AND MY very cool design idea!!!! (PIC INCLUDED!!!!)

[Morning_Star]

This is a design idea I have for a studio monitor amp plus four channels of headphone amps. Along the same lines as the input selector idea a few posts back.

Image:
http://i7.photobucket.com/albums/y292/kniki3/Backgrounds/Custom/ClassAStudioAmpfrontpanel2.jpg

I posted my idea at HeadWize but I think this would be a better place to get ideas. I'm going to use a design from headwize projects section unless someone recomends a better one.

My design calls for three inputs to select from. A RCA type and two sets of TRS. To be divided up into five signal paths. One to the power amp and the other four to the headphone amps. Then the power amp output should have a selector switch for a set of TRS outs or speaker terminal outs. And to top it off a led db meter with clip indicator for the power amp. This will be a must have for studio's if it anyone can help me make it a reality. Please, any help is appreciated.

This will be handy because you could use one set of TRS to monitor your DAW and the second set to play a synth or something through when you don't want to run it through your DAW. And the RCA could be used for patching in other sources to listen to in the studio such as a radio. And with the power amp people could hook up home speakers and passive monitors. Maybe the design could have a straight through patch for active monitors.

Specs: "Class A" design (and I know how much you hate that phrase), Tube power amp, any headphone amp, 100w x2 @ 8ohms or at least 50w x2 @ 8ohms.

The headphones are rated at 24ohms up to 500mW

Any suggestions to power amp designs and how to branch and combine signal paths with help greatly. I think I could design a pcb from a schematic and combine different designs to work together. I just don't know how to select a signal other than running it through the pot. Or branch to other circuts without just wiring it in series and/or parallel.

 

[Samuel Groner]

Welcome here!

Did I get you right: you want to put a stereo 100 W class A tube amp plus some other circuitry into a 1 U rack?

Samuel

 

[Mbira]

Also, it seems that you are assuming that the monitor mix will be the same thing that all four headphone users are going to desire in their mix. This is almost always not the case. Just throw a 4 buss mixer in there too, and you'll be ready to rock!:green:

If you really want something that "every daw user can't live without", I would suggest maybe making the headphone section solid-state. Usually, hi-fi toob sound is not the most important thing when yer bass player just needs more cowbell in his mix.

Joel

 

[bcarso]

kubi wrote: "For me it looks like 2HU. But still very small for all the electronics, especially the tubes.
I'm not even sure if the iron to swallow 100W would fit into the housing.
Nevertheless, the heat from the two 100W tube amps would melt the housing, anyway. "

Well he didn't say how deep it was.... :razz:

With forced convection you might pull it off, but the fan noise would be unacceptable in most applications.

 

[bcarso]

Sean Olive once joked about the depth of the soundstage of an amp, and said it was about 18"....

 

[Morning_Star]

[quote author="Mbira"]If you really want something that "every daw user can't live without", I would suggest maybe making the headphone section solid-state. Usually, hi-fi toob sound is not the most important thing when yer bass player just needs more cowbell in his mix.

Joel[/quote]

I laughed my ass off when I read that.

And yes, I have figured out that it won't fit in a 1U case definatley, that's why I went ahead and designed the 2U layout. And it doesn't have to be tube but I would like the power amp to be. I don't mind the color. And I really don't need a four bus mixer. Screw what the other three people wanna hear. Lastly, I can settle for 50w per channel but I would really like to try to get anywhere above that. And fan noise will not bother me. Plus any space I have left I will use for heatsinks.

Any design idea??? Once I pick which power amp design and headphone amp design I can get started on that. But I really don't know how to design the circut to switch between inputs and outputs and remain clean. Can I just wire the signal in parallel to each board or will I need to compensate for the current draw increase? Also will I need to adjust the RCA signal for the circut designed to take the TRS connection. And last, should I even use a balanced signal?

 

[pstamler]

I'm going to assume you're talking about 100W per channel. You said you wanted class-A tube power amplification; folks, correct me if I'm wrong, but my recollection is that class-A is 25% efficient, max, which means this amp will be dissipating 800W from the output tube plates, never mind the filaments and driver tubes.

Amplifiers like this do exist; for the outputs they either use transmitter tubes (and 1200V plate supplies) or many 6550-class tubes in parallel. But they won't fit into any 2RU cases; more like each amplifier channel occupies two 17x17" chassis sitting on the floor behind the rack.

It might be -- just -- possible to cram something like a Dyna Stereo 70 circuit into a 2RU chassis, with the tubes mounted on the back panel. That's about 20-30W/channel of clean tubed power. But if you want 100W/channel in that space, you're talking solid-state, and not class-A. A Hafler P3000 would do it very nicely.

Peace,
Paul

 

[Morning_Star]

[quote author="pstamler"]I'm going to assume you're talking about 100W per channel. You said you wanted class-A tube power amplification; folks, correct me if I'm wrong, but my recollection is that class-A is 25% efficient, max, which means this amp will be dissipating 800W from the output tube plates, never mind the filaments and driver tubes.

Amplifiers like this do exist; for the outputs they either use transmitter tubes (and 1200V plate supplies) or many 6550-class tubes in parallel. But they won't fit into any 2RU cases; more like each amplifier channel occupies two 17x17" chassis sitting on the floor behind the rack.

It might be -- just -- possible to cram something like a Dyna Stereo 70 circuit into a 2RU chassis, with the tubes mounted on the back panel. That's about 20-30W/channel of clean tubed power. But if you want 100W/channel in that space, you're talking solid-state, and not class-A. A Hafler P3000 would do it very nicely.

Peace,
Paul[/quote]

Thanks for the info. I knew that they weren't as efficient but damn. And I've been researching tube amps more and I realize how much power that 30W per channel would accually be. I could even go for 15W per channel for the tube or 30+W for the solidstate. That will be pleanty of power for what I'm using it for. I do know that Crate makes a "Class A" 30W tube guitar amp that fits everything in a fairly small place with the pre-amp poweramp and fx's. But I'm going to check out them suggestions. Thanks alot.

Ohh, and couldn't I strech the pcd layout so that I can just lay the tube down? I have a couple boards with tube sockets on them already that are used to fit tubes in a small space.

 

[Morning_Star]

Well, I checked them out. Are my dreams crushed? I guess what I will do now is have an external power supply to make room for the amp. The headphone amps will be no problem since people fit them into mint tins. And I like the Dynaco Stereo 70. I could probally work out the fit some how. The Hafler P1000 and the P1500 looks interesting too. I can't deside what to what to go with. I'm going to start work on the headphone amp board. What kind of input do I need to have for it to be devided among four channels? Can I just connect them all at the same place? Where can I get good schematics or pcb print outs for the power amps?

 

[northsiderap]

Don't feel crushed. You'll know it's a possibility when you see this:

On a serious note, build it!

Personally I don't care if it's as big as a table if it sounds good and does what I need it to do. After all, studio reference amps aren't going anywhere... Are they? :?

 

[PRR]

> folks, correct me if I'm wrong, but my recollection is that class-A is
25% efficient, max,

Wrong. Class A can touch 50%. Ignoring heater, you can actually meet and beat that:
original 6L6 with 19 watt plate dissipation limit has a suggested condition with
10 watts output. (It doesn't really beat 50%: the theory assumes sine-waves and
the real amp runs very bent, 15% THD.)

25% applies to the degenerate connection with a constant-current DC feed instead
of the superior choke (transformer).

We may quickly estimate the size of a tube amp by looking at great tube amps
of the past. Nothing has changed from the last days of commercial tube-work.

A Dynaco Mark VI makes 120 Watts, Mono, in a 4U rack chassis that would
tear-out some rack rails. Real wrist-breaker. The maximum "safe" dissipation of
its four output bottles is 140W, so it is clearly not close to running Class A.
By today's standards, the Dyna power amp is "nostalgic", not monitor-quality.

Bogen made a few 2*150W amps in about the same size, with a custom sharp-pencil
blistering-edge power transformer that ran so hot it had a sticker warning you.
It actually worked very well for driving projector motors in a video transfer
facility. In days of bad transistor PA amps, the Bogen was a nice PA amp,
except hauling that beast around was a back-breaker. And even hot-rodded,
it could not be confused for the Dyna, and far-far from Class A.

Guitarists will know the (original) Ampeg SVT, Traynor BTO, and a similar monster
from Fender. A 100W Hi-Fi Stereo Class A tube amp would be at least the size of
these, with more bottles, and serious heat-rash.

And I could argue that any elegant push-pull tube amp will have lower THD in AB
than in A. Class A may be more euphonic in single-ended form, but the iron for
100W SE boggles the mind and dents the floor.

You can buy fine 35Wpc AB tube amps for under $999 stereo. You can buy a multi-output
headphone amp, more than good enough for cow-bell tracking, for $49.
You have a lovely front panel layout. It isn't big enough for what's behind it
(even at 35Wpc): consider it the control panel for a remote-mounted power amp.
You want the controls at hand, but you do NOT want your hand on a high-power
tube amp (ask the man who has scars from doing that).

You have a company-name on that layout. I'm not sure if there is a market for
this product. But if your marketing skills are better than your electronic skills,
there are people here who can be contracted for design work.

And DANG! don't embed 1,425-pixel-wide images IN posts: they blow-up my poor
800-pixel monitor. Shrink it or link it.

 

[Samuel Groner]

Folks, correct me if I'm wrong, but my recollection is that class A is 25% efficient.

A complementary output stage makes it up to 50%.

I could even go for 15 W per channel for the tube or 30 W for the solidstate.

Er, so you want to say that a tube amp needs less power for the same loudness or what?

From you comments and questions I'm not sure if a power amplifier is the right project for you. If you don't have the slightest idea how to design a four-channel headphone amplifier I'd rather suggest that you focus on that first. Remember: if your DIY amplifier decides to fail, your speakers are in great danger to follow.

If I'm wrong I suggest that you forget the tube idea, get a copy of D. Self's power amplifier book and check his website: www.dself.dsl.pipex.com

Once you think you've got the important bits you can think over it again. A soldit-state 20 W class A or 100 W class B is feasible for experienced people. This will look similar to this: dpafig33.gif
The only thing you'd need to add here is:
* a unregulated PSU
* short-circuit protection circuitry
* protection relais
* thermal protection
* DC protection
Yeah, it will need some serious research from your side to design that.

For complete schematics check: www.crownaudio.com/gen_htm/legacy/legacamp.htm

But you still need to design a PCB for that. And to design a PCB you really need to understand the circuit or it will get messy.

Samuel

 

[Morning_Star]

Thanks for all of the replys. And I really like the idea of it being a remote panel layout and I could go ahead and lay the four channel headphone amp in here. But I still think that I could fit it all with the right choice of design and an external power source. My plan, if it comes together, is to start offering it to the local producers that I know. I really am not planning on this to be some million dollar product. Even though I think it could be with the right designing and marketing.

I do know enough to follow a schematic and create a pcb board from it. And I know how to figure out modifications to get a different result. I just don't know what solutions that you would want to go with to make sure you don't lose quality. I was just going to find a design for the power amp and build one for each channel and four seperate headphone amps and the only thing I would have to design is the circut to switch the inputs and outputs. And I really don't mind the AB designs either. Class A is an over used term anyway.

Er, so you want to say that a tube amp needs less power for the same loudness or what?

No. But solidstate is easier to fit. So I probally could fit a more powerfull design.

Also, what about an amplifier design similar to the ones on the Mackie HR824. They are small with alot of power.

 

[PRR]

> A complementary output stage makes it up to 50%.

"Complementary" or "push-pull" is not needed to approach 50%. Choke-loaded 6L6 will go there. See early 6L6 datasheet, page 2. 43%-46% nominal plate efficiency at high plate voltages. Push-pull is somewhat lower THD, but not more efficient (until we leave Class A).

 

[Mbira]

[quote author="Morning_Star"] My plan, if it comes together, is to start offering it to the local producers that I know. [/quote]

Er, so basically, you made a flashy front panel-took some design ideas from headwize-and now you are here asking for people to design something so you can sell it to your "producer friends"?

OK, good luck with that.

Joel

 

[burdij]

This unit puts out 100Watts with a quad of 6L6GCs and 50Watts with a quad of EL34s. Biasing and switching allow the unit to be set up as Class A or Class AB in pentode or triode mode. The output falls to about 50 and 25 Watts respectively in Class A and to about 12 and 6 Watts in triode mode, primarily controlled, I think by the somewhat poorer impedance match in triode operation, as the transformer is set for the parallel pentode plate impedance.

It is big and heavy. The total weight is 45 pounds which necessitates the use of steel rack mounts that extend the full length of the sides of the unit. The height is 5 1/4 inches (3RU) set primarily by the height of the cores in the transformers. It should be used with at least a 1RU air space above the unit, preferably with a screen across the front. It does have a small fan to provide forced air cooling but if there is any obstruction to the air flow, the output tubes tend to fail rather rapidly (and in some cases spectacularly).

 

[Morning_Star]

[quote author="Mbira"][quote author="Morning_Star"] My plan, if it comes together, is to start offering it to the local producers that I know. [/quote]

Er, so basically, you made a flashy front panel-took some design ideas from headwize-and now you are here asking for people to design something so you can sell it to your "producer friends"?

OK, good luck with that.

Joel[/quote]

No, jack-ass. I need one for my studio. But I was going to offer to build one or two for my friends if they wanted one. I was going to make availible the final design to anyone that wanted to build one on their own. But I wasn't going to build them for free. I would never take someone elses design and sell them to make money. So go to hell.

Thanks everyone ELSE for you help so far. Does anyone have any ideas or sorces for creating a switching circut? I can't find what I need.

BTW. I'm not really dedicated to what is called "class A". I just want a really clean signal for monitoring my mixes and amping my headphones. I do like the sound of a good tube amp but it's not necessary.

 

[Viitalahde]

Watch your language and stop bashing regulars.. :evil:

Sorry, but that's exactly how it looks like. You did a pimpy front panel without having any idea what's involved in building it. A front panel won't get you too far on the way for a finished unit. Neither does a schematic.

 

[Mbira]

Morning_star. You said:

This will be a must have for studio's if it anyone can help me make it a reality. Please, any help is appreciated.

and:

I'm going to use a design from headwize projects section unless someone recomends a better one.

and:

Any suggestions to power amp designs and how to branch and combine signal paths with help greatly.

and, oh nevermind, I guess I'm the ******* :roll:

 

[Moby]

BTW. I'm not really dedicated to what is called "class A". I just want a really clean signal for monitoring my mixes and amping my headphones. I do like the sound of a good tube amp but it's not necessary.

So, nice, modern, class "d" can be great for you :green: :thumb: