« on: March 29, 2013, 10:58:00 AM »
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Topics - joecool85
« on: March 29, 2013, 10:58:00 AM »
My brother has a Hartke Bass Head (I believe the 2500). He wants to add a balanced line out. He had an issue recently where the sound guy wouldn't hook him into the PA because that was all he would work with, wouldn't take the preamp out (effects send).
Anyway, is there a way to add a balanced line out?
« on: December 19, 2012, 12:02:17 PM »
I just installed a snap disc to trigger a shutdown of our servers at work. These things work all the way below freezing and up to 300+F. Tons of different mounting configs and temp ranges. They go for about $10 each and are made in the USA. I'm thinking it'd be real easy to install one on a heatsink and have it shut the amp down or turn on a fan. No added noise in the circuitry and keeps it simple.
Check 'em out: senasys.com
Anyone have any idea what it uses for a chip? Also, I doubt the 5w rating considering it asks for 9vDC @ 600ma which is only 5.4w...must be a VERY efficient design, no?
Alright, I've come up with a fan controller that I'm happy with. It can run up to 1amp of current for a 12v fan so long as it is heatsinked. With the fans I've played with, 4.5v is when they turn on and start blowing any sort of noticeable amount and 12v is full tilt.
When R3 = 0K
4.5v happens at 40C/104F
12v happens at 75C/167F
When R3 = 5K
4.5 happens at 28C/82F
12v happens at 63C/146F
When R3 = 10K
4.5 happens at 18C/65F
12v happens at 55C/131F
Notice how as the resistance increases, the turn on/full tilt temperatures decrease. To make this more natural in how it works, I would wire the pot backwards so that all the way clockwise would be the hottest temps and all the way counterclockwise it would turn on the soonest and run the coolest.
**This circuit is untested, unverified and not recommended for anything other than testing purposes!**
This is what I came up with for a simple temperature driven fan controller. It is a fan controller I worked on, based on the Temperature Controlled Fan I found online.
This is good for a maximum of 1.5amps, but really you should keep it below 500ma to keep it reliable.
In this version, R1 is a 10K NTC thermistor (shown in schematic at 20C, which is 12.5k). Adjust R2 for the turn on temperature and R4 for the full speed temperature. Fan is a 12v PC fan that draws 0.11 amps.
Note that if you change R4 (full speed temp) you will need to re-adjust R2 (turn on temp). Due to this behavior, I suggest using trim pots for R2 (5k) and R4 (500R) and adjusting R4 (full speed temp) first and then R2 (turn on temp).
Circuit behavior also changes upon load of fan, IE 0.11 amp fan will have different temp ranges than 0.25 amp fan.
*Note: I have not actually built this circuit, only played with it in LTSpice.
**Note #2: I just noticed in some more simulations that the values change if the fan isn't exactly 0.11 amp, I don't know in practice how much it will matter, but it is something to consider. For a controller capable of high current (up to 1 amp) that doesn't care what the amperage of the fan is, see my new 12v DC Fan Controller (LM317)
Apparently I missed the memo, but Dean Markley is back at it making amplifiers again. Very cool! They bought out UltraSound in 2007 and then in January 2011 they started making their own amps again including some tube re-issues as well as a nice lineup of solid state gear.
Here's a link to their page: http://deanmarkleyamps.com/
The DM60RC looks like a nice amp with a 12" speaker, 2 channels, reverb and chorus all footswitchable. It uses digital reverb which is too bad though. The DM15R and DM30RC both use spring reverb units which is cool. The DM15R has no footswitch options, the DM30RC can only switch channels (not reverb and chorus like the 60).
They are more pricey than Fender Frontmans and similar, but so far reviews have been that they sound WAY better and seem to be built a lot stronger. I gotta find one and try it out, they look nice.
MSRP pricing can be found here: http://deanmarkleyamps.com/Downloads/DMElectronicsAmpsPrices.pdf
« on: November 19, 2011, 06:45:58 PM »
I'm working on an amp that has me a bit stumped. It is a Fender Champion 30 and it has hardly any volume passing through from the guitar to the speaker regardless of which channel it is on. There is a good deal of hum/static as well. The volume does work, but even zeroed out there is quite a bit of hum coming through the speaker.
What's more weird is that when you shut the amp off, there is a split second where the amps sounds pretty loud and relatively clean - I'd dare say pretty much normal. I've only looked at it for a few minutes and did some quick voltage checks and things appeared to be in order.
ORIGINALLY POSTED BY user Evil_Food
Something strange was happening with the forum software and this thread wasn't viewable so I had to re-make it.
I was browsing Schematic Heaven and I found a Musicman PP power amp design that uses hybrid cascodes consisting of transistor on the bottom and a valve on the top.
I started analysing the design and decided to make my own low power version with a 12AU7 double triode.
The output transformer is a £12 3.5W Oxford Electrical Products Audio Transformer http://uk.rs-online.com/web/p/products/2106475/?searchTerm=3.5w+audio+transformer&relevancy-data=636F3D3226696E3D4931384E44656661756C74266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E285C772B5B2D5C2E5C732F5D292B285C772B293F2426706F3D3926736E3D592673743D4B4559574F52445F4D554C54495F414C5048415F4E554D45524943267573743D332E357720617564696F207472616E73666F726D65722673633D592677633D4E4F4E4526
If you click on the "Range Overview" tab, there's a picture with the turns on each tap on each side of the transformer. The datasheet says 16k as maximum impedance, but if you do the calculations you can get other values.
What I think might be more interesting is the power supply. It uses a Cockcroft-Walton voltage multiplier to step up and rectify the voltage from 24VAC to ~280V DC. My main reason to do it with a multiplier was to save some money, as I already had a 2x12V power transformer. This way I can heat the tube with 12Vac and provide +/-12V DC.
What I liked in the voltage multiplier was one of its shortcomings - poor regulation. The power supply has high output impedance and when the amplifier enters class B operation, there's a voltage sag on the HT rail.
I haven't looked with an oscilloscope, but the DVM shows about 30V sag whit "harder playing".
I haven't got a preamp for it yet, but I quite like the sound when it's overdriven on its own.
I haven't got a camera or anything I can make a sound clip with, but next week I'll ask a friend (who's actually a musician) to bring along something to record what it sounds like.
If anyone is interested in the voltage multiplier power supply I can post the equations needed to design one.
I want to make a cab with three speakers and have an output of 4ohms. I figure I will use two 4 ohm speakers wired in series, then wire that set in parallel with an 8 ohm speaker making the total load 4 ohms. Would each speaker get the same wattage or would it split the watts between the two 8ohm loads, IE - one speaker gets 50% and the other two get 25%?
So how large of an amp are you guys using these days and what for? I had been playing with a small group including drums with a 50w Vox but now just play by myself or jam with my brother (bass) and use my 20w Dean Markley. Been thinking about getting a bigger amp or at least more efficient speakers but can't justify it when I'm only playing by myself most of the time.
If you have an amp that puts out the most power at 4 ohms and you want to use a single speaker that is rated at 8 ohms, is it possible to attach a 1:2 ratio transformer to the speaker and put full wattage (minus any loses from the transformer) to the 8 ohm speaker?
The best I can find right now is 93.2db/w spl and that is the 8" Jensen Mod 20. Anyone know of an 8" guitar speaker with better output? I can't mash a 10" into my K20-X, just won't happen.
There is also the 94.4db/w spl 8" Jensen Mod 20 C8R although some sites list that as 92.7db/w spl.