DiMarzio Forum
DimarzioForum.Com => Gear Closet => Topic started by: LPBII on October 07, 2015, 01:02:35 PM
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I have always liked the concept of a 6V6 Plexi, so when it became apparent that the DSL15H heads are availabe used for not a lot of money I snagged one with intention of modifying it.
The word on these amps was that the green channel is too clean and the red channel is too much gain. Well the DSL 15 watt only offers those two modes that nobody used on the old JCM2000 amps. What was the thinking here? They probably expected the customer demographic for this amp to complain if the gain was not over the top, and the clean was not clean enough. The amp can be modded, but if your not into modding amps these amps are pretty much useless to players other than modern metal players in its stock form. I will be following the mods pioneered by the guys over at the Marshall Amp forum, and the My Les Paul Forum. I hope nobody minds if I log the journey here.
First impressions:
Not very loud. Even through a 4x12 and cranked up it sounded not very loud. There is no way this amp can be used with a live drummer at this volume level. But then I noticed that the pentode-triode switch on the back was set to 1/2 power, or only 7.5 watts.
In 15 watt mode it was totally different. It can get loud. Exploring both channels through various knob settings and with both humbucker and single coil guitars revealed the following;
Green Channel. Way too clean and rather boring sounding. I had to use the Green channel gain knob on ten at all times for it to have any character at all. Turn it down to 9 and it became very weak and thin. I normally use PAFs and single coils and do not want to back to high output pickups.
There is a tone shift button that should never be used. It makes it sound like one of those 1970s Fender Twinns that we all hated. Even with the gain on ten the Green channel sounded "plinky". It had no sustain. Even more troubling, was that the bass notes were boomy through the Green Back loaded 4x12. It was a like a kick drum when ever a bass string was touched, especially with the Deep Switch engaged. The Deep Switch was not usable with the 4x12 when using the Green Channel.
Both the tone shift and the deep switches affect both the Green and Red channels.
Red Channel- What a fizzy mess! Bright, harsh, and fizzy, and waaaayyy too much gain. It is basically unusable. At least for me. Even with the gain knob at only 9:00 it is too distorted. With very low gain settings the Red is still too distorted although thinner. With low gain settings and the volume whacked up to ten, I think I can hear some mojo from the 6V6s under all that fizz. I think.
With the Green channel on ten/ten it is still too clean. And boomy.
What I disliked most about the amp, though, was how stiff it both sounds and feels. It does not breathe like a traditional tube amp at all. In fact despite the all tube signal path it feels almost solid state. Stiff and tight to the point of brittleness. The Red channel does not sing, and the Green channel is plinky sounding.
Many have modded the Red channel into something usable but left the Green channel alone. I will be modding both.
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Cool stuff - and yes, the way you describe it modding both channels seems obvious.
Good luck with the project,
Stephan
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Thanks,
I took the chasis out and checked the bias before running it loud at my current loud playing space yesterday. The bias was way out of whack. One tube was dissipating 94% of max dissipation and the other was at 82%. I set them both to 70%. It did improve the basic tone on both channels. The green is much less boomy now, but still needs the gain on max to sound decent. The red is smoother but still fizzy. Gone was an annoying treble spike on the Red Channel.
While I had the amp apart, I noticed that the filter caps are 100uf. This explains the stiffness of the amp. 50uf filter caps are on the list of things to try now.
Previous to the bias check I tried it in some different cabs with Vintage 30 speakers.
V30 1x12 open back- It sounded better than through the 4x12 for the most part. The Red channel was boxy and a bit nasal, but the Green now wasn't boomy at all with the Deep Switch not engaged. This speaker is a 90s Mesa spec that doesn't have the infamous upper mid spike.
V30 large volume 1x12 closed back- Smoother yet and a little less boxy. Solid lows without too much boom.
I also A/Bed the amp against some others of mine for reference tones.
Green CH vs MetroAmp JTM45- Should not have done this. The DSL Green ch sounded like a transistor radio compared to the JTM45 run clean.
Red Ch vs Silver Jubilee 50/25 watt. I expected this. The Jub completely destroyed the DSL's gain channel. The Jubilee gain channel just sings and is so 3d and dynamic. The Jubilee has not near the hiss and buzz when its not playing a note either. The DSL red Ch is real noisy.
Orange Micro Terror 20 watt. Should not have tried this either. The 1/2 solid state Orange sounded way more tubey and organic. And dynamic. Although the Orange only has three knobs you can set the gain knob up to about 3 O'clock and control the tone from your guitar volume. Turn your guitar down and the Orange cleans up (not completely of course) and crank the guitar volume on a humbucker and its a nice driving overdrive with out fizz. It is as loud as the DSL15.
At the rehersal space, which has high ceilings and hard wood floors and plenty of natural hall reverb, the DSL sounded pretty good. The fizz gets lost, for the most part, in the mix and also the woosh of the room. You can still hear it but with the masters cranked up, you can hear the 6V6s starting to take over and overide the fizz and thinness. Below 6 on the masters and it is noticably thinner. The triode mode cranked is good on both channels. I ran it through the V30 closed cab.
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While I had the amp apart, I noticed that the filter caps are 100uf. This explains the stiffness of the amp. 50uf filter caps are on the list of things to try now.
Are you saying 100uf also for the preamps? Way too much IMHO. For the preamp 20-22 uf is sufficient. I don't mind 100uf on the power tube plates and screens but 50uf mostly works.
Green CH vs MetroAmp JTM45- Should not have done this. The DSL Green ch sounded like a transistor radio compared to the JTM45 run clean.
The JTM45 is one of my favorite clean tones - hard to beat.
Red Ch vs Silver Jubilee 50/25 watt. I expected this. The Jub completely destroyed the DSL's gain channel. The Jubilee gain channel just sings and is so 3d and dynamic. The Jubilee has not near the hiss and buzz when its not playing a note either. The DSL red Ch is real noisy.
It is long ago that I had a Jubilee (the 50W top). I should have kept it. It sounded really nice and was not as loud as the regular 50W Marshalls are.
Cheers Stephan
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All the caps are the board. These caps are on the power amp, and the pre-amp derives its power supply from there through a resistor instead of a choke.
50 watt Marshalls have always used 50uf filter caps through out, including 50uf on both sides of the choke. The original JTM45 only used 16uf . Many run a 32uf on the power amp side of JTM45s (including mine) to prevent ghosting.
The 100 watt circuits have general ran 100uf on the power amp side, and 50uf on both sides of the choke like the 50 watt, but there is quite a complicated history of the evolution of the filtering of the 100 watt amps. Early plexi 100s had low filtering (often ghosting) and then by about 69 they had high filtering. Then in about 1986 they reduced the number of the filter caps on the 100s to make them easier to build. A lot of people think that the pre 86 100 watt JCM800s have more punch.
Hiwatt 100s make an interesting comparision. Hiwatts ran 200uf on the power amp, 100uf on the screens, and 50uf on both sides of the choke. (BTW the Jubilee tone stack and taking the signal to the tone stack from the plate instead of the cathode are based on the Hiwatt amps design)
Orange and Matamp ran 100uf and only 16 uf on both sides of the choke.
Fender Tweeds ran about 20uf caps throughout. The Black Face Fender amps started running about 70uf on the power amp side which became more standard after the CBS take over going into the silver face era. By the 70s many Fenders were running 200uf on the power amp side.
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I can't seem to find any schematics for the DSL15 online. Plenty of JCM2000 DSL schems but the boards and lay outs are different. That makes it it kind of a puzzle to find the components affecting the green channel. The Red channel mods are well known.
The plate voltages are up around 425V, which means I can't use old stock 6v6 tubes pulled from an old radio or something. The max rating on old style 6V6s are 315v and 12 watts max dissipation. Apparently new design 6V6s can handle up to 450 volts and have 14 watts max dissipation (and sound more 6L6 like).
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Fixing the Red CH might be as simple as using a 12DW7 pre-amp tube in V1. The 12DW7 has a 12AX7 triode for the A triode ( pre-amp tubes are actually two tubes or triodes in one bottle) and a 12AU7 for triode B. A 12AU7 has only 1/5 the gain of the standard 12AX7. So if the Red Ch uses V1B, that will be a far easier fix that modding the printed circuit board. Still need to up the gain of the Green Ch in that case, though, because the Green Ch sux if its master volume and gain are not dimed. If the Red Ch uses V1A then it won't affect the Red Ch and will totally gut the already gutless Green CH.
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It certainly does not hurt to try lower output preamp tubes, especially the 12DW7 came to my mind as well. The 5751 would also be a good candidate.
Cheers Stephan
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The main problem with using lower gain pre-amp tubes, is that I don't want to lower gain on the Green CH at all. In fact I would like to increase it so it behaves more like the Green Crunch mode on the big DSLs.
Just to clarify the signal chain of the DSL: The guitar signal goes to one side of V1. After that the Green CH signal goes on through both V2 triodes and into V3A and then into V3B. The signal is taken from the cathode of V3B to the tone stack (EQ). The amplitude of the Green signal from V1 to V2 will determine how clean and how much gain the Green Ch will be/have.
The Red CH signal is split from the Green CH signal right after V1 and re routed so that that it cascades into the other V1 triode at a clipped level. It then cascades through both sides of V2 and V3, making it five cascaded gain stages at overdriven levels. But I really need to find a Schematic of the 15 watt version. The JCM2000 schem of the DSL preamp design is almost unreadable, it so convoluted and complex. The DSL15 only has Green and Red modes, without crunch, and lead 1 modes.
I have seen some internet postings that 12AU7 side of a 12DW7 actually pins out to the Green CH when used for V1. That would be exactly opposite of what I want. JJ makes a 12DW7 with the triodes reversed, but I don't know how easy it is to obtain that tube in the USA. It might be just as well to mod resistors and capacitors on the board......
The nuclear option is to just gut the amp and use the chassis and transformers to support a 6V6 Vintage /Modern type build.
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The project is kind of at a stand still until I can order parts online. Local mom and pop electronics supply stores don't exist anymore. I don't want to place an order until I find out what I need to up the gain on the green channel. I may have to trace the traces on the PCB to draw a schematic, because I have had no luck in locating a schematic.
In the meantime, I read that a 12AU7 lowers the gain on the red channel down to a crunch. That would be not enough gain on the red channel for soloing, so a 12DW7 (reversed?) may not be the ticket anyway.
Playing the green ch with a ToneZone and Bluesbucker loaded Charvel sounded good (gain still dimed). Obviously they have engineered the green Channel for high output pickups. This of course makes sense because that's what most people play with these days. I don't though. I play mostly vintage type single coils and PAFs these days.
The green channel sounds better through a open backed V30 loaded cab than through a closed back cab. It breathes some life into the clean sound if the room is a little dead. This amp could have used a reverb at least for the green ch.
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Still have not made in mods (been too busy) but its apparent that DSLs are wicked bright. Just to get the JTM-45 into the same range required diming the treble and presence knobs. And the Red Ch is even brighter than the Green Ch.
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I finally found a schematic of the DSL-15H:
*The signal is split between V1a and V1b with the red channel driving directly into V1b to create distortion. This signal path dead ends before V2 unless i's switched in.
* The Green (clean ) Ch signal path by- passes V1B but does not go straight to V2. There is a Fender Black Face style EQ section or tone stack (it's fixed internally by the resistor and capacitor values with no adjustment knobs). Moreover, this tone stack is located, as in a Black Face Fender, right after the very first gain stage.
*From there, it's on to V2. Once again the Green Ch signal path is dead ended unless it's switched in. Either the Red or Green Channels are switched in just before V2- at the expense of the other.
*V2 represents the extra tube we would find added to a modded Marshall JCM800 2203, or the typical modern high gain tube amp. Apparently V2A will overdrive if the signal it receives is strong enough (as in the Red channel signal). V2A cascades into V2B.
And V2B also cascades into V3A.
V3B is a cathode follower that goes to the master tone stack, or EQ controls. This is the amp's master EQ section for both channels-although the green channel is pre-EQed
After the tone stack are the dual volume controls (for the Red or Green Chs switched in and out with them) and it's off to the PI and output tubes.
OK, how do I mod the Green CH more to my liking? On the big DSL's the crunch mode essentially by-passes the pre-EQ. The DSL15 doesn't have the alternative circuitry that the signal path for the crunch mode would follow. I could add these on a separate bread board, but all I really want is a little more gain. It looks like I can just change the value of R 76 to get that. I may need to change the slope resistor for the green ch pre-EQ tone stack as I suspect that is why it is so bright.
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What is the function of R76 - is that the fixed resistor for the midrange? You could increase that for a boost effect. To tame the brightness you could add a capacitor in parallel to the resistor. The older Mesa Boogie Mark IIs have a 33k in parallel with a 0.005uf cap in between the ground connection of the mid control and ground. This can be bypassed (for normal operation) or inserted as a "gain boost". For less gain boost, decrease the resistor.
The Hughes & Kettner Puretone has a 1 meg pot between the ground connection of the mid control and ground, labelled "Growl" - turned up it is like lifting the tone stack as in the Mesa Boogie Mark I. This is quite a radical boost.
Cheers Stephan
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Thanks for the tips and all your comments Dark Blue Murder.
I think the mid range setting resistor in this case would be R75
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I found a well stocked electronics store and have acquired everything I need-I think. I haven't had time to remove the board yet, though, and I'm busy replacing filter caps in another amp.
I did pull a 2x12 with G12T75 speakers out of storage. Not good. It accentuated just about everything I don't like about the stock amp. I need to play through G12T75s every once in awhile to remind myself why I don't like them.
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Well I finally got some mods done.
Green Channel: Changed the slope resistor of the internal tone stack from 100k to 56k. This is actually a very common mod on black face and silver face Fenders. It makes the green ch sound more like a tweed and less like a silver face. This alone boosted up the midrange and increased gain. It also reduced bass boom. So it did what I wanted. I went ahead and lowered the signal padding resistor as well, but I think I'll go back to stock there. Once that is done, I'm done with the green channel. With the guitar volume all the way up it has some grit, but cleans up when I roll it back a bit. Just the way I like it.
Red Channel: I did most of the established mods for the red ch. I'm not happy with the results yet. But I don't have the V1b cathode by-pass cap in right now, and the added gain pot load resistor is way off spec, because I read the stripes backwards. :-[
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BTW, if your a novice don't try this at home. I have experience playing around with amps and follow the standard safety procedures.
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Okay, I fitted a more correct value resistor (100K) for the gain pot load resistor, and put the cathode resistor by pass cap back in*, with a 10k resistor between it and ground. Success! This amp sounds very good now.
The fizz and sack full of bumble bees buzz are gone gone gone. The red channel now is actually mostly clean up to 3 on the gain knob. From 3 to 4 its more of a crunch, but by 5 its starting to get some serious gain. Up to 5 1/2 to 6 you can get a higher gain overdrive with the guitar volume up, but turn the guitar down a bit and/or back off on the pick attack and it cleans up fairly well. You can just ignore the green channel and play the red channel exclusively if you want. Up to 7 your getting into searing high gain real estate. And its all usable gain, unlike the stock amp. The tone controls now work quite well if you want more cut or a warmer girth.
The amp works this way with my Tone Zone loaded Charvel as well as with vintage output pickups.
The main draw back is that it makes the green channel more or less not very useful. The main purpose of the green channel now becomes loud cleans, or a pedal platform, but this only a 15 watt amp. I may revisit the green channel mods, or de-mod, the green channel now.
I will have to go through and replace some of the carbon comp resistors I used with metal film, because I had them on hand, to lower the noise floor of the amp. The noise level is still unacceptable to me.
* The original mod list calls for just clipping this cap out. But I found that it needs to be in there. The tone is fatter and smoother and the amp has less noise.
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Well how does the amp do in a gig volume situation with a drummer? I ended up using the Red Channel throughout, because the Green Channel by itself isn't quite loud enough. The Red Channel is loud enough. Channel switching isn't absolutely needed with the modified Red Channel, because it now cleans up fairly well by turning the guitar down, and you don't disappear in the mix. The down sound is the back ground noise on the Red Channel when a note isn't ringing out. Is there a small waterfall nearby?
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I need to post an update, since I solved the noise problem.
I changed the cathode cap on V1 with one of the same value and type. It is an electrolytic cap. This got rid of the nasty hiss and back ground noise. It really lowered the noise floor of the red channel. It was a bad cap causing the noise apparently. The green channel is dead quiet now as well.
But this also brought back some fizz on the red channel it seems. I tried rolling some tubes through V1 to see if that helped. First, I tried an old Groove Tubes from the 80s. That got rid of the fizz and drastically improved the tone. However, it also brought back a little noise. I ended up using a Tung Sol re-issue in V1. No fizz and hardly any noise. That gave it a much fatter and richer tone, especially on the Green Channel. The Green Channel is no longer sterile. It's dynamic with the guitar volume and pick attack and has some swirl now.
The Red Channel seemed brighter than the Green Channel now as well. I lowered the red channel bright cap to 150pf. This seemed to do the trick and its not a really problem sharing the Eq controls.
Overall, the amp sounds really good now. It sounds like a much more expensive amp. Not quite the overdrive higher gain tone of a Silver Jubilee, but quite acceptable, and this amp is no longer headed for ebay.
The Green Channel gets huge clean tones going now. It presents a big sound stage at playing with a drummer volume levels. I'll have to see how well it takes an overdrive pedal next.
To recap the mods:
)Adjusted the bias from 93% to 70%
) Changed the slope resistor in the internal Green channel fixed tone stack.
) Changed the Red Channel from the Lead 2 to Lead 1 specs of that of the big DSLs.
)Rolled some tubes with a Tung Sol RI in V1 when done.
)Lowered the Red Channel bright cap from 470pf to 180pf and then to 150pf.
Replaced a bad electrolytic cap.
The Red channel sounds best through Vintage 30s or Green Backs. The Green Channel sounds really good through G12T75s for cleans, especially in a big room with some natural reverb, but the 75s don't sound good with the Red channel for my style of playing, in my opinion. They just don't sing.
The deep switch is not needed unless your at absolute bedroom volume levels. At gig or rehearsal volumes the bottom end is plenty strong.
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Congratulations to the successful tuning project!
Cheers Stephan
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Sorry for reviving a good old thread, but hopefully LPBII will read this
To recap the mods:
)Adjusted the bias from 93% to 70%
) Changed the slope resistor in the internal Green channel fixed tone stack.
) Changed the Red Channel from the Lead 2 to Lead 1 specs of that of the big DSLs.
)Rolled some tubes with a Tung Sol RI in V1 when done.
)Lowered the Red Channel bright cap from 470pf to 180pf and then to 150pf.
I have already modded the red channel to taste as per instructions from other fora.
I do however agree that the clean channel is a little 'dull' sounding, and I want to know what number on the schematic is the slope resistor (R??).
Also, did you adjust the R75 value with good results?
lastly; have you revisited any of the modifications and/or made new ones since this topic closed?
Kind regards, Christian.
EDIT: After studying the schematics again, I'm assuming R97 is the slope resistor?
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EDIT: After studying the schematics again, I'm assuming R97 is the slope resistor?
You are correct, R97 is the slope resistor of the non-adjustable tone stack, which is the equivalent of a Fender style tone stack with bass (R72) and mid (R73) controls turned up full, and the treble turned up partially. Adjust R74, R75 and R76 to get a different treble control setting.
Cheers Stephan
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lastly; have you revisited any of the modifications and/or made new ones since this topic closed?
Kind regards, Christian.
EDIT: After studying the schematics again, I'm assuming R97 is the slope resistor?
Sorry I missed this. I have a love hate relationship with the amp. A few weeks ago I played it for a few minutes and turned it off as I thought about selling it. Then a few days ago I grabbed it because it was handy and light weight for a jam. It sounded great! Just killer! Then at the same place yesterday, but through a small 1x12 cab, it was kind of disappointing again. Before, when it sounded so killer, it was through a THD design 2x12 with Vintage 30s.
What I think is very important with this amp is the speaker cab. It loves Vintage 30s and needs at least a 2x12 cabinet.
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The speaker cab is an often underestimated piece of the sound chain.
Seems like this amp needs low end support from the two V30s.
Cheers Stephan
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Well I forgot to engage the deep switch with the smaller cabinet. It doesn't need the deep switch with the larger cabinets, but its a good thing its there if you need to play through a smaller cab. I played it last night through the same 1x12 cab, and with the deep switch engaged. It sounded great!
The red channel modded is great to play through. It really responds to volume knob riding well. Even with the gain cranked up to 7.5 you can clean up fairly well just turning down the guitars volume knob. But with the volume knob, turned up, it can still do heavy. Just a great range in the sweep of the gain knob compared to stock. And that is even with a PAF clone. Even with the gain at 7.5 it doesn't get farty or mushy. Most EL84 powered amps in this class can't say that. At lesser gain settings below 5 you can go from semi-clean to heavy blues with the sweep of the guitar's volume knob.
Here's a youtube of some of the Johnny Eggz mods that I used:
https://www.youtube.com/watch?v=ewx4U5Hiv5I
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I have already modded the red channel to taste as per instructions from other fora.
I do however agree that the clean channel is a little 'dull' sounding, and I want to know what number on the schematic is the slope resistor (R??).
Kind regards, Christian.
Stock, the green channel can be a good pedal platform -for front of the amp pedals. The green channel gives a better range of tones with the 56k slope resistor in my opinion. At least you don't need to run the green channel gain on 10 all the time. Stock, the green ch seems very scooped to my ears.
This amp is best used as a single channel amp. Pick the red channel and dial it in, or pick the green channel and dial it in, but it's not a great channel switcher mid song or mid set. The big DSLs are that way too in my experience.
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Greetings, my first post to this forum. I like this head a lot. I had the first 3 steps of the johnnyeggz mod done but the C34 was just snipped. I'm going to do the rest and was wondering if I should replace C34 and add the 10k resistor? Also, is the green channel mod worth doing at the same time? Does it add gain or change the tone?
On the subject of speakers, I've played mine through a few cabs. At a pickup jam one night I ran through the speakers of a Peavey Duel and it was amazing, I don't know if it was the Black Widows or 16 ohms or even the weight of the amp (80 pounds) but it rocked!
I know this is an old thread but any advice would be appreciated. Thanks, Bob
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Yes, you should replace C34 not just snip it. C34 just snipped can be a source if back ground hum and noise as well as hiss.