Bluesmaster CLEAN optimized for STRAT (Blackface cap values)

[greiswig]

Looks like we have lost a little of the tube amp knowledge the former generations of amp builders had. We need to shape up.

Heh...well, thank you for sharing this! I'm hopefully going to try this this weekend.

[bluesfendermanblues]

Does it sound like a harshness on top of the signal?

On my #102 clone it did get rid of something that sounded like 'white noise' artifacts - the OT is made 20 years ago to custom specs. by a local vendor. I had it laying around for all those years for a Soldano SLO100 that I never build.

On Bluesmaster with a Mercury Bassman (FTMM) it didnt have quite the same impact.

Tom, try it one of your amps and have a listen...

[Structo]

Thanks Claus, I've been dusting off my math skills today.

Man, there are a lot of zeros in those RC calculations!

Something I don't quite understand, is how high of a frequency the ringing is.
I mean, it's into the radio frequency range.
But, I guess that is to be expected with the harmonic distortion and ringing.

I wish I had an oscilloscope.

[markusw]

Hi G and stevlech

You use the scope/10KHz square wave to monitor OT ringing

Thanks for sharing your observations!

What signal strength do you have at the OPT? You perform the test with a dummy load, I guess?

Peace,

Markus

[bluesfendermanblues]

Hi G and stevlech

You use the scope/10KHz square wave to monitor OT ringing

Thanks for sharing your observations!

What signal strength do you have at the OPT? You perform the test with a dummy load, I guess?

Peace,

Markus

around 0.5-1 volt and
yes a dummy resistor

[markusw]

yes a dummy resistor

Thanks a lot!
I know that this question seemed a bit stupid
In
http://www.siteswithstyle.com/VoltSecon ... xfmrs.html
this guy could get rid of the ringing with adding a dummy load.
Therefore, I asked.

Peace,

Markus

[llemtt]

Do all output transformers have the artifacts known as ringing?

And if they are above human hearing range, (20KHz) how does one perceive it?

Does it sound like a harshness on top of the signal?

Yes! Some more some less, this relates to the perceived sound of different OTs. Ringing is just a symptom of instability of the global feedback loop at frequencies where the phase shift turns toward 0° (positive) instead of 180° (negative).

Ringing cause non harmonic distortion of the signal (mainly IMD).

Indeed not a truly good sound even with "clean" guitar signals, everything gets worst when driving the amp with "squared" signals.

cheers

[angelodp]

I have a Dlite 22/33 optional 6L6/ 6V6 build. I am running 6L6 at 33 watts. I tried the 15pf parallel on the 6k2 and I concur that there is subtle change in the high highs for the better. As described earlier, more relaxed and cleaner high in OD.

Thanks

Ange

[SoundPerf]

I have a Dlite 22/33 optional 6L6/ 6V6 build. I am running 6L6 at 33 watts. I tried the 15pf parallel on the 6k2 and I concur that there is subtle change in the high highs for the better. As described earlier, more relaxed and cleaner high in OD.

Thanks

Ange

Hello Ange...Did you arrive at the 15pf value in conjuction with using a scope, or did you just take a guess? I tried a 120pf with a 4k7 NFB. I need some more comparison time to be sure. I have a scope, but didn't use it for this testing yet.

One question for anyone...Is there a better type of cap to use than another? I just had a ceramic disc of an appropriate value.

[greiswig]

Here's what is probably a siilly question about this cap:

Did the hi-fi amps that this applied to have presence controls? I'm wondering because it almost seems like if the goal is to keep VERY high frequencies in the GNFB loop, rather than just bypassing the first resistor with this cap, you might want to bypass directly to ground? In essence that first resistor plus whatever the presence pot resistance is set to?

[angelodp]

Well... I was wondering how subtle this was, so I ( should have started with this ) lifted one side of the cap and tried chop-sticking it on/off while playing to hear that difference... so now its seems the power of suggestion may have been at play ( at least for my ears ), so I went to a 100pf and tried the same experiment but still not hearing that audible difference with an on/off attempt. I am going to try this with a pal while playing more vigorously at level an see. just wanted to report back.

[wjdunham]

Thanks Claus, I've been dusting off my math skills today.

Man, there are a lot of zeros in those RC calculations!

Something I don't quite understand, is how high of a frequency the ringing is.
I mean, it's into the radio frequency range.
But, I guess that is to be expected with the harmonic distortion and ringing.

I wish I had an oscilloscope.

I'm not sure where the MHZ range came from - the scope trace and the articles posted indicate the ringing is in the 100-300KHz range. Well above the audio frequency, but not in the RF range. The real question is, what does all that high frequency energy in the transformer doing to the signals in the audio band? Since real life transformers are non-linear devices, there can certainly be some effect, if they were perfectly linear then not...
As a matter of principal, I would think it's a good idea to damp those unwanted oscillations as they are not in the audio band, makes the signals look nice anyway, but some times it's those unwanted things that contribute to the tone... Remember too, that a perfect square wave has lots of frequency components that are not in the audio band, and is not highly representative of the frequency content of the amplified guitar signal as the edges are much softer in the latter. Therefore the resonances that are showing up in the scope plots are not being excited as heavily by the signal in a real usage condition.
Bill

[bluesfendermanblues]

Thanks Claus, I've been dusting off my math skills today.

Man, there are a lot of zeros in those RC calculations!

Something I don't quite understand, is how high of a frequency the ringing is.
I mean, it's into the radio frequency range.
But, I guess that is to be expected with the harmonic distortion and ringing.

I wish I had an oscilloscope.

I'm not sure where the MHZ range came from - the scope trace and the articles posted indicate the ringing is in the 100-300KHz range. Well above the audio frequency, but not in the RF range. The real question is, what does all that high frequency energy in the transformer doing to the signals in the audio band? Since real life transformers are non-linear devices, there can certainly be some effect, if they were perfectly linear then not...
As a matter of principal, I would think it's a good idea to damp those unwanted oscillations as they are not in the audio band, makes the signals look nice anyway, but some times it's those unwanted things that contribute to the tone... Remember too, that a perfect square wave has lots of frequency components that are not in the audio band, and is not highly representative of the frequency content of the amplified guitar signal as the edges are much softer in the latter. Therefore the resonances that are showing up in the scope plots are not being excited as heavily by the signal in a real usage condition.
Bill

You are right, my mistake 150kHz is not Mhz - or if so, its in the lower end 0.15 Mhz.

On my (BM, #102 & #183) amps it had a positive effect on the tone.

The OT's are

Mercury Magnetics FTMM, Locally build 4x6L6 & Partridge (4xEL34)

[greiswig]

I'm hoping this just got lost in the middle of the hijack of the first hijack of this thread. . Anybody have an answer to the following?

Here's what is probably a siilly question about this cap:

Did the hi-fi amps that this applied to have presence controls? I'm wondering because it almost seems like if the goal is to keep VERY high frequencies in the GNFB loop, rather than just bypassing the first resistor with this cap, you might want to bypass directly to ground? In essence that first resistor plus whatever the presence pot resistance is set to?

[bluesfendermanblues]

I'm hoping this just got lost in the middle of the hijack of the first hijack of this thread. . Anybody have an answer to the following?

Here's what is probably a siilly question about this cap:

Did the hi-fi amps that this applied to have presence controls? I'm wondering because it almost seems like if the goal is to keep VERY high frequencies in the GNFB loop, rather than just bypassing the first resistor with this cap, you might want to bypass directly to ground? In essence that first resistor plus whatever the presence pot resistance is set to?

Here is a good link to all the classic HiFi tube amps - no presence knobs

http://www.drtube.com/audioamp.htm