved the turntable motor to adjust the belt drive higher on the platter, so I put the motor back into it's original position at the very bottom of the platter. Finally, I changed the 2 meter interconnects from my Walker Signature phono stage to my VAC integrated amp from unshielded XLO Signature 3 to shielded Von Gaylord Chinchilla, and Viola!! The noise floor is gone. Licorice Pizza sounds wonderful again, I'm spinning Jazz at the Pawnshop right now. I've notice that the volume control knob is lower now, control knob at 11 o'clock. This I can't explain, except that maybe I was trying to turn the volume up louder to hear the music, but in doing so, it also raised the noise floor too. Anyway, many thanks to all again for all of your help. A happy and healthy new year to all! Cheers, John |
Congratulations John. Good to hear the noise is gone. I had serious hum issues with my system when I used the Jade Hybrid IC (unshielded) from Counterpoint head amp to Aria preamp. I quickly learned that only a shielded cable would work here. But so many ICs were destructive to the musicality of the system. I too tried a Chinchilla IC and it was much better than the MIT 330, but still I was disappointed. Finally, I ended up trying the awesome Silent Source Silver Signature sent to me from Lloyd Walker. The hum was gone and the sonic result was VERY impressive. I got a little more upper detail but a slight loss to the spatial attributes that I had with the Jade. Ultimately JD tweaked his IC for me as he grounded the carbon-fiber jacket to the casing on the RCA connector on one end. That did the trick with the hum issue. The Jade IC was now usable. Ultimately I kept the SS cable in this link as the little more detail was attractive. But jumping to the new Jade Ref IC changed everything. Wow! I hope you get a chance to hear this one day. John |
Hello John, Thanks for the information. I'd love to hear the new Reference, but my life has changed quite a bit, and ultra high end hi-fi is no longer a part of it. I looked at the SSSS, but it was out of my price range now. I use a 2 meter run from my Walker phono stage to VAC integrated amp. A 2 meter run of Chinchilla was $550, I just traded my 2 meter XLO Sig 3 for it straight up. So obviously the Jade Reference is out of the question. I won't rule it out in the future, but right now, I can't foresee ever spending big $$$ on any audio stuff. Speaking of Jade, they sure are hard to sell on the used market. I've had no luck selling my 2 meter balanced pair of Hybrid Gold for over a year now....even at a 60% loss. I guess I should just tear out the conductors and sell the gold. Thanks again for your input, as always, it's very valuable. Cheers, John |
