Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: basschops1528 on October 07, 2016, 03:29:05 pm
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Hey Guys,
I was musing the other day and had an idea about silent operation at a potential full volume for Power Tube OD. I would never try this on a larger amp but anything less than 10W seems ok.
My friend lives in an apartment and can't blast the amp for a full rich sound so I had the idea, as the heading might imply, to rig up an internal or external dummy load and switch with a line level/ headphone out with a common imp. for headphones.
The switch would require the amp be off before changing from speaker to load, and there would be a divider and pot for volume control.
I thought I'd try this out on my Champ build since it's only 5W and the resistor(s) needed would be easily implemented inside or outside the chassis.
You could turn the amp all the way up, wide open, and get a nice full sound yet make the volume comfortable in headphones.
Any ideas on how I could do it? I've made sure to take heat into account.
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I am sure there are "other ways" to do this, but I know this will work.
You can use a 100w dummy resistor from Parts Express into speaker jack. Then have a Red Box speaker cabinetulator (plugged into a line out) & go from XLR (on the Red Box) to a preamp like EMu Tracker Preamp. Plug headphone into the preamp.
OR do what I do and have the EMu Tracker Preamp plugges into a USB port on my computer which allows the amp to be played thru computer speakers at a very low volume without headphone.
http://www.ebay.com/itm/8-Ohm-100W-Non-Inductive-Dummy-Load-Resistor-/221743323805?hash=item33a0ee9a9d:g:3bEAAOSwpDdVK8ZS (http://www.ebay.com/itm/8-Ohm-100W-Non-Inductive-Dummy-Load-Resistor-/221743323805?hash=item33a0ee9a9d:g:3bEAAOSwpDdVK8ZS)
http://www.ebay.com/itm/Hughes-Kettner-Red-Box-5-Classic-DI-and-Amp-Simulator-LN-/361749240948?hash=item5439ef5c74:g:f4wAAOSwNRdX7A7q (http://www.ebay.com/itm/Hughes-Kettner-Red-Box-5-Classic-DI-and-Amp-Simulator-LN-/361749240948?hash=item5439ef5c74:g:f4wAAOSwNRdX7A7q)
http://www.creative.com/emu/products/product.aspx?pid=17511 (http://www.creative.com/emu/products/product.aspx?pid=17511)
With respect, Tubenit
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Sounds great, but unfortunately that's way out of budget for what I'd want to spend. I thought I could just use some resistor rated at least twice the highest wattage at full roar and a simple divider network like Sluckey gave me for a line out on my marshall; two resistors and a pot.
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I did like you are suggesting, mainly for signal tracing, not tone, used something kinda like this;
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Do a google search for "Firezog". http://www.charlestonarea.com/octane/wiring_a_firezog.pdf (http://www.charlestonarea.com/octane/wiring_a_firezog.pdf)
Believe that will do what you want. Just be sure that the 10 ohm resistor power rating is large enough. I ran this set up on an AX84 P1 amp.(5 watt). Son used it to drive a Peavey Classic 50.
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Id borrow from the Garnet Herzog, then tweak it for driving phones.
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> use a 100w dummy resistor
Maybe overkill for--
> my Champ build since it's only 5W
5 Ohms 10 Watt resistor is ample to load the Champ.
Next problem is to cut the signal way-way down, adjustably, to set headphone level. Herzog only drove Amp inputs and used a high resistance divider. Headphones are low resistance. Low-R pots are getting hard to score.
Below I sketched a fairly minimal path using low-cost parts.
However this may not be entirely satisfactory. Main problem is that even a little Champ some of what you "hear" is really felt in chest and feet. Can't get that with irate neighbors. Next the loudspeaker plays a large role, razzing up midrange and losing the high-highs. Headphones may be "too good". Tubenit points to cabinet simulators, which help, but don't typically output headphone level, so you need another box after.
Build the below, try it. It will save the neighbors. If it is "too good", change the output jack and start trying add-ons to get the tone more speaker/room-like.
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This is why I love you guys and this site! I will look into all of that, especially PRR's drawing. Sounds exactly like what I want. Good thing is I can rig it up before totally finshing the amp since it's simple.
Now, how hot would a 5 ohm 10W resistor get? I'd probably use a good old white cement block with thermal paste underneath and on the chassis and cover it with epoxy.
Should I incorporate a heatsink into the chassis, or maybe I can get use it to load my bench power supply at a calculated 5 wattsand measure the heat?
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Those cement block resistors are meant to be air cooled, not mounted to a heat sink. Just give it a 1/2" air clearance on all sides. It's only gonna get hot while you're playing. It's gonna be chillin' otherwise.