Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Laudanum on July 13, 2011, 04:09:03 AM
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Im considering adding a modest turntable source to the Crack headphone system. I brought the Crack into the main system and hooked directly to the phonostage just to have a listen. If I figured it out correctly, with a 4mv cart and a phono stage with 40db gain, you end up with around 400mv max, does that sound right? I really had to goose the volume knob on Crack to get to decent listening levels.
I have never used a pre-amp / linestage. Would the Foreplay III add the additional drive to a phono stage to bring that output level up? Or is that not one of the functions that they are used for?
My phono stage in the main system feeds a 75wpc hybrid integrated which give me more volume than I ever need for the speaker system so I never thought about actual voltage levels.
A linestage like the foreplay would be completely new to me.
So for the headphone system I was considering either a vintage table or maybe one of the new, budget tables (Pro-ject, MH, Rega ...) to Seduction, to Foreplay III to Crack. The Foreplay would allow me to not have to do the cable swapping/plugging when switching from the digital player to CD player. Both those sources have ample gain for direct into Crack. But Im trying to wrap my head around how to properly bring the gain up for a phonostage. Am I on the right track here with using the Foreplay for the added gain as well as, obviously, easy source selection and level matching between sources? Or is this the wrong approach?
Also, how does Foreplay work in terms of matching levels between sources? Do you adjust the dual mono attenuators every time you switch sources? Or is the input selector meant to be padded accordingly for each source?
As you can see, Im a complete noob with this particular topic.
Thank in advance.
ps. The good news is I got my wifes blessing already :-)
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im running an SL1200 with a shure m97 into the seduction and i have plenty of gain..... i realize its a probably not nearly as nice of a table as most of you guys are running but it sounds pretty good.
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There is nothing wrong with the Technics table. My main table from the late 70's until my 10 year hiatus from vinyl about 1990 was a 100 dollar SL-D2. I use mid priced Shure and AT carts through those years and every LP that I still have, including those that saw boatloads of playing time on that table still sound absolutely fantastic.
The main system now has a Music Hall 5.1, the original version when it was MH's top table. Still very much a budget table (and I bet that old D2 wouldnt give up a fraction of an inch to it). Also with a Shure M97. The phonostage is the original Hagerman Coronet, which I believe has 44 db of gain and with a fairly high output level LP (blues/rock), I was up past 2 o'clock with the volume knob on the Crack for what would be about a normal listening level for me with that type of music. Sometimes I would listen louder and sometimes not as loud. This was with the Beyerdynamics. That same album transfered from CD to my digital player (about 2V out) would require probably 11 O'Clock on the Crack volume knob for same level. So I can see that some lower output LP's with the AKG 601's are going to be a problem, especially with 4 db less gain from the Seduction (with C4s ... compared to Coronet) if I use the same cart or cart with same output level (4mv).
Which brings me back to my questions on the Seduction and Foreplay III in relation to Crack. Ive been reading that the FP III it's intended for unity gain but Im wondering if it can be used to goose the output from seduction atleast a bit with still sonically good results. Again, never used a linestage or preamp so this is new territory for me.
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I believe that PJ posted recently that the FP III was designed for unity at a 12:00 volume setting above that it has 10-15dB of gain. Maybe I got the additional gain wrong but it has "copious" gain. It will not improve the Seduction S/N ratio, nothing can. My Seduction is from the IPO and is doing fine, with very low noise.
So, the answer is yes, the FP III can goose the output of the Seduction in front of the Crack.
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Thanks for the reply Grainger. So then I would just have to adjust the dual mono attenuators to add needed gain when listening to lower level LP's? Would using the Foreplay to increase the gain of the seduction in that manner hurt the SN ratio / sonics signifigantly? Like I mentioned, I have never used a linestage before. I read some related posts and seems like you know the seduction and foreplay pretty well so I hope you dont mind me drawing on your experience and opinion here.
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So, the answer is yes, the FP III can goose the output of the Seduction in front of the Crack.
Just as an aside from this..... the numbers alone suggest that using an Eros directly into the Crack would give approximately the same gain as the Seduction into the FP3. Obviously you don't have I/O switching with this setup, but I suspect that it could potentially sound better? Cheaper too.
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For the best sounding solution I would be inclined to do as Beefy suggests.
As an experiment - this is probably not optimal but you might try a driver tube with higher gain for the Crack. It shouldn't hurt anything to try a 12AT7 in place of the 12AU7. Since this is a direct coupled circuit and the plate voltage on the driver stage affects the bias on the output stage you would need to check voltages if you try it (I have not) to make sure they don't get too far away from the spec.
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So I take it that there is a sonic penalty using some gain from the foreplay III. I think that I read earlier that it was mainly designed for unity gain.
So this may be a dumb question but why is the gain available? Is it a matter of having the gain available if needed and accepting the sonic penalty? Im assuming here that the more gain used from FP III, the higher the penalty. I think there will be plenty of gain from seduction with most LP's and my Beyers and Quarts but the AKG 601's for example, with lower level LP's will be a problem without some extra gain.
The Eros sounds like an option but losing the 3 source switching, and level matching to a degree as well, would be a bummer. Im already doing a plug swap for 2 sources, I'd hate to do it for 3. And upping the gain of the Crack just for vinyl with a 12AT7 (or 6922 with socket rewire) when I have two other sources that dont need it isnt too tempting.
I'm inclined to give the Seduction and Foreplay III a go here and maybe go with a higher output cart on the headphone system. The Eros may be less than both Seduction and FP III combined but the bang for the buck takes a hit for sure.
My test was with a 4mv Shure (although the Cornet has a bit more gain than the Seduction). But if someone could give me a quick and dirty rundown of the possible sonic consequences of using some gain from the FP III to goose the Seduction output, I could better get my head around things. Are we talking potential higher noise like audible hiss, hum, distortion etc?
Thanks guys, good info so far.
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So I take it that there is a sonic penalty using some gain from the foreplay III.
Well, you are running through two volume controls instead of one, and adding noise floors from two devices instead of one, distortion and noise from an additional set of active devices - every measured spec will take a subtle hit. It isn't so much that the Foreplay specifically is imparting a sonic penalty, but rather an inherent problem with inserting *any* extra device into the signal chain in order to compensate for your phono amp not having enough gain. So it plain makes more sense to use a single device - just the phono stage - with sufficient gain in the first place.
Further, I would imagine that the Eros simply being a better phono stage than the Seduction. That surely makes the Seduction/FP3 combo less attractive. If you are worried about loss of functionality, build yourself a nice little passive switch box with the savings.
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One shouldn't really take too objective an approach to analyze the situation. One crappy sounding piece of gear will sound worse than two good ones in series. But I don't feel that we are talking about any bad sounding pieces of gear here. Both phono preamps sound very good. The Eros sounds a little better to me than the Seduction. That has to be the case for me to put out two kits at different price levels. The Foreplay will be a great choice for giving a little extra gain as well. The volume control setting will have little effect upon the overall sound quality. You could even leave it set wide open and use the Crack to set listening levels. Theoretically, it would be better at higher settings anyway and if you need the input selectivity Foreplay III is the best choice.
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Desmond,
See if there are some Bottleheads in your area, ask for them to bring a FP over to your place, or you take the Crack to theirs. Just a pragmatic answer.
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I appreciate all takes on the subject, thanks for the input Beefy, I appreciate it.
The Seduction has had a great reputation well outweighing it's pricetag for a long, long time. Im sure that the Eros is the better sounding phonostage, it should be for the extra money.
Thanks Doc, it sounds like the FP III is definitely a feasible choice for what Id like to do which, right now, is adding source selection and also giving me the ability to add some gain to the phono if I need it. The additional set of outputs will also be great for future use. Im wanting to do this all to the dedicated recliner side headphone system built around the Crack, for the time being anyway. I may very well add one of my amplifiers and speaker pairs to this system in the future. There are actually 4 different systems in the speaker listening room and it is far from ideal as a listening room. This makes FP III by far the most versatile choice with everything considered. Eros and a source selector is a good idea but there just seems to be far more flexibility and options with the FP III and Im confident that Seduction with C4s will sound more than good enough.
I do have another question though. I wouldnt have thought that the dual mono attenuators, being "only" 11 step (and dual mono) would actually be great for system "volume" control. I think thats something that has been throwing me off a bit. I was thinking that they were mainly for adjusting source level with actual "volume" control being handled by the amplifier itself. Of course, I can understand their use for system "volume" control if the amplifier has no volume control itself. So I can see that they would have versatility in that regard. And perhaps that versatility was the whole idea? ... That they could be used for "volume" control if needed or more as source level control if the amplifier has a "volume" control of it's own. But again, I could be missing the boat here, again.
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A few technical points here:
1) Phono cartridges are rated for a nominal output, while digital devices are rated for a peak output. The difference is usually around 14dB, a factor of 5. So the peak output from a "4mV" cartridge is closer to 20mV.
2) The above is strongly affected by how much compression is used in making the disc. Bizarrely, digital music is often more compressed even though it has a larger signal to noise ratio available.
3) The Foreplay III is designed to allow each input to have its own gain, so that similar settings of the volume controls will give similar loudnesses. I don't think very many bottleheads have actually done this - it's a bit of an effort to get all the data and then swap out the resistors - but it was designed from the beginning to make that possible.
4) As long as the Crack volume can be set loud enough you do not need more gain. It's (as Doc B said) actually better when the control is set higher for the same loudness - though the effect is pretty small!
5) I would expect the 6DJ8/6922 types to be the best higher-gain tube in Crack, because they will give the same plate voltage with the same bias LED and the same plate current (plate resistor or Speedball).
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Thanks Paul, very helpful.
On point 3 ... You're talking about padding the input selector switch accordingly for each source/input, correct?
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Thanks Paul, very helpful.
On point 3 ... You're talking about padding the input selector switch accordingly for each source/input, correct?
yes, exactly.
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I've often wished the Crack had a pair of inputs! I usually listen to records with it, but occasionally I like to stream some internet radio.
I think a tube headphone amp (Crack/Speedball) with a pair of switchable inputs and a built-in phono pre (Eros? Seduction? even -shudder- Solid State?) would be my dream machine!!
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One trick setup might be to combine a Seduction and a Crack on one custom drawn 12" x 12" chassis from Front Panel Express. The only other customization you would need to do is to add a second set of RCAs and a two pole two position switch for the input selector.
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And if you wanted to try that, I'll be glad to send you the stock base parts from my stereomour. I won't be using it and I don't like to waste good parts.
You could probably use the stock top plates from the crack and seduction and put a 3/8" divider between the two halves so that's flush with the bottom of the rabbet.
-- Jim
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I know this isnt as slick but I originally set up Crack just to use with a digital player as the source. Cable is star quad with a 1/8" mini plug (players line output) to RCA's into the Crack. Shortly after I added my old AH Tjoeb 99 CDP that wasnt getting much play in the main system. To make that easier, I again used Star Quad to make up a cable with RCA's for the CDP to a 1/8" mini jack. So source swapping is done by plugging the 1/8" plug directly into the Digital player or plugging it into the 1/8" jack for the CDP. I was actually thinking about adding Seduction the same way, atleast temporarily. Cable wise, it wouldnt be the best solution as the cable run would be a little too long and capacitance of Star Quad type cable is relativey high not to mention that Im not sure how a 1/8" plug to 1/8" jack affects it if at all. But it would have worked and source selection is pretty easy with the plugs, much better than full cable swaps. But I bit the bullet and also ordered the FP III at the same time I ordered Seduction. I liked the versatility of being able to add a small amp and speakers later on if I decide to. I have small amp and the Fostex full rangers from the main system that I may move in the future and FPIII allows that with the two outputs. I also wanted the additional gain on tap just in case I needed it for vinyl and the rather ineffecient AKG 601's (which are growing on me more and more).
Im curious to see how it all works out. It's nice going source direct to Crack ... nice and simple so we'll see how adding the Foreplay in the chain works out.
Im getting ansy now ... need some wood to glue, sand and finish and some solder fumes to sniff but I think I still have a while to wait :-P
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I would suggest a modification of Doc's suggestion. Add a pair of RCA jacks and a DPDT toggle switch. I can walk you through the wiring of that switch if you need it.
Here is a link to another pair of Gold plated RCA jacks:
http://www.parts-express.com//pe/showdetl.cfm?&Partnumber=091-1120
I keep a couple of pairs of them around in my parts box "just in case...."
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Desmond,
Slightly OT, but really glad t hear about the AKG K601s. When Smack comes out, it will be interesting for sure to compare it to the Crack with the 601s
Looks like the BH bug has itten -- figured that would happen :-).
-- Jim
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Hey Jim ... Yeah, the 601's are pretty nice phones. They were really bass shy out of the box. Definitely a long break in on these. But they actually exhibit some palpable bass now and they are still getting better across the board. I can go from any of my phones now (except the Beyer 990's) to the 601's without suffering lack-o-bass shock which is a signifigant change from out of the box. Widest stage of all my phones, most evident on live recordings. They are my primary phones for live recordings (mostly live electric blues) for sure. Im comparing with Beyers, my old K141's the Quart closed phones, M-Audio Q40's (closed) and Fischer F-011.
The Bottlehead bug has hit ... Great stuff, fun to build, affordable and Im still loving Crack so much that I HAVE to add vinyl. I cant think of a better way to do it than with what still has to be the best deals in DIY tube audio. But, Im impatient as hell and that hasnt extinguished with age ... the waiting drives me nuts :-D . But its worth it.