First design

[wouter]

Hello,

I have just finished my first amp design but i am not shure if i did the right thing especially in the power amp. The 5k resistor there is the output transformer.
I am planning on a HT of 250 volts.
Can somebody take a quick look at it?
Also where can i find information about the design of a power supply?

Thanks in advance

[Chuck H]

It looks good to me. One thing, the use of a resistor as a sub for the OT for design purposes doesn't work because an actual OT will have very low DC resistance and a 5k AC impedance. All kinds of things can come out wrong if you're SPICEing this design without that in mind. I also think the 1n high pass cap may let in too much midrange and the 1n high cut cap may not cut enough to make the amp "bright" at higher tone knob settings and "bassy" when lower. But this is just a matter of a couple of cap values that should probably be tweaked by ear in the end anyhow.

[eschertron]

+1 to the 'tilt' control for tone. I'm a big fan of that

I am curious why you chose 100k grid stoppers for the 2nd and third stages. 2nd stage especially might allow the Miller capacitance to darken the sound more than you want? Also there might be a need to add a grid leak to the pentode stage. Most pentodes want 220k or less to ground at the grid.

[Chuck H]

Also there might be a need to add a grid leak to the pentode stage. Most pentodes want 220k or less to ground at the grid.

Good call. I think the 570k 0V reference in the diagram is probably fine, but WRT modern tubes I try to keep it below max. Another 1M from the grid to ground right off the grid would give about 360k 0V reference. Which is well within spec for cathode bias (stated even though I don't know what actual tube the OP intends to use).

[wouter]

Thanks guys.
I wans't planning on using an actual resistor as a substitute for the output trafo but the program i use to draw the scematics didn't have a symbol for a trafo so i used this.
Btw the output tube is a EL84.

[Chuck H]

I wans't planning on using an actual resistor as a substitute for the output trafo but the program i use to draw the scematics...

As long as you don't use it in a SPICE model to figure things like voltages, phase margins and frequency response. Those results would be pretty useless.

[überfuzz]

wouter - In what software are modelling this amp? You won't get any good results if you model a transformer using a bunch of resistors. Try coupled coils instead, so that you can model the impedance rather than a just dc resistance. This set up won't model the magnetic flux behaviour, but will certainly get you simulation into the right ballpark.

Edit, I see that this already been addressed...

[wouter]

I use diy layout creator but its not a simulator or anything just for drawing.
diy-layout-creator - Free multi-platform schematic, layout and guitar wiring diagram editor - Google Project Hosting

[überfuzz]

Try LTspice or some circuit modelling software instead.

[Tooboob]

Don't be afraid of the LTSpice. It's free and easy. Get it here (along with some other nice power tools): http://www.linear.com/designtools/software/#LTspice

The schematic capture is fast and easy, though it won't dump out the netlists and things you'd need to go to board layout. Add a bit of text, and it would be fine for hand-wiring. It's a general purpose SPICE program, and it used to come with a nice amp example, complete with modeled tubes, transformers, etc..
Linear Technology funds the development as a tool for designing with their parts, especially their opamps and switching power supply solutions, and virtually all of their linear products have accurate models, available in the LTSpice library. The creator doesn't care much for limiting the tool to this task, and it used to come with many examples that had no Linear Tech content. These have been stripped from the current package, but folks like me still have them. Once you get your design in, you can feed it swept frequencies, and even .wav files, simulate the results, and vew them, or even extract them as .wav files. Yes, you can record your guitar (using other software), play it through your design (not real-time), and hear the results. You can plot frequency response as amplitude and phase, etc.

The user interface is a comparative masterpiece, once you get a few basics (e.g. clicking on the little running man opens the simulation results window). It eats SPICE, so there are lots of models and tools from other parties if you want to expand your horizons. A few people have made decent tube models, but it takes a little skill to merge such things into the LTSpice library.

I was studying an amp circuit that had a five-band GEQ built with opamps, caps and resistors. I was able to capture it and plot the response range in about two hours. Good stuff.

[Chuck H]

I'll second LTSpice. I finally downloaded it because (it was free, and) I was becoming too reliant on prefab SPICE based services and calculators like Duncan PSU/TSC, the ampbooks site and a couple of others. Leaving me at their mercy if I changed computers or suffered a data loss situation. I figured it was time I caught up with the rest of world and stop taking whatever was spoon fed to me. For a low tech designer without a proper electronics education and no prior exposure to SPICE type programs it took some getting use to, but totally worth the time.

[überfuzz]

The schematic capture is fast and easy, though it won't dump out the netlists and things you'd need to go to board layout.

You can use layout topology, but only if you place your components that way in the editor. There is no interaction going on except ohmic, i.e. you won't get any ground loops and such. But like you said it's super if you know how to wire once you got a working circuit.

[eschertron]

I use diy layout creator but its not a simulator or anything just for drawing.
diy-layout-creator - Free multi-platform schematic, layout and guitar wiring diagram editor - Google Project Hosting

I use a freeware program called ExpressSCH to do my drawing. I've looked at LTSpice, but that's all I've done. The learning curve seems steeper than what I'd like.

[Chuck H]

I've looked at LTSpice, but that's all I've done. The learning curve seems steeper than what I'd like.

Same here. A couple of buckle down hours and it gets better. Not as far over my head as I initially thought. Put another way, I downloaded it long before I started using it because on initial trial I was utterly lost. Once my pride got the better of me and I buckled down it got better. It's not any electronics that will confuse you. Rather the learning of how to manipulate a new piece of software.

[überfuzz]

Same here. A couple of buckle down hours and it gets better. Not as far over my head as I initially thought. Put another way, I downloaded it long before I started using it because on initial trial I was utterly lost. Once my pride got the better of me and I buckled down it got better. It's not any electronics that will confuse you. Rather the learning of how to manipulate a new piece of software.

It seems you're on the same page as some MEF:ers. That the initial contact was unsatisfying but that spice-ware slowly grows on you. I bet that in a couple of years time there'll be a dedicated section in MEF for spice-talk. Actually... not a bad idea, since most of what we do in spice-ware is quite repetitive, once you get the hang of it. My point is that with some good example-files we can help MEF users to get going.