foreplay and seduction/eros in same chassis

[howardnair]

yes --that is what i am thinking -combining the foreplay and seduction/eros in one chassis--on top one unit --underneath totally separate units right down to  maybe even the power cords--probably separated with a copper plate--4 pole 2 deck selector switch with the phono direct to that--just thinking out loud -the more experienced among you may tell me to not think so much as i weaken the team--howie

[Doc B.]

The EF86 tubes in the Eros might pick up hum from the PT-3 power transformer in the Foreplay if they are too close to it. The PT-5 in the Eros has an especially low radiated magnetic field so that it doesn't interfere when sitting closer to the tubes, but the PT-3 was designed for less sensitive line level applications so it needs to sit a little farther from the EF86s than the PT-5 does. In a Tube Repro the EF86s are about 14" away from the PT-3 and sitting more or less along the PT-3s long axis. At that position they are very quiet.

[Lee Hankins]

This was my version of the FP III/Seduction combo, no problems with hum.  The output of the Seduction is directly connected to the FP III.

 http://cgim.audiogon.com/i/vs/i/f/1193602095.jpg

[howardnair]

i like that --so it is a viable option --ob boy something to plan and build--i really should just get a tv and zone out--ahhh thats no fun---howie

[epistaxsis]

I am seriously considering getting an eros and was planning on using one chassis for the lot (eros, fp3 & active crossover).

I hadn't realised that the PT-3 was a noisy tranny

What could be done about this in terms of, say, shielding / potting?

[Grainger49]

Doc didn't say that the FP III (PT-3) was noisy.  He said it could cause hum in the Eros input tube if it were too close.  Here is his quote:

The EF86 tubes in the Eros might pick up hum from the PT-3 power transformer in the Foreplay if they are too close to it. .  .  .  

The FP III deals with much higher voltage levels so its transformer doesn't need as much sophistication/shielding as the Eros transformer. 

I would expect with all three in one chassis you will have a bunch of transformers.  They could be clustered to one side.  The Eros circuitry, the most sensitive to hum/noise, could be diagonally across the chassis.  If you give yourself room that would be safe.  There are a number of Eros preamps out there next to a FP III chassis with no problems.  Putting the crossover circuits between the two would give copious room.

[epistaxsis]

Just to clarify I have attached a quick mock up of what I want to do.

The idea is that for the stereo section everything is kept as close to together as possible so that I may be able to dispense with coupling caps...

Each section will be separated by 5mm aluminium and 2mm copper sheet (sort of like the boxes on the drawing) - also a barrier between PSU sections and audio sections - the 1st valve below the transformer is the relevant power supply valve (they're all be extended foreplays!)

I hope this helps.

[Grainger49]

I suspect there is a reason that the Eros EF86 tube is as far away from the power transformer as it is.

In your layout it appears that one of the EF86 tubes is closer to the second from the left transformer than the stock EF86s are from the Eros transformer.  I suspect you will need more acreage. 

Your layout is compact, have you seen all that is under the Eros top plate?  I don't think there is any way it would all fit.

Take a look here:

http://www.bottlehead.com/store.php?crn=220&rn=428&action=show_detail

Four circuit boards, one is on top of the power transformer.  But that is a lot to fit into your layout.

[Paul Joppa]

...
I hadn't realised that the PT-3 was a noisy tranny

What could be done about this in terms of, say, shielding / potting?

The PT-3 is significantly quieter (in terms of radiated magnetic field) that most transformers, but the PT-5 is much quieter still.

Our experience was with the Seduction, where the first version of the power transformer caused some hum. The current PT-1 has a molyperm tape wrap (as well as a copper tape wrap) to reduce its magnetic and electric field radiation, which solved that issue. Ever since, we have been especially cautious about power transformer hum fields, and have not had any problems. Of course that means we haven't learned any new things either!

From the sketch, it looks like you are planning to revise the layouts. Just be prepared for unexpected issues to arise; layout is complex enough that it borders on a black art...

For what it's worth, you could use the Eros power supply for a Foreplay circuit, with some revisions for the higher voltage (225v vs. 150v stock). I haven't done a detailed design, just enough to be confident it should be possible. I'll work out some numbers if anyone actually plans to try it. We sell the PT-5, but do not sell the PT-3 by itself.

[howardnair]

epis-can you spell Montana--you need some real-estate for all that equipment--sorry i couldn't resist--

 you have way too much in there--to be honest your stereo should be your stereo and surround sound should be surround sound--for a sub-bass--you should be able to add another pair of rca outs to a foreplay-ck with grainger or paul--that way foreplay eros and active xover--in one box would be a little more doable

[epistaxsis]

OK I'll remake the sketch tomorrow when I have access to a proper computer!

Yes this will be a large chassis as there is a lot to get in.

Hopefully I can quickly explain why the orientation has been put through 90degrees...

As I said the idea is to shorten the audio signal flow as much as possible in the stereo section (I'll explain the other bits below).

So keeping to the current confusing sketch for now and looking at the fp3s top down the valves work as 12AU7 shunt regulator, 12AU7 left and 12AU7 right i.e. the signal path is running left to right <-- if this makes sense!

The reason there might be a couple of extra foreplays at the end is that I have a highly modified Oppo BDP-83 player which is for 8cm shiney disc duties. It has built into it a proper multi channel DAC. i.e. no need for an AV processor! :-D

Anyway as I said once I have access to my RISC OS computer tomorrow I'll be able too make a sketch that should (hopefully!) clarify things a bit.

[epistaxsis]

As this is not really just foreplay3 specific any more I am starting a new subject on this in the technical section of the website here: http://www.bottlehead.com/smf/index.php/topic,1323.0.html

[Williston]

>For what it's worth, you could use the Eros power supply for a Foreplay circuit, with some revisions for the higher >voltage (225v vs. 150v stock). I haven't done a detailed design, just enough to be confident it should be possible. >I'll work out some numbers if anyone actually plans to try it. We sell the PT-5, but do not sell the PT-3 by itself.

So would this result in a lower noise floor for a FPIII? I'm just about to rebuild my Foreplay and if a PT-5 would be quieter I'd like to give it a try

[epistaxsis]

There is that other tweak at the top of this forum that lowers the noise floor - this would alter the voltage of the HT line.

A 12AU7 will run at 225V but I suspect that the shunt regulator valve / components (in an extended foreplay) would need altering.

Would be interesting to see just how much would need to be changed and the effects of running the extra 75V on the HT (according to their specs 12AU7s max at 300V...)

[Paul Joppa]

Hey, it was just an off-the-cuff remark!

Doc B is offering the PT-5 by itself currently. I have thought that it would be possible to offer the Eros power supply board and the Eros dual shunt regulator also - this would make a fully-regulated power supply for DIYers, capable of 6.3vDC at 0.71 amps and dual regulated 225vDC at 13.5mA per channel (this is the actual Eros current consumption). These are not currently being offered - there are other priorities for kit development right now - it's just a potential I have been thinking about.

Foreplay III operates with a power supply of 150vDC, direct coupled with each tube at 75v plate to cathode, 1.57v bias (the LED) and 3.8mA per triode. Running 225v would give 112.5v per triode, and using 2.5v bias with about 6mA plate current. The 2.5v could come from a 431 shunt regulator chip, since that is on the C4S board anyhow. Adding in the 1 or 2mA C4S bias current, the total draw is 13-14mA per channel, and 0,6A at 6.3v for the 12AU7 heaters - just about exactly what the Eros draws. It could be a bit quieter, at least with respect to hum, a bit more stable with line voltage fluctuations, and a bit more drive capability, headroom, and less distortion. Small improvements in most parameters.

At one time, I thought this could be a super-Foreplay. But it would probably cost twice as much as an Extended Foreplay, and at that price level, we think we could probably do better - there are some research efforts under way, based on the balanced line drivers we are exploring for custom and studio gear. All very experimental or even untried so far!