FX Loop from TUT - Kevin O'Connor

[yankeerob]

Hi guys - new to the forum - I was browsing and came across a DIY Bassman by John Edwards in which he's fitted the tube FX loop a la Kevin O'Connor's 'The Ultimate Tone' - I've emailed him on the addy in the story but no reply - I've also emailed Kevin and he thought it was on the AMPAGE site but I can't find it. He's a busy guy and I'm gonna buy the books when I've got the spare cash but I'm hoping that someone here may have the schematic. I'm building a 5F6A clone from the tattered remains of my HRDv and want to fit an FX loop in it - the K O'Connor circuit comes highly recommended - unless someone out there has something else up their sleeve...

If you want to see the project so far go to TFF - Amplifiers - 'Maybe not a rebirth after all' thread...

Also here's a link to the scematic and layout...

http://images.lilypix.com/albums/use...A-Dv_schem.jpg

http://images.lilypix.com/albums/use...F6A_layout.jpg

Thanks in hope!!!

[yankeerob]

If you want to see the project so far go to TFF - Amplifiers - 'Maybe not a rebirth after all' thread...

Erm - sorry the tread's called 'Not quite a rebirth after all...

[Matt T.]

Just my opinion but putting an FX loop in a 5F6A circuit doesn't seem like a very good idea. If you're turning the amp up enough to get it to distort then the loop is (very likely) still going to be before the bulk of the distortion and you haven't really accomplished anything...time modulation effects will still tend to sound like crap. If you're not turning it up enough to distort then you can just put all your effects in front of the amp (i.e. into the input).

You're also putting something between the last gain stage (or CF in this case) and the PI...which will likely affect the tone. I'm not saying it can't be done where it's relatively transparent...but since it's going to be a fairly useless FX loop...why bother?

I don't have a schematic for KOCs FX loop. Most of the loops I've seen/used are simply a cathode follower Send and a common-cathode gain stage Return. Below is a loop I've used before and it was acceptable...it seems every amp I put a loop in gets some sort of tweek but this is where I usually start. I drew this a long time ago...but you get the idea from this schemo. NOTE: that input cap should be 47n (.047uF) but the output cap from the CF is actually .47uF.

[yankeerob]

Hey Matt

Thanks for taking the time to write - I know this is a volatile thing to attempt on this particular circuit - it was just that this guy John Edwards wrote about his DIY Bassman - let me see if I can find the link...

http://www.firebottle.com/ampage/hom...50146928QmGqcc

there you go - para 5 he mentions this effects loop from 'TUT' - which I'm gonna buy as previously posted - they're meant to be the best books for someone just getting into amp building - I've been a bench wireman and electronics systems installer for 20+ yrs - so I know a little - and have gotten some help from the guys at TFF and now you .... but really want to get right to grips with it - and Kevin's books are mean to be written so a complete dunce could get it.

The fact of the matter is that all the guys at TFF said - 'why do want to put an FX loop in that amp?' - and I don't know if you've had a look at the circuit but it'll be running at slightly higher voltages than the standard Bassman circuit due to the HRDv PS - what effect this will have remains to be seen but I'm using all double rated resistors - still carbon - no metal film or anything daft - but correct me if I'm wrong in thinking that I'll just be increasing the heat dissipation and this should have the effect of increasing reliability and shouldn't effect the sound as such. All the power caps are F&T's and the 100uF & 22uF's in the preamp are Roedersteins - all good quality stuff - but the point is - it's gonna be a bit hot - but I have a great mate standing by to test it once it's build and before we just fire it up - with some great test gear he managed to salvage from his many years at the BBC...

To answer the question of why an effects loop - I play in various circumstances - sometimes it's just 'crank it up and give it some rock & blues' - sometimes it's something requiring a bit of finesse - I have a T.C. Electronics G# that's about the best rack effect for going in the fx loop of an amp that I've ever heard - and I've pretty much tried everything under the sun at one time or other - but it's designed for guitar and specifically for the fx loop - and has a wonderful tone for doing so - you'd be very surprised I'm sure - and it's got a fantastic tremolo, the chorus is ok too and the reverbs aren't bad. I suppose something like the Re-Vibe would be good but I - as stated in the earlier post - am brassic at the moment and already own the G# - so I was just hoping to maintain the versatility I had before the HRDv gave up the ghost...

Anyway - that just about sums it up - thanks again for your post - it really is most appreciated!!!

[Ptron]

How much higher of a voltage are we talking about? A higher voltage should give you more headroom but if it's only a small difference I wouldn't think you'd notice. It would have to be way higher before you need to start worrying about doubling the rating of the resistors and at that point there would probably be other things in the amp that might start to get unhappy with the voltage, like the tubes for instance. Nothing wrong with metal film resistors, or regular caps for that matter. It's possible the fancy caps are more reliable but don't expect them to improve your tone. That's snake oil. There's something to be said for carbon comps as plate resistors. Something about them exhibiting a slight change in resistance over large voltage swings but I bet it's fairly insignificant compared to other factors and they're noiser anyway.

[yankeerob]

Hey Ptron,

Thanks for replying - yer - voltages - hmmm - hard to say until we actually get the thing built - which is taking a little bit more time than I'd like due to sourcing parts - some of which I have to get from the likes of Mouser in the States due to some odd value components not being available in the UK - finding a UK supplier of G10/FR4 - which I've actually done - likewise a UK supplier of suitable turrets etc... but it's gonna be worth it in the long run as I will - once the thing's up and running - be able to share the experience in the form of pre-built or kit form - 5F6A boards for HR Deville chassis' - mainly I'd have thought to European enthusiasts...

What we've done is taken the HRDv PS as is and applied it to the 5F6A circuit as is - everything's been uprated more for reliability than anything else - I'd done a load of mods to my HRDv when things started going south on it - nothing that'd put a strain on it - uprated all the PS caps and resistors but then I started having problems with the channel switching relays and just got totally fed up with it as the PCB - as anyone knows who's worked on a HRDx or Dv - is absolute garbage - I mean the worst quality PCB I have ever worked on in any device - ever!!!

I'd been reading a lot of stuff on TFF about putting tweed circuits in HRDx's using the HRDx iron and thought - could we do that with the HRDv? So with the help of a coupla guys there we came up with the circuit as per my original post in this thread - which is basically the starting point - the idea being to get the basic amp up & running and then tweek it for any probs that it might have - then perhaps figure out a mid boost/freq tweek, I'd ideally like an FX loop in it though everyone seems to think that's not a good idea - and I'd normally go along with that but the TC Electronics G# is a real exception to the rack mount FX norm - because it's designed to go in the FX loop - you can't just plug a guitar into it and it really doesn't affect tone anywhere near the likes of almost everything else - I'm guessing that it'll be a case of making sure the I/P & O/P impedances are correct - but that'll come in the 2nd or 3rd stage of development!

I do know from having worked on the HRDv that Fender basically just beefed up the HRDx PS and OT to produce/accept slightly higher voltages - which is the only difference between the two amps on paper - presumably to drive the 2x12 and 4x10 scenarios a bit more efficiently - and that we measured about 70 filthy watts out of the thing while it was still running - though another annoyance was finding out that it had been set up for 230v operation from the factory and shipped to the UK- where it'd been run on 240v for 9 yrs before I got it - hence our measuring even higher voltages at test points when we started troubleshooting it in the first place and why the damned thing ran so hot!!!!

I won't know what's hitting the plates etc until I actually take measurements -but do know that the HRDv PS - which is also a FWBR design as opposed to a tube or copper cap - will be producing slightly higher voltages than the standard 5F6A one before any load is applied and it'll be a case of finding out when the thing's all together - my only hope is that we'll wind up with something that's reliable and sounds half decent

[Heartlion]

Hey guys, does still anybody has good schematical solution for this? I also have G# processor and it doesn't friends with Cobra's FX loop set in my 15 watt Fender-like amp(twin-copy preamp and 2*6v6 in power amp, into 10"Jensen sp.).

Wanna buy the TUT later, but now just need to know the schematics for a good KOC's FX loop. Could anybody help?...