ok amp gurus.. 0 loss effects loop tone change?

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Kapo_Polenton

Kapo_Polenton

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Thought i would start a fresh thread to get some insight from those of you in the know.. I installed a Granger zero loss effects loop : http://grangeramp.com/ufxloop.php

Looks good, I liked the two accessible trimpots from the outside of the chassis. Problem is, I def. hear a tone change. I feel the highs are being attenuated and i am getting some added grit which affects the delays in my opinion. Curt had mentioned lowering the return trimpot and i did that, however that tone change is there. Is this anything i can tweak elsewhere?? I figure a lot of these loops are very similar. Is there something somewhere else that i might want to tweak? resistors or caps??

Oh and for the record, this is a vertical input 4010 JCM800 from 82.

Thanks friends!
 
Could be the effects themselves. Are they true bypass?
 
G major II that's it.. just for delays :( Very standard.. maybe there is a conflict with buffers. That's all I can think of.
 
The Grainger, Mojotone loops are all copies of the Metro loop. And they all change the tone a bit. Most likely because they are using LND150 FET transitors which are not really optimized for audio.More for high voltage switching. But these loops are good for amps that don't have regulated DC power supplies to power more conventional OP Amps like TL072, etc. the LND150's can run on very high voltage like the B+ on most tube Amps.
Even with no effects in these loops they do alter the tone just a bit. I have installed all of these and have observed the exact same sound qualities. Slightly rolled of highs and a little more gain or hair. It is not a huge issue but is noticeable. But is probably the best compromise instead of adding a buffered tube loop, etc.

This loop is much more transparent and does use OPAmps that are more suited for audio. Instead of using high voltage FET transistors. It uses a attenuation circuit that takes the B+ and drops it down to +30 volts for the TL072.

http://www.ironsounds.com/

Obviously a little to late but for others who are interested this loop is much more transparent, has +4/-10 levels and true bypass.
 
I think I might try it with pedals..maybe a unit operating at line level is not the best use for this particular delay. Worth a try anyway!
 
Level matching.
Impedance mismatches.
Cable capacitance.

The effects themselves can suck tone - true bypass isn't truly true bypass after 10 FX. Line boosters actually can help. But ya, the joints of each connection, the under powering of the pedal itself in the line, etc, etc, etc. all contribute to ghosts in the machine.

Hang in there.
 
Well considering I haven't heard anything back from Granger when i reported my latest findings asking for suggestions, maybe I am the one in a hundred with an issue and it is easier for me to just go away. Too bad i drilled holes in an 82 2204 combo to find that out. I'm going to try it with my BYOC delay i dug out late last night and see if it changes anything. I'm pretty sure it won't. Checked all my joints, double checked any possible wiring errors. Guess maybe down the line I can throw a switch in those holes for a gain mod or PPIMV. Should just stayed wet/dry. Lesson to all you kids out there.

The end.

The Prince that stayed a Frog.
 
yep... always a tone change. even on a top of the line tube loop. the great thing is it does have a true bypass.
 
Did you measure the B+ voltage to the unit? Also, did you decouple off the screen of a power tube socket or from the PI?
 
I am not a huge fan of the zero loss Metro Loops or equivalents and they are installed in some of the amps of the best amp builders out there. That is just my opinion and it does not mean they are bad loops. Just do not work for me.
 
Did you measure the B+ voltage to the unit? Also, did you decouple off the screen of a power tube socket or from the PI?
Click to expand...

B+ voltage was 280v which was right in flavour country as optimal was 250-300v for the unit. I decoupled off the PI.

So what other options are there? How about the more traditional serial "tone sucking" loops that come with a lot of late 80's Marshalls? What type of loop is in the 2205? Could I make that work here?
 
Maybe something like the below? Borrowed from the Ceriatone site with the only diff being the fact that there is no control over levels. That leaves me wondering whether or not this design would only be for line level gear or instrument level gear? Would be ideal because could be stuck on a switch..
 
Kapo_Polenton":3mrjutwd said:
Maybe something like the below? Borrowed from the Ceriatone site with the only diff being the fact that there is no control over levels. That leaves me wondering whether or not this design would only be for line level gear or instrument level gear? Would be ideal because could be stuck on a switch..
Click to expand...


No, you definitely would not want this. This is a passive loop and not a buffered one. Tone suck city here :thumbsdown:

How does the Granger sound with pedals. The reason I ask is you said you are using a G-Major II.

The G-Major II digitizes the analog guitar signal (dry) and causes a weird phase shift. It does not pass analog signal though it. It converts the dry signal to digital and back to dry again. It is much better used in parallel loop. Most good rack units keep the dry signal analog and don't convert it to digital and then back to analog. The ADA converts IMO are crap in the G-major II.

I have owned some pretty good rack gear and the G-major II was the worst as far as dry signal was concerned.

Also with nothing plugged into the loop do you get the same tone changes with the loop switch switched in? Because this will put the loop between the preamp and power amp. If so it is the loop, if not it is the G-major II

I wonder if Grainger copied the Mojotone loop exactly, the PCB almost looks identical including the trace design. If so they also copied a design flaw too. In the Mojotone loop they use a 470K resistor on the return side of the loop which is not needed since the return side is trying to increase the gain back up since it was attenuated on the send side. This causes the highs to be rolled off quite a bit. The fix is to replace it with a .022uF capacitor.

I have modded several amps with the Mojotone loop and have had to modify it to work correctly.


I can't understand why most can't design a quality loop :doh: It is not that hard:)
 
Thanks for the feedback... yes I have only tried it with the G major II so far ( was out all day so had no time tonight to try a pedal) BUT I can tell you the tone shifts the minute i engage the loop into the circuit with nothing plugged in. Def. adds some hair and cuts some lows and low mids to my ear. In this case i am not sure the capacitor would do what I want considering my highs are not rolled off but rather attenuated? I can always try it though... better than having nothing to try at all..
 
baron55":18tf6lo9 said:
The Grainger, Mojotone loops are all copies of the Metro loop. And they all change the tone a bit. Most likely because they are using LND150 FET transitors which are not really optimized for audio.More for high voltage switching. But these loops are good for amps that don't have regulated DC power supplies to power more conventional OP Amps like TL072, etc. the LND150's can run on very high voltage like the B+ on most tube Amps.
Even with no effects in these loops they do alter the tone just a bit. I have installed all of these and have observed the exact same sound qualities. Slightly rolled of highs and a little more gain or hair. It is not a huge issue but is noticeable. But is probably the best compromise instead of adding a buffered tube loop, etc.

This loop is much more transparent and does use OPAmps that are more suited for audio. Instead of using high voltage FET transistors. It uses a attenuation circuit that takes the B+ and drops it down to +30 volts for the TL072.

http://www.ironsounds.com/

Obviously a little to late but for others who are interested this loop is much more transparent, has +4/-10 levels and true bypass.
Click to expand...

Sounds like the Metro, Granger and Mojotone loops are optimized for pedals and not so much for rack effects units?

Can you elaborate on the loop from Ironsounds and how it compares tonewise to the Metro loop?

I'm looking to install one in a modded 2204 amp and use pedals I just want one as transparent as possible of course. I liked the looks of the Granger/Metro until this poor update on it's tone effects.

I thought the Metro was the one of the better/best loops out there?
 
Yeah guys to be honest, not at all impressed... ugly distortion and high end added with a cut on the lows and low mids. I tried it with a delay pedal i had on hand and didn't like it any better. It def colors the tone. I let Granger know asking for suggestions (heck maybe they want to use it as part of their documentation) but haven't heard anything back. Go metro if anything at all... to be honest, if i could do it all over again, i'd just sell my 800 and get a 2205 with the loop built in no matter how tone sucking it is.
 
I will try not to be overly technical in the hopes that it helps the gentleman who were commenting on the tonal changes with regards to the Metro effects loop; We have installed the Metro Loop for a few customers who have requested it and the loop can be made to sound transparent but there are some hurdles to over come.

In no particular order; Every effects loop has an ideal B+ voltage operating point in order for the loop to sound transparent. IE: the tone/feel remains the same in an A/B comparison when using the bypass switch to engage/bypass the loop. I did find that the Metro loop does have an ideal B+ operating voltage for it to sound transparent. The B+ voltage is not identical from amp to amp therefore the dropping resistor value changes from amp to amp. Installing an effects loop that contains circuitry will change the voltage in an amp. In order for the amp to sound/feel the same after the loop is installed you first must document the B+ voltages throughout the amp. Once the loop has been installed the B+ voltages can be restructured so that tone/feel of the amp is the same.

When you install the loop and the B+ pick off point is to the screens or PI (IE: running the B+ in parallel, as the instructions with the Metro loop suggest), restructuring the B+ voltages tends to be time consuming as small changes in the value of B+ dropping resistor(s) results in wide voltage changes making it difficult to restructure the voltages. A more logical solution is to set up the B+ rail so that the effects loop is in series thus making it much easier to restructure the voltages. In other words, break the B+ rail, send it to the loop and then return it from the loop to the rest of the preamp so that the B+ rail is in series. This will ensure a “zero loss” or transparent effects loop.


Hope it helps & have a great weekend
Trace
 
So can I just disconnect the B+ tap and measure before tapping or will the fact that i have leads from the send/return running to the pots now affect the voltages? If not i might opt to do that and measure it before it went in compared to after and following that, I guess use metro's method of adding a resistor or doing as you mentioned and breaking the B+ and running it straight to the board and then back to the circuit? Have I understood that correctly?

Thanks very much for the suggestion by the way! This is why Voodoo amps has such a good reputation!
 
Also just to add into the equation, there doesn't seem to be a decoupling resistor that gets added in the granger kit unless he as added one to the board ( I see a 2 watt there ) to cover a range of voltages most commonly found? I wonder if i tweak this first using the metro suggestions and see if this fixes it..
 
Kapo_Polenton":1lnzz1c7 said:
Also just to add into the equation, there doesn't seem to be a decoupling resistor that gets added in the granger kit unless he as added one to the board ( I see a 2 watt there ) to cover a range of voltages most commonly found? I wonder if i tweak this first using the metro suggestions and see if this fixes it..
Click to expand...
I'd find that odd. There's no one "right" value resister to work in all amps. :confused:
 
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