Gyraf Pultec Style EQ Finished

[Ben M]

Thanks for the nice comments guys.

I had a good play around yesterday with a few different sources and I'm still very happy with these. Big round bottom end, smooth top end with a broad Q. Really worth the effort imo.

Oliver there are probably easier first diy projects like Bo DI but like Nick has said this one isn't rocket surgery.

I might have some spare parts if people need some things for their Gpultec.

[waitup]

They look great, how hard is the build?
looking for a first time DIY

I'd say it's an OK first DIY. It's by no means a difficult project, but you might stumble over a few things. There's no detailed bill of materials for this project for a start, so unless you know what you're looking at on the PCB then it may be hard to choose correct components. That said, we're all here to help, so we can hold your hand through that part.

The other thing is the metalwork. The switches and pots for this project are board mounted, so you have to be pretty deft with a drill press and some software for laying out drill templates to get your front panel to line up with the PCBs. You can of course buy a case like the one Ben did, but as he found out you have to wire the switches and pots off board... not that big of a deal.

The final word of advice I'd give if you do choose this one as your first DIY is PLEASE PLEASE PLEASE be careful. Something like the GSSL operates on +/-15V rails, and whilst you might get a bit of a bee sting from that, it's nothing like the wolloping you can get from MANY spots on the Gpultec board. That said, every project that plugs into the wall is potentially lethal, so you shouldn't just be careful with high voltage tube projects, of course!

I would say get a BYOC guitar pedal project to brush up on the old PCB soldering work, and then dive into a pultec... Come get us when you need a hand!

[Ben M]

I made a BOM for he Gpultec while I was at it. If you want it PM me, anytime.

[waitup]

I made a BOM for he Gpultec while I was at it. If you want it PM me, anytime.

Ben 'Organised' Moore

[what_noise?]

They look great, how hard is the build?
looking for a first time DIY

I'd say it's an OK first DIY. It's by no means a difficult project, but you might stumble over a few things. There's no detailed bill of materials for this project for a start, so unless you know what you're looking at on the PCB then it may be hard to choose correct components. That said, we're all here to help, so we can hold your hand through that part.

The other thing is the metalwork. The switches and pots for this project are board mounted, so you have to be pretty deft with a drill press and some software for laying out drill templates to get your front panel to line up with the PCBs. You can of course buy a case like the one Ben did, but as he found out you have to wire the switches and pots off board... not that big of a deal.

The final word of advice I'd give if you do choose this one as your first DIY is PLEASE PLEASE PLEASE be careful. Something like the GSSL operates on +/-15V rails, and whilst you might get a bit of a bee sting from that, it's nothing like the wolloping you can get from MANY spots on the Gpultec board. That said, every project that plugs into the wall is potentially lethal, so you shouldn't just be careful with high voltage tube projects, of course!

I would say get a BYOC guitar pedal project to brush up on the old PCB soldering work, and then dive into a pultec... Come get us when you need a hand!

cheers, will look into some smaller projects before I tackle this, got plenty of time this summer to blow.

I made a BOM for he Gpultec while I was at it. If you want it PM me, anytime.

thanks, that'll be a massive help, sent you a PM

sorry to hijack the thread

[Ben M]

I made a BOM for he Gpultec while I was at it. If you want it PM me, anytime.

Ben 'Organised' Moore

You rang?

Oliver the BOM has supplier and part number links to local suppliers where possible. All nice and neat in an excel spreadsheet. A good head start.

Take Nick's good advice above and see how you go. Drop us a PM if you get stumped.

Ben

[Mixed_Messages]

Sorry to resurrect an old thread but I have just bought a gyraf style Pultec clone off Ebay and I find it has a decent amount of buzz in the high freqs. It has 2.1k, 2.5k, 3.2k, 6.8k, 12k, 18k in the high band and the 2.1k buzzes like crazy. The seller was nice enough to take it back and do some additional grounding and has posted it back to me. It has improved it a little but is still too buzzy for me. He says that is just the way they are. At 2.1k it is bad, it gets better the higher you go until it is silent at 6.8 and then gets buzzy again on 12k and worse on 18k. The Q is not consistant on each band. It is widest at 2.1 and 18k. Taking the metal lid off the unit helps a little with the noise too.. It has a Lundahl 5402 output tranny and no input tranny and one ecc88 on the tube stage.. From what others have said, it is nice and quiet unit.. Does this sound normal to you guys ?

[Paul Maybury]

Mine don't do that.
One of them however, has developed a kind of ringy oscillation sound when switching frequencies with the boost is up. I's most noticeable at the lower end of the hi boost range. Hmm....
Paul

[mylesgm]

Mixed messages, I think that the circuit absolutely requires an input transformer as the load seen by the eq is very important. If you inspect the unit and can see no faults in the wiring or glaring errors in soldering etc then I would almost entirely lay the blame at the lack of input transformer. Of course make certain that you are looking at the output transformer though as the Gpultec uses the same tx for both input and output. Paul is correct though, if the unit is built correctly there should be little to know hum, the units I've built were well under -80db noise into +4db. If all else fails and you're not up to the full trouble shooting I would send it to a tech to be brought up to spec.

Also, you might notice that we all use our real names either as our usernames or in our signatures and a location always helps too. Keeps the web anonymity at bay...

Paul, check the tube for microphony, just pop the lid and tap the tube lightly with a pencil. If it rings or resonates in the audio output then the tube needs to be replaced. Is the sound only when you use the switch?

[Mixed_Messages]

Thanks Guys.. I have added my name and location to my profile.. So an input tranny is needed.. You say it needs to be the same as the output right ? I will just clarify that the buzz is like a RF type buzz rather than a low hum like from the power tranny.

[mylesgm]

yes the easiest way is to insert the LL5402 as the input transformer. Can remember who the local dealer is but there will be a few options for internet purchase too. Check that the original builder has not jumpered any connections on the board to make unbalanced work and then it should be just a drop in and solder fix.

[Ben M]

Pretty sure the input transformer is optional for Gpultec. Both of mine have in and out lundahl's though.
There could be grounding problems with the chassis.
Take all power away for the unit and let it sit for 10 minutes so it drains then have a look at the ground connections. There should be a star ground under the main board...check that is secure. Sometimes grounding doesn't stop there... On my two I scraped some of the coating away from the chassis (including the lid screws) where the lid sits on the chassis body. Doing this will give you better metal on metal and improve grounding throughout the unit.
If you're unsure don't mess around...give it to a tech.

[Mixed_Messages]

On the circuit board it says "optional input transformer".. The builder said it is unbalanced.. He said he star grounded it. It is near silent on 6.8k which is strange.. He has scratched away the points where the lid would contact the rest of the chassis to get a good connection going.. It still makes less buzz without the lid. I just turned it on and used the lid to shield the inductors from the PS and the tube stage and that makes a big difference. So it seems to me me that the cheaper inductors (they look like black caps) are picking something up from the tube stage.. Does that make sense ?

[Mixed_Messages]

I just grabbed my heavy cast iron fry pan in used it as to shield the inductors.. That almost eliminated the buzz.. If that gives us any clue..

[mylesgm]

yes you can shield the power transformer, i/o transformers and inductors. You can do this with some mu-metal shielding but I didn't have to do this to achieve excellent noise results. I'm not sure which inductors you are using and I can't remember which ones I used (I think they were a custom hand wound job from a forum member) but if shielding them works then it work and you are in business. I would still get an input transformer and I didn't think it was optional.

[Mixed_Messages]

Ok, thanks Myles.. What will the input traffo do to the sound ?

[Ben M]

Hey Jeremy, many of these have been built without input transformers and haven't experienced the same noises you're hearing. Just so there's no mixed messages. Hehe
I built my two units in 3 unit cases so I could mount the toroidal vertically on the side of the case to increase the distance away from the main board...and then pushed the main board as far as I could in the opposite direction. Might not be possible if yours is in a 2 unit case. Keeping these components as far away from each other is the name of this game. Is there a picture you can post of the install? It might reveal some answers.

[Mixed_Messages]

Hey Ben, cool to know about the input transformer.. Do you know if it would make the unit better ?
Here are some pics of the build..



More pics here - http://s958.photobucket.com/user/NotThe ... t=3&page=1

[Paul Maybury]

Hi Myles, thanks, yes, I thought the valve might be microphonic. I'll have to check that and have a closer listen.
I really enjoy these eq's, I am learning more about what they can do beyond the usual smiley face settings.
They are great hi/lo filters and the lower hi boost frequencies are very sweet. I quite like running things through them with the eq flat as well.
Cheers,
Paul

[mylesgm]

many of these have been built without input transformers and haven't experienced the same noises you're hearing.

I wasn't aware of that, happy to be corrected. On to the shielding then. Don Audio has mu-metal shielding stuff, link at bottom. I would add the input tx anyway, galvanic isolation and the other tx benefits along with good lundahl tone.

Looking at your pics,I would tightly twist the black cables going from the amp pcb to the filters. What is the white cable going from the output xlr to the amp pcb? If it's ground that seems an odd way to do it. I would try removing this and test without it, with it connected directly to the earth point and also look for the correct ground terminal on the pcb.


http://www.don-audio.com/radiation-shie ... ing-sheets

[Ben M]

Yes not sure about the white cable either. Check this photo of mine with the earth going under the main pcb at the back. That cable is going to pcb ground connection.
download/file.php?id=312

Should cable tie the black joiners and fix them to the side of the chassis...away from the action.

[Alistair]

That white lead does appear to be the ground. Pretty odd to run 2 core + shield cable and then cut the shield at both ends...
It looks like an attempt at only having path to ground, perhaps not expressed in the most logical way.

I'm always impressed by how simple this circuit is. Gyraf is a smart man.

[Mixed_Messages]

Your unit certainly looks more impressive inside Ben.. The builder has come back to me with a solution of wrapping the inductors in folded over alfoil (he said 1/2 an a4 sheet worth) and securing it in place with electrical tape in order to shield them. There must be something in the orientation of the components that is causing a buzz here. I see you have 2 power transformers on yours Ben. Apparently mine has a dual windings so it only needs the one. I do really love the sound of this unit.. It is just what I was looking for.. It is fantastic on bass which is mainly what I want it for. The surprise was how nice the highs are. I thought these were more about low freqs.

EDIT: The builder also added this - "If you disconnect the filter PCB from the mainboard, theres no noise at all. So its isolated to the filter PCB" so I am thinking there might be a better solution than the alfoil trick.. What do you think ?

[Alistair]

Start with tightly wrapping and getting those 3 black leads out of the way as other people have suggested. They could easily be picking up interference as they currently are.

[Barney Loveland]

I just typed a response and closed the window! Doh.

Short version.

It's is a tube circuit, it has potentially lethal voltages!! If you are not comfortable draining the circuit or worked on them before best to find someone to show you.

The two wires going to the power switch are not a twisted pair, potential source of interference.

Also the orientation of the toroidal transformer will make a difference with or without mu metal around it. Where the in/out wires from the toroid are facing will make a difference.

First I'd get rid of the screw connector and solder and heat shrink that connection or any other potentially dangerous parts. Like the back of the power switch etc.

Unscrew the bolt and try a small turn either way to see if it gets quieter?

Mu metal shield may still be needed but this may get you close enough like the other builders above.