potential Eros buyer... couple of questions

[tiller]

Hi all,

 

I am the proud owner of a Seduction phono stage and have been loving it for a couple of years now. However, I am beginning to feel the pull of upgrade-itis and am considering building an Eros. The other kit I am considering is the tubes4hifi PH16. I like the aesthetic of the Bottlehead kits better, and I certainly appreciate the documentation and support of the company. I have a couple of general questions for you guys if you have a moment to help me out:

 

1. I plan on running the phono stage directly into my gainclone power amp which has a switch and passive attenuator on the input. I believe the attenuator is 25k, if I recall correctly. Will this pose problems with the Eros?

 

2. If so, will an active buffer stage between the Eros and power amp help out?

 

3. Currently, the biggest issue with my setup is a very uncontrolled low end (50-300Hz range) and very recessed mid-range (1.5-2kHz). I unfortunately don't have any colleagues into hi-fi and not enough gear of my own to swap in to try and deduce where the problem is coming from. I suspect it is mainly room factors. However, could the aforementioned impedance mismatch present itself in such a way? Could tubes affect the tonal balance as significantly as this (i.e., could changing them improve my issue)?

 

4. This is probably a big one, but seeing as how I am not the most knowledgeable when it comes to differences in audio circuits, could someone summarize the major differences between the Eros and PH16 (http://www.tubes4hifi.com/PH16.htm) and how such differences translate into the reproduction of audio?

 

Thanks in advance for your help. Looking forward to your replies.

 

Adam

[Doc B.]

could someone summarize the major differences between the Eros and PH16
Adam

Here's a major difference-

I charge for excess technical support on kits (more than 20 minutes total). Although this is rarely needed, if you send me 5 emails of questions
and I spend 20 minutes giving you answers and you still can't figure out what you are doing, then I will be billing you for payment before answering
additional questions for you ($1 per minute, 5 minute/$5 minimum).

You shouldn't need a buffer into a 25K load.

[tiller]

Thanks for the quick reply Doc. As I mentioned in my post, the great customer support of Bottlehead is what makes me want to purchase (another) kit. I've already built up a Crack and a Seduction. I was more curious about the technical differences of the circuits, for education more than anything. Sorry, I did not mean to have you try and defend Bottlehead as a company!

 

Regarding the 25k load. I am not exactly sure if that is what the (potential Eros) will see. The attenuator is wired in series before the inputs on the amp circuit. So, is the input impedance effectively the resistance of the attenuator? Sorry, it's been a while since I did electronics.

 

Thanks again,

 

Adam

[Doc B.]

Yup the load seen by the Eros would be the resistance of that attenuator. We have found that you can get away with as low as 15K, so 25K should be fine. With respect to the circuits, I have a policy of not trying to make sales by trashing the competition's products - maybe their attitude about tech support, but not their products

But I would be happy to say what I think makes Eros an upgrade from Seduction. The EF86 as the first stage gives it 10dB more gain and even though a pentode it is running at such low signal levels that it sounds very linear like a triode. It is also a very quiet tube and the C4S feeding it gives it great power supply rejection. It has a lower noise floor than Seduction. The regulation of the Eros gives it a sense of broader bandwidth and a little more transient speed. Bass is a little nicer too, and lots of users find it does a better job of imaging. The gain is high enough that, if you are using LOMC, you can typically use the lower turns ratio of a step up transformer that has multiple ratios. And that can give you better bass too.

[tiller]

Fair enough Doc -- I appreciate your diplomatic response

Sorry to press you further, but what do you mean when you say "better" bass. Lower frequency response? Better control of resonances? Response times?

I am very picky about my low end as my ears are very sensitive to it. And it is a general low end bloom (uncontrolled low end, smeary, blah blah blah so many adjectives) that is making me want to change up my system. More than likely it is my room that is causing this, but if the Eros can help out a bit I'm all for it.

Now that I think about it, there must be a particular component that controls the bass emphasis in the RIAA eq, no? Is it possible to add a switch in there with different values (a resistor i presume?) to control the general bass emphasis of the RIAA eq? I.e., one setting for less bass, one for stock RIAA, one for more?

Thanks again for your help with this

Adam

[Doc B.]

Yes the bass is better with the Eros. It is tighter and more even.
However I would suggest figuring out where the problem you perceive lies befoe you buy any more gear. It might be worth buying an inexpensive measurement mic and some room measurement software to see if there is indeed a room problem you need to fix. If there is a bass problem in the room, no piece of gear will get a fair shake.

[tiller]

The problem is almost certainly the room, and probably my speakers (old Dynaco A-25s). Sadly there's no fixing the room -- such is the reality of renting. I don't mind alleviating the issues upstream if I have to. Thanks again for the info!

[Doc B.]

You can make some simple steps to improve just about any room. Addding items that will absorb sound like rugs, drapes, and soft furniture is usually a very good direction to go. Simply moving your speakers a foot one way or the other can sometimes make a huge difference in the bass boom as you get the speaker away from an antinode of one of the room resonance modes.

[tiller]

Thanks for the tips, Doc. I am an audio professional (recording, sound design) so I'm pretty familiar with room treatment and what not. My main work room is treated and sounds satisfactory (for an office space). Sadly the main (leisure) music setup is in the living room and, well, it's not only me who has a say, if you get my drift, haha!

Thanks again. I think I'll be selling my Seduction and getting started with an Eros build.

Cheers!

Adam

[Paul Joppa]

Not sure what to say about the bass - the old A-25 is a classic for sure but it's old - are the surrounds still in good shape? I hear they do have a mid-bassy tendency.

For the recessed midrange, check the crossover - if the original electrolytic capacitor is still there, replacing it would be advisable, preferably with a film cap. Some have reported a big change by cleaning the switch contacts, too. Maybe these things have already been done, but just in case ...

The Eros output stage is the same as the Seduction, except for a larger output capacitor. If the Seduction sounds OK, the Eros will be a hair better in the deep bass for that reason. Most of the sonic difference is the EF86 first stage, the direct coupling between stages, and the shunt-regulated power supply.

[tiller]

Thanks for the reply Paul. The speakers are in good shape, and I capped the crossovers not too long ago with some Solen metalized film jobbies. The more I've read about the A-25 design the more I read about their tendency to emphases low-mids and their mid-range hole due to the very basic crossover design. I'm not an authority on this stuff -- just what I've seen written. I have good ears and can identify problems, but my technical knowledge of electronics and loudspeaker design is lacking. Honestly, I imagine it's my room and the speakers causing the sound I dislike. Actually I think I'm going play around a bit with speaker placement tonight to see if I can notice any positive changes. Either way, I think I'm also going to attempt a DIY speaker build in the near future as well. Something with a flatter frequency response, or even tilted up in the highs.

Regarding the Eros, I think I may just go for it. I've been wanting another DIY project and I like the Bottlehead stuff. The generous sharing of info on the board just seals the deal for me.

Back to the output impedance question. Do you think I could mod the Eros to lower its output impedance (resistor in series after output cap)? I guess this would come at the expense of some output, but might make me feel a little more at ease matching it to my amp.

-Adam

[Paul Joppa]

Put a resistor in series at the power amp input, not at the phono preamp. (Between the input jack and the level control.) That will raise the amp input impedance, leaving the phono preamp output impedance unchanged. If the attenuator is 25K then another 25K in series will lose 6dB but make the total 50K; that still leaves 4dB more gain from the Eros compared to the Seduction.

Once you've done that, short it out to listen to the difference. I predict it will be small or non-existent, but your ears are the only ones that count!

Incidentally, stock Eros output cap is 1uF (sometimes a bit more if that part is hard to get). Into 25K, that's -3dB at 6.3Hz, -1dB at 12.5Hz. Trust me; the A25 does not go that low! There will be a small distortion improvement from a higher load impedance; I doubt it's audible but - again - your ears are the only ones that count. Try the experiment, share the result; we all learn!

[tiller]

Cool, thanks for the tip Paul. I think this maybe the simplest solution yet. I certainly won't miss that bottom, bottom octave. The distortion however is a little more sensitive. I will report back with my findings

Thanks again all!