Serious Modifications

[rlyach]

Here is another suggestion. Since I have JJ 40W tubes, I started with the Stereomour, moved the loadline using a 3K output transformer that BH can get, and moved the cathode resistor to 800 ohms. The result is a 6W amp with 4.33% distortion. I have not run the power supply simulation yet but I suspect I am going to be a little short. Is this something that I might be able to do?

[Paul Joppa]

You are suggesting taking more current from the power supply. Since heat goes as power which is current squared, that is always a risk! Fortunately in the present case, the PT-6 is able to handle 75mA per channel.

You will get less plate-to-cathode voltage when you draw more current - not a lot less, but maybe 5-10v less(?). You have shown 325 volts, but the design point (at nomimal power line voltage) is 300v, so you can probably count on 290v.

You'll need a new plate choke as well, to handle more than 50mA. The PC-2 that we use in Paramount, and the BH-7 that Magnequest offers, both have exposed terminals with plate voltage on them, and are unsuitable for mounting topside for obvious safety reasons. When looking for an available choke, remember that as a plate choke it must handle a large AC signal as well as the direct current - most power supply chokes are rated for max current near saturation, so look for a rated current about 50% higher than the actual DC current.

[rlyach]

In order to compensate for the drop in plat voltage I was planning on raising B+. I ran a simulation and the most I could get was 395V using diodes to maintain channel separation in the power supply in place of the 270 ohm resistors and increasing the supply caps. Based on this data, in order to keep the 2A3 biased at 60V, the most plate current I can get with the current power supply is 60ma and not 75ma. This hardly seems worth it. The Power calculated at this operating point is 5W, which would only increase the volume by 1db. If I had a different power supply I could raise the B+ to 450 and thus run a 325 plate to cathode voltage. This would get the target 6W but too many things will have to change. I did find a 150ma 15H 256 ohm plate choke, but I think the inductance is too low. I did check into custom iron but that gets expensive very quickly. I am currently re-evaluating the Paramount with BeePre.....

[Paul Birkeland]

I did check into custom iron but that gets expensive very quickly. I am currently re-evaluating the Paramount with BeePre.....

Yeah, custom iron can get pretty scary in a hurry! 

I know I'll annoy PJ a little bit by saying this, but the Paramount is an outstanding test bed for experiments. 

[drewh1]

Hey Randy - There are Paramounts in my future too.  Is there any way to use the Stereomour as a pre-amp, beyond just passive control?

[Paul Birkeland]

Hey Randy - There are Paramounts in my future too.  Is there any way to use the Stereomour as a pre-amp, beyond just passive control?

Theoretically there could be a way to wire it for 45's with a single shunt regulated B+ supply using a completely different power supply, and some kind of DC on the 2A3 filaments.  This would turn the circuit into a preamp, but I'd expect the parts to be very expensive (maybe more than the Stereomour was in the first place), and there's a good possibility that a lot of R&D work would be required to get good results.

(Remember, a Quickie is only $99)

[drewh1]

Well I think knew the answer to that question anyway 

I will likely build the BeePre next. I have been wanting to use my expensive balanced interconnects anyway. All of my current gear is balanced and I got suckered into buying these things! Then I'll build the the Paramounts (after I let Randy figure everything out)

[earwaxxer]

Balanced has piqued my curiosity lately as well. I was previously a skeptic.

On a lark I bought some Blue Jeans balanced interconnects about 6 mo. ago since all of my gear has balanced outputs. I was pleasantly surprised. Thats why I retired my quickie there for a spell. The quickie is back in now with the 'new' digital front end. Of course the proposition of going full balanced with beepree is gnawing. It would be cool if someone could give their impressions of the prebee sound over balanced vs. unbalanced.

[drewh1]

I used to be a musician and so was used to always using balanced cables - I kind of always thought it was the best way to go.

My Ayre equipment is balanced all the way through - I do imagine? I notice a difference with the balanced cables. I think that is specific to the Ayre gear and isn't necessarily strictly because of the balanced interconnects.  having said that, I like the sound of the Stereomour better than the Ayre with my DIY magnet wire single ended interconnects so that says something . . .

I think we hijacked Randy's thread 

[rlyach]

No problem hijacking the thread. I have literally run into a wall anyway. The more I dig the more I find out how little I know about amp design. I attempted to do my own simple parafeed circuit. I actually designed it around iron that I could get easily. Then I submitted it to a friend of a friend who builds custom iron and designs. He thought my circuit was a good attempt "for someone who is new to tubes," but then proceeded to point out several issues. I now know I don't really understand reactive plate loads, and I am finding I don't have time or the resources to find out. If I really wanted to design my own amp I will need to build, test, change, test, change, test... I guess that is why BottleHead amps sound so good. They have put in the time and effort, and they have built the knowledge to design something that works and sounds amazing to boot. I have resigned myself to purchasing an integrated kit based on the 300B just to satisfy my need to build something else. Besides, I need to replace my solid state amp (Linn LK140 if anyone is interested  )

[drewh1]

I hear ya Randy - Feelin your dilemna - thinking about selling my Ayre but need it right now for videos. I definitely don't have enough juice with the stereomour for videos. I guess the output is much lower from my DVD player.

I liked your idea about building the Paramounts on one platform. I am used to an integrated amp and struggling with whether to have all the different components needed for the monoblocks.  Sounded like a reasonable compromise.

Let us know what you build.  BTW, i am lovin having a remote for the Stereomour, now I can sit back and relax . . .

[rlyach]

Drew,

Your woodworking skills have inspired me. I am getting ready to build another Stereomour kit for my Pastor. We purchased a pair of Hoyt Bedford monitors for his amp, so I purchased this nice piece of Sycamore to match. I plan on finishing with tong oil and wax, as per a woodworker I met in the Woodworkers Source. This should look cool, especially with the dark edge. I plan on doing a 1/4 or 3/8 round over around the top outside edge as well. Plus I am making it 1/2 inch taller than the supplied kit base.

Incidentally, I have chosen my next amp project but it is not a BottleHead kit. I really wanted an integrated stereo amp based on 300B's

[drewh1]

that is a beautiful piece of wood - and rounding the edges will add a great finished look. Good call to make it deeper - I am glad I made my base a bit deeper (4"). it easily accomodates the stepper motor I added.

Post pictures when you are done!

[rlyach]

Drew,

Here is the finished base. This is the first time I have used wax and I must say that I like using it. Much better for the wood and less messy. Plus I was able to use a buffing pad on a drill to give it a nice sheen. Now I am waiting for the kit to come so I can start building.

[drewh1]

that's gorgeous, I really like the rounded top edge. I also think the extra depth has an elegance too it, as well as allowing more room for large expensive caps!

very nice work - be careful, you might have to try making your own tubes soon     Still awaiting my new "improved" crossovers. I almost bought a couple of Clarity MR caps for the coupling but am saving my money for the paramounts.

Oh, I picked up a matched pair of Telefunken NOS tubes, don't need two, just happened to be a good deal. Let me know if you want to try one in your Stereomour, I'll send you one so you can compare. So far I like the stock tube alot though.

drew.