6100/6101 (No) Power Amp Distortion?

[james_johnes]

Hi everyone, this is a question for owners (or past owners) of 6100/6101 30th Anniversary Amps.

I own a few 90s Marshall: two 4100DR (one with 5881 and one EL34) and one MkIII 2500. All of these amps sound much better with the power section driven hard (basically with the MV at close to the max), otherwise they sound shrill (hence the hatred for the 4100 played at bedroom volume!).

However, I recently got a 6101LE (with EL34) , and this does not appear to be the same. Turning the MVs (there one per channel + a global one) full on does not seem to improve the tone very much. Even pushed hard, it seems to me that the power section was designed to say relatively clean, unlike previous generations of Marshalls (including the JCM900s).

In fact, played on its own at ‘bedroom’ volume (circa 85db) does not appear to sound differently (once the low volume compensation mode activated) as driven super hard through a reactive attenuator and re-amped.

For those of you who know these amps, it is indeed the case? Are the 30th Anniversary radically different, architecture-wise from the SLP, 800s, 900s, and closer to the latter day DSLs?

Thanks for your lights on that.

Cheers,

 

[Trelwheen]

I'd pull the chassis and see if MV pot(s) or other parts have been changed.

Also I'd check the bias on power tubes (also it's possible a power tube is going south on you), and check the preamp and PI tubes to see if somebody stuck an AU7 in there or something

 

[anitoli]

The power amp is basically that, a regular tube power amp with a few extra things attached. 6100's should sound fine without having to drive the power amp into clipping, the preamps is where all the sound is created anyways. What do you mean by "putting the MV's"? Has this amp ever been properly serviced?

 

[marshallmellowed]

Hi everyone, this is a question for owners (or past owners) of 6100/6101 30th Anniversary Amps.

I own a few 90s Marshall: two 4100DR (one with 5881 and one EL34) and one MkIII 2500. All of these amps sound much better with the power section driven hard (basically with the MV at close to the max), otherwise they sound shrill (hence the hatred for the 4100 played at bedroom volume!).

However, I recently got a 6101LE (with EL34) , and this does not appear to be the same. Turning the MVs (there one per channel + a global one) full on does not seem to improve the tone very much. Even pushed hard, it seems to me that the power section was designed to say relatively clean, unlike previous generations of Marshalls (including the JCM900s).

In fact, played on its own at ‘bedroom’ volume (circa 85db) does not appear to sound differently (once the low volume compensation mode activated) as driven super hard through a reactive attenuator and re-amped.

For those of you who know these amps, it is indeed the case? Are the 30th Anniversary radically different, architecture-wise from the SLP, 800s, 900s, and closer to the latter day DSLs?

Thanks for your lights on that.

Cheers,

Most master volume amps are designed with a "clean" power amp in mind. The preamp is designed to provide the overdrove/distortion. The fact that you like a 900 better with it's master on 10 is fine, and a personal thing, but not how a master volume amp is designed to be used.

 

[james_johnes]

I'd pull the chassis and see if MV pot(s) or other parts have been changed.

Also I'd check the bias on power tubes (also it's possible a power tube is going south on you), and check the preamp and PI tubes to see if somebody stuck an AU7 in there or something

Hi Trelwheen. Sorry my post was not clear. I did not meant that there was anything wrong with the amp. It works fine. It's just I feel that it works differently from the other Marshall that I own. Hence my question.

 

[james_johnes]

The power amp is basically that, a regular tube power amp with a few extra things attached. 6100's should sound fine without having to drive the power amp into clipping, the preamps is where all the sound is created anyways. What do you mean by "putting the MV's"? Has this amp ever been properly serviced?

Hi Anitoli. Sorry, there was a bit of the sentence missing. I corrected the original post. Indeed the 6100 sounds "fine" (at least not worse) without the power amp clipping, which it seems to me is different from the other 90s and 80s Marshall, where the general opinion seems to be that the power section needs to be at least a little bit 'cooking' / clipping for the 'magic' to arise.

 

[james_johnes]

Most master volume amp are designed with a "clean" power amp in mind. The preamp is designed to provide the overdrove/distortion. The fact that you like a 900 better with it's master on 10 is fine, and a personal thing, but not how a master volume amp is designed to be used.

Thanks, marshallmellowed.

That's the thing: my understanding (from my avid readings) is that the first MV Marshall were not designed as MV amps. There were simply more or less the usual non-MV Marshall, in which Marshall engineers fitted an extra pot before the PI.

And indeed, it seems to me (and to quite few other people, if I believe what's I read on the forum ) that the MV JMPs, 800s and 900s did not have the 'Marshall' growl unless the MV was set pretty high (and the amp pretty loud) – and indeed the power section in those amps appeared to start clipping rather rapidly –, and sounded shrill otherwise (or fizzy in the case of the 900s when relying only on the diode-assisted preamp overdrive fed to a clean power section, because of a MV set too low).

As far as I understand, other amp designs at the time – e.g. Mesa – were specifically built as you describe, i.e. "with a "clean power amp in mind", with "the preamp designed to provide overdrive/distortion". But, not the Marshall amps, as far as I understand, which, until and including the 900s, pretty much carried the SLP/JMP legacy.

But, to me, the 6101 appears different. There is a crazy array of preamp tubes, and it looks like, indeed, the power section remains pretty clean until you push it really hard, a bit more like a Mesa would do.

Which is why I asked this question .

 

[anitoli]

Keep in mind that as you increase the individual channel volumes you will hit a point near max when the 5201 op amps will saturate and square wave way before you can get the master volume up high enough to clip the power amp.

 

[marshallmellowed]

Keep in mind that as you increase the individual channel volumes you will hit a point near max when the 5201 op amps will saturate and square wave way before you can get the master volume up high enough to clip the power amp.

Good point...

 

[Trelwheen]

Hi Trelwheen. Sorry my post was not clear. I did not meant that there was anything wrong with the amp. It works fine. It's just I feel that it works differently from the other Marshall that I own. Hence my question.

I didn't think you thought there was anything wrong with it.

 

[TheKman76]

Not personally familiar with the 6100 range, however, you're line of though rings true. I've experienced this with modern Mesa, Orange and Marshall amps where the power amp is intended to be largely linear.

Depending on the design you can boost in the effects loop to get the PI and power tubes driving. That said, doing this to a DSL40CR sounded like hot garbage, something to do with the resonance control in the power amp I think. Better to use it the way it's intended and get the tones from the pre-amp.

 

[james_johnes]

Keep in mind that as you increase the individual channel volumes you will hit a point near max when the 5201 op amps will saturate and square wave way before you can get the master volume up high enough to clip the power amp.

Oh! That is a useful piece of information that I did not have! So there are op amps between the preamp and the power section?

This would explain indeed the phenomenon I noticed: no point in attenuating the amp to drive the power section harder!

Any thought on why Marshall put op amps there? To keep the power section clean?

Thanks for the information. This is super helpful .

 

[anitoli]

Oh! That is a useful piece of information that I did not have! So there are op amps between the preamp and the power section?

This would explain indeed the phenomenon I noticed: no point in attenuating the amp to drive the power section harder!

Any thought on why Marshall put op amps there? To keep the power section clean?

Thanks for the information. This is super helpful .

Yes, the 5201's there are 4 of them are used for the channel switching. Pin 1 is a current sense switch, high flow channel 1, low flow channel 2. Behind those are TL072's use for the fx send/return buffers.

 

[james_johnes]

Yes, the 5201's there are 4 of them are used for the channel switching. Pin 1 is a current sense switch, high flow channel 1, low flow channel 2. Behind those are TL072's use for the fx send/return buffers.

Wow! I had no idea. I tried to read the schematics, but they are way too complex for my little brain .

That's odd though, why would Marshall design a circuit where switches can be overloaded by the preamp signal?

So, basically, if I understand well, this 30+ year old amp has to be treated like a "modern" amp: set the amount of distortion with the gain knob, and use the MV to set loudness, as opposed to 'early’ MV Marshall amps, where the MV serves de facto more to mix/blend preamp distortion and power amp distortion.

And in terms of tone, there is no benefit – quite on the contrary, actually – in setting the MVs higher. There are just there to balance the respective loudness of the three channels. Correct?

Sorry if that sounds obvious, but my experience of ‘early’ MV Marshall makes that it was not obvious to me at all.

Consequently, I also guess the triode/pentode switch should have no impact on tone, since the power section remains clean (except if you actually blast out 100W)?

Thanks.

 

[Thoma]

... Even pushed hard, it seems to me that the power section was designed to say relatively clean...

I did some testing with both a Tom Scholz Power Soak (Version 1) and - very recently - a Marshall Power Brake PB100.

The Power Amps of my 6100LEs (EL34) compress and distort very nicely even through the green Channel.
Goal of my tests was to get good tone, not maximum distortion of the Power Amps.
So I used the power amps at a level that would give me tone breaking-up and preamp gain would add another layer of distortion to give the tone more sing, drive and power. (Think about stacking 2 or 3 overdrive/distortion pedals.)
I found it very important to dial in sweet spots of a (relatively high 70-80%) Channel Volume/Gain and Master Volume (40-60%).

By the way: After driving the Power-Amps into clipping with 2 power Tubes and 4 Power Tubes, I definitely preferred the 4 Tube Power Amp sound as it gives me natural compression.

Some time ago I did similar exercises with a '83 JCM800 2210 and would get similar results.
For my preferred tones that is.

Same for my 6100LM (5881).
The sound LM sounds a little differently than the LE. As I love both, that's why I keep both.

As to the architecture question - I actually never tried to get to the bottom of that.
Whenever I get a new piece of kit, I try to make it sound good.

Marshall's idea of the amp was to put all classic Marshall tones (and more) into one package and make them available at low volume.
For me the 6100 delivers perfectly, even though I think that low volume premise was a little flawed in the first place:

As the prerequisite of classic Marshall rock tones was always volume.
Marshalls shine when properly cranked.
AND when air is being moved...
Preferably by at least 8 speakers with 12" diameter.

 

[Guitaraficionado74]

I experience the same as OP: the 6100/6101 amps are much less dependent on increasing volume to sound good. They sound great at ANY volume level! Meaning, the full range of frequencies is there from the start, at sensible volume levels. This is indeed different from other Marshalls - and I own quite a few. Other MV amps, like the JCM 2203/04's and for example the Vintage Modern, benefit hugely from setting the MV well past noon.
This is the reason I use my 6101 at home, as well as in pub-gigs: ALWAYS a great sound!

 

[Jethro Rocker]

Consequently, I also guess the triode/pentode switch should have no impact on tone, since the power section remains clean (except if you actually blast out 100W)?

You could try it and see to your own ears but Triode always sounds mushier to me, less attack and punch. I never use it.

 

[anitoli]

If using any gain at all the triode mode makes it sound like ir took a quaalude..

 

[Mentalo]

I agree that being a 100W head it sounds incredibly good at lower volumes however to my ears there seems to be a „magic“ combination of channel volume and master volume where it has a sweet spot and starts to sound incredible. The speaker has a significant part in that, too. A 12“ speaker at bedroom level just sounds anemic.

 

[RickyLee]

Yes, the 5201's there are 4 of them are used for the channel switching. Pin 1 is a current sense switch, high flow channel 1, low flow channel 2. Behind those are TL072's use for the fx send/return buffers.

Hello my old buddy! I hope all is well.

I have recently went back to try my two 6100 amps, the '94 and the '97 and I am still not digging them at all like I was telling you about all those years back.

I still have not installed the chip sets I got from you, but being I am out of work from that work injury permanently now, I plan on getting back to some projects. And my bad, I still never installed the full set of elytic caps to redo my '94 6100 lol. Man how time is flying by.

Recently, I have been going back and forth between a few amps chasing tome again: my 2007 JVM 410 that I modded the OD channels for much less gain/signal drive and then my modified TSL100, my hand wired Jubilee 2555 (which I am considering converting to a 15W - 20W) and then the 2555 Silver Jube and even the '89 Black 2550 Jubilee and modified DSL100 and then a couple amps I built myself. The 6100 amps compared to all those mentioned sound like something is not right to be honest. , mainly CH3 which was always my favorite with Gain set 4 to 5. CH2 modes B C sound dull, lifelss and a bit shrill as well. Yet, both 6100 sound the same and I have ruled out all vacuum tubes.

Anyway, I am still trippin why I am just not feeling the magic I experienced gigging with my first 6100, the '94, all those years ago. I went with that amp for about a year or so, and ZI thought back then I finally found that tone close to what is in my head lol. Went on for awhile doing well with my 6100 for many many gigs back at that time, then gave 6100 a break a break.

Then came back to the 6100 few years later when I joined the Trower Tribute band around 2015 and I ended up thinking at that time something was wrong with it. Then drug out the '97 6100 and it sounds exactly the same. Then they got stashed away until this past year I been trying them again this past year.

So, to not take up too much more space here, maybe I am running my channel volumes too high and maybe I damaged those chips? I have always ran the channel volumes CH2 & CH3 @ 7 to 10. I do the same thing with my JVM as well.

I wish I wasn't so broke these days being out of work and you being so far away, as I would just ship one of these to you and have you go through it lol. I am getting frustrated for sure. I am going to start selling off lots of gear, cabs and FX as well soon, way too many amp heads here not being used really lol. But I really do not want to sell my 6100 amps even though I have two of them to be honest.