Vintage Windings EQ-1A inductor in EQP-1A builds - the ring is gone!

[AusTex64]

Some of you may remember a high frequency ringing problem at around 26KHz I ran into (it was actually GDIY member Sasarist that pointed it out to me) on my Drip V2 EQP-1A builds. The problem was most noticeable when boosting at full at 10K, 12K & 16K, bandwith at narrow. I used the older version Vintage Windings EQ-1A inductor, along with the suggested Sowter transformers. I discovered a few things along the way - most significant was that the inductor rings the worst when loaded with a low impedance. Evidently the original Triad HS29 with it's 20K source impedance was a good choice. I ended up using a UTC A-18 with a 15K source impedance, then tuned the interstage Zobel to suit. But I still was having problems with ringing on the Vintage Windings inductor, but was able to make the Carnhill behave in my build. So that's what I went with, and somewhat loudly endorsed.

I was corresponding with Chris Preston at Vintage Windings while this was going on. A few weeks later, he sent me another EQ-1A inductor to test. And I didn't have to ask - Chris is a stand up guy. It took me several months to get around to testing it (sorry Chris), but finally installed it in one of my EQP-1A builds last night and tested it with my QA401. Great news - the HF ring is gone! It's also really cool that Chris has discovered the discrepancies in the "accepted" EQP-1A cap and and inductor values and corrected his current EQ-1A inductors to get the frequency centers closer to the published specs.

I can now endorse the Vintage Windings EQ-1A inductor without reservation. Happy building!

 

[emrr]

Awesome, thanks for the update.

 

[59flame]

i had the same problem and the same good results with the new set.

 

[peskado]

Hello!
Could you share your Zobel setup for A18?
I want use A18 in my build.

 

[AusTex64]

Hello!
Could you share your Zobel setup for A18?
I want use A18 in my build.

https://groupdiy.com/index.php?topic=63955.msg809404#msg809404

And the A18 is an awesome choice, IMHO.

 

[sasarist]

https://groupdiy.com/index.php?topic=63955.msg809404#msg809404

And the A18 is an awesome choice, IMHO.

Hi AusTex64 ,
well it seams that we are in same  "inductor" mode again , because  I was really pissed off with all issues that I was gone through with VW and to some degree also  Carnhill inductor , so I decide to try resolving those problems  once for all .
Tnx to Moby , first I bought decent LC meter which can measure inductance  at 4-5 different frequencies.And that was crucial to understand what was f...g going on with all of those "mathematical correct" 100$ inductors which give wrong resonant frequencies in circuit.Some core resins are simply nonlinear and if manufacturer says it is 27mH , well it is...but at  1k or maybe 10k , at 16k it can goes up to 33mH which means that res. frequency with 3300pF in serial will be much lower than desired 16K.That was issue with Carnhill inductor , and first VW inductor that I bought come with more serious issues.It come with some type of foil shield which was grounded at the centre of core.......worst thing that you can do with toroidal.Ringing like mad and frequencies was totally messed up ,probably becouse of wrong core resin .
So long story short , I ask Moby to help me (if you check his bv transformer masterpiece , you will understend why) and after only one week I receive perfect inductor .It give right values at right frequencies , and most interesting thing is that all ringing was gone......no meter what interstage transformer is in the circuit, actually I was using lower impedance Sowter model and it work great.

 

[Moby]

Hey guys. Yes, I accepted the challenge from Sasarist  to work on this  "irons". So far,  I did  my homework regarding output transformer (no osclillations, no motorboating) Sasarist is doing detailed audio examinations and it sounds great so far, compared to the modern competitors.
Intestage tx is completed,  I still wait comments from him. Also, Inductor is on the way. I did research with possible cores, picked few of them and it looks really promising. We still have to decide between two of them, both are toroid moly-permalloy cores but with slight different AL factor. Listening tests will give the final decision. 
My plan was to help Sasarist to have best possible sounding irons for his projects, but it's possible that those parts will be available commercially. 

 

[ruffrecords]

I can now endorse the Vintage Windings EQ-1A inductor without reservation. Happy building!

So what did he do that was different?

Cheers

Ian

 

[damiangiannis]

My plan was to help Sasarist to have best possible sounding irons for his projects, but it's possible that those parts will be available commercially.

Great news and seems like a nice option for the ones who are in EU. But let me get that straight . Are you also building  interstages xfrms for eqp-1a ?  Would you also consider making inductors for the meq-5 ? Is it too soon to ask for an estimated price on your goods ?

 

[Moby]

Great news and seems like a nice option for the ones who are in EU. But let me get that straight . Are you also building  interstages xfrms for eqp-1a ?  Would you also consider making inductors for the meq-5 ? Is it too soon to ask for an estimated price on your goods ?

Yes, I'm working on complete transformers and inductor set for EQP1a. As soon Sasarist confirm and we finish all revisions I will post the results. Price? Well maybe we should start new thread with possible Groupbuy to make prices best possible. Sasarist, somebody?
Meq5? Why not?

 

[AusTex64]

So what did he do that was different?

Ian, I am not sure what Chris did differently. I asked but never received a response.

 

[thecr4ne]

So what did he do that was different?

Cheers

Ian

Apparently, Math.
http://vintagewindings.com/products/VintageWindings%20EQ-1A.html
http://vintagewindings.com/tech%20swag/Pultec-Facts-&-Fiction.pdf

 

[ruffrecords]

Apparently, Math.
http://vintagewindings.com/products/VintageWindings%20EQ-1A.html
http://vintagewindings.com/tech%20swag/Pultec-Facts-&-Fiction.pdf

Those two refer to inaccuracies in the values used in clones. Unfortunately they do not address the ringing question.

He also unfortunately ignores the tolerances in the L and the C and also the inaccuracy in measuring them at a frequency other than the one they are intended to work at.

Cheers

Ian

 

[Moby]

Those two refer to inaccuracies in the values used in clones. Unfortunately they do not address the ringing question.

He also unfortunately ignores the tolerances in the L and the C and also the inaccuracy in measuring them at a frequency other than the one they are intended to work at.

Cheers

Ian

Yes, ringing issue is the serious one. Measuring at working frequency is "must". I really don't know why he had ringing problem. Maybe because of the windind tehnique he use. I did a test with several Molypermalloy toroid cores and the main problem was AL frequency nonlinearity, but finally I found the "right one".  Btw, I never had that ugly ringing.

 

[emrr]

I may be wrong, but seem to remember there was a similar high boost report with a Cinemag or a Sowter as well.  Maybe I'm remembering measuring one Lassoharp brought by, which I think was a Cinemag. 

 

[ruffrecords]

I may be wrong, but seem to remember there was a similar high boost report with a Cinemag or a Sowter as well.  Maybe I'm remembering measuring one Lassoharp brought by, which I think was a Cinemag.

I think you are right. I am fairly certain the problem occurs only with the small inductance taps of multi tapped inductors. when used in a series resonant circuit.  If the larger inductance values are large enough, the winding capacitance appears across the inductor which creates a parasitic parallel resonant circuit. With the smaller inductance values (higher frequencies) this can created a noticeable dip just outside the audio band. It is only when you measure the frequency response of such filters above 20KHz that you see this. The in band manifestation of this dip is to apparently pull the expected frequency down a bit so you need to reduce the series capacitance to get the resonance on frequency. I noticed this effect on both my Helios 69 and and 3 band Pultec designs.

The effect usually occurs when extra frequencies higher than the original design's are added (16KHz in the case of the Helios).

Solutions include using separate inductors instead of multi-tapped ones or reducing the characteristic impedance of the EQ so the inductor values are reduced.

Cheers

Ian

 

[JW]

I used the permalloy Carnhill that Audio Maintenance had for sale at one point (same one from their pultec kit I believe?)

Anyway, cap values needed to get the Pultec frequencies were dramatically off. Finally did get them dialed in, but if I ever build one of these again, I'll probably just but the whole filter section from Vintage Windings if 1. It doesn't ring and 2. Final frequencies are correct. One of the bigger pain in the asses that I've come across, selecting and stacking caps.

Moby, are you starting your empire or what? . . . . .  Can't wait to see what else comes out of your shop there. . . . .

 

[Moby]

I used the permalloy Carnhill that Audio Maintenance had for sale at one point (same one from their pultec kit I believe?)

Anyway, cap values needed to get the Pultec frequencies were dramatically off. Finally did get them dialed in, but if I ever build one of these again, I'll probably just but the whole filter section from Vintage Windings if 1. It doesn't ring and 2. Final frequencies are correct. One of the bigger pain in the asses that I've come across, selecting and stacking caps.

Moby, are you starting your empire or what? . . . . .  Can't wait to see what else comes out of your shop there. . . . .

Hey JW. Yes, I'm very close to the complete "inductive" set for Pultec EQP-1A. Input 600:600, interstage 80K:20K, and toroid molypermalloy multitap inductor are completed. I still trim the S-217D transformer. I tried with  Ni78, but it lacks  some headroom and new cores are on the way to me. I must say that i'm very pleased with the results.  Sasarist can confirm about sonic impressions. Honestly he is the guy who is pushing me very hard to finish this, because he is not happy with existing replicas. Some of them are OK but not great, some of them are totally wrong, poor sounding or inaccurate (inaccurate inductors values). Wish me some luck with new S-217D cores 

 

[ruffrecords]

I used the permalloy Carnhill that Audio Maintenance had for sale at one point (same one from their pultec kit I believe?)

Anyway, cap values needed to get the Pultec frequencies were dramatically off.

Can you be a little more specific about how far the capacitor values had to change? How did the amount very with frequency?

Cheers

Ian

 

[Moby]

Can you be a little more specific about how far the capacitor values had to change? How did the amount very with frequency?

Cheers

Ian

Question is not for me, but I can answer from my experience (knowledge). Soft Magnetic materials are not linear by frequency by many aspects, so in this case by permeability. So, Al value is different for different frequencies. Especially with molypermalloy cores. People who produce this "innacurate" inductors probably measured their values on 1khz what's not enaugh for this kind of filter.  Producing accurate multitap inductor for Pultec's has to be calculated and measured carefully.