Being a newbie to audio stuff, I'd like to hear your opinion whether should I replace my preamp. To get to a reasonable loud volume, my preamp has to be at around 1PM to 2PM position for most of CD and music DVD. Should I get another preamp with higher gain? If so how much more? Why don't the manufacturers make higher gain? Probably some sonic compromise with high gain active preamp?
Any suggestions are welcomed.
Preamp: Conrad Johnson PV-10AL, gain 18 dB. Amp: Shuguang S845MK (tube amp 848) Speakers: Tekton Lore (Sensitivity 98 dB) Room: 25 x 17 x 8'
1 to 2 o'clock is just fine, in fact it may be the best postition to get the maximum performance out of your pre-amps volume control.
26db was common when vinyl was king and low output phono pre-amps were used. Amps also had lower sensitivity. With the digital outputs are high (anywhere from 2v the standart I think to 6v), the pre-amp really no longer needs to add much if any gain at all. In fact many digital sources need no gain what so ever from the pre-amp, more probably some attenuation. Note all of the folks complaining that their volume is to high if the VC is higher than 8 or 9 o'clock. In a way you are blessed. :-)
A lot of CJ stuff inverts polarity and since you said you were relatively new to high end audio, you might double check to see if you have the proper polarity.
My guess with your 98 dB efficient speakers and your normal 18 dB preamp is that your power amp has voltage gain on the low side, probably to reduce tube noise coming from your speakers. As long as you are not getting too much noise from your system you should be fine with your preamp.
I read several years ago from a well regarded designer that the "sweet spot" is between 12:00-3:00 o'clock on the dial. This is where you are achieving near zero attenuation of the signal and getting the maximum benefit from the preamp. Mine has 20db and sounds superb!
If you like what you are hearing I would not change. Your next step may not be for the better. Listen first!
My CJ preamp is inverted phase. I made a mistake but corrected. Frankly I could not tell the different between correct and incorrect phase. No volume gain or loss after correcting phase. Good call Montytx.
Thank you all. Sound like I have been worried out of nothing.
Initially I hooked up the amps with a passive preamp Lightspeed Attenuator and the volume was low, dialing around 2:00 to 4:00 to have reasonable sound. Figured that active preamp would help, swapped out to CJ and it did. The volume knob is now at 1:00 to 2:00
The amp sensitivity is 4V. Is it low or high? I have no idea what 4 Volts really mean in term of sonic amplification.
Tom6897, I will strongly disagree with designer's statement weather he/she well regarded or not simply because zero attenuation can ONLY be achieved at volume knob turned all the way clockwise or 'up'. Other than that, preamp will always have fixed gain of certain magnitude. There are variable gain preamps, but neither of the posters I believe have those so far in this discussion. I also know that some of the units built to have a smooth gain control(there indeed you can gain a point of 0db gain) instead of volume control, but with great risk of loosing stability of the circuit.
I also disclaim to happen to be an ordinary techie for live sound and recording studios also having an incomplete Electrical Engineering from college drop-out simply because I'm more of the craft's man rather than scientific.
Nguyen 878, 4v sensitivity is quite low which I think was implied by Marakantz in his first post. A sensitivity between .5v and 1.5v is much more common and fairly high.
I have the Lightspeed and use it with an amp that is not very sensitive, around 3V or so. You will have to go further around the dial to achieve adequate SPL levels but that really isn't a problem. If it were the opposite and you had very little flexibility with the switch then I would be more concerned.
Marakanetz- I will defer to your expertise/training.
I will try to find the reference. (It may have been Roger Sanders or Saul Marantz)???
Anyway, It would make sense that as you approach the limit of the volume dial, (lets say it goes from 7:00-5:00 o'clock, Between 12 & 3 quite loud by now!), you are approaching zero gain and not many can let their systems play at full steam without strain or damage to ears or equipment as you mention. The preamp needs to get out of first and second gear to hit it stride. I think I was left to presume that the volume control would sound best when operating in the latter part of the dial.
I have very little knowledge of EE or Audio design other than being a user of such items. I may have completely misunderstood the conversation. Although, I know I have read comments from others stating nearly the same in that their system sounded best with the volume on the pre turned more clockwise. Where that is on any individual dial is another matter.
Do you kind of get what I am saying?... Mine has 1db detents but will spin forever.
Nguyen787. A very good quote from god! Cheers George
"Nelson Pass, We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more. Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up. Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control. What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection. And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."
Coming into this late but the first thing you need to do is differentiate between gain and attenuation. Gain is fixed at 18dB and attenuation is variable.
The 800 pound gorilla in the corner is lumping gain and attenuation into an arbitrary setting of a dial without reference.
A decade ago I measured some flavor of the day 10K pot to relate the gain to rotation in both dB and voltage ratio. By no means is this a standard, it is just a statistical sample of one but hopefully it illustrates the issue. (remember these values are for attenuation only)
(Apologies the formatting doesn't hold it is a three column table)
Rotation Db attenuation voltage ratio 7.00.00 AM 0ff NA 8.00.00 AM -50.798242 400 9.00.00 AM -37.669889 78.78787879 10.00.00 AM -28.995433 28.10810811 11.00.00 AM -21.98006 12.14953271 12.00.00 PM -13.492213 4.727272727 1.00.00 PM -8.299467 2.524271845 2.00.00 PM -5.2231697 1.818181818 3.00.00 PM -2.7932399 1.382978723 4.00.00 PM -0.7861947 1.06122449 5.00.00 PM -0 1
This is where it gets fuzzy without the actual numbers of "your" attenuator wrt "clock rotation" If we make the grand leap and assume all attenuators have this particular taper, it becomes easy.
With 18dB of gain, you would have overall unity gain between 11 and 12. (again assuming you have the attenuator I measured installed) This means if you listen at 1-2 the concept of a passive is really not an option since you would actually need gain. (again look back at the assumptions in this story)
Unfortunately there is no bureau of standards for the audio industry so you have either have to roll with it or put in the time to learn some of the basics to make an informed decision.
My gut feel is adding more gain to simply add more attenuation is not the way to go.
It is also important to realize I have only addresses the gain aspect of this situation. There are two other key points that play a more important role in system synergy which are impedance matching and headroom. Unfortunately neither of them can be directly read by the dial rotation value.
Hi Dave, Thank for sharing the detail of your measurement. I swapped the active preamp CJ 18 dB gain with a passive Lightspeed Attenuator, and I found that most of CDs, I have to push the volume knob to 3 - 5 PM (MAX == 5 PM) to obtain the desirable volume. The low sensitivity amp, 4 V, seems to be an issue. Bought this amp without understanding the input sensitivity spec...
What is attenuation voltage ratio and what does it tell us?
Some amps have high input gain because they are designed to be used with passive preamps which have no gain at all. I can tell you that CJ amps need a preamp with relatively high gain to properly drive them. 18db of gain is higher than average.
I have owned some CJ preamps and they do invert phase. I corrected the phase by reversing the wiring to the speaker binding posts. I couldn't tell any difference myself. It could be because some recordings are already recorded with inverted phase.
'between 3-5pm' are just arbitrary numbers and without seeing an actual attenuation plot vs. knob rotation of the LDR, you really don't know that much. Also seeing an input and output impedance plot of the device WRT attenuation would be needed to see if any red flags go up.
Nguyen hi, just looking at the factory specs for your 845 amps they are very sensitive at There is something not right with your system as Red Book standard for cdp is 2v out and most are higher than this so your Lightspeed should be below half way. What is your cd or source (has it been modded?) please give model no's
Nguyen hi, just looking at the factory specs for your 845 amps they are very sensitive at less than 1v for full output. There is something not right with your system as Red Book standard for cdp is 2v out and most are higher than this so your Lightspeed should be below half way. What is your cd or source (has it been modded?) please give model no's
The amp spec is confusing because the website and the manual state two different spec:
Grant Fidelity website Output power: 25w Response: 10Hz to 30KHz SNR: ≥85dB THD: ≤1.0% Input sensitivity: ≤1.0V Output impedance: 4Ω, 8Ω Tubes: Standard Shuguang 845B×1, 300B-98 x 1, 6SN7GT ×1 per amp
Manual: Input impedance: 100kohm Input Power Voltage: 4.0V Output Power：28W Output impedance: 4、8Ω Frequency Response: 10Hz-30KHz THD: less than 1.5% S/N Ratio：85dB Power supply：AC 115V 60Hz Power consumption: 170w per channel
The discrepancy between 1V sensitivity (for full rated power output) and 4V is 12dB -- huge! Grant Fidelity and Shuguang really need to get in sync on that one -- it's very confusing/misleading, on such an important spec that can make or break a system.
A 25Watt amp with 4V sensitivity WAY on the low side -- I don't know what the hell they intended that amp to be used with. If would be great for high-output pro sources > 4V. The issues with a typical 2V hifi digital source are one thing; a low-output MC cartridge would be almost impossible to step up enough to coax a satisfying output from those amps.
As a comparison, the Rogue Apollo KT90/KT120 tube amps have a sensitivity of 1V for 250 Watts output. That's 22dB more gain than the Shuguang 845! Yep, they're on the high side of gain.
Another example on the (very) high side: the old Eico HF-87 amp (runs a quad of EL34; cathode bias; 35W/ch), which was spec'd (according to the assembly manual) at 0.34V for +3dB over full output (70 Watts). That's a whopping 26dB over the Shuguangs!
Both the Eico and the Rogue use a 12AX7 input tube...
my 845 amp is very high, 200mv. I wonder if I am losing any performance since my volume is at 9pm for normal listening. it sure sounds good though despite the touchy volume control. the manufacturer said I could swap out two resistors to make it less sensitive, which might do.
Nguyen787, A doubling (2x) in voltage is (almost exactly) 6dB. A 10x in voltage is exactly 20dB. So for example if you have a 20x factor in gain then you could say: 20x = 2x * 10x = 6dB + 20dB = 26dB
Note that dB values are always added together (since dB values are really exponents), while their corresponding multiplication factors are multiplied together.
When comparing power: a 2x in power is approximately 3dB, while 10x is exactly 10dB.
The precise formula for converting Voltage ratios to dB is: dB = 20 * log(V1/V2), where V1 and V2 are two different voltages, and the log function is base-10. Note that if you flip V2/V1, you get the same magnitude dB value but with a different sign. For power ratios, it's: dB = 10 * log(P1/P2), where P1 and P2 are two different powers in the same unit (e.g. Watts).
So in my example with the Apollos, you start out by comparing Voltages: 20 * log(4V/1V) = 12.0412 dB
Thus, the 4V amp will require a 12dB higher input signal to achieve its "full output" (the typical definition of amplifier sensitivity), versus the 1V amp. Next we have to compare the difference in "full output" between the amps:
10 * log(250Watts / 25 Watts) = 10.0 dB
So the amp that puts out 250W will be 10 dB above the 25W amp when both are at full output. Add the two together: 12 + 10 = 22dB difference in amp gain.
An input sensitivity for an amp of 1v is quite normal as nearly every amp I've seen on the market has been .5v to 2v for max rated rated output (to clip/distort). An input sensitivity of 4v is wrong/bad and I would call the amp broken or seriously badly designed. You have a problem ask the manufacture to give you a fix to make the amp/s 1 to 2 volt input sensitivity, as the standard is.
Nguyen787 Here is a way out there thought on your problem. You say your running the amp on 115v mains? It is possible that this amp/s are set up for 220-240v mains operation, this could? drop your gain/input sensitivity.
Another thought, your Oppo cdp has a remote volume control, is it at full output level? As it may default to 1v or less when powered up and you need to bring it up on the remote to full 2v output.
More on the Oppo's stereo only output, are you getting the siganl from the FL and FR outputs on the back to the Lightspeed?
Also taken from the manual are you setup it the programing for this way. "4. Output Volume: Allows you to enable or disable the analog volume controls (also known as Variable Audio). The available options are: �� Variable – Enables the analog volume control. Use the VOL+/- buttons on the remote to increase/decrease the analog audio output level (the maximum is 100). �� Fixed – Disables the analog volume control. The VOL+/- buttons on the remote will no longer affect the analog audio output, and the volume level is fixed to 100."
And then this also "For the stereo outputs, if the audio system you are connecting to does not have surround speakers, set the Down Mix option in the Setup Menu to Stereo. If the audio system has surround speakers and Dolby Pro Logic or other surround audio decoding capabilities, set the down mix mode to “LT/RT”. (For more information, refer to “Down Mix Mode” on page 68)."
Checked and corrected Oppo setting per suggestions, do not see any different on sound level. Volume --> fixed at 100%.
George raised an interesting concern - main voltage. The amp power outlet plug written "115 V, 50/60 Hz" seems OK for US AC electricity. I am wondering Shuguang started out design as for 230 V and made shortcut to convert to 115 V for North America market, compromised the amp voltage? I really don't know, just speculating. I did send my question to Grant Fidelity about the spect mismatch, but have not heard back from them yet.
You know what's completely screwy? I just checked the GF product page again, and they're recommending the matching S200MK preamp -- which is spec'd at a MAXIMUM output voltage of 3V. So you can't get full output power from these amps without 4V from your preamp, which the suggested S200MK can't supply. Madness!
Jeez, what a s**t fight this has turned out to be, most any active preamp is going to have trouble with this as you have found out with your Conrad Johnson PV-10AL and all passive preamps as well. To make the input of a power amp 4v sensitivity is totaly wrong there has to be something else amiss somewhere either with the amount of output comming from the cdp or the amp it's self which needs to be changed to 1-2v sensitivity. To boot I just saw you have 98db efficient speaker, if you had normal speaker 88-92db you would get nothing but a whisper comming out at full volume
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