Toft AFC owners: ringing?

riantide · Post by **riantide** » Tue Jan 12, 2010 1:32 pm

Hey folks! I recently got a Toft AFC-2 and while so far I really like this thing, I have noticed that when I crank the gain knob on the HF, especially in the top range of the frequency pot, I get a really bad ringing/feedback sound. Is this typical, or is mine broken? I'm familiar with the way that some inductor EQs ring at certain frequencies, but this is considerably more obnoxious. Any info would be greatly appreciated!

Jim Williams · Post by **Jim Williams** » Wed Jan 13, 2010 11:22 am

Inductor ringing? How is that possible? Actually, all of them ring, like a bell. That's why I don't use them. Everytime I try one out, I gag. YMMV.

riantide · Post by **riantide** » Wed Jan 13, 2010 12:22 pm

thanks?

calaverasgrandes · Post by **calaverasgrandes** » Thu Jan 14, 2010 1:19 am

I thought inductors were the good eqs?

Jim Williams · Post by **Jim Williams** » Thu Jan 14, 2010 8:17 am

I would call them "fashionable". We used them in the 1970's as that's all we had. By the 1980's most had abandoned that topology.

The vintage revival brought them back, along with their problems...

calaverasgrandes · Post by **calaverasgrandes** » Thu Jan 14, 2010 12:41 pm

So you prefer gyrators or...?
This is a topic that has really bugged me ever since I read Traisters book about power supplys which had a chapter on filter design. Kind of like "if you like hot dogs dont visit a hot dog factory". Now I almost never want to use EQ to boost on anything because I know it will screw with the phase, and/or it will ring at the boosted frequency.

Jim Williams · Post by **Jim Williams** » Mon Jan 18, 2010 9:50 am

Gyrators, bandpass filters, etc. All are better than coils for me. Ever look at an inductor based EQ frequency sweep? Look at the tops of those bell curves. With inductors, every top is different and will shift around if it's a switchable frequency. You will see sharp peaks, bends and slopes tilting. Run a phase sweep and see the non-linear phase shift from those.

A view of gyrators or bandpass filters will show a very smooth bell shape regardless of frequency or boost levels. Run the phase plot and it's all linear.

I like an EQ that can be boosted or cut 15 db without weirdness or ringing.
I use active filters and R/C networks to get there. One should be able to crank 2k hz +15 db without barking. It is done here, but no coils.

calaverasgrandes · Post by **calaverasgrandes** » Mon Jan 18, 2010 10:43 am

+15db at 2k? ouch!
But I see what you are saying.
I used to be much more into electronic circuits a long time ago. Just getting back into soldering and stuff.
So I suppose inductor eq is popular because of the nonlinearity?

riantide · Post by **riantide** » Mon Jan 18, 2010 1:49 pm

So, any actual Toft AFC users experiencing this problem?

Jim Williams · Post by **Jim Williams** » Mon Jan 18, 2010 2:16 pm

calaverasgrandes wrote:+15db at 2k? ouch!
But I see what you are saying.
I used to be much more into electronic circuits a long time ago. Just getting back into soldering and stuff.
So I suppose inductor eq is popular because of the nonlinearity?

I suspect a bit of that with the low fi crowd, but mostly it's just because they are old and everyone in audio knows EVERYTHING that is old is better, except for people.

Good inductors can be made. If you are into precision, hysteris and core material design, good coils can be made and made consistantly. You will pay so much the EQ would cost a fortune.

I regularly demo EQ designs for picky audio folks. I can crank 2 khz +15 db without barking, ringing, nasel tones or plastic transistor sonics. Sure, you have too much 2k hz, but you can't make it an ugly 2k which is the goal.

That new Basson bass head does it and does it very well. No bark, no bite.

strdsk · Post by **strdsk** » Wed Jan 20, 2010 9:07 am

I had that same Toft piece and nothing but problems with it...

riantide · Post by **riantide** » Wed Jan 20, 2010 3:38 pm

Problems? Do tell.

strdsk · Post by **strdsk** » Wed Jan 20, 2010 4:18 pm

I'll start by saying that I won't slam you for your choice of gear. People have all types of reasons for choosing the gear they do. Price point, footprint, features, etc. Not sure if the problems were specific to my piece or across the board, but the build quality for the price and reputation let me down immediately. Mine chirped and oscillated as well.

riantide · Post by **riantide** » Thu Jan 21, 2010 3:56 pm

I got one because I've always loved Trident and Daking pres and one of these Toft thingies came up on CL for $400, so I pulled the trigger. So far, I'm pretty happy. The pres aren't nearly as cool as Trident and Daking, but the EQ is pretty great and the pres are definitely useable. Still haven't decided if I'm going to keep it, but we'll see.

So far the only problem I've had is the one I mentioned, where some of the more extreme boost settings will cause a feedback-type ringing that is just gross. I was hoping to get some feedback here but I guess I'll just contact Toft like I should have done in the first place.

Sean Sullivan · Post by **Sean Sullivan** » Thu Jan 21, 2010 4:00 pm

riantide wrote:
So far the only problem I've had is the one I mentioned, where some of the more extreme boost settings will cause a feedback-type ringing that is just gross. I was hoping to get some feedback here but I guess I'll just contact Toft like I should have done in the first place.

Inductor-based EQs tend to have this problem, I'm not sure what other feedback you're going to get. Are you looking for modify it?

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Toft AFC owners: ringing?

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