Ceriatone Chupacabra

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Colossal
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Re: Ceriatone Chupacabra

Post by Colossal » Sat Sep 17, 2011 8:45 am

Stephand wrote:About the Diode, are you using normal Zen like 4747?
Yes, 4747 (20V), 4742 (12V).

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Re: Ceriatone Chupacabra

Post by Roe » Sat Sep 17, 2011 8:45 am

I recommend larry grounding very much
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Re: Ceriatone Chupacabra

Post by Colossal » Sat Sep 17, 2011 9:04 am

Stephand wrote:Oh Forgot
Colossal, is Larry's Grounding Schem make a huge difference?

Should I change my original Marshal one?

Stephane
My results with Larry's Scheme were very good. The amp was very quiet. If you find your amp with the original Marshall grounding scheme to be sufficiently quiet to your standards, I don't think it should require changing. Also, I used upright transformers (both OT and PT), not a lay down PT so I was careful to minimize any coupling as sometimes happens with lay down PTs. What is important about Larry's scheme and what makes it work so well is the order in which the circuit is grounded. It adheres to the best practice of localizing ground loops. Ideally, wherever there is a power supply node, all components that are served by that node should be grounded to it. Then the individual nodes (ground points) are linked together. With the Chupa that I built (with Larry's Scheme), the amp was really, really quiet, even while idling at high volume. When only two gain stages were engaged, you would be hard pressed to tell the amp was on. With the added gain stage in front (330k/820R/0.68uF), there was some added hiss due to the jump in gain, but really not even all that apparent.

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Re: Ceriatone Chupacabra

Post by Stephand » Sat Sep 17, 2011 7:20 pm

Colossal wrote:
Stephand wrote:Oh Forgot
Colossal, is Larry's Grounding Schem make a huge difference?

Should I change my original Marshal one?

Stephane
My results with Larry's Scheme were very good. The amp was very quiet. If you find your amp with the original Marshall grounding scheme to be sufficiently quiet to your standards, I don't think it should require changing. Also, I used upright transformers (both OT and PT), not a lay down PT so I was careful to minimize any coupling as sometimes happens with lay down PTs. What is important about Larry's scheme and what makes it work so well is the order in which the circuit is grounded. It adheres to the best practice of localizing ground loops. Ideally, wherever there is a power supply node, all components that are served by that node should be grounded to it. Then the individual nodes (ground points) are linked together. With the Chupa that I built (with Larry's Scheme), the amp was really, really quiet, even while idling at high volume. When only two gain stages were engaged, you would be hard pressed to tell the amp was on. With the added gain stage in front (330k/820R/0.68uF), there was some added hiss due to the jump in gain, but really not even all that apparent.

Very interesting. I think I will try it.
On the same subject to reduce noise, I saw that Lee Jackson is rounding a grounded wire around the tone stack wires (all together) and place it under the tone pots against the chasis. He said that this reduce significantly the hiss.

What do you think about thisone mod?

Thanks again for your tricks and advice
Stephane

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Re: Ceriatone Chupacabra

Post by Colossal » Sun Sep 18, 2011 8:49 am

Stephand wrote:On the same subject to reduce noise, I saw that Lee Jackson is rounding a grounded wire around the tone stack wires (all together) and place it under the tone pots against the chasis. He said that this reduce significantly the hiss.

What do you think about thisone mod?
A grounded coil of wire around sensitive wire runs is shielding them in a Faraday cage of sorts. In my builds, I am careful to lay out all tone stack wiring runs so that they hug the chassis floor and walls whenever possible as they go from the preamp board to the pots themselves. The Chupa amp was very quiet and even in 'hi-gain' mode, the hiss was very manageable and there was no hum of any kind. I think a shielding coil around the tone stack wires couldn't hurt but good lead dress should result in a quiet amp.

:rockon:

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Re: Ceriatone Chupacabra

Post by Stephand » Sun Sep 18, 2011 10:07 am

Excellent, good point.

I was reading this tread and saw that one of the member was noting the NFB/Presence is 5KL pot, .1uF cap, 39k on 8ohm tap.

If I look at the schem, the presence is 25K and the 39K res is connect to 16ohm tap.
Which one is wrong? :what:

I just have too much time to read this schem before I gets all the parts :scratch:

Thanks Colossal

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Re: Ceriatone Chupacabra

Post by Colossal » Sun Sep 18, 2011 3:37 pm

Stephand wrote:Excellent, good point.

I was reading this tread and saw that one of the member was noting the NFB/Presence is 5KL pot, .1uF cap, 39k on 8ohm tap.

If I look at the schem, the presence is 25K and the 39K res is connect to 16ohm tap.
Which one is wrong? :what:

I just have too much time to read this schem before I gets all the parts :scratch:

Thanks Colossal
No bad thing doing your research beforehand. Yes, there are some discrepancies with the schematic. I should have edited in my changes and updates according to the gut shots of the Chupa. For what it's worth, I used 39k on the 16ohm tap. I just looked at the gut shot photo and the feedback is actually taken off the 8Ohm tap.

I always use a 5k (or 4k7) resistor in parallel with a 25kB pot with the 0.1uF presence cap *in front of* the pot (to keep DC off the pot). This is how it is done on the later Marshalls. On the Chupa schematic, the 0.1uF cap should be in front of the pot, not behind it to ground. As shown on the schematic, the Presence pot will have DC on it and may give scratching sounds. Just reverse the two. I wired the feedback loop as shown on the schematic so if you want to be 'correct', you'll want to wire to the 8Ohm tap. My amp sounded very good and was quite stable (no oscillation at dimed volume and 10 on all knobs). The resonance circuit works very well. I did add a Larry/Ken Fischer PPIMV (250kA-Dual || 2M2) and it will reduce the effectiveness of the feedback loop at lower volumes; that's just a compromise that has to be made there. For a test cab, I use a closed back 2x12 with EVs and it sounded utterly monstrous with a 7 string. Dialing in the resonance gave a massive, tight tone which retained its clarity. There are higher gain amps than the Chupa, but if you are looking for Plexi foundation tone plus a "little more" this amp is a good build. As I said, I liked the added 12V zeners. They give very smooth tight compression that is quite musical (to me at least) and a bonus was that it reduces the volume so that the amp could be really opened up and would not be deafening. Recall too that I used an OT that could drive either 6L6s or EL34s so the tone is also not going to be pure EL34 Plexi. The person I built it for was looking for some flexibility and wasn't set on pure Van Halen tone but wanted a more modern grind with some classic tones as well. If you switch off the zeners and switch out the first gain stage, the amp is really pure classic Plexi and you can get that tight ringing grind. I kept the filtering higher with 50-50uF can caps.

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Re: Ceriatone Chupacabra

Post by Stephand » Tue Sep 20, 2011 8:24 pm

Hi Colossal

" I kept the filtering higher with 50-50uF can caps."

My amp is a standard 1959SLP with a metro PTP in it. So the Filtering 50-50uf cap is on the chasis not on the board like the chupa.

In theory the rersult should be the same if I keep it where it is today but just wonder if you agree with this...?


Stephane :scratch:

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Re: Ceriatone Chupacabra

Post by Colossal » Tue Sep 20, 2011 10:28 pm

Stephand wrote:Hi Colossal

" I kept the filtering higher with 50-50uF can caps."

My amp is a standard 1959SLP with a metro PTP in it. So the Filtering 50-50uf cap is on the chasis not on the board like the chupa.

In theory the rersult should be the same if I keep it where it is today but just wonder if you agree with this...?


Stephane :scratch:
Sure, you should be fine.

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Re: Ceriatone Chupacabra

Post by Stephand » Sun Oct 02, 2011 10:41 pm

Hi Colosal
So far my amp sound great but I'm not finish yet. :thumbsup:

Power section now :twisted:
For the Resonance control, did you really put the 100nF just before the NFB?
I can't find this cap on the pics....

Is the 39K res can place before or after the Resonance control ????
on the chupa Schem, it is in between the Pot and the NFB... on The SDM layout it is , the POT is in between the 39K and the NFB. I assume it make no difference.

And last did you add the 22k res on one of the filter cap? (R11). Is this make any difference?

Thanks a lot for your help
:rockon:

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Re: Ceriatone Chupacabra

Post by Colossal » Mon Oct 03, 2011 11:34 pm

Stephand wrote:Hi Colosal
So far my amp sound great but I'm not finish yet. :thumbsup:
Great! Did you use a 430k plate resistor on the extra gain stage in front? I used 330k and found it to be plenty of gain without getting too mushy.
Stephand wrote: Power section now :twisted:
For the Resonance control, did you really put the 100nF just before the NFB?
I can't find this cap on the pics....
Yes, I used 100nF there. This just keeps DC off of the resonance control so it does not make scratching noises.
Stephand wrote: Is the 39K res can place before or after the Resonance control ????
on the chupa Schem, it is in between the Pot and the NFB... on The SDM layout it is , the POT is in between the 39K and the NFB. I assume it make no difference.
I built it as shown in the schematic I posted, so, feedback resistor then the resonance circuit. Shouldn't matter though.
Stephand wrote: And last did you add the 22k res on one of the filter cap? (R11). Is this make any difference?
Yes, I used 22k. If you mean is there a difference between the standard Plexi value of 20k versus 22k in that position, probably not much that you can hear (although I can't say for sure having not A/B tested it...) but it will lower the preamp voltages very slightly and increasing the filtering frequency cutoff very slightly.
Stephand wrote: Thanks a lot for your help
:rockon:
No problem. I hope your amp turns out well. I love the higher gain sound! The resonance control is really nice and you can get huge tones by dialing it in. With my 7 strings I was able to get some very heavy but tight rhythm sounds. Really more of a "modern" take on a plexi sound rather than death metal kind of heavy but I like clarity and separation, not overly saturated mush. The post-cathode follower clipping diodes really add to this if that's the kind of sound you are after. The 12V diodes sound great, nicely compressed but still very musical, but they do drop a lot of volume. I also used a 5k8 primary OT if I recall correctly and this is not going to sound like a classic plexi so your amp might sound quite a bit different if you used a classic Plexi OT.

Let me know how it goes with your build.
:toast:

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Re: Ceriatone Chupacabra

Post by Stephand » Wed Oct 05, 2011 9:20 pm

Colossal wrote:
Stephand wrote:Hi Colosal
So far my amp sound great but I'm not finish yet. :thumbsup:
Great! Did you use a 430k plate resistor on the extra gain stage in front? I used 330k and found it to be plenty of gain without getting too mushy.
Stephand wrote: Power section now :twisted:
For the Resonance control, did you really put the 100nF just before the NFB?
I can't find this cap on the pics....
Yes, I used 100nF there. This just keeps DC off of the resonance control so it does not make scratching noises.
Stephand wrote: Is the 39K res can place before or after the Resonance control ????
on the chupa Schem, it is in between the Pot and the NFB... on The SDM layout it is , the POT is in between the 39K and the NFB. I assume it make no difference.
I built it as shown in the schematic I posted, so, feedback resistor then the resonance circuit. Shouldn't matter though.
Stephand wrote: And last did you add the 22k res on one of the filter cap? (R11). Is this make any difference?
Yes, I used 22k. If you mean is there a difference between the standard Plexi value of 20k versus 22k in that position, probably not much that you can hear (although I can't say for sure having not A/B tested it...) but it will lower the preamp voltages very slightly and increasing the filtering frequency cutoff very slightly.
Stephand wrote: Thanks a lot for your help
:rockon:
No problem. I hope your amp turns out well. I love the higher gain sound! The resonance control is really nice and you can get huge tones by dialing it in. With my 7 strings I was able to get some very heavy but tight rhythm sounds. Really more of a "modern" take on a plexi sound rather than death metal kind of heavy but I like clarity and separation, not overly saturated mush. The post-cathode follower clipping diodes really add to this if that's the kind of sound you are after. The 12V diodes sound great, nicely compressed but still very musical, but they do drop a lot of volume. I also used a 5k8 primary OT if I recall correctly and this is not going to sound like a classic plexi so your amp might sound quite a bit different if you used a classic Plexi OT.

Let me know how it goes with your build.
:toast:
1) I have used 430K but probably I will try 330K later..

2) So then we need one on presence and Resonance...Ok then I will put 2

3) I have 10K+8.2K on the Metro board. I will A/B testing it..



4)Thanks. I have the 20V only for now but will also try the 12V later. About the OT, I do not know which value I have but is the standard OT and Choke from the SLP reissue. I just received the C1998 Metro OT. I will put it at the end. I 'm doing small change at the time and play with it to look at the difference step by step. I did not buy any choke because I do not know which value a should have.....

I also need to change the 47pf to 100pf in between the output cap and the screen resistor as well from 1.K to 5.6K. I heard will also made a difference.
Do you suggest to change the resistor on pin4 down to 750 ohm from 1K? I have read that it is depend of the voltage of my amp. but not sure about this one....


I also see the 2x 220k resistor on the choke by oppose of the classic 56K. not sure here as well...

I really appreciate your input since so far everything you said was 100% right.

Have a good day :-)
Stephane :shred:

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Re: Ceriatone Chupacabra

Post by xenrelic » Wed Nov 02, 2011 10:51 am

Got bored...doin up a 4100 with the grande.

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Re: Ceriatone Chupacabra

Post by Roe » Wed Nov 02, 2011 3:58 pm

personally I don't like the hot bias and the 430k anode resistors, prefering 2k7/.68u and 320k respectively. although the capitance divider reduces noise greatly, it also reduces gain and dynamics
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Re: Ceriatone Chupacabra

Post by Stephand » Wed Nov 02, 2011 8:01 pm

xenrelic wrote:Got bored...doin up a 4100 with the grande.

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Nice job, really nice layout. What are you using to cover the diode?
And a 4100?

Stephan

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