Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shortfuse on May 23, 2014, 01:04:27 pm
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Hey Guys been away for a few months work is killing me, but I am starting to get back to normal.
I have a friend that just picked up a brand new 1959HW Plexi and wants me to install an effects loop (in the amp not external).
I have looked at the Iron Sounds, Mojo, and Metro ones. Also looked at London Power's Tube one as well.
Which would you use and why? Pro's and Con's from experience. I know a lot of them say zero insertion but I think they all have some change to tone. Any info positive or negative will be appreciated.
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I've installed the Iron Sounds loop in 2 JCM-800 style amps and they work as advertised with very minimal impact on tone. And I wouldn't call myself a builder, I put them in amps that I use and I'm pretty picky about tone.
I've heard good things about the Metro Zero loss fx loop as well.
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Thanks JustMike good to hear from someone that installed and actually uses one. I dug through some past posts and saw where Tubenit likes those as well.
Was hoping someone would have chimed in on the London Power one.
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Was hoping someone would have chimed in on the London Power one.
I believe Loose Change has installed 1 before, send him a PM.
Brad :icon_biggrin:
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Thanks Brad will send him a message now.
I found this as well which was a bit helpful http://el34world.com/Forum/index.php?topic=10208.0 (http://el34world.com/Forum/index.php?topic=10208.0)
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Well finally had time and this got me back into the swing of things for building and soldering. Install the loop and with a bit of side input from LC it was a very successful mod and install. I give the London Power BFX "Best all-tube Effects Loop" a thumbs up. I read some posts where it was said to be sterile but I found it to be very very good once adjusted correctly. I really like it with delay chorus and Phase shifting I dont think I would ever use the Series setting. I have installed the Metro one and it was ok, never installed or played through an amp with the iron sounds one. Maybe once I finish my d'lator and try it out I will just add that type from now on wont know until I get to that project.
While in there he had me switch out the caps to Sozo's I think they improved the sound greatly form what was installed at the factory. I was amazed at the size difference compared to Mallory. Also glad I read the section on the foil end and the direction it goes because I would not have paied attention on a non polarized cap. Changed out the bias caps to Sprage 10uf/150v from the itty bitty 10uf/100v ones that were installed at the factory. The factory ones may have worked fine but everything I have ever read on this forum says they should be 150v, plus it was a very easy swap for the few cents more for all the other things that we did. Replaced the silver mica caps to better quality ones and the 1K 3w resistors Pin 4 to Xicon 1K 5w. Biggest change in tone and performance was the replacement of the caps and mica's.
We also installed a PPIMV I give this an ok from being wide open set at 10 like its not installed to 7 or maybe as low as 5 for globally knocking down some volume and retaining tone. But to turn the master way down and vol way up to generate distortion as in and old JMP MV amp I say it is horrible. I think I am going to remove the dual pot and associated hardware and Install a single 1MA pot and tie it in as it would be in the JMP and see how that works. This also means I will have to change the insertion point of the Loop. Happy modding.........
Other mods in progress right now are dual bright caps on the bright vol channel 500p, 250p, and off no cap. I personally like it with no cap but he likes to brighten things up here and there so the other 2 are useful to him. He inquired about adding a switch to the V1 coupling cap where a 330 or 250 could be switched. Is that enough value difference to make a tonal difference? never messed with these before always just used a 820/330. Need comments and or opinions.
One other question I have is every plexi 100 schematic I have seen shows a 5.6k resistor attached at pin 5 this amp has a 1.5k shared between two tubes. See pic. Should I remove those and add the 4, 5.6k resistors at each tube.
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Almost complete. But what would make the PPIMV sound so bad. I believe I have it hooked up correctly (I have it hooked up as in the attached pic) but can not rule out I may have done something during installation just when you turn it down it go to mush for lack of a better word.
I was hoping someone might have answered the question on the 5.6k resistors on the tubes from my previous post could this have something to do with it.
While re-biasing if I move the PPIMV knob at all it will start to hiss and then pop bias on the meters doesnt move says constant at 42ma. If the PPIMV is wide open the amp sounds great I will call that 10 any thing down to 6 sounds bad. I removed the PPIMV wiring and put it back to stock and it still sounds great. With the pot and wiring remove I checked all connections to the housing of the pot there was no continuity between the wires and and the housing. Could it be that I just received a bum pot? It is a bit perplexing as I had a bluesbreaker a few years back with a PPIMV and it sounded very good.
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Layout drawing looks nice...
You appear to be missing coupling caps between the PPIMV and the bias supply feeding the 5.6K grid stoppers....they would block the bias DC from getting back onto your PPIMV pot
Also, I'm not so sure about the 2M value of the resistors on that pot, and because the pic is blurry, I can't tell if two of the lugs are going to ground.
I'm used to this application: (sorry if you've already iron'd this out,,,i didn't have time to read back over the thread(s))
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Layout drawing looks nice...
I believe it is from the metro site there are several on the web
You appear to be missing coupling caps between the PPIMV and the bias supply feeding the 5.6K grid stoppers....they would block the bias DC from getting back onto your PPIMV pot
Looking at your layout you are referring to the .1uf caps after the 1ma dual pot. Your layout also has an additional resistor inline form the amps existing .1uf (on my amp .022) going to the additional .1uf caps along with those tied to a pair of 220k resistors to the bias.
What i did was i removed the 220k resistors that were tied to the .022 caps, from there used a shielded pair from the far right lug (input) on each of pots of the dual pot shield to the far left but not grounded to the pot housing. Other end of that pair 1 wire each tied to the .022 cap where the 220k was tied to it. From where the (2) 220k resistors tied together on the board there is now a wire that goes to the far left lug on the pot and ties to both pots but nothing attached to the pot housing grounding it. The 2m resistors go from the left lug to the center (wiper) on each pot. From the center lug of each pot 1 wire each of another shielded pair ties to it and then goes to pin 5 for each pair of tubes (where I think a 5.6k resistor should be instead I have (1) 1.5k shared between 2 tubes (factory installed). The shield goes to far left lug again not making contact with the pot housing and to ground.
Also, I'm not so sure about the 2M value of the resistors on that pot, and because the pic is blurry, I can't tell if two of the lugs are going to ground.
2m resistors are what I found on a lot of PPIMV layouts no they do not go to ground.
I'm used to this application: (sorry if you've already ironed this out,,,i didn't have time to read back over the thread(s))
No problem i appreciate your reply
The schematic you use is like this layout where it shows keeping the 220K's adding .1uf and the pot grounded? Hummmm????
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Y'all are talking about two different PPIMVs. Both should work just fine. I prefer the one without the extra caps.
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Y'all are talking about two different PPIMVs. Both should work just fine. I prefer the one without the extra caps.
Sorry shortfuse....
Be thankful we've got sluckey here to keep us thinking clearly.
That was my attempt at helping. :l2:
The schematic you use is like this layout where it shows keeping the 220K's adding .1uf and the pot grounded? Hummmm????
I used that one and it worked.....that's all I've got
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I am always thankful for Sluckey's advice he has helped me out numerous times.
I ordered a new pot from Doug today along with (2) .1 caps (that I wont need now Dave!!! LMAO) will retry in two days when it arrives.
I think I either have a bad pot or did something wrong when I hooked it up.
I also have the 5.6K resistors and will add them to pin 5 tonight. Dont know if that will make any difference but every schematic I see has one at each tube socket. Not sure why Marshall did it the way the did?
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The pot was the problem. Replaced the pot and all is fine with the PPIMV. One I had on hand was a no name brand one ordered was a Alpha guess you get what you pay for.
Changed the resistors on pin 5 as stated above and put it back the way it came from Marshall it sounds better that way.
Amp is finally complete I give the Sozo's and the London Power BFX Loop a thumbs up. Now off to my Dlator project. Hopefully that will not take me as long but the way works been going I just have no time.