Taming The Treble

[katopan]

That's really interesting Tillydog. I've always hated those discussions where people who can hear the difference get shot down with the theory that the roll off is above the range of hearing. There is something happening there that does effect the audible range, we just don't understand it yet.

[bluesky636]

Nobody is shooting anybody down here.

[romberg]

I used 100 ohms (just by chance).

The difference was immediately noticeable in terms of reduced hiss and harshness, and was the final piece in the jigsaw for this amp for me (and I had been tweaking it for over 2 years). It didn't sound *bad* before, just... unimpressive...

I would be interested in whether it makes any difference for you.

I tried this out the other day. It did make an audible difference (for the better). In my case, 100 ohms did not cut it. The lowest I could go was 10k. And at 10k it made something go away. There was a bit of a harsh crackle thing going on that is now gone with the grid stopper. I'm starting to see why Merlin sprinkles them all over the place in his book.

Mike

[bluesky636]

I tried this out the other day. It did make an audible difference (for the better). In my case, 100 ohms did not cut it. The lowest I could go was 10k. And at 10k it made something go away. There was a bit of a harsh crackle thing going on that is now gone with the grid stopper. I'm starting to see why Merlin sprinkles them all over the place in his book.

Mike

Not surprising. With a 100 ohm grid stopper, the -3dB point is about 38kHz (see earlier graph). Now with a 10kOhm grid stopper, the -3dB point is down to 30kHz.

[img807]http://farm4.staticflickr.com/3712/9429 ... 78f4_o.jpg[/img]

[leadfootdriver]

JJ 6CA7's are the answer to all your prayers.

[bluesky636]

JJ 6CA7's are the answer to all your prayers.

I'm running JJ E34Ls which I like very much.

[bluesky636]

Just placed an order with Sweetwater for a full compliment of Celestion G12M Greenback reissues to go in my Crate 4x12 cab. Yeah, they are the made in China ones, but I can't afford the British made Heritage series. The only thing that made them affordable is that Sweetwater has a 2 year, no interest program going with their credit card. Also, I found this demo on line and they sound pretty sweet.

http://www.youtube.com/watch?v=2GLVcvwq4C8

[romberg]

This thread has inspired me to crack open the java kit I built many years ago. It was the very first "big" amp I ever built and was mostly stock. I discovered something. The more I changed it to be like an express the better it got (big surprise I know .

Eliminating the cathode follower made the volume thing on the guitar deal much nicer. Changing the feedback resistors... nothing big. Then the biggie. The tone stack.

I'm sure Ken must have played around with this and the "stock" weber one and the one on your wrecking ball are not really the same thing. I'm going with the one on the kelly schematic and current BoM on this site. The 1M audio taper pots (especially the treble) make a big and very noticeable difference. And express tone stack has pretty flat highs with all controls set at 12:00.

Check out this comparison done with the Duncan tone stack calculator. The yellow line is the express. The green is a stock java and the blue is your wrecking ball (switched to the marshall tone stack which it is). Note how the express smooths out the highs and the mid dip is not as extreme. I'm waiting for another 1MA pot to replace by bass pot. But that should not matter as much as the treble I've done already.

Mike

[bluesky636]

This thread has inspired me to crack open the java kit I built many years ago. It was the very first "big" amp I ever built and was mostly stock. I discovered something. The more I changed it to be like an express the better it got (big surprise I know .

Eliminating the cathode follower made the volume thing on the guitar deal much nicer. Changing the feedback resistors... nothing big. Then the biggie. The tone stack.

I'm sure Ken must have played around with this and the "stock" weber one and the one on your wrecking ball are not really the same thing. I'm going with the one on the kelly schematic and current BoM on this site. The 1M audio taper pots (especially the treble) make a big and very noticeable difference. And express tone stack has pretty flat highs with all controls set at 12:00.

Check out this comparison done with the Duncan tone stack calculator. The yellow line is the express. The green is a stock java and the blue is your wrecking ball (switched to the marshall tone stack which it is). Note how the express smooths out the highs and the mid dip is not as extreme. I'm waiting for another 1MA pot to replace by bass pot. But that should not matter as much as the treble I've done already.

Mike

You plots didn't show up, but that's OK. I did the same plots using the Duncan tool when I was analyzing the tone stack prior to starting my build, so I understand what you are saying.

I initially did the Trainwreck tonestack that you refer to when I first built the amp. However, I had all sorts of squeals and oscillations and while attempting to solve them I switched to the stock JAVA design. It wasn't until it was suggested that I swap the physical locations of the bass and treble pots that most of my problems were solved. I got things finally working with the more Fender/Marshall tonestack and never bothered to change the treble pot from 250K back to 1M. Since I have everything stable now and like the tone I have, I didn't want to upset the apple cart and make any more changes in that area. When I get home tonight, I will post the overall response of my current tone stack.

My new speakers should arrive tomorrow, so I'll see what affect they have on the sound before making any other changes to the amp.

Edit: Oddly enough, your plot just showed up. I didn't see it earlier.

[bluesky636]

Just finished installing and trying out my cab loaded with the Celestion G12M Greenback Reissues (16 ohm, 25 watts), I decided to go with the 16 ohm versions just for that old time Marshall grind. Holy shit Batman! These things have completely changed the sound of this amp. If they sound this good just out of the box, I can't wait to hear what they sound like after they have been fully broken in. They are that good sounding. Even though they are the Chinese built Greenbacks, they are well worth the money and definitely a better value than the British built versions. If this were a vintage Marshall cab (plywood instead of the pressed wood the Crate is made out of), I doubt you could tell the difference. Here is a shot of the wired up cab followed by a close up of one speaker.

[img:716:800]http://farm4.staticflickr.com/3792/9472 ... 85e2_c.jpg[/img]

[img:800:567]http://farm8.staticflickr.com/7377/9475 ... 049f_c.jpg[/img]

I also made some final tweaks to the amp itself.

I had a slight, low level hum that could be heard with the volume turned all the way down (at normal levels it is not noticeable). I rearranged the grounds a little bit (all AC grounds to one bolt, all DC power supply grounds to a second bolt, and all signal grounds to a third bolt. The hum is still present, but reduced a little more.

Also, since I have been able to quiet the amp as much as possible, I went back and installed a DPDT bright switch with three selections: 100 pF bright cap, no bright cap, and a 250 pF bright cap. I tried a 500 pF bright cap but found that to be way too noisy. The 250 is just slightly noisier than the 100, but gives a nice boost further down in the mids.

The final schematic looks like this:

[img846]http://farm3.staticflickr.com/2867/9475 ... 3654_o.jpg[/img]

[Kassie]

Instead of grid stoppers, which actually can add to white noise (speaking of experience). I prefer shielded cable for v1 grids. Also to stabelise an amp.. you can create negative feedback. Running anodes/kathodes parallel. And the PI wires twisted. Still experience too much hiss? Then I prefer to place a small pf cap. 20/47 parallel on one of the anode resistors off the v1 in the preamp (like an enhancement cap). You can experiment which triode. But obviously the earlier in the amp.. the more it's influence since it's a series chain. The same technique can be used for the PI. But I would use a 100-120 pf on only one of the anode resistors.

Hum might be induced by the lazy filament loop around v1. You could tightly twist filaments with a drilling machine.. and take the filament from v1 up into the air to v2 (as per Fender/Dumble).

my 2 cents.

[bluesky636]

Instead of grid stoppers, which actually can add to white noise (speaking of experience). I prefer shielded cable for v1 grids. Also to stabelise an amp.. you can create negative feedback. Running anodes/kathodes parallel. And the PI wires twisted. Still experience too much hiss? Then I prefer to place a small pf cap. 20/47 parallel on one of the anode resistors off the v1 in the preamp (like an enhancement cap). You can experiment which triode. But obviously the earlier in the amp.. the more it's influence since it's a series chain. The same technique can be used for the PI. But I would use a 100-120 pf on only one of the anode resistors.

Hum might be induced by the lazy filament loop around v1. You could tightly twist filaments with a drilling machine.. and take the filament from v1 up into the air to v2 (as per Fender/Dumble).

my 2 cents.

Thanks. I am very satisfied with the current performance of my amp and have no further changes planned.

[romberg]

Just finished installing and trying out my cab loaded with the Celestion G12M Greenback Reissues (16 ohm, 25 watts), I decided to go with the 16 ohm versions just for that old time Marshall grind. Holy shit Batman! These things have completely changed the sound of this amp.

Yea. It is amazing what a better sounding speaker can do. Even a pretty good amp can sound like crap through bad speakers. Speakers are one of those components that I can actually hear a clear difference when changing. Different brands/types of caps and resistors.... not so much.

Mke

[bluesky636]

Just finished installing and trying out my cab loaded with the Celestion G12M Greenback Reissues (16 ohm, 25 watts), I decided to go with the 16 ohm versions just for that old time Marshall grind. Holy shit Batman! These things have completely changed the sound of this amp.

Yea. It is amazing what a better sounding speaker can do. Even a pretty good amp can sound like crap through bad speakers. Speakers are one of those components that I can actually hear a clear difference when changing. Different brands/types of caps and resistors.... not so much.

Mke

My ears are pushing 60 years old. I'm happy if they can hear overall changes in sound. Subtle differences not so much.

[Clyde]

Bluesky, I ordered the last G12H UK-manufactured Anniversarys that New Sensor had in stock several years ago. When I A/B'd them with the Sino models, I could not hear any difference. There is a huge difference between these drivers and the Heritage however. For the money, they're great, for the tone Heritage are the way to go.