DIY Tannoy MG 15 Crossover - Help Needed

[AlfredA]

I am planning to build an external crossover for my Tannoy MG 15 based on the attached schematic. I am thinking to wound an air-core inductor with multiple tap of 4mH and 4.5mH to replace the autoformer. I know many AOS members have done this before. Can anyone let me know whether this a right way to do?

[Wakefield Turntables]

Speak to paul at RFC

[danilo]

Erm that's a Messed Crossover.
Don't use it ! The alleged "Tannoy' schematic underlying it is Wrong.
Some twit mislabelled the thing ..years ago. And the error spread like mold.
Read This Tannoy info first :
http://www.troelsgravesen.dk/Diy_Lou...ts.htm#Vintage

All 3 parts of it, before going further

[Reffc]

I am planning to build an external crossover for my Tannoy MG 15 based on the attached schematic. I am thinking to wound an air-core inductor with multiple tap of 4mH and 4.5mH to replace the autoformer. I know many AOS members have done this before. Can anyone let me know whether this a right way to do?

Those are completely the wrong values Alfred, as Danilo suggests, but also, Troels versions use the wrong values for the crossover too, so don't use those either as there is equally some glaring errors in his circuit. I have emailed you with advice. You cannot remove an autoformer and replicate exactly with fixed inductors due to the voltage step and electrical Q differences. What you can to is to provide a more linear response than the originals but you do need to compensate for the electrical Q of the circuit in the HF.

[walpurgis]

Some good advice here Alfred. Have fun with your Tannoys. They will sound great with good crossovers.

[AlfredA]

Many thanks for all the valuable advises! Paul has sent me many good recommendations that I need to sit down and digest. For simplicity, I may keep the original autoformer and change the rest of the inductor to air-core.

[Reffc]

Many thanks for all the valuable advises! Paul has sent me many good recommendations that I need to sit down and digest. For simplicity, I may keep the original autoformer and change the rest of the inductor to air-core.

I'd keep the laminated cored inductor for the LF. It wont have the coupling issues of a large air core in the bass position. I do have manufactured purpose designed and wound laminated steel E&I cored inductors for this purpose which are available in uprated spec (ie there's no chance they'll saturate) which are an upgrade over the standard ones, but the standard ones are fit for purpose. The HF and notch filter benefit from being air core. Don't forget when working out the notch coil's DCR to account for the overall impedance required at low frequency (ie DCR equivalent) from the whole LCR filter. Just because the schematics don't show DCR values it doesn't mean they don't exist! Measure your current notch filter inductor (ref WC3121) and ensure that the total DCR for the notch filter = this value plus around 0.5 Ohms. Leaving out this series resistor or using a way lower DCR inductor here will create an effective short to ground in the HF and kill your HF response (as well as not doing the amp any favours).

[AlfredA]

Many thanks for your explanation! Need to go back to the drawing board and rework.

[danilo]

Dunno What? yer expecting from a crossover remake. I've been Foolishy Dicking with Golds' Crossovers since 1980
Tried pretty well ALL permutations, likely preceeding all the bespoke/for a price variants from the 'proliferation' of shed makers of recent years.
The OEM crossover, simply recapped with Moderne Film 'n Foils (ONLY) has Proven to be damned near indistinguishable from ANY bespoke variants.
At least to Human ears
Once recapped... the BEST Tannoy upgrade possible is a Worth Owning Amplifier... and a music source/.input that isn't Crap.

Have spent time with an Active setup.. Which did/does work to expectations.
But In truth it's a bit of a PITA to implement. Currently it's shelved (but not forgotten) with only minor audible losses resultant.
Do Note that 'active' IS a superior path to an udulterated Crossover... If willing to deal with the complexities/inconveniences of an Active setup.

Tannoys for reasons that likely only GRF knows (if he even did :-) respond spectacularly to upstream Gear Quality improvements.
As small aside; Nelson Pass uses Tannoys in Imperial cabinets.. as his Reference speakers.. which in itself speaks volumes imo.
He's the man who had auditorium sized Keigellhorns built/installed in his home at one point
Tannoys.. despite views that these may not be the best speakers possible but rather because these respond/display even the smallest of Nuances in upstream gear quality.
Seriously important to a man who comes up with a fresh Amplifier Design topology every few weeks/months
Sooo. IMO spend up to /no more than ~50$ on decent film 'n foil caps for your oem crossovers... and stop there... saving yourself a couple of decades of "wild goose chasings :-)
THEN save up your $$ for gear Worthy of the rascals. You won't be disapointed.

[AlfredA]

Dear all,

I know you guys have walked this path before and your valuable recommendations or suggestions are welcome. The more I think, recap might be the only way to go. The reason I want to build a new crossover is to preserve the original crossover if I decide to sell the MG15 later. I hope the air-core inductor can further proivde sonic improvement. I have no intention to fool around with the schematic.

By the way, any of you have taken the recommendation from DIY Louspeakers on using 1.2mH, 6.8Ohm and 30uF for the LH? If yes, any good?

Best regards,

Alfred