Hi Folks.

Sorry I do not speak German so I hope someone can help me out in English.

I installed this mentioned effects loop into a high gain amp - something like an Avenger/SLO/Dual Rec type preamp with a JCM/JMP type 100 Watt power section.

when jumpered the loop sound fine but when I try to loop it through my Eventide H9, I can not get the output quite low enough to not clip the H9, though it gets close. But doing so the amp sounds extremely thin and small with much less volume. At this point the return is maxed as well.

Is this perhaps an incompatibility with the preamp/H9 or is there maybe something I can do to remedy this?

Loop is attached at InA from the treble pot and feed out to the master volume. B+ going in is just under 300VDC.

Any help is greatly appreciated :-)

Hi,

Try to remove one side of the Mica cap (the 500pF). That should solve your problem of thin sound.
I did that on my last build to solve this issue.

Cheers
Laurent

Zitat von: Laurent am Nov 01, 2017, 01:30
Hi,

Try to remove one side of the Mica cap (the 500pF). That should solve your problem of thin sound.
I did that on my last build to solve this issue.

Cheers
Laurent

Hi Laurent.

That made a HUGE improvement in the tone, but I still have a pretty big volume drop. 100k send pot is almost off and the 500k return pot is maxed.  Any ideas to correct that?

Thanks!!!

Did you wire the first pot in the right way? If I'm not wrong this is a log pot.

Hallo,

please check the level of the input signal and make sure that it is within the specs. Also make sure to use the correct input:
InA: 30 - 60 Vss, max. 65 Vss
InB: 10 - 15 V ss, max. 18 Vss
If you exceed the input level some adjustments are needed but this can not be done without more details about your build and correct measurements.

Best regards, Dirk

Zitat von: Laurent am Nov 01, 2017, 08:28
Did you wire the first pot in the right way? If I'm not wrong this is a log pot.

I used the small trim pots, so there is only one way they can install.

Zitat von: Dirk am Nov 01, 2017, 10:06
Hallo,

please check the level of the input signal and make sure that it is within the specs. Also make sure to use the correct input:
InA: 30 - 60 Vss, max. 65 Vss
InB: 10 - 15 V ss, max. 18 Vss
If you exceed the input level some adjustments are needed but this can not be done without more details about your build and correct measurements.

Best regards, Dirk

Thank you for the info - at the moment I am without oscilloscope but it is in my immediate future.... been putting it off way too long if for not other reason than the shipping costs. But I need it for several reasons.

Since this is in question, and I thought it may be from the start, I will revert to a loopless amp until I get my hands on a scope.

I am wondering if a PC based is worth the pain or if I should swallow it ang get the real deal, be it used of course.

Thank you!!!!

Zitat von: Gtr0 am Nov 02, 2017, 10:47
I am wondering if a PC based is worth the pain or if I should swallow it ang get the real deal, be it used of course.

I am sorry, I have no experience with such scopes. Maybe someone else here can give you some hints but maybe you should try to get a used scope like a Hameg.

Best regards, Dirk

Zitat von: Dirk am Nov 02, 2017, 08:32
I am sorry, I have no experience with such scopes. Maybe someone else here can give you some hints but maybe you should try to get a used scope like a Hameg.

Best regards, Dirk

Okay. Finally got an oscope - a used Tektronix 475 from eBay and it seems to work fine.

So how exactly do I read for the Vpp correctly? What I did was connected the probe at the PI input where a master volume would normally connect - I have decided to install this loop in a Fender AB165 style amp, so thwo channels both non-master volume and the third gain stage for both channels converge here at the plate of the third stage and go from plate to PI input's .1uF cap.

Assuming this is correct, I fed a 1kHz sine from a function generator iPhone app into the amp and ended up reading about 10Vpp at this area.

Does anyone know from experience if this is all correct?

Then if this is correct, I would break connection here and using the InB.

Thanks!

Well, operating under the assumption (and hope) that I was somewhat right, I went ahead and installed the loop. My problem this time is the exact opposite of last time in that I can't get enough juice out of the amp into the eventide. Now I have the mix knob cranked. The return is even worse, I have the return knob cranked and I had to crank the output of the eventide (some 8 or more db) and it still isn't close to the volume with the loop disengaged.

What should be my assumption here? Of course realizing this loop will not work with all amps.

Thanks.