Impedance Mismatch / To much gain, need education

Gaara

Alright I need an education, either here or links to sites with the proper info. I believe I have a major mismatch in my system and I am wondering how it happened. The issue is with my 2 channel system, a Jolida JD-100 (tube cdp) to a Modwright SWL 9.0SE (tube pre) to a Earthquake Cinenova (big frickin amp) and a Gallo SA Amp (second voice coil amp) all powering my Gallo Ref 3.1s. I had the same problem when I had the LSi9s in the system. I also use a Pioneer Elite 47ai and a B&K Ref 50 for surround duty.

OK enough background, the issue is that I seem to have way to much gain and to little control over the sound. When watching movies with the Ref 50 I usually listen around -20db, sometimes pushing to -10db and -5db when demoing. Now that is all fine and dandy, but not so much with the two channel system. The modwright is a analog volume control, with a range from about 7:30 to about 4:30. When I first got it I used to hover around 8:30 and 9:00 was about all I could take. Since then I got a set of 10db Rothwell Attenuators, and replaced the 12ax7 tubes with some nice GE 3 Mica blackplate 5751 tubes, which are supposed to have a gain factor of 70 instead of 100. Well this helped things out, but not enough. Currently I listen around 9:00-9:30 and about 10:30 is all I can handle. The loudest I have ever played it is about 11:00 which was when I was doing cleaning on the other side of the house. See specs below for more detail:

Jolida JD-100
Line Output Voltage > 2V
Output Impedance: 47 Kohms
Using 5751 (gain factor 70) instead of 12AX7 (gain factor 100)

Rothwell 10db Attenuators

Modwright SWL 9.0SE
Gain: ~15dB.
Input Impedance: 50 Kohms.
Output Impedance: ~ 600 ohms.

Earthquake Cinenova
Input Impedance 27 Kohms
Input Sensitivity 1.9 Volts
Gain?

Ref 50
Voltage 2 V in 1.5 out (0db)
Max out 3 V
Input Imp 50 Kohms
Output Imp 221 Ohms

Ok what I want to know is...everything. I know basics about impedance but not how they interact, like how a 600ohm impedance works with a 27kohm impedance. I want to know about gain and how much you need, how much is to much, and how to reduce it. I want to know about voltage, how that equates to gain, how it interacts with impedance, all of that. I want to know why a 600ohm load sounds so much louder then a 200ohm load. I want to know how this mismatch happened and how it can be prevented, and if I should have seen it coming looking at the specs. I want to understand impedance, gain, and voltage.

Whatever info, insight, or links that can be given would be greatly appreciated.

Jared

jdhdiggs

You could try som 12au7's to reduce the gain further or add in more line level attenuation. Gain is gain and anyway you can reduce it will help. I am very suprised that you have more than 10dB of gain difference. I thought my setup was bad at 9dB.

Gaara

A few more side notes, I also have the 47ai hooked into the Modwright, with the same issue. I currently listen at around 8:30 to my DVD-As and SACDs, 9:00 is to loud.

Is there a rule for impedance matching that I am not aware of? I remember hearing about a ratio 1:10 but can't find info on it now. For example with my PC system the sound card is 150ohms output, and my gainclone is 22,000 ohms input. The maker of my passive pre said a value of 2500 ohms would be best in this situation, giving a 1:15 and a 1:9 ratio.

jdhdiggs,

I didn't realize that a 12au7 could be used in a 12ax7 circuit, I will have to look into these. As for attenuation, this was what I have been researching for a while, and may end up with a high end attenuator like a EVS Ultimate Attenuator. I am just not sure how much to go, since 10db made a difference but not as much as I would hope for. Maybe 20db would be better. I also emailed the maker of the pre to see if he has any insight, or any mod he can do to fix this.

Jared

jdhdiggs

An apperant doubling of volume is 10dB. You could check that with your linear pre with how much you need to turn it up. Before buying really expensive attenuaters, buy some cheap ones. Try a 3, 6, 9 and 2 1dB attenuaters and test out combos and then you can buy the good ones of the same total value.

zombie boy 2000

I know this is an old thread... but I have a quick question, albeit a somewhat stupid one.

Spec-wise for a preamp, what is considered high gain? (15db? 20db?)
Conversely, what's on the low-end?

bknauss

jdhdiggs wrote:

An apperant doubling of volume is 10dB.

Maybe I'm misreading this, but doubling volume (power) is +3dB. 10dB is a 10x increase in power.

madmax

Doubling power is 3db (I think). 3db is just noticable as far as perceived volume goes.

cbl117

bknauss wrote:

Maybe I'm misreading this, but doubling volume (power) is +3dB. 10dB is a 10x increase in power.

yessir you are correct. for every 3dB its an increase/decrease by a factor of 2. +3dB would be 2x the power, +6dB would be 4x the power, +9dB is 8x the power, etc...

John K.

ZB, since you have a "passive preamp" which has no gain at all and therefore isn't literally a "preamp", it's unclear why the preamp gain spec is the subject. Nevertheless, below about 10dB for preamp line stage gain can be considered low and above about 20dB can be considered high(phono stage gain runs between about 40dB to 60dB). Just in case amplifier gain was actually your interest, it typically falls within the 25-30dB range.

Since a doubling of voltage is a 6dB change(the formula is 20log(V1/V2), and since the log of 2 is about 0.3, 20 times that results in a 6dB gain), it can be seen that a preamp with a 12dB maximum gain could increase the input voltage by about 4 times and an amplifier with 30dB of gain could increase input voltage about 32 times.

The formula for power change in contrast is 10log(P1/P2), so a doubling of power is only a 3dB change, which is a noticeable, but not major change in loudness. It's said that to be subjectively "twice as loud"(whatever that means)an increase of 10dB, which requires 10 times the power(the log of 10 is 1)is required.

F1nut

ZB, since you have a "passive preamp" which has no gain at all and therefore isn't literally a "preamp", it's unclear why the preamp gain spec is the subject.

HUH???

zombie boy 2000

John K. wrote:

ZB, since you have a "passive preamp" which has no gain at all and therefore isn't literally a "preamp", it's unclear why the preamp gain spec is the subject.

Understood.... passive volume control... tomato... potato. Let's call it a passive pre, if you wish. More than a few people call it a passive preamp, and since I like the ring of it, I'll do so myself.

However, my question is not in regards to the passive unit I own, but directed toward any future active preamp I might possess. The high sensitivity of the SM-70 Pro greatly limits the number of preamps I can even consider, so the gain specs of a preamp unit are very key in making such a decision.

Thanks for the info...

tryrrthg

I don't know how sensitive your Monarchy amp is, but my McCormack amp was designed to be used with Steve McCormack's passive pre's so it has pretty high sensitivity also. I started out with an Audio Research preamp that had 18db of gain and it was WAY too much. I couldn't get to 9 o'clock on the volume dial before it was too loud. Obviously the McCormack TLC-1 passive pre I went to next was perfect. But then I moved to the Musical Fidelity that I have now (12db gain) and no issues, plenty of volume control.

I'd say (for once) I agree with JohnK. 18db+ is probably getting pretty high. 10-12 and below is about average.

zombie boy 2000

Thanks Troy... that's exactly what I was looking for:)

edit: I tried looking up the specs on your amp in order to do a comparo.... was unsucessful. Would you happen to have this info handy?

Midnite Mick

Okay, I need help here.

Why is this an issue. If you have too much gain does it increase the noise floor? I too have the Modwright and yes it is very loud. The volume nob never goes past the 10:00 oclock position for me.

Thanks,
Mike

tryrrthg

zombie boy 2000 wrote:

Thanks Troy... that's exactly what I was looking for:)

edit: I tried looking up the specs on your amp in order to do a comparo.... was unsucessful. Would you happen to have this info handy?

here is the info for the DNA 1, which is probably similar.

http://www.stereophile.com/amplificationreviews/520/index3.html

Sami

Midnite Mick wrote:

Why is this an issue.

I would suspect it has to do with the ability to control volume. If you have too much gain then it makes it harder to adjust the volume, fine tune it to "right where I want it". F.e. one click on the volume knob only increases volume by .5dB, not 1dB.

zombie boy 2000

Sami --

It's also my understanding that too much gain coupled with a highly sensitive amp will lead to distortion at the same listening levels where it wouldn't with a preamp with less gain, but I may be way misinformed here....
Source should also be taken into account, but since Redbook output voltage rarely exceeds 2.0v, it is generally a non-issue... again I may be way off base here.

bknauss

cbl117 wrote:

yessir you are correct. for every 3dB its an increase/decrease by a factor of 2. +3dB would be 2x the power, +6dB would be 4x the power, +9dB is 8x the power, etc...

I know I am correct... I'm AAALLLLLWWWAAAYYSSS correct
Anyway, I was unsure if he was saying 10dB was doubling the volume/power, which would have been incorrect. Didn't want to jump down his throat if it was a misinterpretation by me.

organ

I don't think you really have a mismatch. Generally, you'd want the amp's input imp to be higher than the pre's output imp.
My system is also very loud at the 9 o' clock position. 10 is the highest I dare to go.
DON'T swap a 12AU7 for an X7. If you want lower gain, use a 5751. I doubt this will do anything because I don't think your pre-amp is adding gain at the 9 o clock setting.

Gaara

Wow I like to start threads and forget about them, my b.

I talked to the manufacturer Dan Wright back and forth for about 12 emails, very helpful and informative by the way, and he said if I wanted to send it to him to turn down the gain it would ruin the sound. I took jdhdiggs advice and tried some different attenuators, and found that around -12d b works quite well. I wound up ordering some stepped attenuator from Endler Audio which fit the bill nicely. I put these in line from my CDP to my Pre and left then at -12db. These also double as a nice cheap passive pre if I ever need a simple preamp for whatever reason, but I am getting ahead of myself.

Well while I was waiting for my stepped attenuators I orderd a Luminous Audio Axiom to use in my pc system. I ended up throwing that in the system and loved the sound, plus I had more flexibility. I tried comparing it to the SWL and found slight differences, but not nearly enough to justify keeping it ($2200 v $150) so I boxed it up. I then compared the Axiom to my Ref 50 in direct mode, and found minor differences, but not enough to buy another Axiom, so that went into the pc system and I kept the Jolida running through my Ref 50.

Well a few months went by and I listened to my music less and less. Actually I used the system overall less and less, and started to get discouraged that I spent all this money and never use the system. If your wondering what happened to the endlers they sat in a box in my basement for over a month, never even opened. He could have sent me two rocks and I would have never known. So I tried to figure out what was wrong with my system and then it hit me, I started listening to music less soon after I switched to the Ref 50 instead of my Modwright. So I unboxed the Modwright and hooked it up, and then hooked the Ref 50 to the HT/Bypass switch on the Modwright. That way, after I level calibrated, I could hit the switch and instantly change between the two pres. Well I preferred the Modwright but not by a lot, again I was disappointed. Well I went to have dinner and came back, and realized I forgot to turn the Modwright off. I did a comparison and right off the bat big difference. I was listening to the soundtrack of Silent Hill 3 (pretty good disc, amazing game), I think the 12th song with singing and piano and then the drum picks up. Anyways it just had more life with the Modwright, the voice seemed to come from within my room, the drum had punch and was quick, and the piano sounded like it was a few feet behind the speakers. I tried a few more tracks and more of the same. The music just sorta came alive, voices were more natural, drums had speed and punch to them, and everything was more coherent.

In the end it seems that the Modwright needs a good deal of time to warm up. I compared the earlier tests for fifteen to twenty minutes each time, right when the thing kicked on. I assume it is something having to do with the tubes but this one really came together after around half an hour of being on. I now switch it on half an hour before serious listening. And the endlers came out of the box and now are between my Jolida and my Modwright at -12db. This lets me play normally around 10 oclock, and my loudest around 12.

Organ,

I currently use GE 3 Mica blackplate 5751 tubes for the Jolida. It made a slight difference in where I could play it, but the sound quality improved a good deal over the stock tubes. I never thought of it but your right, I probably never even reach unity gain with this unit.

Midnite Mick,

Sami nailed one of my problems, that without the attenuators one push of the volume up button and it was to loud. Being able to fine tune the sound is a big thing for me, and with this unit it was difficult to do because I listen so low. For me noise floor is not an issue, but I was worried about things not coming together. I personally find that everything clicks at about 9 oclock with this unit, so many times I would listen louder then I wanted just so everything came together.

Zombie,

I am under the same impression as well. Higher input impedance works well with higher output impedance sources, but is more susceptible to noise.

In the end I am currently looking into passives, as I obviously don't need any gain whatsoever for 2-channel listening. Currently I have a Promitheus Audio TVC on order, I decided on a TVC because it is my understanding that they are the best sounding at lower volumes, and as you go higher they sound worse. Regular pres on the other hand sound best at less attenuation, and sound worse as the volume decreases. We shall see, as I now have stepped attenuators, a potentiometer pre, and soon a TVC pre. Good times.

Jared