Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on June 16, 2012, 05:00:57 pm

Title: Adding MP3/CD input to reverb unit
Post by: jeff on June 16, 2012, 05:00:57 pm

 Hi guys

I picked up a tube amp a little while ago that was an extension unit to a record player. Basically the RP unit amped one side (L or R) and this unit looked exactaly like it but just amped other channel for stereo. The amp inside has 6AU6-6AQ5. Not enough gain to play guitar, but sounded good with my MP3 player.

I'm going to add an extra stage and use it as a speaker driven reverb unit and thought it'd be cool if I could have a MP3 input too. So my main amp would be dry my guitar and this unit would just amplify the wet reverb signal plus music to play along with. I don't want to damage my MP3 player and am not sure if this is how to do it but can I just use mixing resistors for the right left and 12AX7 gain stage and plug that into the front end of the amp? I don't want the signal from the tank/12AX7 hurting my MP3 player.

What value should I use? Do I need a resistor to ground from the point where the mix resistors meet?

Thanks
  Jeff

Title: Re: Adding MP3/CD input to reverb unit
Post by: PRR on June 19, 2012, 11:59:02 pm

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Title: Re: Adding MP3/CD input to reverb unit
Post by: tubeswell on June 20, 2012, 12:36:57 am

Quote from: jeff on June 16, 2012, 05:00:57 pm

Do I need a resistor to ground from the point where the mix resistors meet?

The pot (250k in PRR's schematic of values) in conjunction with the (100k) resistor is already doing that.

Title: Re: Adding MP3/CD input to reverb unit
Post by: jeff on June 20, 2012, 07:27:24 am

That's great thanks for the help.

I also want to add a dwell pot. I remember the dwell was a pot before the 500 Ohm resistor. I can't remember the value/rating because  I never tried using one because I didn't have the right one. I hate asking the same question twice, but I can't find the old post about speaker driven reverb and can't find any info online. Could you plaese remind me what value/rating pot to use as a dwell?

 I did happen to find an 8 ohm L-pad in my parts stash. Would using the L-pad after the 500 ohm resistor, instead of a pot before, be a better way then using a pot before the resistor/tank?

Thanks
 Jeff