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Author Topic: New Amp Kits  (Read 23294 times)

jpfamps

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Re: New Amp Kits
« Reply #15 on: August 20, 2008, 07:06:31 PM »
Sounds like a good project.

It's great you can get flat packed cabs as this takes out the heavier woodwork.

There is no tone control on a Tweed Champ. I suspect your circuit is nearer a Tweed Princeton, which is a very cool amp too! You can always add a switch to disable the tone control which will give you more gain.

sgmypod

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Re: New Amp Kits
« Reply #16 on: August 20, 2008, 07:25:32 PM »
Just had a listen to a princeton..yeah mine ain't far off that sound have a jensen c12k with it
« Last Edit: August 20, 2008, 08:07:07 PM by sgmypod »
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WezV

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Re: New Amp Kits
« Reply #17 on: August 20, 2008, 08:53:26 PM »
i did a champ kit from Stf-electronics a few years ago that i thought was pretty good for the money and had great instructions - i did that before i had even done a BYOC kit.  I added a tone control and master volume to it as well

took a while to arrive though

i never realised how good it actually sounded because i built it with an 8" ceramic speaker but hooked it up to my dual greenback cab before i got my little rock and it did make me wonder if i needed the matamp... till the matamp turned up.

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tomjackson

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Re: New Amp Kits
« Reply #18 on: August 20, 2008, 09:56:46 PM »
Sounds like a good project.

It's great you can get flat packed cabs as this takes out the heavier woodwork.

There is no tone control on a Tweed Champ. I suspect your circuit is nearer a Tweed Princeton, which is a very cool amp too! You can always add a switch to disable the tone control which will give you more gain.

Would that work like the 'E.Q cut switch' on a Cornell Romany?  It's nice to have the versatility of a tone control but it would also be good to go back to vintage mode if required.  Sounds like a good idea!

jpfamps

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Re: New Amp Kits
« Reply #19 on: August 20, 2008, 10:07:47 PM »
Indeed it would (and by co-incidence I was working on a Cornell Romany at the weekend).

If you lift the ground from the bottom of the tone control you will disable it. In practice it is better to tie a large value resistor (say 10 M) between the bottom of the tone control and ground and arrange a switch to short this out to enable the tone control. This will avoid any loud pops due to DC level shift.

Re Speakers for Champs, I agree you can often get a better tone through a larger speaker, although a decent 8" speaker records really well. All Champs, and most Champ copies though only have an 4 ohm tap on the output transformer. I've seen plenty of Champs with repro 8 Ohm speakers in them (I've got one in the work shop at the moment). This generally doesn't sound that great.

FELINEGUITARS

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Re: New Amp Kits
« Reply #20 on: August 20, 2008, 10:14:53 PM »
Indeed it would (and by co-incidence I was working on a Cornell Romany at the weekend).

If you lift the ground from the bottom of the tone control you will disable it. In practice it is better to tie a large value resistor (say 10 M) between the bottom of the tone control and ground and arrange a switch to short this out to enable the tone control. This will avoid any loud pops due to DC level shift.


Would that result in a gain increase then like on the Romany or is there something else happening on that
I have a Cornell Stinger - the precursor of the Romany and it works pretty much the same- all except it doesn't have the reduced power switching
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WezV

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Re: New Amp Kits
« Reply #21 on: August 20, 2008, 10:20:45 PM »
i have nothing against 8" speakers but i did skimp on that bit.  i built the stf with a 4-ohm tap but i think there was the option of adding other outputs  

i have my 2x12 8ohm speaker cab wired with a series/parallel switch  which i hope gives me the option of 4 or 16 ohms.  4 for the champ kit, 16 for the little rock... hopefully

jpfamps

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Re: New Amp Kits
« Reply #22 on: August 21, 2008, 10:16:03 AM »
Indeed it would (and by co-incidence I was working on a Cornell Romany at the weekend).

If you lift the ground from the bottom of the tone control you will disable it. In practice it is better to tie a large value resistor (say 10 M) between the bottom of the tone control and ground and arrange a switch to short this out to enable the tone control. This will avoid any loud pops due to DC level shift.


Would that result in a gain increase then like on the Romany or is there something else happening on that
I have a Cornell Stinger - the precursor of the Romany and it works pretty much the same- all except it doesn't have the reduced power switching

All passive tone controls load down the signal (usually referred to as insertion loss) by shunting signal to ground. By lifting the ground you disable the tone controls and thus giving an apparent increase in gain, although in reality you actually have less loss.



sgmypod

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Re: New Amp Kits
« Reply #23 on: August 21, 2008, 11:32:36 AM »
This is an inside shot of mine....although tidied up a bit inside since

And how its wired

I have one question..could I make the single tone control..either have a larger range or is it possible to have a bass and treble seperatly controlled
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tomjackson

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Re: New Amp Kits
« Reply #24 on: August 21, 2008, 11:34:00 AM »
Indeed it would (and by co-incidence I was working on a Cornell Romany at the weekend).

If you lift the ground from the bottom of the tone control you will disable it. In practice it is better to tie a large value resistor (say 10 M) between the bottom of the tone control and ground and arrange a switch to short this out to enable the tone control. This will avoid any loud pops due to DC level shift.

Re Speakers for Champs, I agree you can often get a better tone through a larger speaker, although a decent 8" speaker records really well. All Champs, and most Champ copies though only have an 4 ohm tap on the output transformer. I've seen plenty of Champs with repro 8 Ohm speakers in them (I've got one in the work shop at the moment). This generally doesn't sound that great.

How come they don’t sound as good with an 8ohm tap/speaker?  I was hoping to try a Celestion blue.  I was thinking that the increased sensitivity of the bigger driver, coupled with the sweetness of the fabled Alnico speaker would give a match for some great fenderish cleans.

Perhaps that’s why you don’t see champs with 12 inch cones.  Is it a limitation of the circuit, the transformer or just that the champ circuit suits and 8inch driver?

If this is the case I’m presuming a Jensen P8R or C8R would be the best choice?

jpfamps

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Re: New Amp Kits
« Reply #25 on: August 21, 2008, 12:21:07 PM »
Indeed it would (and by co-incidence I was working on a Cornell Romany at the weekend).

If you lift the ground from the bottom of the tone control you will disable it. In practice it is better to tie a large value resistor (say 10 M) between the bottom of the tone control and ground and arrange a switch to short this out to enable the tone control. This will avoid any loud pops due to DC level shift.

Re Speakers for Champs, I agree you can often get a better tone through a larger speaker, although a decent 8" speaker records really well. All Champs, and most Champ copies though only have an 4 ohm tap on the output transformer. I've seen plenty of Champs with repro 8 Ohm speakers in them (I've got one in the work shop at the moment). This generally doesn't sound that great.

How come they don’t sound as good with an 8ohm tap/speaker?  I was hoping to try a Celestion blue.  I was thinking that the increased sensitivity of the bigger driver, coupled with the sweetness of the fabled Alnico speaker would give a match for some great fenderish cleans.

Perhaps that’s why you don’t see champs with 12 inch cones.  Is it a limitation of the circuit, the transformer or just that the champ circuit suits and 8inch driver?

If this is the case I’m presuming a Jensen P8R or C8R would be the best choice?


If the transformer has an 8 ohm tap then that will work fine. However if you have a repro replacement transformer will only have a 4 ohm tap, like the original Champ OT, so you really need a 4 ohm load. A 12" speaker won't fit in a Champ, although I've see Champs that have had 10" speakers put in them. I would not advise doing this to a vintage Fender amp!!

Re speakers, I would not recommend the Jensen speakers — I'm not a huge fan to be honest. If you want an 8" 4 ohm speaker your best bet is getting a Mojotone or Weber (they are the same speaker) from Allparts UK. These sound really good, and are the same price as the Jensen.

jpfamps

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Re: New Amp Kits
« Reply #26 on: August 21, 2008, 12:27:01 PM »
This is an inside shot of mine....although tidied up a bit inside since

And how its wired

I have one question..could I make the single tone control..either have a larger range or is it possible to have a bass and treble seperatly controlled


You can vary the range of the tone control by changing the value of the cap conected to ground from the bottom to the tone pot. High values will cause more mid frequencies to ground and lower values will cause less mid being bled to ground. You can wire in treble + bass controls, and there are tons of circuits on the web for these. You will get more insertion loss though  with this type of control when compared to a simple tone control though.

sgmypod

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Re: New Amp Kits
« Reply #27 on: August 21, 2008, 12:31:36 PM »
Ok so if I wanted a little more bass (I know am a heathen to add more bass to a this champ style of amp) what would I change the 0.0047 to

Also like the tone removal idea...so would need a 10m resistor...what w rating
« Last Edit: August 21, 2008, 12:38:05 PM by sgmypod »
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jpfamps

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Re: New Amp Kits
« Reply #28 on: August 21, 2008, 01:12:26 PM »
Ok so if I wanted a little more bass (I know am a heathen to add more bass to a this champ style of amp) what would I change the 0.0047 to

Also like the tone removal idea...so would need a 10m resistor...what w rating

You can't really boost bass by altering the tone control, you can only cut less bass. Experiment with small caps, say 0.0022 to start with.

You could also try increasing the size of the cap on the cathode of the second valve stage. I can't read the value (I suspect it is 0.68 µF) but it is the polystyrene cap second from the right in your photo. Try up to 20 µF.

You could also try increasing the value of the coupling caps, although without knowing their values (I can't read values on the schematic), then I can't advise whether this will help or not.

To disable the tone control connect a 10 M resistor between ground an the 0.0047 cap. Then wire a switch to short out the 10 M resistor. Any 10 M resistor will do — to dissipate 0.25 W in a 10 M resistor would require 1.5 kV across it!!

A word of caution though too much bass and you might encounter the dreaded blocking distortion.

sgmypod

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Re: New Amp Kits
« Reply #29 on: August 21, 2008, 01:29:00 PM »
Ok...have sent an email..easier to read schematic....thanks for the help
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