Getting rid off the brittle high end in BF Princeton Reverb???

[olddawg]

Maybe a cab with one 8 and one 12" in it.

[kleuck]

Try a conjunctive filter, or a Zobel.
I tried and use Zobels, and they are great.

[Bluefinger]

What's the difference? These frequencies are there, no matter if I plug in a guitar or a harp. And I don't like them with either one. I tried different speakers and cabs as well (1 x 12, 2 x 10, 2 x 8, 1 x 12 + 2 x 8). The tonal range changes of course but it is a voicing issue. If I could somehow get rid of the very top end that the treble pot doesn't seem to affect. Maybe I could isolate them and send them to ground with a cap but I'm not quite sure how to do it ... like a high cut ... I'mnot far from where I want to be so I'm sure it's just a simple thing that can do it.

I tried different kathode resistor/cap combinations and that seemed to have helped a bit though my understanding is that this should only change the bass response, not the treble ... ???

The tone stack comes next but I haven't tried a lot of things yet ... too many gigs, too little time for tinkering.

[Bluefinger]

I have no idea what either one is to be honest but I'll ask my friend, Mr. Google

[Bluefinger]

nope ... tried all kinds of speakers

[kleuck]

Thread here :
http://music-electronics-forum.com/t7810/
A good start point is a 10 ohms resistor and 2Mf non polarized cap, with higher values for the cap you will change the speaker response, but it still sounds good, not at all like a pre amp hi-cut or the like.

[kleuck]

Most of the times, when an amp is too brittle or harsh when driven and you cannot get rid of that with the tonestack, this is not a voicing issue, but an impedance issue, the raising impedance from the speakers loading the power tube through the primary of the OT.
A zobel on the secondary or a conjunctive filter on the primary side flattens this impedance raise (more or less depending on the cap you choose, i choose lower value than the ones the Hi-Fi maths gives, guitar amps are not hi-fi stuff, and you don't want to kill the speaker's tone, just tame it a little)
That's really a magical trick, give it a try.
BTW, lots of vintage amps came with conjunctive filters for example Wattkins ; interestingly enough, the Marshall 1974X directly derives from a Wattkins amp, and is prone to fizziness, lacking this conjunctive filter, but users who add a zobel or conjunctive in their 1974X clone filter do not have this issue.

[Bluefinger]

Thanks a lot, that sounds like something that might help. I'll try that and repot back ...

[Bruce / Mission Amps]

Most of the times, when an amp is too brittle or harsh when driven and you cannot get rid of that with the tonestack, this is not a voicing issue, but an impedance issue, the raising impedance from the speakers loading the power tube through the primary of the OT.
A zobel on the secondary or a conjunctive filter on the primary side flattens this impedance raise (more or less depending on the cap you choose, i choose lower value than the ones the Hi-Fi maths gives, guitar amps are not hi-fi stuff, and you don't want to kill the speaker's tone, just tame it a little)
That's really a magical trick, give it a try.
BTW, lots of vintage amps came with conjunctive filters for example Wattkins ; interestingly enough, the Marshall 1974X directly derives from a Wattkins amp, and is prone to fizziness, lacking this conjunctive filter, but users who add a zobel or conjunctive in their 1974X clone filter do not have this issue.

It has been a number of years since I've seen and worked on one, but I think the old Orange-asaurous high powered KT88 PA amps had these filters too... two of them, I believe they were 10K@15watts? in series with a .0022uF-high voltage cap, Installed from the OT center tap to each outside leg.
As a filter, the knee Freq of a 10K + .0022uF is around 7200Hz.

[kleuck]

I'm french, so it's not easy for me to express myself in English on technical subject with all the details, but what i think i understood, and i experiment exactly the same with 3 identical amps (VHT Special 6) is that the kind of fizziness or harshness you can get rid off with Zobel/Conjunctive filters doesn't always occur : depends on the OT quality AND the speaker connected on the secondary, and i suspect, but i'm not 100% sure, the power tube you are using.
One of the SP6 doesn't exhibit this issue at all, whatever tube i use or speaker i use, one is really prone to, but depends on the speaker, and the third exhibits just a little fizziness only with my Jensen P10R.
However, the Zobel is THE trick.
Actually, with a 10 µf cap, it turned the P10R in an awesome JAZZ speaker, but not a dull thing, a lively sound, so not only can you tame the harshness of some circuits, but you can also tune a speaker to your taste, a magical trick

[guitician]

Why not try a simple series low pass filter using one air core inductor? -6 db per octave should just take that harshness away.

[kleuck]

And the highs too...

[dai h.]

Most of the times, when an amp is too brittle or harsh when driven and you cannot get rid of that with the tonestack, this is not a voicing issue, but an impedance issue, the raising impedance from the speakers loading the power tube through the primary of the OT.
A zobel on the secondary or a conjunctive filter on the primary side flattens this impedance raise (more or less depending on the cap you choose, i choose lower value than the ones the Hi-Fi maths gives, guitar amps are not hi-fi stuff, and you don't want to kill the speaker's tone, just tame it a little)
That's really a magical trick, give it a try.
BTW, lots of vintage amps came with conjunctive filters for example Wattkins ; interestingly enough, the Marshall 1974X directly derives from a Wattkins amp, and is prone to fizziness, lacking this conjunctive filter, but users who add a zobel or conjunctive in their 1974X clone filter do not have this issue.

if a mic is being used for the harp and the mic contains a transformer, the rising impedance could be happening at the input. If that is true, I think the mic (namely the transformer in the mic) wants to see a more appropriate load (more in the range it was designed/intended for) to damp ringing (the rising impedance towards the high freqs.). (As I understand) an inductor (if you see the transformer in the mic as two side by side inductors) with its L, C, and R elements forms a tank circuit (has a peak and resonates around a frequency). An appropriate load (an R, a Zobel, or both) will flatten the response.

[guitician]

And the highs too...

too many all ready....

[Chuck H]

WRT harp, I've noticed that many popular harp mics are painfully bright. Part of the sound. But then the highs need to be tanked on the amp in order to compensate. BF type amps have a much narrower high end and more of it. Perhaps this doesn't work well with all harp mics? You mentioned that presence and treble arent the same. Your right. But the suggestion of simply turning the treble down still applies. Why wouldn't you if the amp is too bright? What you probably feel you need is more upper mids. On a BF type tone stack turning up the treble won't give you much of that where a tweed type amp will.

Is this relatively small amp with a pair of 8" speakers being used so you can overdrive the amp? This opens up other possibilities about why the amp sounds too harsh.