uhuhum R0ck FX loop

[tsl602000]

I was wondering if anyone tried the FX loop on the attached schemo.

[glasman]

I looks like a modified Dlator with no cathode follower. Probably would work but anything pluged into the loop will load the signal down.

Just my 2 cents.

Gary

[FUCHSAUDIO]

I looks like a modified Dlator with no cathode follower. Probably would work but anything pluged into the loop will load the signal down.

Just my 2 cents.

Gary

The "send" impedance is variable (based on volume control, not good), and generally a high impedance (for a loop) as well. Anything without a really high input impedance (forget solid state things), will likely not sound very good. It's not really a true "loop" without the cathode follower. It doesn't really fully buffer anything. Shall we agree to call it a "semi-passive loop" ?

[tsl602000]

Thanks,
That's pretty much all the info I needed..

[FUCHSAUDIO]

Thanks,
That's pretty much all the info I needed..

Build in a D'lator (with both sections), but put in a switch to completely bypass the loop unless you plan to use the loop. This way you have a good sounding amp, and you are not listening to the loop if you don't want-to. FWIW, the real D'lator loop sounds just fine imho.

[ayan]

Thanks,
That's pretty much all the info I needed..

While perhaps non-standard, the TR loop leaves out the CF by choice. I remember, years ago, talking to Bill K. and he said he preferred the sound of the loop without the buffer. For historical purposes, note that the more evolved Boogie "Mark" amps had loops that had a common cathode "send stage," apparently deliberately avoiding the CF as well. Being the owner of a IIC+ and an IV, in the past, I can say that both of those amps' loops sounded fine.

I have heard a few TR amps and they have all sounded good to me, loop and all. So the best thing to do would be to give it a shot, if you're curious, you may end up agreeing with Bill K. One man's poison, another man's medicine...

Cheers,

Gil

[dogears]

He told me that too. That said, I prefer the sound of my loop with the 27K/1.8K cathode biasing and not what most use in their loops (from the schematic heaven Dumbleator schematic). I prefer the loop integration with my effects and build in reverb by retaining the cathode follower. I also have a loop bypass switch should I want pure unadulterated tone.

Thanks,
That's pretty much all the info I needed..

While perhaps non-standard, the TR loop leaves out the CF by choice. I remember, years ago, talking to Bill K. and he said he preferred the sound of the loop without the buffer. For historical purposes, note that the more evolved Boogie "Mark" amps had loops that had a common cathode "send stage," apparently deliberately avoiding the CF as well. Being the owner of a IIC+ and an IV, in the past, I can say that both of those amps' loops sounded fine.

I have heard a few TR amps and they have all sounded good to me, loop and all. So the best thing to do would be to give it a shot, if you're curious, you may end up agreeing with Bill K. One man's poison, another man's medicine...

Cheers,

Gil

[JimiB]

do you use a choke? if so do you place it before the 15K droping resistor?

[glasman]

do you use a choke? if so do you place it before the 15K droping resistor?

It is optional but it does help in a standalong box. I built one that I could hear the power supply roaring in the background. I installed a choke from a deluxe reverb and problem was gone.

Ted weber sells some cheap chokes that are perfect for that use.

Gary

[JimiB]

do you place it before the 15K droping resistor?

[tsl602000]

I actually built a loop in my amp based on a schematic by Heistl. Unfortunately I didn't have a few parts which I substituted for "nearest values". I made the loop switchable and right now the loop takes away alot of hi end. I hope the new caps and resistors come in soon so I can experiment some more.

I'm still not 100% what exactly the Dumbleator is. There's quite a few schemos out there.

Thanks for the help!

[Tonegeek]

FWIW I put a very simple loop in my Twin that has no level controls but does return to a recovery stage on to the Master volume then the PI. It works very well and I see no need to change it. The amp has plenty of highs.

[Rob Livesey]

, but put in a switch to completely bypass the loop unless you plan to use the loop. This way you have a good sounding amp, and you are not listening to the loop if you don't want-to.

Hi Andy, in my SLX100, does the loop bypass function on the artist+ footswitch completely take out the loop stage? ie, does it reverse the phase of the signal path? It's been discussed again over on the gearpage about reverse wired speaker cables etc.

Thanks,
Rob.

[Fischerman]

I'm still not 100% what exactly the Dumbleator is. There's quite a few schemos out there.

Here's the schematic I use, if it's wrong maybe someone will correct it...however I deviate from it anyway. I used a 1.8K/33K instead of the 1K/10K on the CF cathode and I also used a 500K-A Send Level pot. I originally used the 500K-A there because I didn't have any more 250K-A...then I later bought some and put it in and noticed I had lost some high-end and punch so the 500K-A went right back in. The bypass cap on the Return stage might supposed to be 25uF instead of the 5uF I have shown there.

I should probably mention that I don't do my power supply like the original either. I just use one node for the whole thing and mount the 100K plate resistor right on the socket and run the B+ straight to pin 1. I have 330vdc on the CF plate and 225vdc on the Return plate. I would think many here would tell you not to do this though.

I have had problems in the past with the cathode follower Send sort of caving in and distorting/squashing the signal when using the 10K/1K pair on the CF cathode. Seems that the increased cathode resistance and increased Send Level pot help prevent that.

All this is just FWIW, FYI, YMMV, etc.

EDIT: I just now noticed that the TR schemo in the OP shows a .047uF cap in the LNFB loop...I thought the D'lator used a big honkin' .22uF cap there (but the ODS uses the .047uF in it's LNFB loops). That might make a slight difference right there because the low-lows aren't getting NFB'd.

[FUCHSAUDIO]

, but put in a switch to completely bypass the loop unless you plan to use the loop. This way you have a good sounding amp, and you are not listening to the loop if you don't want-to.

Hi Andy, in my SLX100, does the loop bypass function on the artist+ footswitch completely take out the loop stage? ie, does it reverse the phase of the signal path? It's been discussed again over on the gearpage about reverse wired speaker cables etc.

Thanks,
Rob.

Actually Rob no. The circuit in the ODS/TDS retains the loop in-circuit, whether you are plugged into the loop or not. The bypass works the same way. The active circuits in the loop are in circuit, the send and returns are disconnected. It's the equivalent of unplugging everything and switching the loop to parallel mode basically.