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Vintage threads from the first ten years

previous: Joe Z. Thanks, I tried the amp w/ no neg f... -- 4/29/2000 4:33 AM

Re: vibro-champ- observations (Long)

4/29/2000 4:07 PM
MBSetzer	Re: vibro-champ- observations (Long) Hey Joe: Where you wanna go with those highs? Where are they coming from? Are the highs always too much, or just above or below a certain volume? Does every guitar have a problem with your amp? Have you compared it to anybody else's known outstanding Champ? With the repair phase pretty well complete, and some other configurations for the same basic tube circuit within reach, now its much tougher to fine tune it to your taste. Are you still using the original speaker? This is very important since it could just be a lack of bass due to speaker size. Or if too much bass left over from the stock circuit is still getting to any 8inch speaker, it will physically roll off the low end audibly more than bigger speakers while still (hopefully) handling the relatively high energy subsonic components electrically, leaving less room though for the higher frequencies that 8inch cones are best at reproducing. The highs will still be reproduced, but under these more stressful conditions, they will intermodulate more, producing distortion products that are even higher in frequency and more annoying than just a gradual peak in the HF response. Conventional wisdom would be to tweak the tube circuit until it was more ideally matched to the speaker, instead of the virtually generic Fender '60's layout which is proven to be much better for speakers capable of moving much more air. And that's what I would do after making sure what you want to really do with it. These practice amps have enough tone stock, that it has always made me question why they are not more common professional tools. But if you really want to be able to play it at full volume, you need to move way beyond the original speaker, even though it has exceptional tone up to a point. Plus there will be less tweaking required, its just hard to make an 8inch speaker sound like $1000 So my approach for one amp was to load the circuit with a professional 4ohm cabinet instead of the 8inch speaker, then pick out my favorite set of tubes, then adjust the values & quality of the coupling & bypass caps until I thought I was getting the best performance up to the highest volume I could. After eliminating the tone stack, the coupling & bypass caps were about all that was available for tone shaping. Then when I plugged back in the built-in speaker for portability, I was willing to accept that it would lose its composure earlier on the volume dial. The amp still sounded better to me than stock, if it didn't I would have changed it back Then got a WeberVST P8Q 4ohm, and it sounded even better while being able to go up a couple more notches. But the circuit tweaking I would not do until I had gotten all the other external stuff together, besides just the speaker: What kind of guitar & pickups, guitar settings? Are you plugging straight in or using any pedal(s)? Are you really sure there is nothing else wrong with the amp? I have wasted time before trying to tweak out an undesirable sound in an effort to customize the tone, when there was really a defect or low quality part causing the problem. So I would hook it up to a big cabinet where you can really hear what its doing, make sure there is no more restoration required, check guitars, intonation, adjust pickups, try different cables, picks, etc. Become intimately familiar with a stable configuation of this unique Fender class A amp, whether you have just gotten it to work in stock form, or have already reached a defect-free modification you like better than stock. Such a short time ago it was needing repair, now that its at least working you owe it to yourself to play it a lot more hours (days, weeks) than you have worked on it, then after that adjust your guitar to make the combination even better. Then enjoy that for a while before going forward with circuit changes that could have much less benefit for the time & effort required, regardless, the longer you get accustomed to a good stable amp as soon as its working, the better you will be able to judge the more subtle changes you might want to make later. Hope this helps, Mike

4/29/2000 4:07 PM

MBSetzer

Re: vibro-champ- observations (Long)

Hey Joe:

Where you wanna go with those highs? Where are they coming from?

Are the highs always too much, or just above or below a certain volume?

Does every guitar have a problem with your amp? Have you compared it to anybody else's known outstanding Champ?

With the repair phase pretty well complete, and some other configurations for the same basic tube circuit within reach, now its much tougher to fine tune it to your taste.

Are you still using the original speaker? This is very important since it could just be a lack of bass due to speaker size. Or if too much bass left over from the stock circuit is still getting to any 8inch speaker, it will physically roll off the low end audibly more than bigger speakers while still (hopefully) handling the relatively high energy subsonic components electrically, leaving less room though for the higher frequencies that 8inch cones are best at reproducing. The highs will still be reproduced, but under these more stressful conditions, they will intermodulate more, producing distortion products that are even higher in frequency and more annoying than just a gradual peak in the HF response. Conventional wisdom would be to tweak the tube circuit until it was more ideally matched to the speaker, instead of the virtually generic Fender '60's layout which is proven to be much better for speakers capable of moving much more air.

And that's what I would do after making sure what you want to really do with it. These practice amps have enough tone stock, that it has always made me question why they are not more common professional tools. But if you really want to be able to play it at full volume, you need to move way beyond the original speaker, even though it has exceptional tone up to a point. Plus there will be less tweaking required, its just hard to make an 8inch speaker sound like $1000 ;-)

So my approach for one amp was to load the circuit with a professional 4ohm cabinet instead of the 8inch speaker, then pick out my favorite set of tubes, then adjust the values & quality of the coupling & bypass caps until I thought I was getting the best performance up to the highest volume I could. After eliminating the tone stack, the coupling & bypass caps were about all that was available for tone shaping. Then when I plugged back in the built-in speaker for portability, I was willing to accept that it would lose its composure earlier on the volume dial. The amp still sounded better to me than stock, if it didn't I would have changed it back :-)

Then got a WeberVST P8Q 4ohm, and it sounded even better while being able to go up a couple more notches.

But the circuit tweaking I would not do until I had gotten all the other external stuff together, besides just the speaker:

What kind of guitar & pickups, guitar settings? Are you plugging straight in or using any pedal(s)?

Are you really sure there is nothing else wrong with the amp? I have wasted time before trying to tweak out an undesirable sound in an effort to customize the tone, when there was really a defect or low quality part causing the problem.

So I would hook it up to a big cabinet where you can really hear what its doing, make sure there is no more restoration required, check guitars, intonation, adjust pickups, try different cables, picks, etc. Become intimately familiar with a stable configuation of this unique Fender class A amp, whether you have just gotten it to work in stock form, or have already reached a defect-free modification you like better than stock. Such a short time ago it was needing repair, now that its at least working you owe it to yourself to play it a lot more hours (days, weeks) than you have worked on it, then after that adjust your guitar to make the combination even better.

Then enjoy that for a while before going forward with circuit changes that could have much less benefit for the time & effort required, regardless, the longer you get accustomed to a good stable amp as soon as its working, the better you will be able to judge the more subtle changes you might want to make later.

Hope this helps,
Mike