Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SleepLess on February 13, 2016, 03:41:46 am
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Hi there!
I built a Princeton reverb for myself a few years ago and I'd like to tweak it a bit as I now find it has two things I'd like to improve.
1. The tremolo is too fast. I actually can't use it beyond 3, it's too fast beyond that for my taste and use. What should I change to slow it down and be able to use on a larger scale?
2. I think it's a bit too trebly. Are there any resistances I should change to reduce the treble or any caps? Or perhaps increase/decrease the treble pot value?
Here's a picture of the board of this amp:
(http://img15.hostingpics.net/pics/188780Photo0462136x1424.jpg)
Thanks a lot everyone! ;)
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Saved this ( & another somewhere) a while back for the AB763, looks like the same circuit.
LINK (http://el34world.com/Hoffman/files/Hoffman_AB763_Mods.pdf)
I'll be interested to see the recommendations for tuning treble. I was amazed how much the by-pass caps/ coupling caps affected taming the bass on my last project.
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Increasing the value of the tremolo caps will slow down the tremolo.
from ARCHIVES: http://el34world.com/Forum/index.php?topic=604.0 (http://el34world.com/Forum/index.php?topic=604.0)
Look at Duncan Tone Stack Calculator. You can change values in the tone stack and see how it impacts the tone.
http://www.duncanamps.com/tsc/ (http://www.duncanamps.com/tsc/)
Often too much treble is a speaker issue? Look at Weber VST 10" Alnico speakers such as the 10A100
http://www.tedweber.com/10a100 (http://www.tedweber.com/10a100)
I had an original PR and thought it was too "bright" meaning the bass and treble was accented so much that the mids were neglected and the amp lacked the warmth that I wanted. So, IF I was building one from scratch this would be how I would approach it & I would add 1.5k grid resistors to the 6V6's. (see attached schematic) In another words, I don't think of the PR as too trebly but instead lacking warmth and too bright.
Looking at the schematic, what I would be doing would be taking the bass and treble down a notch and increasing the mids a notch. I think using 10uf, 5uf, 5uf cathode caps will help smooth the tone out some. Dumble amps for example use 5uf cathode caps in four preamp gain stages and the amps are noted for mids and smoothness.
With respect, Tubenit
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Thank you guys, that's helpful!
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I've got a Weber 10A150T in my PR build and there's no lack of bass and warmth. The output transformer can make a big difference here also IMHO. I also added capacitance to the power rail. Sorry but don't have the schematic available this second to confirm but think I have parallel 20uf caps for the power tube plate node and an extra node along the power rail.
Respectfully,
Chip
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2. I think it's a bit too trebly.
With what guitar, what speaker, and what tone control settings?
The amp is too trebly with the Bass on 10 and the Treble on 0? It's too trebly with your guitar tone control all the way off?
I ask the questions for 2 reasons:
1. I've owned quite a few blackface and silverface Princetons (both with and without reverb). Most (not all) of those amps were very warm with single-coil guitars. The speaker has a LOT of influence.
2. Sometimes people use standard tone control settings (amp Treble on "X" Bass on "Y" and guitar tone full-up) and have a preconceived notion of what that should sound like (I've been guilty of this in the past), but then don't fiddle the control available to see how they really interact.
Separately, there's a lot of discussion over on the Les Paul forum about the 2014 and later Custom Shop reissues. Some say the latest Les Pauls are too bright and don't sound like a Les Paul. Others note the new reissues sound much like the original Les Paul bursts, said to be Tele-like with tone controls you could roll back for warmer cleans and max out for cutting distorted leads. And while no one wants a harsh sounding guitar, if you start out with something too dark you can never get it bright-sounding again. John Knowles once said of a classical-style guitar being made for him, "... I asked to make it brighter. I can always make it sound darker with how I play, but I can't add back in treble."
Just something to think about.
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HBP - you gave us all good stuff to think about.
Thanks,
Chip
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Saved this ( & another somewhere) a while back for the AB763, looks like the same circuit.
LINK (http://el34world.com/Hoffman/files/Hoffman_AB763_Mods.pdf)
I'll be interested to see the recommendations for tuning treble. I was amazed how much the by-pass caps/ coupling caps affected taming the bass on my last project.
I'll let you know about the treble a bit later. But going back to slowing down the tremolo, could someone please tell me what cap I should change to a 0.022uF using a red circle on the picture I posted above? I'm not familiar enough (though I'm getting better at it everyday) with schematics to be 100% sure I'll be changing the right one!
Thanks!
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Change either in blue.
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Looking at the Princeton layout, should be these disc caps.
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Thanks a lot guys! :icon_biggrin:
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If it is way too fast, try doubling all THREE caps.
That maintains the same operation but at half the speed.
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Thanks PRR!
So, as for the treble, I find it a bit too trebly with a Nocaster, Volume on 5, Treble on 3, Bass on 6 and Reverb on 3. Is there just a simple way to have a bit less treble? I'd just like to have a bit wider useable treble range with my Nocaster.
Thanks!
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2. I think it's a bit too trebly.
With what guitar, what speaker, and what tone control settings?
The amp is too trebly with the Bass on 10 and the Treble on 0? It's too trebly with your guitar tone control all the way off?
I ask the questions for 2 reasons:
1. I've owned quite a few blackface and silverface Princetons (both with and without reverb). Most (not all) of those amps were very warm with single-coil guitars. The speaker has a LOT of influence.
2. Sometimes people use standard tone control settings (amp Treble on "X" Bass on "Y" and guitar tone full-up) and have a preconceived notion of what that should sound like (I've been guilty of this in the past), but then don't fiddle the control available to see how they really interact.
Separately, there's a lot of discussion over on the Les Paul forum about the 2014 and later Custom Shop reissues. Some say the latest Les Pauls are too bright and don't sound like a Les Paul. Others note the new reissues sound much like the original Les Paul bursts, said to be Tele-like with tone controls you could roll back for warmer cleans and max out for cutting distorted leads. And while no one wants a harsh sounding guitar, if you start out with something too dark you can never get it bright-sounding again. John Knowles once said of a classical-style guitar being made for him, "... I asked to make it brighter. I can always make it sound darker with how I play, but I can't add back in treble."
Just something to think about.
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Try this. Easy to do or undo. Larger value cap eliminates more treble.
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Thanks a lot Sluckey! The speaker is a Weber 10F150T which is what they call "the favourite for Princeton Reverbs"...
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Is there just a simple way to have a bit less treble? I'd just like to have a bit wider useable treble range with my Nocaster.
A sledgehammer approach to dropping treble is to simply tack a small value cap from the signal path to ground.
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A sledgehammer approach to dropping treble is to simply tack a small value cap from the signal path to ground.
Meh, too easy and so many options available... a simple small cap across v1's load resistor, or across the plate - cathode, or simply plug into the "Lo input" lol - and do NOTHING.
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Thanks a lot Sluckey! The speaker is a Weber 10F150T which is what they call "the favourite for Princeton Reverbs"...
So, as for the treble, I find it a bit too trebly with a Nocaster, Volume on 5, Treble on 3, Bass on 6 and Reverb on 3. Is there just a simple way to have a bit less treble? I'd just like to have a bit wider useable treble range with my Nocaster.
Thanks!
Something's not right. A 10F150T and those control settings should not be trebly and that's with guitar volume on 10. I don't think I've ever had Bass over 4 or 5 tops with my PR.
My first guess is that there is a component value off somewhere by a factor of 10 (as in 68K instead of 6.8K going to ground in the tone stack or .01 coupling cap instead of .1 uf). Another question would be how hot are the power tubes biased? Really cold bias might be the issue.
Do you have voltages posed for this build?
Respectfully,
Chip
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It's all good now! Thanks a lot guys! :worthy1:
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It's all good now! Thanks a lot guys! :worthy1:
What cured the problem?
Respectfully,
Chip
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I changed the ceramic disks for the tremolo and doubled their values. And I added a 47pF cap for the trebles. It's perfect now! Thanks again!
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Thanks a lot Sluckey! The speaker is a Weber 10F150T which is what they call "the favourite for Princeton Reverbs"...
I don't know who said that, but my '78 Princeton Reverb really sounds excellent with an Eminence 10-CS-8-50. In fact I much prefer it over the weber.