| Author | Message | ||
     Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
I know there are cross over threads about each and every issue, but I need to start from scratch here. This HD210 had no tremolo when I bought it and I fixed that by replacing the 16 volt zeners. I changed the two transistors too, but they were actually fine. I have ordered new caps from here and there as replacement is recommended. The issue at this point is very loud surf type white noise. Especially when the master is full and I creep up on the volumes in either channel.It is also worse with a guitar plugged in. The white noise will pulsate also with the tremolo setting. maybe that is a clue as to what area the cause is? The tubes are not microphonic, but I don't know much else about them. If the noise is caps, which ones would be the most likely suspects? If when I change all these caps, and the noise remains, then where would I go from there? BTW, the bias seems to be set right. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Without blanket replacing everything(which I don't suggest), you migt be better off building a signal tracer and starting at the beginning(or end, like I do). Here: http://www.tedsforums.com/forum/index.ph p?topic=8797.0 This will allow you to track the sound through the amp and see which section it's in. Just because it's feeding in the trem just means that it could be in front of the trm circuit or in it. I assume you have another amp to use as a sounder so this might get you in the right direction. Mike. | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
Thanks Mike. I'll just say that I have replaced some of the caps, but not the 5 little ones yet. Here is another observation. With the max volume at 10, and the volume at zero, there is still guitar sound from the speaker, but thin, and with no effects. When the volume is turned to 3, then the sound become rich and the effects come into play. Shouldn't the guitar be silent with the volume at zero? I have been staring at the schematic and am confused, because it is a ganged pot. I don't understand why there is a pot for the reverb portion, when the reverb already has a pot of its own? I think that signal tracer is a very good idea. | ||
| Lars Verholt (lmv) Username: lmv Registered: 11-2009 |
Hi Peter, Can you tell us if your HD is a solid state or tube phase splitter type? The dual volume system for the reverb is a way to make the sound more even regardless of the amp setting. By controlling both the drive and recovery volume, the reverb blend stays contant and there is less risk of overloading the drive circuit. This is yet another cool detail in the MM amp design. Sincerely, Lars Verholt | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
It is a solid state unit, and not the 12AX7 type. Here is my lastest discovery. If I unplug the tank, then the volume control acts correctly and increases nicely from zero, however, it only has to be the white rca connection that causes the problem even with the red plug free. This tells me the transducer in the tank is grounding the output of IC-5. Since IC-5 has nowhere to go, because the tank circuit isn't complete it must be somehow affecting IC-4's bias and causing some volume at zero? Any ideas on that one? | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
I solved the tank issue. The one slapped in this amp is an 8 ohm input. I should be a 1425 ohm unit, so I am basically putting the output of the IC to ground. Still will have to deal with the white noise though. | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
I make a simple signal tracer and checked out for this surf sound caused by each channel as their volumes are increased separately. I had the master at zero, so the power amp isn’t involved. I checked the sound at that point, turning up the individual volumes and the sound is there. What would be common to both channels in that situation except the IC 7 and related components?...Ideas??? | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
Got my new Reverb tank today and the final 5 little caps. I make a simple signal tracer and checked out for this surf sound caused by each channel as their volumes are increased separately. I had the master at zero, so the power amp isn’t involved. I checked the sound at that point, turning up the individual volumes and the sound is there. What would be common to both channels in that situation except the IC 7 and related components? | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
Just to add to the last post about IC 7 being common, I just swapped it for the input IC of the plain channel. The noise is the same. The other common item is the +/-16 vdc bias, but that is good. I have changed the zeners there before to fix the tremolo issue. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
At what point did you detect the surf noise on both channels EXACTLY? | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
I had installed all the parts I needed and just said, "The heck with it, I'm gonna slap this thing together. It sounds great. The noise to signal ratio, means I'd be peeling paint off the walls and never hear the white noise. Besides I needed my workbench back.  I did cosmetic work and replaced rusted hardware. The eBay pics with the yellowish background are all I have for befores. https://picasaweb.google.com/10564149946 6626593469/Amp# | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Good on you. Sometimes, we make it a little too complicated for ourselves. You picked the right approach, obviously. Congrats. Mike. | ||
| Peter Harvey (oldpete) Username: oldpete Registered: 01-2013 |
Yes thank you. Now I can focus on other things. If I ever see an MM amp laying around now in a second hand store or some place where it might be cheap due to appearance or some issue, I might take it on as a project for re-sale? Now I have the confidence. |