Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: BarnBand on March 21, 2012, 03:58:01 pm
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I would like to run my "Hoffman" ac30 with an effective flexible line out (1/4" inch / SWITCHCRAFT)...how is this done?...can anyone help me out?...layout diagram is appreciated...I'm a little "not to good" with schematics...thank in advance ...
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Searching for "line out" on this forum turned up this pic that was posted 2 weeks ago...
(http://www.el34world.com/Forum/index.php?action=dlattach;topic=13304.0;attach=28604;image)
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respecfully with all due respect...its a bit hard for me to discern the "schematic"...If you will...can you simplify it for me...IOW...1K RESISTOR IN SERIES W/ 10K RESISOR CONNECTS TO NEG. CONNECTION OF SPEAKER JACK??... ETC...yes, I am humbled...but its all I can understand...thanx in advance...Frank.[/b...PS...I don't want to blow anything up in this fine sounding amp.
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Ok, I'll break it down a bit. First, the switch near the top that switches between the hot terminal of the speaker (or tip of the the speaker jack) and the 8R/20W resistor is simply a "dummy load" so that the line out can be used without a speaker plugged in. Since the amp always needs a load, when using the line out, you could switch the switch to activate the 8R dummy load.
If you were to use this feature, you'd want a 8R/50W resistor to safely handle the max output of the AC30.
On the other hand, of you are just planning on using the line out to drive another power amp or to feed a mixing board, then you don't need the 8R resistor and switch. In that case, you only have to worry about the bottom portion of the schematic.
The 10K to 50K resistor is there to initially drop the voltage coming off the OT secondary tap to get in the right line-out level range (between .5VAC and 1.5VAC). The 1K is not a resistor, but a potentiometer with the wiper going to the tip of the line out jack, which allows for fine adjustment of the line-out level to what ever you need for the device it's feeding. This could also be a 5K or 25K pot, but I wouldn't go any larger.
Hope that helps, but I suggest you put in the effort to learn to rad schematics - it will be very empowering!
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Heh..."old dog knew trixx"...you R rite tho...but...say I just wanna' run it into another 'ERr AC15 (2 separate speakers)...1 for each amp...is there a "set" ("sweet-spot?")...resistor value that'll work ala Gerald Webers' way in his book ( pages 37-38 ..." A desktop reference of hip vintage guitar amps" ) for a 5e3 Tweedy...although the concept of the variable pot is a great idea!...Is that a middle lobe/tab on the line out jack in the schematic?...could I use a simple switchcraft output jack?...again...I need to humble myself...ps...I'm a player, not an amp builder in it for business / profit...thanx in advance, respectfully frank.
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Hey Barnband, I'm gonna spoon-feed you, but just because I like you :)
Here's some good values for with no adjustment pot that will put you right at proper line-level. You can use typical 1/2W resistors. These are the right values for the 8 Ohm tap. If you don't have one or need to use another tap, then the values need to be adjusted to get the right level. I'm sure this is similar to Weber's method.
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Thank You Gaz...appreciate it...I do need to brush-up on my schematic reading...Frank