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

[Kapo_Polenton]

Either way , i think i'll try the metro equation tomorrow and see what happens. Can't hurt to try!

EDIt: metro specs suggest that a B+ voltage in my range should be using a 4.7 k resistor vs. 10k which is what I have on my board. I might try that swap.

 

[Kapo_Polenton]

Just me again, beating a dead horse... if you look at the Jpeg below I've circled where I measured my B+ and that is where i've tapped onto the effects board. Should it have been measured instead further up where I drew the arrow? I don't think i was at the PI after all as in the documentation it suggested that tapping at the first filter cap was ideal. Just trying to cover all the bases. Arigato!

For some reason i can't append the pic.. i'll keep trying..

 

[Kapo_Polenton]

Sunday bump for all the problem solvers out there!

 

[projectx102]

Just me again, beating a dead horse... if you look at the Jpeg below I've circled where I measured my B+ and that is where i've tapped onto the effects board. Should it have been measured instead further up where I drew the arrow? I don't think i was at the PI after all as in the documentation it suggested that tapping at the first filter cap was ideal. Just trying to cover all the bases. Arigato!

For some reason i can't append the pic.. i'll keep trying..

The yellow arrow is where I tapped for my installs.Loop sounds fine

 

[projectx102]

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..

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

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 It is not that hard

do you have a picture showing which resistor you change to a .022 cap? What type and voltage cap do you use?

 

[projectx102]

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 where does one break the B+ rail in say a Metro Plexi to do it this way?

 

[guitarmike]

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.

They are hit an miss for me. I have had 2 Friedman's and 2 Cameron's and the CCV and the JCM800 I had Dave mod (and then sold like a dope) had the best loops. The Atomica and my 75 Superlead are/were not as good.

 

[guitarman967]

I installed the Metro Zero loss loop with lukewarm results. Although after adjusting the internal trimpot I didnt have any noticable loss with the loop engaged, I do have an amp that doesnt sound the same as before the mod with loop bypassed.
The feel is now stiffer and there's a noticable loss of either gain or some compression. Sounds like someone turned the mid control all the way up. It just honks..

I used a 22K decoupling resistor which gave me 310 volts when measured at the loop board. Perfect range according to the Metro literature.
I think what Voodooamps mentioned here about the loop being in parallel to the B+ may have something to do with why I'm not happy with the results. Something has to be tweaked a bit somehow. Too bad though, the loop itself seems to be working ok.

 

[glassjaw7]

Dave and Trace bringing the knowledge!

 

[baron55]

The problem with these loops is that they use N Channel depletion Mode FET transistors, these are great for Solid state relays, Normally-on switches, Converters, Power supply circuits, Constant current sources, Input protection circuits. They are used because they can take the high B+ voltage, but they are not "audio grade" transparent. You will have some tonal changes when using it. How much it bothers you is based on personal preference.

The best loops are loops with audio grade Op Amps, like the TL072 or equivalent. But they operate on low DC voltages, no more than 30 VDC. Since they require a DC power supply (low) they are not practical for a mod add on.

This loop www.ironsounds.com is a audio grade OpAmp loop that is 100% transparent, and requires zero adjustment, it has +4/-10 dB pad and 100% bypass. It uses low DC volts as well but reduces B+ to 30 volts with a resistor,/Zener clamping circuit. Also it has much less pull down of the B+ than the other zero loss type loops. It was also designed by a audio engineer.

I uses these for guys who want an added on loop to their existing amp.

 

[guitarman967]

The problem with these loops is that they use N Channel depletion Mode FET transistors, these are great for Solid state relays, Normally-on switches, Converters, Power supply circuits, Constant current sources, Input protection circuits. They are used because they can take the high B+ voltage, but they are not "audio grade" transparent. You will have some tonal changes when using it. How much it bothers you is based on personal preference.

The best loops are loops with audio grade Op Amps, like the TL072 or equivalent. But they operate on low DC voltages, no more than 30 VDC. Since they require a DC power supply (low) they are not practical for a mod add on.

This loop http://www.ironsounds.com is a audio grade OpAmp loop that is 100% transparent, and requires zero adjustment, it has +4/-10 dB pad and 100% bypass. It uses low DC volts as well but reduces B+ to 30 volts with a resistor,/Zener clamping circuit. Also it has much less pull down of the B+ than the other zero loss type loops. It was also designed by a audio engineer.

I uses these for guys who want an added on loop to their existing amp.

Good info here. Honestly though, I'm not sure if the problem I'm having has anything to do with coloration of the loop itself. Tried to post on the Metroamp forum to get some feedback but apparently the mods have to view your posts beforehand? Maybe because I have a low post count..