Kevin O'connor parrallel effects loop

[rockstah]

anyone used the effects loop on page 7-11 of kevin oconnors books TUT?

"fig 7-16 "the best all tube effects loop"


thinking about putting one in one of my plexi builds.

Mark

[Motörbööt]

hmm, don't have the book...

Greetz M
.

[Noel Grassy]

I'm not familiar with it either, perhaps you could post it

[dug]

I did. Very transparent. Sounds very good. Though it did seem to drop the gain down a bit, the chacter of the amp stayed the same. I don't know if I wired it up wrong or if that's just the nature of the loop.

I haven't been using any rack effects in awhile, and since I wired it to a switch to bring it in/out of the circuit, I haven't gotten around to trouble shooting it.

HTH

dug

[drz400]

anyone used the effects loop on page 7-11 of kevin oconnors books TUT?

"fig 7-16 "the best all tube effects loop"


thinking about putting one in one of my plexi builds.

Mark

It works fine but you might have to adjust the return gain by adjusting the input resistors to 100K, read up at Randalls site on a plate follower, it doesnt have to be as complicated as the London Power version.
Also the output impedance is high for most line level effects, try putting the send control before the cathode follower
Like Treble pot ---330K resistor 250kA pot then cathode follower but there are followers with higher input impedance than his.

[mhuss]

TUT 5 has a slightly tweaked version.

--mark h

[David Root]

Are you referring to the Sigma circuit in TUT 5? It's a lot simpler than the TUT 1 version. I'm going to use the TUT 1 version in my next amp, and I posted two questions about it in the Trainwreck section, which I'll repeat here as you guys seem to have some direct knowledge of it.
(1) I don't think the 6.8 uF coupling cap off the buffer needs to be that big, any opinions? My reason is I like to use PIO tone caps in the direct signal line, which this cap is, and I don't have the space for a PIO 6.8 uF 100V cap, not to mention its cost and lack of availability.
(2) I inferred from earlier text that the B+ for this design is 340V. That's fine for the return triode but the buffer B+ is right on the plate and the 12AT7 is rated for 300V. Now I know that pushing max design ratings is a time honored practice in MI tube amp design, eg the Komet 60 V2b plate is at 404V or 74V above max design for a 12AX7, but how far would you push a 12AT7?
(3) One of you mentioned that the gain dropped a little. Does this have anything to do with the pair of 1M series resistors either side of the earth node? (Just thought of this). Probably not.

[dug]

(3) One of you mentioned that the gain dropped a little. Does this have anything to do with the pair of 1M series resistors either side of the earth node? (Just thought of this). Probably not.

I don't know. As I said I really never got around to twaeking it. I did us it for awhile as it was (this was a couple of years ago) and I did like the "sound" or maybe I should say lack there of. It was a the time the most transparent loop I had played.

One of these days I'll get around and rebuild it just to make sure I did everything ok. I heard the Mesa loops in the recitiers were pretty good.
I was going to try one that had a mix control as I like the idea of a parallel loop.

dug

[drz400]

(1) I don't think the 6.8 uF coupling cap off the buffer needs to be that big, any opinions? My reason is I like to use PIO tone caps in the direct signal line, which this cap is, and I don't have the space for a PIO 6.8 uF 100V cap, not to mention its cost and lack of availability.
(2) I inferred from earlier text that the B+ for this design is 340V. That's fine for the return triode but the buffer B+ is right on the plate and the 12AT7 is rated for 300V. Now I know that pushing max design ratings is a time honored practice in MI tube amp design, eg the Komet 60 V2b plate is at 404V or 74V above max design for a 12AX7, but how far would you push a 12AT7?
(3) One of you mentioned that the gain dropped a little. Does this have anything to do with the pair of 1M series resistors either side of the earth node? (Just thought of this). Probably not.

The 300V max is the voltage across the tube, measure from pin 1 to pin 3. The plate doesnt know what the voltage is without a reference. All Marshalls have more than 300V on their cathode follower plates.
There should only be the loss from the cathode follower which isnt much but you can play with those return resistors like change the 1M dry to a 470k. The 6.8 is excessive but it depends on what you are driving as a load. 6.8uf is good for full bandwidth and a 10k load In most situations you are fine with 1uf. If you hear low end loss then increase it. You can also use an electrolytic and bypass it with a 1uf non electrolytic

[drz400]

(3) One of you mentioned that the gain dropped a little. Does this have anything to do with the pair of 1M series resistors either side of the earth node? (Just thought of this). Probably not.

I don't know. As I said I really never got around to twaeking it. I did us it for awhile as it was (this was a couple of years ago) and I did like the "sound" or maybe I should say lack there of. It was a the time the most transparent loop I had played.

One of these days I'll get around and rebuild it just to make sure I did everything ok. I heard the Mesa loops in the recitiers were pretty good.
I was going to try one that had a mix control as I like the idea of a parallel loop.

dug

Horrible passive mix loop, much better off using the London power or Aiken plate follower as a mix

[dug]

Horrible passive mix loop, much better off using the London power or Aiken plate follower as a mix

Thanks. I haven't tried Aiken's yet. Maybe I'll try that one next.

dug

[David Root]

Thanx for the input folks. On the plate voltage issue, all I can say is "Duh!" 340 minus 50 = 290, OK. Must have had a brainfart, I'm real involved with my current build right now, which I have some DC footswitch relay issues with. On the 6.8 uF cap, thanx, I couldn't see it either.

[jazzyjoepass]

I've TUT1, but I'd like to know how the TUT5 version of the FX Loop looks like. Can someone post it here on the forum?

[guittguy1]

I did the TUT1 version about 7 or 8 years ago. Seemed like the fx side was lower volume than the dry side. I tweaked it somehow to bring up the level. Don't remember what I did though.