5751 for DSL40CR headroom?

[SkyMonkey]

Cheers for the explanation AMS.
I expect when the new DSL schematics finally leak out there will begin a wave of experimental mods, similar to the Mk II DSLs.

 

[SkyMonkey]

I did just found this post from @scozz in a thread from yesterday that seems to be in the vein of what I am looking to do.

If your looking for headroom why would you buy a 1 watt amp?

As far as fizziness goes I think that 8” speaker has something to do with it. I own a Dsl1hr,....I play it thru a 1-12 cab loaded with a Creamback, it sounds phenomenal!!

Also, Marshall Dsls have more gain than I would ever use, so I changed out the V1 position. I put a 5751 tube in place of the stock 12AX7, a 5751 tube has 30% less gain than a 12AX7.

So that tube change really opened up the amp, it sounds more musical to me. I can now put the gain on 9:00 or 10:00 o’clock and the volume wherever you want it.

I usually want it on 10!

I know the amp referred to is a DSL1HR, but this is what I am wanting to try out with a DSL40CR.

 

[BftGibson]

Hi BftGibson.

I won't list my pickups as they are all in my signature, but as you can see they are generally on the high output side. Generally they are set at about 4mm clearance from the strings. I am a metalhead at heart, hence the high Ultra gain setting I keep quoting (notch 6, between 1 and 2 O'clock). At this setting I get upto but not over the point of mush compression and can still use overdrive to push for more harmonics. But the Ultras are too together close for what I want them for.
Ideally I want to set and forget OD1 for rock and OD2 for metal, but there is not enough distinction to my ears.
Don't get me wrong, this is the best amp I have ever had for what I want out of it. I just want to see if I can tweak it to suit me slightly better. The range of tones from my different guitars keep things nice and varied, and the tones are lovely and fat, especially with the new speaker.
I will try using the MVs higher though. I am guilty of keeping them low. I guess as I am not a gigging musician I tend to keep the MVs low at bedroom levels, and set the gain and channel balance with the channel knobs.
I am also running my DSL with a BOSS GT-100 in 4CM, which adds extra layers of gain/volume/boost/overdrive complication.

I do love to tweak though.

very cool...you are in the ball park for sure..you are prob 1 or 2 tweaks away..i sense it !!! I will encourage you that in the end..this amp can give the 1 -2 switch from od1-2....looking for your post soon...for...ah ha got it !!...if i was still doing the heavies..the DSL is def my amp..setting it up just like you want...rock on !!

 

[scozz]

Hi @SkyMonkey,....if you’re looking to tame the gain on your Ddl40cr, a 5751 in the correct position will do it.

I use either a 5751 or a 12AT7 on all my higher gain amps. My Dsl and a couple of other of my amps have more gain than I would ever, use so this works perfect for me.

Also as @pedecamp mentioned, depending how much you want it lessened, there are other tubes that will do the job.

Check out this gain chart,....

 

[calzone]

Hello, I'm glad I found this thread My problem is that in red ultragain channel at around 5-6 gain the sound becomes heavily overcompressed. The initial pick attack (or palm muting - even more) causes volume dip-out.
I already ordered 5751 and 12AT7 for experiments with swapping V1/V2 tubes. But as much as I understand the real problem looks more like described by @ampmadscientist. It's not the amount of gain but low-frequency, unmanageable content.
If for the mod the schematics are needed, there are some already posted on this forum:
http://www.marshallforum.com/thread...-dsl-schematics-are-finally-out-there.105345/
Which is the V1A cathode bypass capacitor? Is it C79 2u2 50V?

Cathode bypass cap DSL40CR?

• calzone
• Jun 14, 2020

Or, since the first triode of V1 is a common preamp (buffer?) for all channels, is it better to manipulate C69 680n 63V, as it is on ultra gain channels only?

 

[calzone]

I just used a Cathode Bypass Capacitor Calculator: https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/
Here are results with values of actual components in V1B circuit (R96=1.8k, R97=100k, R94=1M, C69=680n):

Response

• calzone
• Jun 14, 2020

The second curve is after changing 680nF cap to 470nF. Even with original components it looks like a high-pass filtering in ultra channel is already applied by Marshall. Is it simply not enough?

 

[calzone]

After playing with the Cathode Bypass Capacitor Calculator I realized that simple changing the bypass cap value results in a left-right shift of a freq curve. I'd rather have lowest frequencies attenuated, not losing low-mid range which is essential for a guitar. So instead of playing with a cap I changed the value of cathode resistor - originally 1.8k. Making the value higher makes the curve drop on the left, low-freq side. Now I think that's the way to remove a mud from hi-gain distortion.
Am I right with this? Can I safely change the value of the R96 from 1.8 to 3.3k? How far can I go with this?

Resp2

• calzone
• Jun 15, 2020

 

[SnickSound]

What you're describing as "mushing out" is basically the treble cap (C74) having less effect at high settings. See the treble cap allows mids and highs to basically bypass the gain knob, but as you increase the Gain setting the lows get injected back into the path and take over the distortion sound, aka mush. This is a defining factor of most Marshall amps: the Gain knob is more about how the overdrive sound than how much overdrive there is.
(No treble cap makes things worse because lower settings mean more high end loss aka mushier due to the tube's capacitance, that's the whole reason treble caps came to be)

Can you compensate somewhere else? Sure, you can play with coupling caps and bypass caps as you are discussing about, you can increase R101, etc. But there's a fundamental aspect of the amp's design you can't overcome: none of this will give you MORE overdrive. All you can do is attenuate the lows more, you can't boost the mids and highs more than they already are.

The result would thus be: you'll be able to increase the Gain setting, but it will sound the same as it did before at a lower setting.
If you want more drive with the same sound as it has on a lower setting, it would make more sense to keep the same settings but use a HIGHER gain first tube.

Or just do it like guitarists have been doing it for decades: slam the front end with a Tubescreamer or SD-1.

Or if you're happy with the way it sounds at a lower setting, then just stop looking at the knob. You'll never get the same sound at all ranges, not without fundamentally changing the way the amp works, or at least not without changing how it sounds where you think it sounds best.

 

[SkyMonkey]

none of this will give you MORE overdrive

It isn't more gain I am after, it is the same useable gain but at 9-10 on the Ultra Gain dial instead of at 6-7.
Also the 2 Ultra channels sound fairly similar. It is me being picky. And I am using ODs to increase the differences between Ultras in my GT-100 4CM MIDI setup.
I never did get around to buying a 5751 BTW.
But I have heard things said about the ECC823 and some DSLs that now pique my interest again.

 

[calzone]

@SnickSound I see what you mean. The C74 cap (why it's marked NF with no value?) kinda "bleeds" higher frequencies into distortion tube V1B with no respect to gain VR3:1 potentiometer. I don't mind that. Also, I don't need more distortion. It's just to much utra-low spectrum which causes the mud and almost farting. I need tight, clearly defined bass tones. Why not cut the low-freq the way I presented?

 

[SnickSound]

It isn't more gain I am after, it is the same useable gain but at 9-10 on the Ultra Gain dial instead of at 6-7.

That's what I'm saying, the amp's fundamental design makes it so higher gain settings will always be mushier because at that point you can only increase gain in the low frequencies.
A lower gain tube could make it less "mushy" but only because you'd have less distortion at higher settings.

 

[SkyMonkey]

Someone in another thread has tried the ECC823 in a DSL40C (V1) to good effect.
I think I will try it out.
http://www.marshallforum.com/threads/ecc823-has-arrived.109888/page-2

 

[SnickSound]

@SnickSound I see what you mean. The C74 cap (why it's marked NF with no value?) kinda "bleeds" higher frequencies into distortion tube V1B with no respect to gain VR3:1 potentiometer. I don't mind that. Also, I don't need more distortion. It's just to much utra-low spectrum which causes the mud and almost farting. I need tight, clearly defined bass tones. Why not cut the low-freq the way I presented?

I'm gonna assume it's a 1nf which is quite common there.

Cutting low frequencies further more for a tighter distortion certainly works, but it requires a bit of experimentation to get the recipe right, and it can result in a sound that is too "dry".
You want to see an extreme example? The AC30 Top Boost uses a 500pF coupling capacitor into a 500k volume control, which makes for a high-pass filter with a corner frequency above 600Hz. Yet the lows are still there, it doesn't sound like a megaphone. That's because a simple one-step high-pass filter like this doesn't cut everything under the corner frequency, it just lowers the signal progressively more as the frequencies get lower. The corner frequency isn't where the cut start either, it's where the cut reaches 3dB.

In regards to your suggestion of changing the Rk from 1.8k to 3.3k, sure you can do that. But this changes the bias point of the tube, and thus how it overdrives. You have to try it to see how you like it.
Remember one thing though: the lowest note of a guitar is around 80Hz. Your graph shows about .5dB difference at 80Hz, quickly moving to no difference at all.

C76 however... not unusual to lower that to 2.2nF, even 1nF. That would probably be the most effective spot to try and quelch the lows a bit. Remember: it doesn't remove everything under the corner frequency, just lowers it a lot. As the signal gets squashed with each stage of overdrive, those lows come back a little but stay cleaner.

Also, R101 and C75 form a treble peaker which effectively sets an upper limit on how much lower frequencies can pass to the next stage. A bigger R101 will set that limit lower without being too drastic. I've used 1M here with great effect. C75 can be lowered to move the effect to a higher frequency. I like 1M with 1uF, but that's me (and it was a scratch build, not a DSL).