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Audio Research SP6 + Denon DL160 - gain problem

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Audio Research SP6 + Denon DL160 - gain problem

Postby Spa317 » 24 Mar 2011 13:30

I have a Rega Planar 3 with a Denon DL160, which is a high output MC and supposed to work fine into MM phono's. I just got an Audio Research SP6 preamp, which is supposed to have a good MM phono stage. The Audio Research has an adjustable gain switch on the rear, with a choice of High or Low output.
My problem is, using the High switch, my records sound too bright, but with plenty of volume and gain.
When I switch to the Low setting on the preamp, the sound is much better...but then I dont have enough volume/gain.
Any suggestions or solutions? I dont really want to ditch the Denon DL160, as it is a good match for my Planar 3.
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Postby pivot » 24 Mar 2011 15:51

"The Audio Research has an adjustable gain switch on the rear, with a choice of High or Low output. "

To see if I remember right I looked at a schematic here:
http://www.arcdb.ws/SP6/ARC_SP6_schematic1.gif

The rear panel switch ony impacts the gain of the line stages and should not impact the phono equalization.

Do you have the manual for the SP6? Which 'flavor' of Sp6 do you have? The original or one of the revisions?
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Postby EdAInWestOC » 24 Mar 2011 16:02

The Denon DL-160 is rated to produce 1.6mv and that's not very high for a standard MM/MI cartridge (I know its a HOMC but the stage is designed for MM/MI cartridges).

You need a phono preamp with 44db of gain to produce the nominal 250mv line level output. I don't know what the gain of the SP6 is but there are quite a few MM/MI preamps with gain figures in the 33-35db range. Even if the SP6 has the standard 40db MM/MI preamp gain that still only produces 160mv. A tad low.

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Postby pivot » 24 Mar 2011 16:55

EdAInWestOC wrote:The Denon DL-160 is rated to produce 1.6mv and that's not very high for a standard MM/MI cartridge (I know its a HOMC but the stage is designed for MM/MI cartridges).



The 110/160 really puts out closer to 2.4 mv. A friend uses a 110 with a 36 db gain tube pre just fine.

The Specs for SP-6 and various flavors are here:
http://www.arcdb.ws/SP6/SP6.html

Phono stage gain is spec'ed at 34 dB while overall gain is 60 dB, -10 dB with the gain switch set to "low".

It is fairly quiet as 12AX7 based preamps go (based on memory)and the 2.4 mV cartridge should work with the high gain setting assuming compatablity with the amps driver stage. (what amp is the OP using??)

The odd thing is that the SP6 sounds so different with the gain setting to high. It should not.
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Postby EdAInWestOC » 24 Mar 2011 17:55

pivot wrote:
EdAInWestOC wrote:The Denon DL-160 is rated to produce 1.6mv and that's not very high for a standard MM/MI cartridge (I know its a HOMC but the stage is designed for MM/MI cartridges).



The 110/160 really puts out closer to 2.4 mv. A friend uses a 110 with a 36 db gain tube pre just fine.

The Specs for SP-6 and various flavors are here:
http://www.arcdb.ws/SP6/SP6.html

Phono stage gain is spec'ed at 34 dB while overall gain is 60 dB, -10 dB with the gain switch set to "low".

It is fairly quiet as 12AX7 based preamps go (based on memory)and the 2.4 mV cartridge should work with the high gain setting assuming compatablity with the amps driver stage. (what amp is the OP using??)

The odd thing is that the SP6 sounds so different with the gain setting to high. It should not.

Kevin,
Given that the DL-160 is running at about 2.4mv and the SP6's MM phono stage has 34db of gain (plus 26db at the line stage), the resulting output from the phono stage would be 120.28mv. The 26db of gain in the line stage is certainly helpful but the output of 120 mv is still a bit low.

The different sonic characteristics is interesting. I wonder if this particular SP-6 has been used in high gain before or recently. This could be a problem in the SP6 and not a problem with the 160 itself.

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Postby pivot » 24 Mar 2011 18:54

The OP does report he has enouph volumn in "high" (really "high" is normal)

The questions to answer:

1) Is the SP6 operating to, or near, stock specs? It is a 30 year old piece of grear and they run hot and with some of the components near their limits.

a) Any mods on this SP6? (does the "gain" switch still perform the function as new?

b) What tubes?

2) What amp is the SP6 connecting to?

a) Is the the amp's input impedance presenting too low a load to the output of the SP6? 12AX7 cathode follower circuits are sensitive to loading, could roll off bass if impedance is too low. (I believe the gain switch changes the impedance the output "sees")

b) Could the output of the SP6 be overload/overloading the driver circuit of the amp? (unlikely but....)

c) Is the amp working to spec?
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Postby Spa317 » 24 Mar 2011 22:10

Thanks guys. My model is the SP6B. I dont know much about its history (bought it used), so I cant tell re any mods, repairs or being in original spec condition.
Tubes are JJ's, but I have just ordered some Full Music 12AX7's to try in the phono.
However, the line stage sounds great in the "Low" setting, nice and smooth but still with plenty of gain. When I switch to the "High" setting, it sounds bright and slightly hard sounding in comparison on BOTH the phono and line stages.

My power amps are a pair of Xindak XA8800MNE Class A monoblocks. Their input sensitivity is 1.7V.
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Postby pivot » 25 Mar 2011 14:33

Output impedance spec for the SP-6B

"SP6-B: Less than 500 ohms main output, 1000 ohms tape output. Recommended minimum load for maximum audio quality, 50 kOhms and 250 pF maximum capacitance."

The specification we need on the amp is the input impedance. Sensitivity does not tell us that.

My searching around on the web does not yield the numbers.

I find it interesting I can "Google-up" more complete specifcations on a 30 year old unit them one that's current production.

My thinking, pure guess, is the input impedance on the amp is well below 50 Kohms (many soild state amps are) and you are getting a low frequency roll off that makes things sound bright. Switch in the "low gain" and the line section is loaded down with more resistance and is closer to ideal.

My suggestion is to find out the input impedance of your amps. I would also connect the SP6 to a know good amp with 50K ohm or greater input impedance and see if you hear the same frequency issues with "high" and "low" gain.

I recall we used to connect up the SP6 to an ARC D52 sold state amp which specs a 30k ohm input impedance and things sounded fine. I'd place a small bet that your amps are well below that spec.
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Postby Spa317 » 25 Mar 2011 15:01

Kevin,
I found that the input impendance of my Xindak monoblocks is 47Kw.

Does this explain why I am hearing a brighter sound through the "high" output switch from the pre through the phono?

If yes, does that mean my possible fixes are:

1. Ditch the HOMC Denon DL160 cart and get a better mm cart (if yes, any recommendations to surpass the Denon (for my Planar 3), but not too pricey?)

2. Keep the Denon, and change the power amps eventually, or get a seperate phono? (which doesnt seen that logical, given the the AR SP6 is supposed to have a decent phono stage?)
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Postby pivot » 25 Mar 2011 15:41

Spa317 wrote:I found that the input impendance of my Xindak monoblocks is 47Kw.?)


Do you mean 47 K ohm - 47Kw (kilowatt??) is not meaningful as an impedance spec.

Spa317 wrote:
Does this explain why I am hearing a brighter sound through the "high" output switch from the pre through the phono?


No, frankly leaves me stumped. If 47K ohm is the spec - should seemngly work. 47 k ohm should be close enough to 50 k ohm to work without gross errors.

Spa317 wrote:
If yes, does that mean my possible fixes are:

1. Ditch the HOMC Denon DL160 cart and get a better mm cart (if yes, any recommendations to surpass the Denon (for my Planar 3), but not too pricey?)


It would seem the issue you are having is how the line level stage works with your amps for some reason. You note a harsh sound with the gain setting that only impacts line level. I'd want to get to the bottom of that. Changing cartridge does not fix the function of the line level.

Spa317 wrote:2. Keep the Denon, and change the power amps eventually, or get a seperate phono? (which doesnt seen that logical, given the the AR SP6 is supposed to have a decent phono stage?)


Something is not working to spec. Either the 47 K ohm spec for the amp is not correct or there is something out of wack with the SP6.

I'd want to get to the bottom of that before tube rolling, cartridge swapping or other unrelated actions that only confuse things.

The SP6 SHOULD work at the "high" (normal) gain setting and sound fine.
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Postby bastlnut » 25 Mar 2011 15:58

hallo,

a classic cartridge-preamp mismatch will sound bright and thin.
a preamp-amp mismatch has no 'classic' sound character.
i does sound like a mismatch though.
i would keep the ARC SP6 on low output and find a new cartridge.
the Denon is very outclassed by the rest of the system.
using an MC with any ARC that i have heard is best with an MC transformer.
why not get one of the better Nagaoka or Ortofon cartridges and replace the Denon.
you can easily get your money back by selling the Denon, which is really outclassed in your system.
if you like the Denon sound, get a DL-304 or DL-S1 and a tranny.

regards,
bas
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Postby Spa317 » 25 Mar 2011 22:57

Thanks for the feedback guys, it is much appreciated!
Just to clarify, my line stage (ie. cd) sounds great using the "Low" (50ohm) setting on the pre, so does the phono but there's just not enough gain then to get decent phono volume.

Bas, can you suggest specifically some carts/models that will outperform my Denon DL160 please? To save on having to get an MC transformer, is there any MM carts that will sound better than the DL160, plus provide a better match to my MM phono (so I can use it in the "Low" setting and get the best quality sound from my pre?

With only a humble Planar 3, I guess I dont want to spend too much on the cart as then the table might not be up to bringing out the best? Thanks.
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Postby bastlnut » 26 Mar 2011 08:59

hallo,

i would suggest a Nagaoka MP 200 or a Goldring 1012..
an Audio Technica AT 150 or Ortofon Bronze would also work.
i would not use a grado with a Rega tonearm though many do and enjoy the combo.

i recommend you stick with an MM or MI cartridge unless you use a step up and an MC cartridge.
i have heard about gain problems more than once when an ARC preamp was used in combination with an high output MC.
a great combo would be a Dynavector or Benz low output MC in combination with a step up.
you can use this cartridge on any new TT when you want to upgrade later.

regards,
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Postby Hanuman » 26 Mar 2011 12:33

Now wait on here. I agree with Bas that the Denon is outclassed and looks like a prime upgrade target but I completely follow Kevin's diagnostic approach. Your pre-power combo appears to be not working properly. If I were in your position I'd want get that worked out first. You should forget the phono for the moment and find out why even the line level inputs are being mis-handled.
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Postby Spa317 » 28 Mar 2011 11:09

Had another good listen tonight...actually, the line stage (cd) sounds pretty good with both the "High" and "Low" gain settings on the pre.
Its just a little smoother in the "Low" setting playing cd's, but when I switch to play vinyl through the phono input, the phono is definitely vastly better in the "Low" setting than the "High" - but then I cant get enough volume in the "Low" setting for my LP's!

Does that still sound like a problem with the pre-power amp side, or is it likely that the Denon DL160 isnt a good match for the Audio Research MM phono?

Quiet a few seem to rate the Denon DL160 highly, and everything I have read seems to indicate it works fine into MM phonos (ie. no SUT needed).

I am a little confused by my issue still...Bas, are you sure the Nagaoka or Goldring would be a definite improvement with the RB300 arm? I read somewhere that the Goldring can let a lot of surface noise through, but the DL160 is quieter in this regard?

Sorry for so many questions, keep the help coming please! :-)
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