Design questions

[Paul Joppa]

Here are some notes on the not-yet-released Stereomour, based on questions recently asked on the old forum:

The circuit is pretty much the old Paramour circuit, with new plate chokes and output transformers (similar quality to the Paramount iron, and a step up from the old stock units).

Specifics:

12AT7 driver, shared between channels

0.1uF/600v coupling cap

coupling cap 3.3uF/600v (nominal optimum would be 2.5uF for 2A3, 5.0uF for 45)

three switched inputs, single volume control, no headphones

C4S driver load is standard

2A3 uses paralleled resistors in the power supply and cathode bias, one of which is removed for 45 operation, and the plate choke tap is switched between 45 and 2A3. No other changes.

Can operate a 2A3 as if it were a 45, for more conservative operation

If there is enough demand, and when he gets caught up, I expect Magnequest will have some upgrade iron, but there is no suitable output transformer yet.

For what it's worth, the (hopefully!) final iteration on the power transformer and output transformers have just arrived in the lab. I'll be checking them out while Doc B sorts out some other final details of parts selection and layout before we assemble the production prototype for the manual photos.

Incidentally, once this is a going concern I hope we can assemble the various bits of prototype parts into a few unique, assembled versions of the amp.

 

[BNAL]

Will there be room to install another tube for a shuntreg 45?

 

[Paul Joppa]

Looking at the earlier prototype (sitting here in my lab, i.e. basement) I don't think so. I do have a couple other ideas though:

1) A farm of Zener diodes could provide shunt-regulated power to the 45 version. Not as good as the hybrid, of course.

2) A new, fully shunt regulated 45 amp, with DC filament power. This would be a higher-end amp, maybe something like Eros as compared to Seduction.

 

[shelby1420]

Hi Paul, what would the difference if any in wattage output?

 

[Paul Joppa]

Stereomour will have the same power and distortion as the Paramour, except in the deep bass where the new Stereomour iron will do better in the distortion department. That's all I can say until we get the final prototype running - which should be pretty soon, actually.

I see this thread is four months old, and just last week we **finally** got the correct prototype iron in the lab. The bum economy has been hitting our suppliers as well as everyone else.

 

[shelby1420]

Hi Paul, what power did the Paramour have?

 

[Grainger49]

The Paramour (1) (2) (Stereomour) is 3.5WPC.

 

[shelby1420]

Thank you, so just to make sure.....  there will be two options of the stermour--one a 2a3 version ( kinda like a seduction level) and a 45 version ( more like a eros level) and they will both have 3.5 watts ,yes?

 

[Paul Birkeland]

It seems to be shaping up to be 2-1/2 options:

1) Stereomour stock with 2A3's - 3.5 wpc
1.5) Stereomour modded for 45's - 2 wpc
2) Some kind of shunt reg 45, probably monoblocks, probably ~2x the price of Steremour - 2wpc

 

[Paul Joppa]

Hmm - I was posting while CB was posting, and mine seems to have failed to get onto the forum.

Mine was much longer, but I think he's covered the basics.

I'll just add a bit about levels. I see the Seduction and SEX amp as entry level, with Eros and Paramount as our high end. The Stereomour, both 2A3 and 45, will fall in between those levels. The shunt-reg 45, if it becomes a product at all, will be at a higher level than the Eros and Paramount. (Quickie is kind of an oddball, but on average I'd call it entry level.)

 

[Paul Joppa]

OK, found a copy of my first try, here it is:

No, sorry for the confusion.

The 2A3 is capable of 3.5 watts in normal use. We've used it this way for a long time - the original Paramour monoblock was my first electronic design for Bottlehead. Some years ago it morphed into the Paramour II, using the same output stage and producing the same power. That design was discontinued last fall, and will be replaced with the Stereomour, still using the same output stage and producing the same power but in a stereo integrated amp design. There have been other improvements, but the output stage has remained the same.

The 45 is a lower power tube, due to a lower maximum dissipation and a higher plate resistance. All versions of the Paramours can be modified to use the 45, but they will all produce only 2 watts that way. The modification adjusts the current and voltage for optimal performance with the 45 tube. For the first Paramour, this was an experimental after-market modification, but with Paramour II and the Stereomour the option is included in the kit and instructions.

Normally Bottlehead does not supply the 45 tubes - they are not available as inexpensive new production, and most enthusiasts have their favorite versions anyhow.

As to "levels", I would say that the SEX amp and Seduction are our entry level products, with the higher end products being Eros and Paramount. The Stereomour (both 2A3 and 45 versions) will fall in the middle between those products.

Earlier in this thread I mentioned a project I am working on, which is a fully shunt-regulated 45 amp - this will be at a level above the Eros and Paramount, and I don't know if there will be enough demand for it to become an actual product. It was probably a mistake to mention that in this thread, and I apologize for any confusion it might have produced. We always have a bunch of projects going on, and only some of them make it to the actual product stage.

 

[shelby1420]

Ahhhhhhhhhhh, ok that clears it up for me Paul!!!  Can't wait to build this baby and hook it up to my Cornwalls or Hersey ll  !!

 

[Grainger49]

Paul,

From what I am reading between the lines, the fully shunt regulated 45 version of the Paramour would need all the power supply to run the 45?  That is kind of a question.  I am only guessing there.

 

[Paul Birkeland]

I don't believe that power transformer for the Stereomour will be compatible with the demands for a fully shunt regulated amp.  (The SR45 idea that is kicking around would be mono amps)

 

[Grainger49]

Ok, so a different power transformer, same chassis as the Stereomour?

 

[Bryon]

Earlier in this thread I mentioned a project I am working on, which is a fully shunt-regulated 45 amp - this will be at a level above the Eros and Paramount, and I don't know if there will be enough demand for it to become an actual product.

I'll buy one! [or should I say two as they will be monoblocks]

Bryon

 

[Paul Joppa]

No, actually I am looking at the Paramount chassis and the PT-3 (SEX and Foreplay) power transformer. There are several variants on my drawing board, so no point in getting specific - it will undoubtedly change!

 

[jrebman]

Paul,

Is the configuration of the output similar to the s.e.x. amp -- i.e. - grounded cathode and We split rail bias, or more like a standard cathode bias with bypass cap?

Thanks,

Jim

 

[Paul Joppa]

Is the configuration of the output similar to the s.e.x. amp -- i.e. - grounded cathode and We split rail bias, or more like a standard cathode bias with bypass cap?

I'm moving back to the standard cathode bias arrangement.

The WE arrangement came aboutwith the SEX amp because we wanted to try an autoformer and use it with headphones, so the entire winding, primary and secondary, had to be at DC ground for safety. The WE arrangement allows for that, at the price of requiring two floating high-voltage power supplies. Then when we were developing Paramour II (monoblocks, hence two power supplies already) we realized the same arrangement would allow us to return the signal current loop to the cathode so it does not go through the cathode bypass capacitor. We could not do that before because the stock output transformer is not rated for any DC voltage.

Now that we have an in-house output transformer of better quality and rated for an appropriate DC voltage on the primary, I am ready to give up the WE arrangement and its complications.

 

[jrebman]

Paul,

Thanks for the explanation.  I'm not sure I quite grasp it all quite yet, but a little more study of the WE arrangement should make things clear.

Thanks againm,

Jim