I recently played a friends Diamond Phantom (5881 maybe?) and was shocked by the clarity of the high frequencies. I would NOT say the amp was bright, or harsh or anything, but more like the frequency response was extended far beyond my 6505. Both amps went to my Mesa 4x12 w/ V30. When I went back to the 6505 it was like there was a blanket over the speaker. Just dull and muffled.
What I didn't like about the Phantom was a buzzing character in the tone that I couldn't get rid of.
Which aspects of an amp's circuit open up the top end end in that way? Again, it's not a factor of turning up highs, but allowing more high frequencies to pass thru.
Thanks so much, and sorry if this has been addressed.
The simple fact of the matter is that the more gain stages your guitar signal passes thru, the more stage to stage coupling caps it passes thru also, and each coupling cap adds a measure of phase shift to the signal, and before you know it your guitar does not really sound like your guitar even in regards to clean tones, and this is without talking about having any stomp boxes in front of the amp, or patched into the effect loop!
If I am not mistaken a 6505 circuit has 6 gain stages before the output section ,where as for example the normal channel in a Fender black or silver face amp has 3 stages before the output stage, the best sounding amp I have ever made just for clean tones has a high gain pentode ( 1 stage ) a PI section and then a 7591 output stage, just 2 gain stages!
The buzzing nature of the tone could be due to many factors and can be tuned out to a large extent most likely but I can not say without seing a schematic of the phantom.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
The number of gain stages may be an issue. I think the real answer is that 12AX7s only have flat(ish) response out to about 150kHz IIRC. That seems like plenty, until you realize that the effects of a 150kHz half-power point actually start being felt about a factor of ten lower in frequency. This is trivial indeed if you only have one or two stages, but with many stages, the consequences of the small "bites" taken out of the treble add up to a slight dulling.
The proposed two-stage design not only has only two stages, but the first stage is a pentode. Pentodes were one solution to triodes not being able to work at very high frequencies. The shielding of the grid from the plate by the intervening electrodes was a key part of getting reliable RF tubes as radios went to higher and higher frequencies. Shielding grids prevent the gain of the tube from multiplying the grid capacitance by the Miller effect, and open up a very much higher frequency range.
It's possible to produce flat high frequencies with 150khz triodes, but you often have to resort to more gain and use negative feedback to do it.
Dragonjaw wrote: ↑Tue Aug 01, 2017 9:29 pm... the frequency response was extended far beyond my 6505... When I went back to the 6505 it was like there was a blanket over the speaker. Just dull and muffled.
What I didn't like about the Phantom was a buzzing character in the tone that I couldn't get rid of.
Which aspects of an amp's circuit open up the top end end in that way? Again, it's not a factor of turning up highs, but allowing more high frequencies to pass thru.
See C87 and C88 in the rhythm channel, C29 and C27 in the Lead channel http://www.thetubestore.com/lib/thetube ... ematic.pdf
These are the 'blankets' making your amp muffled (yet buzz free), by rolling off / attenuating its high frequency response.
I guess that the other amp doesn't have these low pass / shelving filters.
It depends on whether the designer thinks his customer wants bright and open, and will tolerate a buzzy edge to the overdrive, or the customer wants a smooth overdrive and will tolerate a degree of muffling.
