BM Verdict: Death by Conversion

[ayan]

I got to the point where I felt very comfortable with the BM. I tweaked the boost and, to me, that helped quite a bit. Still, the lingering problems with the animal are:

1. It has way too much bass coming out of the clean stages. This makes the overdrive buzzy in the bottom end at some point (when dialing up the gain).

2. Even with the tamed boost scheme I use, dialing the amp to sound good without the boost will make it sound harsh with the boost. Dialing the amp to sound good with the boost makes it sound too clean and lifeless (thanks to HRM seetings, which have to tame high end in boost mode) without the boost. And my boost, compared to the "traditional one" (as found in all but some BM amps) is pretty whimpy already in terms of gain.

3. I took the time to A/B/C the BM with the 80s classic and Skyliner amps... The BM wins on the clean department, but it fails miserably in my hands in overdrive mode.

4. I did a few quick tests to determine what the amp would sound like as a Skyliner/HRM/BM PI, and while the clean is definitely stiffer, the overdrive is a lot smoother. And while it is true that the traditional PAB lops off the bass, at least it doesn't make the OD + PAB harsh, it makes it honky (which I'm already used to anyway).

5. The 3 stage approach sounds good, pretty similar to the 4 stage with the inter-stage OD gain turned way down low. The thing is, once again, that the bandpass boost is a problem. I can get a small boost if I ride the volume pedal, so I don't need the PAB to do that for me. And I can't use the PAB for a mega boost because the sound gets downright ugly to me.

Conclusion: to me the BM cleans are great, and if the OD is dialed in for low gain, it sounds remarkably close to the clean tone. The BM would be great if that's all I wanted from an amp. Alas, that's not the case, so surgery is my next step for this puppy.

Cheers,

Gil

[mdroberts1243]

Hi Gil,
What are the "BM" values you tried in the preamp stages?

I've done a lot of experimentation with my spring-clip main board the last few days and have moved away from the ODS-101-like values to 'sunnyland' values: 150/1.8, 120/2.2, 220/3.3, 150/2.2. BTW, the 'alternate' values I put in my schematic don't make sense and it looks like some transcription problems and crossed Rk values.
I'm using 1uF Ck on CL2, 4.7uF everywhere else.
I have a 72k PAB boost resistor.
I have .01 coupler on the CL2 plate
I have .001 coupler on OD1 plate.
I found the OD-input trimmer very sensitive and kept it around 20-24k to get a clean-ish output from OD1.
I have a switch on the coupling capacitor from OD2 to the HRM stack... sometimes I like the switch shorting the cap, other times I like it open.
I initially found the OD 'raspy' and I can still get that, but I think it is more controlled now with the new values.

I have tried to determine a set of 'max-clean' values... settings that take each stage to the limit of 'clean' with a 'normal' guitar input level on the input jack... in my case: Volume at 3 to 4, OD Trimmer 20-24k (estimated), OD Drive at 2, PAB On, OD On, Tone knobs all in the middle.

Other findings... if the mid-pot is much past '2' it starts to swamp out and reduce the effectiveness of the treble and bass controls. The mid-boost is fairly subtle.

I haven't played with the HRM stack much... left everything pretty much in the middle... any recommended practice in trying to arrive at a setting for that?

[mdroberts1243]

3. I took the time to A/B/C the BM with the 80s classic and Skyliner amps... The BM wins on the clean department, but it fails miserably in my hands in overdrive mode.

I found that the ODS-101 1st stage starts to compress the input around 350-400mV pp. Compression turns to visible distortion around 1.25V pp. And you get 'hard' clipping at 2.7Vpp

The 150/1.8 front-end on the BM can handle 1.2Vpp before it starts to compress.

[Funkalicousgroove]

anyone tried the more common combo of 150K/2.2K, 120K/1.8K on V1? for some readon it seems odd that we've seen that combo on other amps, but in the BM these values are "reversed" on V1.

also, I'm pretty sure the coupler before the HRM after v2b is a mistake in the schematic, but as always, I could be wrong.

[mdroberts1243]

anyone tried the more common combo of 150K/2.2K, 120K/1.8K on V1? for some readon it seems odd that we've seen that combo on other amps, but in the BM these values are "reversed" on V1.

also, I'm pretty sure the coupler before the HRM after v2b is a mistake in the schematic, but as always, I could be wrong.

I can try the other combo quickly tomorrow am. I makes sense that it could be another case of crossed Rk values... it's happened before. I've struggled with the CL2 values a bit and this might help.

When I first used the OD2 coupler I didn't like it at all, but with the shorting switch I have an option so I've left it there and sometimes it sounds gooder

[Normster]

Gil, try a 100k slope resistor to tame the bass in clean mode. I think it sounds much tighter than the 47k. As for the PAB, I like the brassy tone. The OD does indeed sound best with low gain settings. As I've said before, I think you have to take the BM for what it is...definately not everyone's cup of tea.

[dogears]

The Bluesmaster I had at my house had 220K/150K - 3.3K/2.2K on V1. Not any funky combo. I am certain it had no cap before the HRM board. It will be back over in a week or two and I'll see how far I can dig in.

Fwiw, the HRM trimmers were not straight up. Mids were set very low, 10-20% on. Bass was about 25% on. Treble almost half.

[ayan]

Hi Gil,
What are the "BM" values you tried in the preamp stages?

The regular Skyliner HRM values: 220K, 150K, 180K and 150K.

Gil, try a 100k slope resistor to tame the bass in clean mode. I think it sounds much tighter than the 47k. As for the PAB, I like the brassy tone. The OD does indeed sound best with low gain settings. As I've said before, I think you have to take the BM for what it is...definately not everyone's cup of tea.

I didn't get a chance to do that, I was really anxious to get the damned thing converted at once.

The PAB issue was the major deal breaker for me with the BM, too bad cause I really like the cleans but I'll be honest with myself: I don't build these amps for their clean sound.

I am very happy with my Skyliner HRM since last night. My previous experience with those amp had been 7 years ago, with the old PI. I don't know if it's due to the fact that I now have the BM PI in the amp, or that I use Fender-style iron instead of Marshall-style, but the end result is that the amp sounds terrific. Maybe I am also affected by the fact that the BM preamp was too much of a balancing act for me, I guess I am relieved.

Anyway, cleans in the Skyliner/HRM preamp are better with the BM PI VS the old one. The sound is less percussive and not as boomy. The overdrive is definitely more sizzley with the BM PI, but not in a bad way. This amp can sing and is way more focused sounding than with the BM preamp. This configuration sounds a lot more like mid 90s RF to me than the full blown BM amp. This puppy gets to go on a live test over the weekend, after which I'll know whether it stays as is or goes to the next step, which would be to turn it into a non-HRM.

I was talking to Brandon recently about this, it's funny how some amps don't sound so great in a particular configuration but you turn them into something else and they sound better. Such was also the case of one of my non-HRMs, which ended up sounding better with the 100K resistor approach. Its twin brother, a non-HRM with high plate resistor values, sounded terrific from day one, and has remained unchanged since birth. Weird stuff.

Gil

[ayan]

Hi Gil,

I have tried to determine a set of 'max-clean' values... settings that take each stage to the limit of 'clean' with a 'normal' guitar input level on the input jack... in my case: Volume at 3 to 4, OD Trimmer 20-24k (estimated), OD Drive at 2, PAB On, OD On, Tone knobs all in the middle.

Other findings... if the mid-pot is much past '2' it starts to swamp out and reduce the effectiveness of the treble and bass controls. The mid-boost is fairly subtle.

I haven't played with the HRM stack much... left everything pretty much in the middle... any recommended practice in trying to arrive at a setting for that?

One notes: I used a linear (50K) Middle pot, I know you use an audio one. However, my findings are very much like yours in all respects! (something we had already "decided" via PMs ). Anyway, as for the HRM, Scott is the master at dialing that in for that cool sound he gets. Bascially his approachs is, roughly, bass 40%, treble 55% and mids 25%, or something like that. In other words, scoop the midrange a bit.

For me, both on the BM preamp and Skyliner preamp w/HRM, I prefer to turn the midrange control up from 50%. That may require that the treble control come down a bit to avoid excessive brightness. I know Funk also prefers dialing the HRMs this way. Note that I try to voice the thing using an EVM-12L open back cabinet, so very different from what Scott uses.

Gil

[mdroberts1243]

anyone tried the more common combo of 150K/2.2K, 120K/1.8K on V1? for some readon it seems odd that we've seen that combo on other amps, but in the BM these values are "reversed" on V1.

also, I'm pretty sure the coupler before the HRM after v2b is a mistake in the schematic, but as always, I could be wrong.

I can try the other combo quickly tomorrow am. I makes sense that it could be another case of crossed Rk values... it's happened before. I've struggled with the CL2 values a bit and this might help.

When I first used the OD2 coupler I didn't like it at all, but with the shorting switch I have an option so I've left it there and sometimes it sounds gooder

I put in the 'regular' Rk values for CL1. (Thanks Funk! I am embarrassed that I didn't notice the coincidental values and the potential for them to be flipped). Really like the compression/distortion levels it gave me... lots to work with control wise. CL1 is really clean until 800mVpp and doesn't go into visible distortion until 2.3Vpp. It hard clips way up at 8V so should be a pleasant front end. CL2 is clean until Volume at 2 and pretty cleanish until 3.5 really. CL2 is fully clipping fairly symmetrically at 5.9-6 on the volume pot. (Whenever I tested Skyliner HRM V1 values I found that CL1 starts into compression around 360-400mV pp).

There seems to be the same sweet spot for the OD In trimmer at 20-24k, but the results don't get annoying quickly after that and the trimmer doesn't enter 'heavy' distortion up until 40k or so.

The OD Drive pot is clean at 2, heavy distortion starts at 5.5-6 and you get weird around 8.

I haven't found the clean channel to be overly bassy, but I might go to the 100k slope it does have a nicer set of control range. I'm using a 50k linear pot for mids too.

I do think that too much bass might be going into the OD channel however and I think I'll play around with that a bit.

[ayan]

I haven't found the clean channel to be overly bassy, but I might go to the 100k slope it does have a nicer set of control range. I'm using a 50k linear pot for mids too.

And neither did I, I loved the clean channel. But, evidently, there is way too much bass coming out of the clean stages -- unless the OD input network is extensively modified -- for the OD channel to process without giving out that "bark" on the bottom end, which I really dislike.

Gil

[mlp-mx6]

Did you have a cap on the OD entrance? (between the relay and the "low gain OD entrance network") On my first BM conversion I used this position to remove some of the bass from the clean tone before it got into the OD section.

[mdroberts1243]

Did you have a cap on the OD entrance? (between the relay and the "low gain OD entrance network") On my first BM conversion I used this position to remove some of the bass from the clean tone before it got into the OD section.

I have the standard input of 470k || 47pf. I can try something ahead of that.

[ayan]

Did you have a cap on the OD entrance? (between the relay and the "low gain OD entrance network") On my first BM conversion I used this position to remove some of the bass from the clean tone before it got into the OD section.

Not in this amp. As I said, the "bark" was one problem, but the big disappointment was my inability to warm up to a bandpass PAB. Some people really don't like the original PAB because it cuts off the bass, but I happen to like that and it is what I am used to.

I spent two weeks tinkering with the BM and got it to sound good, but for my taste, it ended up being a series of bandaids in an attempt to morph it into something it was probably not intended to be in the first place. Hence the make over.

Gil

[dogears]

LOL! Gil check this clip http://www.scottlernermusic.com/2007/Al ... uesNew.mp3

This is Skyline HRM w/BM 6L6. Stack set at treble about 42% on, bass 30%, and mids up 60%. I also have some proprietary network changes. Wink.


So, my stack settings are not too different!

Hi Gil,

I have tried to determine a set of 'max-clean' values... settings that take each stage to the limit of 'clean' with a 'normal' guitar input level on the input jack... in my case: Volume at 3 to 4, OD Trimmer 20-24k (estimated), OD Drive at 2, PAB On, OD On, Tone knobs all in the middle.

Other findings... if the mid-pot is much past '2' it starts to swamp out and reduce the effectiveness of the treble and bass controls. The mid-boost is fairly subtle.

I haven't played with the HRM stack much... left everything pretty much in the middle... any recommended practice in trying to arrive at a setting for that?

One notes: I used a linear (50K) Middle pot, I know you use an audio one. However, my findings are very much like yours in all respects! (something we had already "decided" via PMs ). Anyway, as for the HRM, Scott is the master at dialing that in for that cool sound he gets. Bascially his approachs is, roughly, bass 40%, treble 55% and mids 25%, or something like that. In other words, scoop the midrange a bit.

For me, both on the BM preamp and Skyliner preamp w/HRM, I prefer to turn the midrange control up from 50%. That may require that the treble control come down a bit to avoid excessive brightness. I know Funk also prefers dialing the HRMs this way. Note that I try to voice the thing using an EVM-12L open back cabinet, so very different from what Scott uses.

Gil