Installation of FX Metro Loop on Blackstar Artisan100

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henter2015
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Installation of FX Metro Loop on Blackstar Artisan100

Post by henter2015 » Thu Mar 03, 2016 2:35 pm

Hi Folks,

I bought a FX loop kit from Metro and want to install it on my Blackstar Artisan-100, Plexi super lead based, point to point.

On Step 1 from the instructions:
15: Now last step is to swap out the 8.2K circled below (in series with the 10K) with the 4.7K metal oxide
resistor provided. This is necessary to compensate for the extra bit of current the loop draws through these
resistors, and keep the amp operating as it was. This is not always absolutely necessary, as voltages will only
be lower in the PI and preamp as a result, but the intent is not to effect the original tone, so swap that 8.2K
resistor for the 4.7K.
- If your amp has a two 2 watt 10K’s in series here, swap out one 10K with a 5.6K 2 watt metal oxide
resistor instead.
- If your amp had only a single 10K here, there will not be as much voltage change, so can leave as is, or can
swap the 10K for an 8.2K resistor to get about right back to where you started concerning voltages
throughout the amp.
- If your amp has a single 8.2K 2 watt resistor here, swap with 7.5K 2 watt resistor if desired though nothing
really need be done.


my amp has a single 22K resistor (R28) and then 1K5 going to all el34s from it… so Im a bit confused on what value I need to replace this resistor to avoid changing the sound and dropping to much voltage when the FX is ON.

Here is part of the schema that shows the resistor:

Image

henter2015
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Re: Installation of FX Metro Loop on Blackstar Artisan100

Post by henter2015 » Mon Mar 07, 2016 9:41 am

bump! anyone? :peace:

danman
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Re: Installation of FX Metro Loop on Blackstar Artisan100

Post by danman » Mon Mar 07, 2016 11:47 am

Measure the current B+ voltage at each preamp tube (pins 1 and 6) so that you have a record of the original voltage. You could try leaving the 22k and seeing if you think the amp sounds any different with the slightly lower preamp voltages. May sound a little browner and softer. If you are not happy with that, you can lower the 22k resistor down to the next value. Might try somewhere around 18k to get the voltages back up to normal when the loop is engaged. I would try it with the 22k first and then go from there.

SDM
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Re: Installation of FX Metro Loop on Blackstar Artisan100

Post by SDM » Wed Mar 09, 2016 3:35 pm

In the cases cited in the instructions for classic Marshall amps, when there are two resistors noted, those two resistors are in series. Nothing connects between them, so could just add them together and think of them as one resistor in effect. So, 8.2K and 10K becomes "one" 18.2K resistor, and gets reduced to 14.7k total for loop install. 20K (series 10K resistors) gets reduced to 15.6K total. 22K total would reduce here to about 18K after loop install to keep voltages where they were originally. Can calculate this exactly, but no need for super precision here. Hopefully can see the pattern here in case this comes up for others.

Gotta keep wattage in mind here too though, a single higher value resistor will be dissipating more than two lower values in series. Here, in an average classic Marshall style amp at least, the original 22K would dissipate around a watt. I do not like to stress parts, would use a 3 Watt minimum rated (preferably flame proof as well) resistor (or higher) for the new swapped in resistor.

So, in short, with a lone 22K there originally, swapping it out for an equal wattage (or as rated above if unknown and circuit is like a classic Marshall) 18K resistor is what you want to do (good call danman).

Alternately could just add in a new resistor parallel across the original 22K for the exact same end result. If you choose this route, a 100K parallel to the original 22K will get you right about 18K total.

RockinRocket
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Re: Installation of FX Metro Loop on Blackstar Artisan100

Post by RockinRocket » Wed Jun 22, 2016 6:16 pm

Do you have a full schematic for this amp? Was interested if this is truly a cloned with options.Thansk

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