Acoustic 320 repairs

[AudioMan]

Hi,
I'm in the process of repairing an Acoustic 320 Bass amplifier for a family member.
It is an acquired unit that has been modified by someone, possibly to get around a fault that they couldn't find.
I'm interested in bringing it to factory level of repairs. I have the schematic as found on this site.

Graphic Equalizer:
Does a normal working amp really have a graphic equalizer range of +20dB and -20dB range?
My LTSpiceIV model says only +-12dB, or so.

My unit's board is messed up with changed inductors that are not original. I'm going to try to acquire some pot cores and wind my own inductors.
Are the 3H pot cores 14mm size?

[gbono]

You can search on this site for info on 320 inductors unofficial acoustic control corp forum Forums

[AudioMan]

Thanks for the interesting link.

I did look there but so far have not found the pot core dimensions, and will need to dig some more.
I don't want their substitute Xicon transformer as the inductor, but want an actual pot core - even if I have to wind them.
I know were I can fins a source for pot cores but was not sure on the physical dimensions. I think they are 14mm in diameter, but wanted to check here.

I also want to know whether the equalizer gain-loss range is as the panel says +20dB and -20dB, to ensure when I have restored my unit to factory specs.

[gbono]

Formula and calculator for winding air core inductor

How to calculate coil inductance (single-layer, cylindrical air core inductors) - Online Javascript

[AudioMan]

Well, after some down time, I finally bought some 14 mm potcores and some 0.1 mm enameled wire from China. The wire took close to 40days to get here.
Winding a full bobbin core, I get about 2.47 H, which may be close enough to the 3H needed. At least two potcores are required to repair a 320 Acoustic amp. I'll let you guys know later if this idea works.

Peter.

[J M Fahey]

You are close enough.

You also found an important parameter: since you fully wound and measured one, now you know maximum value possible and also easily calculate any other value needed knowing indictance is proportional to square of turns.

Hope you counted how many fit in, besides just filling the bobbin.

As of the +/- control range, pure Market Dept creativity, +/- 12/14 dB matches what other graphics do.
Trust your simulation

[AudioMan]

...Hope you counted how many fit in, besides just filling the bobbin...

No I didn't count the turns. I used a portable hand drill and didn't have a counter. One hand on the trigger and the other hand for wire tension. Scramble wound, as it is very difficult to wind it evenly like a garden hose. Worked like a charm.
Secondly, another factor was getting a potcore with a high Al, as it determines the number of turns needed. I think it was around 800 turns, or more.

[J M Fahey]

Not everything is lost, hand wind , no drill, say, 100 turns, measure inductance and there you get the real Al.

I always do that, because almost exclusively buy surplus "mystery" cores, no reliable data on them.

[AudioMan]

Not everything is lost, hand wind , no drill, say, 100 turns, measure inductance and there you get the real Al.

I always do that, because almost exclusively buy surplus "mystery" cores, no reliable data on them.

Your suggestion is sound advice for "mystery" cores.
I found that for the number of turns I needed that my fingers got cramps trying to hand wind. Hence I opted for the electric drill. Secondly, I bought Magnetics AL 8400 W41408UG Ferrite pot cores that wasn't supposed to be "mystery" cores. Thirdly, my stab at it worked out very well. I have no prior experience with pot cores. So, I'm a happy camper.
Fine tuning can be done with capacitors when I get to test these inductors in the actual unit. I'd like the peak resonance to be close to the panel's stated frequency. May need to haul out my spectrum analyzer.

[AudioMan]

One other question;
Is the channel "A" LED always ON of an Acoustic 320 model?
(Assume amplifier power is also ON.)