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Guran
October 11th, 2011, 08:27 AM
I got the urge to turn my TS-7 into something slightly different, a little more Fulldrivish. In many ways I liked the way it sounded, but there were some issues.
1. The characteristic TS mid hump, or more correctly bass-and-treble cut, sounds good with some amps. With some other amps it turns into an overdose of nasality.
2. The drive, or distorsion, is almost too clean. Even when turned up high it can be like too clean while also at the same time being too compressed.
3. The tone control. All the way up to the last ten degrees of the turn it was muddy, then like you hit a trip wire, there's suddenly treble. That treble was not pleasant at all.
To address 1. above I put a switchable .047uF cap in parallel with the .047 C34 (on a TS-7 schematic/pcb), giving a corner frequency of about 360 Hz. After playing it for a while I thought it got a little too thick, or muddy, so I put a .033 as the switchable instead. Corner frequency is now 423 Hz and I like that better. I may even try to raise the cut frequency to the upper 400's.
For 2. I started measuring the forward voltage drop on a number of diodes and transistors I had. The original diodes measured 602 and 604 mV respectively. I found a little baby blue diode that measured just short of 700 mV. Would that do the trick? About 16 % difference in clipping voltage. I tried it in place and I thought I heard a difference. I'm not completely sure though. As I soldered it in place, too much time passed for it to even resemble a A/B test.
Inspired by what I thought I heard I kept measuring around and found a combination of two rectifier diodes that in series measured about 965 mV. That would give about 38 % difference if I kept the ~700 mV blue one in there. After some work to fit them into the limited space I got them in place.
Yes, that is a difference in the way it clips! This is more like what I was after. The only drawback is that raising the clipping voltage reduces the amount of clipping. The result it that in TS-9 mode the max drive is slightly less than what I want if I use it as the only source of dirt. When pushing the front end of a tube amp it's enough though.
On the other hand, the hot mode sounds a lot better now than it did before.
There's two routes to go: upping the gain or finding another combination of diodes that have the same proportional offset as the current combination, but at lower voltages. Keeping the 700 and finding some 500 perhaps? I haven't decided which way to go yet. Would one or another make a difference? Gee, I've gotta find my breadboards!
3. Well, I found some 400V .1 uF film caps. I can cram them in there but it would be a bit bulky and it would be like almost ten bucks worth of a tone cap... I decided that I would get them in there, but I did not have time to finish it before bedtime. I got them in place, tested it and got confused. There was no treble coming by the end of the rotation. Then I realized that I had put the caps in series... Doh! I'll be back about this one.
Some additional steps I would like to do is to lower the gain of the hot mode a bit, to make it usable as a boost mode. Then I would like to replace that little switch to a DPDT foot switch. That would be interesting because there's not a lot of room in this pedal. I keep looking for a very small footswich. Of course a different box could be another solution.
We'll see where this ends!
1. The characteristic TS mid hump, or more correctly bass-and-treble cut, sounds good with some amps. With some other amps it turns into an overdose of nasality.
2. The drive, or distorsion, is almost too clean. Even when turned up high it can be like too clean while also at the same time being too compressed.
3. The tone control. All the way up to the last ten degrees of the turn it was muddy, then like you hit a trip wire, there's suddenly treble. That treble was not pleasant at all.
To address 1. above I put a switchable .047uF cap in parallel with the .047 C34 (on a TS-7 schematic/pcb), giving a corner frequency of about 360 Hz. After playing it for a while I thought it got a little too thick, or muddy, so I put a .033 as the switchable instead. Corner frequency is now 423 Hz and I like that better. I may even try to raise the cut frequency to the upper 400's.
For 2. I started measuring the forward voltage drop on a number of diodes and transistors I had. The original diodes measured 602 and 604 mV respectively. I found a little baby blue diode that measured just short of 700 mV. Would that do the trick? About 16 % difference in clipping voltage. I tried it in place and I thought I heard a difference. I'm not completely sure though. As I soldered it in place, too much time passed for it to even resemble a A/B test.
Inspired by what I thought I heard I kept measuring around and found a combination of two rectifier diodes that in series measured about 965 mV. That would give about 38 % difference if I kept the ~700 mV blue one in there. After some work to fit them into the limited space I got them in place.
Yes, that is a difference in the way it clips! This is more like what I was after. The only drawback is that raising the clipping voltage reduces the amount of clipping. The result it that in TS-9 mode the max drive is slightly less than what I want if I use it as the only source of dirt. When pushing the front end of a tube amp it's enough though.
On the other hand, the hot mode sounds a lot better now than it did before.
There's two routes to go: upping the gain or finding another combination of diodes that have the same proportional offset as the current combination, but at lower voltages. Keeping the 700 and finding some 500 perhaps? I haven't decided which way to go yet. Would one or another make a difference? Gee, I've gotta find my breadboards!
3. Well, I found some 400V .1 uF film caps. I can cram them in there but it would be a bit bulky and it would be like almost ten bucks worth of a tone cap... I decided that I would get them in there, but I did not have time to finish it before bedtime. I got them in place, tested it and got confused. There was no treble coming by the end of the rotation. Then I realized that I had put the caps in series... Doh! I'll be back about this one.
Some additional steps I would like to do is to lower the gain of the hot mode a bit, to make it usable as a boost mode. Then I would like to replace that little switch to a DPDT foot switch. That would be interesting because there's not a lot of room in this pedal. I keep looking for a very small footswich. Of course a different box could be another solution.
We'll see where this ends!