| Author | Message | ||
     Erik Hoversten (erikhoversten) Username: erikhoversten Registered: 11-2013 |
Hi Folks!- I'm new to this forum, and I'm not really sure if I should be posting in the "front panel" section or in the "urgent repairs" section. Apologies in advance for the double post. I've got an HD 130 (with a tube phase-inverter and no reverb) that has a really strange problem. I've had the amp for 20 years, and it's always been great. A few weeks ago, I had it re-tubed with JJ EL 34s. Ever since, something has gone crazy with the inputs. In the past, I always used both of the inputs (1 and 2) together on the "normal" channel. I used this setup in order to use an A/B switch to switch between two sets of pedals. It didn't matter if I used input 1, input 2, or both together. The tone and the output volume were always the same on the amp. But since the tube job, the inputs are behaving differently. Input 1 is much louder and broken up than input 2. I am told that it's "normal" for input 1 to be slightly louder, though I never experienced this difference in the past. The most confusing part about the new input volumes is that if I have signal going to input 1 and I plug a 1/4 inch cable into input 2, the output becomes quieter. On the other hand, if I have a signal going to input 2 and I plug a 1/4 inch cable into input 1, the output becomes louder. I have heard of Fender Twins, etc. having this sort of behavior by design. But I've had this amp for 20 years, and it's never done this before. The guy who re-tubed my amp claims that he didn't touch the preamp or anything else besides the power tubes. I contacted Terry Loose (a musicman repair guy who is highly rated on this forum.) He was very helpful, and indicated that what I was describing did not sound like normal musicman behavior. But before I ship my amp all the way across the country to him, I figured I might ask if anyone has any thoughts on what I'm describing. If I had to guess, I'd wonder if what I'm experiencing might be some sort of impedance issue or something??? Thanks!!! | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
HMMM. Honestly, this sounds normal. The signal coming out of your pedal board must be hot so it overdrives the front end on the 1 input which is supposed to be hotter. I can't explain why it didn't do it before, unless you accidentally had the outputs of your two pedalboard outputs not balanced and one was hotter than the other. If input 2 is used alone, it has two 68k resistors in the signal path. If both are being used, they should be the same. They are then separated from the shorting bar that connects them together. Having the tubes replaced should not have done anything at that stage of the front end, unless I'm not understanding what you are saying. Mike. | ||
| Erik Hoversten (erikhoversten) Username: erikhoversten Registered: 11-2013 |
Hey Mike - Thanks so much for your help with this. Almost everything you describe makes sense based on what I'm experiencing. But there's still one piece that I don't understand... Based on the way you describe the input section on the amp, if I have a signal going to input 1 and I plug a 1/4 inch cable into input 2, the volume should not drop. Right? If the inputs are separated from the shorting bar when both inputs are used, then using input 1 by itself should sound the same as using inputs 1 and 2 together. But that's definitely NOT the case. If I have a tone going to input 1 while a 1/4 inch cable is plugged into input 2 and I then unplug the cable from input 2, the signal gets louder. As I understand your description that shouldn't be happening. Am I missing something? Thanks, Erik | ||
| Ed Goforth (ed_goforth) Username: ed_goforth Registered: 06-2006 |
Nothing is connected to the plug on number 2 input while guitar is plugged into number 1 input jack? If you do not have a load on the second jack, it may have the effect your describing. Having a guitar with a pickup load should load down the signal a bit, nothing there might make the input think it needs to be louder because there is no load, haha! What is connecting to the cable on #2? Anything or is it left unconnected if so, what is the purpose of doing so? lol! We will try to help you resolve this somehow  | ||
| Erik Hoversten (erikhoversten) Username: erikhoversten Registered: 11-2013 |
The behavior is the same regardless of the load on the second input. I am running my guitar through a Morley A/B box to two different EQ pedals. These two EQ pedals then go to inputs 1 and 2 on the "normal" channel on the amp. I opened up the chassis to have a look at the input section. I plugged 1/4 inch cables into inputs 1 and 2 of the "normal" channel and hooked them up to my muti-meter. With cables plugged into both inputs, input 1 showed 0 resistance. Input 2 showed a reading of 84. As I understand it, the two inputs should give the same reading if both inputs are being used. To double-check my methods, I repeated my test on the "bass" channel. With cables plugged into inputs 1 and 2 on the bass channel, I got readings of 83 on both. So it seems like there is something strange going on with the input section of the "normal" channel. But I don't see anything visibly wrong. Any suggestions on how to proceed? I'm hoping that the solid-state preamp isn't the culprit. Many thanks, Erik | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
resistor bad on input jack possibly. Should be a 68k resistor. You say it measures 83 but 83 what. K? M? Ohms? |