SpeakerTalk

Craigb · Posted: Wed Apr 14, 2010 10:25 am Post subject: Monitor Audio Ma1

I recently acquired a pair of Monitor Audio MA1s (mk1?) complete with sales brochure for the MA1 to MA7 and a reprint of a Gramophone June 1974 review, which makes very interesting reading.

They turned out to be as described - the bass is good the, midrange OK, but the treble is very thin.

The units are B139, a B&W BW150/M5 mid range and I assume the Tweeter is the original Peerless (It has no markings but looks the same as in the Gramophone article).

The crossovers have been repaired at one stage - looks like one component on each burnt out!

I'm thinking that I may need to replace or repair the crossovers, which are mounted on a board almost as big as a A4 sheet!

I'm really keen to restore get these back to how they might have sounded 30 years ago. Does anyone have any ideas where I could source a replacement crossover or at least the crossover schematics?

Thanks in anticipation

Craig

ColinR · Posted: Wed Apr 14, 2010 10:51 am Post subject:

If you have rectangular Peerless tweeters with exposed lead out wire you have a pair of mkIs.

Treble is generally o.k. with Peerless DT10HFC, so you need a couple of 4.7uFs.

Monitor Audio did "silly things" with the crossover having resistors in series with the drive units, hence the burn marks on PCBs.

You won't be able to easily source replacement PCBs although sleezeBay "strippers" find the design desirable.

I do have a pair of "prototype" PCBs with no resistive dumps though.

I'm not making any further detailed schematics available due to sleezeBay and others abusing copyright material.

Lists of capacitors may be made avialable though.

The pdf version of the review on Gramaphone.net does not work.
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Craigb · Posted: Wed Apr 14, 2010 11:29 am Post subject:

Thanks Colin,

I can send you a scanned copy of the gramophone review if you would like it, I'm sure I still have your email details. I would be very grateful for the capacitor values and or schematics. Maybe you could send that by return?

John777 · Posted: Sun Mar 03, 2013 6:42 pm Post subject:

Anyone still want help with their MA1s?

I have a 1975 pair, Mk1 then upgraded to Mk2 spec from new.

mr quackers · Junior Contributor 20+ Joined: 20 Jun 2013 Posts: 20

Hello - I still need help with Monitor Audio ma1 series 1 (with Peerless tweeter)- can anyone supply wiring diagram for cross over as I am asking person to renew components but they need values - thank you for your help (I am also asking Proffski).

John777 · Posted: Tue Jul 02, 2013 10:24 am Post subject: Monitor Audio MA1 mk1 crossover

PCB marked on back MONITOR AUDIO LTD MA1-3 left hand side

MF LF HF right hand side

Components from top left, top half of PCB

Resistor 3R9, cap 30uFD, large ferrite inductor ?, cap 30uFD, small ferrite inductor ?, cap 6uFD, small ferrite inductor ?

Components from left, bottom half of PCB

Large ferrite inductor ?, cap 5uFD, cap 80uFD, small ferrite inductor ?, large ferrite inductor?, cap 5uFD

If I was able to translate the PCB tracks into a circuit diagram, I would. If I can find a way of scanning it clearly enough, I will and post later.

audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

Don't know anything about it, never seen it. But you have 6 inductors, 3 large, 3 small, and 6 caps, 3 largish and 3 small?

If it's a 3 way with 3rd order crossover, I guess 2 large inductors and the 80uF supply the bass, two 5uF and a small inductor feed the treble. This leaves two 30uF and a 6uF and one large inductor and 2 smalls left over. I guess the large inductor and two 30uF feed the high pass midrange, in series with the 2 small inductors and the 6uF feeding the low pass midrange. The resistor could be damping across an inductor or cap, or attenuation for a driver. If burnt out most likely in series with a driver for attenuation?

mr quackers · Junior Contributor 20+ Joined: 20 Jun 2013 Posts: 20

Thank you for your reply - as this is high end speaker I thought that Monitor Audio would specify very exact components to ensure top end audiophile sound quality - I would love to recreate exact crossover - I contact Monitor Audio who did not know this speaker - seems strange as they made it - they said they no nothing but speaker badges definitely say Monitor Audio - if circuit board parts were not corroded with white corrosion expert could possibly read but no good because the resistors etc are corroded with some kind of whiteness which means cannot read what they say - speaker too good to crush
many thanks.
Mr Quackers

John777 · Posted: Tue Jul 02, 2013 7:01 pm Post subject:

Monitor Audio now is NOT the same company that made the MA1 and other speakers. I have had this conversation with them before, many times.

They will NOT give you any help whatsoever...

John777 · Posted: Tue Jul 02, 2013 7:04 pm Post subject:

Crossover for Mk 2 MA1 has better components, but I will not be able to tell you the details until I dismantle them again.

I have 2 x MA1 Mk1 crossovers for sale, it looks like. Un-marked, no burnt out components, lead wires to LF, MF and HF still attached.

A very attractive pair I would say... Offers? Would certainly help some forum members, so I don't want to make my fortune, but I have things I need too.

Either here or eBay.

PM if interested.

John

John777 · Posted: Tue May 27, 2014 11:22 am Post subject:

speakerguru · Posted: Tue May 27, 2014 10:20 pm Post subject:

proffski · Posted: Thu May 29, 2014 2:40 am Post subject:

Indubitably! Smile

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man standing in a bucket and trying to lift himself up by the handle.
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audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

sure am!

bdgdpc · Posted: Mon Aug 24, 2015 4:31 pm Post subject:

I've got some questions about MA1's which I hope someone can help with.
I rescued a pair for £40 from a local antique shop. I knew it wasn't a bargain, as a tweeter has gone and both mids need attention. I'm okay with the aspect of the refurb though.
My questions are on the cabinets. (a) they were lined with what looked like original (yellowing) foam, but also stuffed with loose (new looking) polyester fibre, which I think shouldn't be there? (b) the midrange had a foam 'collar' glued round the inside of the mounting hole - is this correct? (c) the main front baffle board can't be removed even when unscrewed because a bit of black plastic trim has been glued round the inside edge of the cabinet lip - should the plastic trim be there? (d) ports have no tubes, just plain holes in the baffle - is that correct?

Ta, David.
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David (UK)