Seduction bass performance question.

[SPaulMac]

I completed my Seduction (non C⁴S) build this Sunday and have put about 20 hours on it so far. The midrange and upper end, while leaner in comparison with my previous phono input, have a delicacy and level of detail which are pleasantly growing on me. One thing that struck me immediately, and which I hoped would improve as the unit broke in, is an extremely light bottom end. While I wouldn't consider the phono stage of my Rotel RA-02 by any means state of the art, and would even consider it "overblown", it clearly presented instruments in the lower registers that I have to listen carefully to pick up on the Seduction. Sam Jones' bass on the "Somethin' Else" LP and the bass guitar on The Civil Wars' "Dance Me to the End of Love" 7" both almost disappear into the background while John Mayer's "Battle Studies" LP is left sounding rather flat and lifeless.

I checked the voltages both upon completing the build and just prior to posting this question and both times they looked good. I did have one set of unusual readings in the resistance checks for A3, B3, A8, and B8 which should have read greater than 1MOhm resistance but failed to register anything on my meter. I put this off to a limitation of my EX330 so I'll check again once my Fluke arrives. I received a pair of 47KOhm (4702F) resistors rather than the 475KOhm (4753F) resistors for the output jacks. Thinking this was an error, I substituted some old Radio Shack carbon 470KOhm resistors until I could get the others replaced. Should I have used the 47KOhm resistors or could the cheap RS carbons be causing a problem?

I understand this may simply be the normal performance of the Seduction and that my previous phono playback system might be skewing my perception, but I am concerned that I'm losing much of the lower registers that where there with my inexpensive integrated amp. Would the C⁴S upgrade or perhaps even the Eros make a significant difference in low end performance? Can anyone think of anything else that might be effecting bass output of the little amp? I'd really appreciate any help I can get with this.

Should it be relevant, I'm using a Shure V15-VMR in a Rega Planar 2.

Thanks for reading this.

[Grainger49]

Your resistance readings can be a matter of how your meter handles high impedances.  Don't worry about what you read.  Once you do voltage checks and nothing is over 15% off the resistance readings don't matter.

Tube rolling can bring on the characteristics you find most pleasing.  I have a thread of tube equivalents here in the Seduction folder in which you can find many of the variants that will drop in to replace a stock 6DJ8.

As you can understand Bottlehead doesn't send the most expensive tubes with the kit.  If you have a friend in your area get him to bring you some tubes for you to try.

BTW, tubes break in, give the stock set 40 hours.  The C4S will lower the noise floor, and maybe tighten up the bass but not extend it.  The Eros extends both the top and bottom end.

[Doc B.]

There should 47K ohm resistors at the input jacks and 470K resistors at the output jacks. Did 470Kohm resistors possibly get installed at the inputs?
 Also, what is the input impedance of the preamp you are plugging the Seduction into?

[SPaulMac]

Thanks Grainger49,

I figured my little meter might be the culprit. I finally broke down and decided to go with something more substantial, so I'm hoping the Fluke will be my last.

I've been following your tube rolling post with interest. I'd read several people here and elsewhere saying good things about the JJ E88CCs and was hoping to give them a try, but I don't know how this might affect the low end.

I'll definitely give the tubes more time to break in. You don't have to tell me twice to sit down to more listening.

Thanks again.

[SPaulMac]

Thank you Doc B.,

I checked again and I do have the correct 47.5KOhm resistors (4752F) at the input jacks. Based on a post I read elsewhere in the forum, I didn't think the value at the output jacks was particularly critical which is why I wasn't in a hurry to get those resistors replaced and just settled on the RS 470K pieces.

It wasn't until you asked the question about the input impedance that I noticed the 50K+ recommendation in the Seduction information. Looks like my little RA-02 is rated at 24KOhm at the inputs and the GFP-565 I'm hoping to replace it with is even worse at 22KOhm. Any chance this could be rolling off the low end, and, if so, anything I could do to better match the two?

I really appreciate you having answered so quickly and thanks for the great kits; they've been a real joy to assemble.

[Doc B.]

You could try upping the size of the .47uF output capacitors, but the Seduction should be pretty OK into a 22K ohm load even with the stock caps. Not quite sure what to suggest next as we don't usually hear about a lack of bass from a Seduction.

[Paul Joppa]

There could be some error or bad solder joints in the RIAA equalization. Check that you have 9.64K ohms between T29 and T30, and between T39 and T40. Then check the 0.033uF capacitor from T30 to ground, and from T40 to ground. Finally, also check the 1 meg resistor from T26 to ground, and from T36 to ground - make sure it is connected, and that it is in fact 1.0 Meg ohms. Check that the right capacitors are in the right places, too - they are all bunched together, and mixing them up could easily cause substantial loss of bass.

If the four LEDs by the tube bases are lit, then tube socket pins 3 and 8 are wired correctly.

[Grainger49]

I just wanted to point out that PJ is saying to make some measurements that are not from ground (like all measurements in the manual) but from terminal to terminal.  If you have the values he calls out, plus or minus 10%, you have the right resistors in place.  I expect that you already have them there since you are careful to read the specified value and the value printed on the resistor.  I have never seen a mislabeled resistor.

I have read posts that say that the Seduction can drive an input resistance lower than you have.  Increasing the output capacitors values might just make the difference you want.  But I will bet on new tubes. 

I have favorites.  Favorite tubes are a personal thing like favorite capacitors because each of us listens to different aspects of music.  I'm a big fan of the Russian military replacements the 6N23P-EV.  The "-EV" is a tighter specification version.  They are reasonably priced for premium tube.

[SPaulMac]

Thanks Paul,

I'm showing 9.32K across both T29/30 and T39/40 and .997M from both T26 and T36 to ground. Please excuse my lack of experience with using a meter to test capacitance, but I measured an initial capacitance of 1.23uF from T30 to ground, but this number drops as I hold the probes to take the measurement. Should I short the capacitor leads before taking a measurement?

Now that I look at the cap from T30 to ground, it's marked as 334K. The best I can determine from the online charts, that appears to be a .33uF capacitor rather than the .033uF called for in the instructions. Could this be causing the problem?

Things will be kind of tight the rest of the week, but hopefully I'll find time to inspect the RIAA section and if no problems there, I'll go through the circuit again from the first step. Should everything look good there, I'll reheat all the solder joints to ensure I haven't left a cold joint somewhere.

I really appreciate all the help I've received. I'm actually rather enjoying troubleshooting this little guy.

[Paul Joppa]

I think you have to detach at least one lead of a capacitor in order to measure its capacitance.

The manual says 333 is the code for 0.033uF, just as you said - 334 would be 0.33uF, which is 10 times too big and will remove the 20dB boost below 500Hz that is part of the RIAA. If that's true, then no wonder you are missing bass! When did you acquire this kit? I hope there are not many others with the same error!)

[SPaulMac]

That's a load off my mind, Paul. I'll get a call in and get those two capacitors and the output jack resistors replaced and post my results here.

I just ordered the kit at the beginning of last month and received it a little over a week ago. It's probably just a one-off mix-up, so hopefully nobody else has had any problems.

[Doc B.]

Just checked the bin and the parts we have are 333, so it's most likely that the supplier accidentally mixed in a 334 or two and we didn't catch it. I have these caps and some 475K resistors set aside for you. Contact Eileen at queen at bottlehead dot com and she will get the correct parts in the mail to you.

This is one reason we request in the forum rules that members sign their real names to their posts. It saves some time if we need to send something to you.

[SPaulMac]

Thank you, Dan, for getting those parts to me. Eileen very kindly tracked me down. I'm sorry for not having my name on the signature line; I'll take care of that right away.

A big thanks to everybody at Bottlehead and here on the forum that helped me through this.

Stephen

[Grainger49]

Stephen,

I edited my post above.  The number for the Sylvania JAN tubes was a 12AU7 variant for the FP not for the Seduction.  So far my favorites are the Russian Military Surplus tubes.  Some of them have been the quietest tubes I have used.

[SPaulMac]

Wow, no subtle difference there. Classic Records' Clarity 45RPM release of Cannonball Adderley's "Autumn Leaves" comes alive on the Seduction since the parts swap. Now for some break-in and serious listening.

A huge thank you to Eileen for getting the parts out to me so quickly.

Stephen