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Old 16th Sep 2020, 12:15 am   #21
CRM-114
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Default Re: Quad FM3 no stereo

OK, thank you Paula and Craig; I'll source a transistor and get back - maybe a couple days (I have BC547/48/49 and BC557/58/59, but no 550). I'll try substituting R105/7 as well.

Thank Dave and Mike. I have already tried with that, but thanks - it's always good to double check the simple things first.

Ted, with stereo encoding being AM, if the signal is 'too loud', for want of a more precise description, and clipped, could that mean it's not usable to the MC1310?

Philippe
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Old 16th Sep 2020, 12:21 am   #22
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Default Re: Quad FM3 no stereo

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Originally Posted by Craig Sawyers View Post
It is not such a bad idea - pin 2 goes high on mono, resulting in about 1.4mA of collector current in TR101. Quad fitted several types of transistor depending on availability, with BC550C being an equivalent. That has a beta of 400 - 800. So it will pull a pretty insignificant 3.5uA to 1.75uA from pin 2 on mono.
I was of the impression – perhaps wrongly so - that the separate mono output, via emitter follower Tr101, was independent of anything that was happening in the stereo decoder IC (MC1310) - available regardless as it were. And that the DC conditions at pin 2 (MC1310 input) were not conditional upon what mode the decoder was in.

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Having met the guy who designed the FM3 (the late great Mike Albinson) he would have thought that through long and hard before deciding on that way of doing mono.
I had wondered who had designed the FM3. Was it Mike Albinson’s first major job at Quad? I think that Quad had been without a designated RF person since John Collinson had left, which might be why the FM3 was somewhat late in appearing.

In the original version, the independent mono output was obtained by summing the decoder L and R outputs (taken ahead of the MPX filters) in an emitter follower. Muting was done in the decoder, from the externally generated muting signal. In the second iteration, it was taken from just ahead of the decoder input, and after the muting transistor Tr100. I’d guess that the use of a separate muting transistor allowed the muting to work on mono as well as stereo. The muting circuit itself was quite intriguing in that it was a noise muting circuit in tandem with the tuning indicator circuit, with the latter also providing deviation muting.


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Old 16th Sep 2020, 1:30 am   #23
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Default Re: Quad FM3 no stereo

I think Paula nailed it.

This morning, the tuner faulted on first turn on within 30 sec, then I replaced R105, no change. Fail after 3 sec.

Then, instead of waiting for the new transistor, I just removed TR101, as it's only providing the mono signal. Just to test if its leaking as Paula suggested.

The tuner has been playing in stereo for 1/2 an hour as I type this.

This is the first time I've changed something and had a clear and immediate effect.

I'll let it play for the rest of the day and let you know.

Philippe

PS, yes I too thought that the mono output was totally independent. Very counter intuitive that the only remaining (mono) audio output actually caused the fault, whilst remaining active.
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Old 16th Sep 2020, 7:29 am   #24
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Default Re: Quad FM3 no stereo

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Originally Posted by Synchrodyne View Post
Quote:
Originally Posted by Craig Sawyers View Post
It is not such a bad idea - pin 2 goes high on mono, resulting in about 1.4mA of collector current in TR101. Quad fitted several types of transistor depending on availability, with BC550C being an equivalent. That has a beta of 400 - 800. So it will pull a pretty insignificant 3.5uA to 1.75uA from pin 2 on mono.
I was of the impression – perhaps wrongly so - that the separate mono output, via emitter follower Tr101, was independent of anything that was happening in the stereo decoder IC (MC1310) - available regardless as it were. And that the DC conditions at pin 2 (MC1310 input) were not conditional upon what mode the decoder was in.

Quote:
Originally Posted by Craig Sawyers View Post
Having met the guy who designed the FM3 (the late great Mike Albinson) he would have thought that through long and hard before deciding on that way of doing mono.
I had wondered who had designed the FM3. Was it Mike Albinson’s first major job at Quad? I think that Quad had been without a designated RF person since John Collinson had left, which might be why the FM3 was somewhat late in appearing.


Cheers,
According to Peter Baxandall (in a long letter to Doug Self reproduced in Baxandall and Self on Audio Power, Linear Audio Special Edition) Mike Albinson joined from Murphy Radio in about 1966/7. His first contribution was the input circuit of the 303 power amp. But the next three products were the FMII, FM3 and AM3, which I reckon were all Albinson's.

When I met him he described the way he did radio PCB's. He'd commandeered a toilet to be a circuit board prototype facility. He had a camera lens screwed in the toilet door, and he put a 4x taped up master on the end of a Dexion component store rack. This was all arranged to produce a correct size image on the wall of the toilet. He'd wait for a sunny day, go into the loo and lock the door. Tape a piece of resist coated board on the loo wall and wait a guesstimated time. He reckoned that was the only way to get an RF layout right. Iterate the layout until it worked as designed.

He'd then send the x4 master to the board house.

I asked him what audio system he had at home, expecting something Quad. "No interest in listening to audio - that is work. I really enjoy fixing up classic motorbikes"

Real character!

Craig
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Old 16th Sep 2020, 7:44 am   #25
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Default Re: Quad FM3 no stereo

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Originally Posted by Craig Sawyers View Post
It is not such a bad idea - pin 2 goes high on mono, resulting in about 1.4mA of collector current in TR101. Quad fitted several types of transistor depending on availability, with BC550C being an equivalent. That has a beta of 400 - 800. So it will pull a pretty insignificant 3.5uA to 1.75uA from pin 2 on mono.
I was of the impression – perhaps wrongly so - that the separate mono output, via emitter follower Tr101, was independent of anything that was happening in the stereo decoder IC (MC1310) - available regardless as it were. And that the DC conditions at pin 2 (MC1310 input) were not conditional upon what mode the decoder was in.
Maybe that is actually the case - if the mono output transistor TR101 is fritzed it might be changing the DC condition on the decoder input. There is little in the decoder datasheet to describe the DC condition of the pins, although there is an internal schematic and block diagram.

Craig
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Old 16th Sep 2020, 8:41 am   #26
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Default Re: Quad FM3 no stereo

Motorola quote the output/input gain as 0.45 in stereo, 0.5 in mono. Both with 3.9k load resistors from the output pins to the 12v supply. The max input voltage for 0.5% THD is given as 2.8v p-p, so we can take it as 1.4v p-p as the maximum output voltage.

Now the output stage pulls current from that load resistor and the current is modulated with the signal.

To fit in the 1.4v p-p, the output pin must be biased further than 0.7v below the 12v rail. For low distortion, it needs to be somewhat more, I would guess between 2 and 4 volts below the 12v rail. Pulling the current is a transistor-tree mixer (Called by almost everyone except Barrie himself, a 'Gilbert Cell') So the voltage to ground is a stack-up of two transistors and a long-tail pair resistor plus gain setting resistors. THese are equivalent to 3.19k per side. Try a guess at 2v DC bias at the emitters of the bottom transistors of the cell and we get 0.627mA per side. Into the 3.9k loads external to the chip, we get 2.44.v...... now that's enough for that 1.4v p-p output swing.

Of our 12v supply, we've lost 4.44v, leaving us 7.56v to share across two stacked transistor stages. Yup, that'll work.

So I reckon the output pin DC voltages (infinite load impedance applied) will be about 2 to 3v below the 12v supply voltage.

A couple of estimates and some fag packet grade calculations!

David
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Old 16th Sep 2020, 9:09 am   #27
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Default Re: Quad FM3 no stereo

OK - the input to the demodulator is an emitter follower, with its DC conditions set by another emitter follower. Looking at the schematic values, it looks like the input emitter follower base sits at around 5.5-6.5V

You can see why Quad chose the technique they did for generating a mono signal when you read the attached method from the decoder datasheet!

Craig
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Old 16th Sep 2020, 9:32 am   #28
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Thumbs up Re: Quad FM3 no stereo

It Lives !

Tuner was on all day in stereo

Thanks Paula

I noticed that the L and R audio trannies were E5270. I have also read on the net (a site analogous with an early 20C art movement) that these could be replaced by BC549. So I did, and recycled one of the E5270 to the Mono output (just in case there was something special about the E5270 specification in relation to the MC1310).

I now have a choice of mono or stereo 'at will' from the 33.

so all good.

Thank you all, this is a great site, with very friendly, patient experts.

Philippe
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Old 16th Sep 2020, 9:50 am   #29
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Default Re: Quad FM3 no stereo

The bias emitter follower takes its voltage from an internal rail, derived from a zener and feeding a darlington pair. There is no value on the zener. However, since the minimum rail voltage is 8V, a reasonable guess is that the zener is ~6V. Which would set the internal rail at ~7.5V

The net effect is that the base of the input transistor is at 5.8V, regardless of the supply voltage to the chip.

So synchrodyne is right - there should be a mono output regardless of whether there is enough signal strength to allow stereo decoding.

The datasheet says that the maximum supply voltage for the decoder is 14V - which is what Quad used! That is sailing rather close to the wind. Particularly since there is a +/-5% tolerance on the zener from which the +/- 14V rails are derived.

The IF chip CA3089 is fine - the maximum voltage is 16V

Craig
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Old 16th Sep 2020, 9:54 am   #30
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Default Re: Quad FM3 no stereo

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It Lives !

Tuner was on all day in stereo

Thanks Paula

I noticed that the L and R audio trannies were E5270. I have also read on the net (a site analogous with an early 20C art movement) that these could be replaced by BC549. So I did, and recycled one of the E5270 to the Mono output (just in case there was something special about the E5270 specification in relation to the MC1310).

I now have a choice of mono or stereo 'at will' from the 33.

so all good.

Thank you all, this is a great site, with very friendly, patient experts.

Philippe
That is really good news! No idea why the transistor had gone west - maybe just one of those part failures that happen 40-odd years after it was built.

Craig
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Old 16th Sep 2020, 12:03 pm   #31
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Default Re: Quad FM3 no stereo

There may well be a slow corrosion or stress problem with early plastic TO-92 etc transistors. THe TI plastic 1854-0071 seem to be going west in a fair bit of HP test equipment.

David
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Old 16th Sep 2020, 1:11 pm   #32
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Default Re: Quad FM3 no stereo

I've had fails in some Tek gear too. I've put it down to stress in early epoxy encapsulation.

Craig
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Old 16th Sep 2020, 10:26 pm   #33
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Default Re: Quad FM3 no stereo

I still hold with the view that biasing the transistor from the MC1310 input is not good practice as a design change to the MC1310 that still met the datasheet specification could kill this usage. It is after all described as an input!
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Old 17th Sep 2020, 12:31 am   #34
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Default Re: Quad FM3 no stereo

Here's another quirk. I was skeptical about the voltage of 14V being supplied to the decoder, so I put the FM3 regulator into Spice.

It is not self starting.

That is why there is a Mullard VDR (the red disc) across the -ve series pass transistor. Even a few hundred ohms there starts the regulator up. But depending on the resistance value you can get quite a range of output voltages - quite different on - and +.

Of course that is not how it would be done now - cheap LM317/337 regulators would do the trick nicely.

Craig
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Old 17th Sep 2020, 6:25 am   #35
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Default Re: Quad FM3 no stereo

Unknown and probably now unknowable is the outcome of any transactions that Quad had with Motorola other device suppliers about its planned uses of their products.

The +14-volt rail was probably fine for the original FM3, for both the TAA661 and the MC1305. Then the MC1310 arrived as the PLL successor to the MC1305, but with a lower maximum supply voltage of 14 volts. Plausible alternatives at the time were the RCA CA3090 and Fairchild µA758, both with >14 volts maximum supply voltages. But Motorola probably wanted to keep its existing business, and may well have OK’d use of the MC1310 with the existing FM3 power supply. Given that Quad used RCA dual-gate mosfets in the FM3 front end, I imagine that RCA had made a pitch for the stereo decoder business once the CA3090 was available. The CA3090 was the first PLL stereo decoder, around six months or so ahead of the MC1310, I think. Whether the µA758 preceded or followed the MC1310 I haven’t been able to ascertain.

Biassing the mono emitter follower from the MC1310 might also have been reviewed with Motorola. But it could have been seen as low risk. The MC1310 internal schematic was part of the data sheet, so a change that would have affected the input pin conditions would have been visible. Anyway, unforeseen consequences from “in-specification” component changes might well have been a normal operating hazard (that was certainly the case in other, quite different industries). I wonder if the bias requirement for the emitter follower was relatively uncritical, such that it would work over quite a range of voltages. In the case at interest, it appears that a failed emitter follower transistor had minimal effect on the mono signal, but did severe damage to the composite signal (or parts thereof) going into the MC1310.

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According to Peter Baxandall (in a long letter to Doug Self reproduced in Baxandall and Self on Audio Power, Linear Audio Special Edition) Mike Albinson joined from Murphy Radio in about 1966/7. His first contribution was the input circuit of the 303 power amp. But the next three products were the FMII, FM3 and AM3, which I reckon were all Albinson's.

When I met him he described the way he did radio PCB's. He'd commandeered a toilet to be a circuit board prototype facility. He had a camera lens screwed in the toilet door, and he put a 4x taped up master on the end of a Dexion component store rack. This was all arranged to produce a correct size image on the wall of the toilet. He'd wait for a sunny day, go into the loo and lock the door. Tape a piece of resist coated board on the loo wall and wait a guesstimated time. He reckoned that was the only way to get an RF layout right. Iterate the layout until it worked as designed.

He'd then send the x4 master to the board house.

I asked him what audio system he had at home, expecting something Quad. "No interest in listening to audio - that is work. I really enjoy fixing up classic motorbikes"
Thanks for that. I looked up the Baxandall and Self book. Baxandall said that Mike Albinson turned out to be a quite excellent and very inventive Chief Engineer. Praise indeed I think from one in the top class.

The fact that audio was the “day job”, not a leisure interest may have helped him to be very objective at a time when objectivity in audio was heading out the door. Interesting that he designed the input end of the 303. That was somewhat unusual, both in terms of having a relatively low input impedance (22 k) for the time, and with that 22 k being the input arm of a shunt feedback arrangement.

The FMII was essentially the combination of the FM and the MPX unit in one case, self-powered, and with Si rather than Ge transistors in the MPX. The basic FM design was done by Geoffrey Horn (who also did the AM), and finished (including the twin neon tuning indicator) by John Collinson, who also did the AMII and MPX. The AM3 was a self-powered AMII, although with some changes in the output filter section.

The FM3 seems to have been mostly “clean sheet”. The front end does look as if it might have had RCA origins, though. At least judging by its literature, RCA appears to have stepped through several iterations in the early mosfet era. It started by using a single-gate mosfet RF amplifier in what had been an all-bipolar three-gang design, then retained that and went to a single-gate mosfet mixer. Next the mixer was changed to a dual-gate mosfet, then finally so was the RF amplifier, by about which time it had moved to dual protected-gate mosfets. Leak, with its Stereofetic of 1969, had gotten off that bus at the third stage, single-gate RF and dual-gate mixer.

The use of the twin-lamp tuning indicator on the FM3 may have been from a desire to continue with the same basic form as the twin neon indicator of the FM, albeit in updated form. By then, others, such as B&O, were already using the twin lamp indicator, although there had been few takers for the twin neon type. Apparently John Collinson had gotten the idea from an American magazine. A little bit of sleuthing suggests that this may have been an article in Audio, 1953 January, describing the Sonocraft ASC-2 FM tuner. Back to the FM3 though, the driving circuitry for the twin lamp indicator also offered a convenient way of providing deviation muting, which was still in the future as part of the industry-standard IF sub-system ICs. Maybe that was an example of the Mike Albinson inventiveness that Baxandall had noted.


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Old 19th Sep 2020, 8:05 am   #36
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Default Re: Quad FM3 no stereo

The FM3 remained in very short supply for over a year after it was launched, and the word at the time was that there was trouble with deliveries from a component supplier - which, I'm not sure.
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Old 19th Sep 2020, 11:39 pm   #37
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Default Re: Quad FM3 no stereo

I recall that c.1972 HFN mentioned the delay in Quad FM3 deliveries, something like a six-month wait, I think, but that aspect is now vague . In part at least it seemed to have been attributed to pent-up demand from folks who wanted a solid-state Quad FM tuner. Quad was quite late with that product as compared with most other hi-fi equipment makers.


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Old 20th Sep 2020, 7:28 am   #38
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Default Re: Quad FM3 no stereo

I think Quad had been hit with a surge of orders for the 33/303 at its introduction. It was one of the first transistor amplifiers to genuinely not be a drop in performance from its valved predecessor, and it had looks to get it into all sorts of designer-y places. It got noticed.

So there was probably a case of 'all hands to the pumps' in Huntingdon which may have contributed to parts availability problems in getting the FM3 into production. They'd have still been able to exhibit the FM3 case with a 'coming soon!' label.

In the end, they turned out a good little tuner.

David
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Old 20th Sep 2020, 8:10 am   #39
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Default Re: Quad FM3 no stereo

It is a pity that the son of Peter Walker, Ross, was so mealy mouthed about just about every quad product in the interview in Ken Kessler's book "The Closest Approach"

"The ESL was a complete nightmare - that wooden frame? The little screws in the back? The millions of pop rivets we used in that ****** thing? Anyway, I don't think we made any money out of that."

"The Quad II was a doddle. 18 years completely unchanged. I don't think we changed a ****** thing in it. They all came with KT66 valves, and how many resistors did it have 18 or 20? It was a piece of s**t - the only secret was the output transformer, that was it"

"When the 33 came out, people said 'I'm not buying it with that ****** marigold thing on it'. Well, Peter loved that, he thought it was great. And customers would come up and say ' well I'm not going to buy that until you take that marigold thing off. You'll have to change that' And Peter would say 'Well I'm not. B****r off. Go buy a Leak. Go on, b****r off"

He goes on and on in the same vein about every Quad product that ever existed. An interview worth reading.

Craig

PS He did not like the lack of mains switch on the FM3 either, and spent a paragraph knocking that decision.
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Old 20th Sep 2020, 8:34 am   #40
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Default Re: Quad FM3 no stereo

Where do I begin?

The ESL is a wonderful speaker to listen to, but it is somewhat fragile. Maybe modern trends in music have exacerbated this, but I do think they are a bit too sensitive to their environment (humidity, dust) and rather fragile. The moving coil speaker, by separating the air displacer from the motor can shift large amounts of air without compromising sensitivity much. The electrostatic speaker is limited in throw by the choice of gap and it's trapped in a nasty compromise where more throw means less sensitivity. Driving such a light air displacer is still a wonderful thing, but it has its limits.

The QuadII really is nothing special, except for the output transformer. I wouldn't call it sh*t, it was rather good but apart from that transformer, everyone else was making similar things.

I love the looks of the 33 and FM3. That flash of orange makes it. In what became a sea of brushed aluminium and then satin black, it was refreshing! Peter had it right.

I don't like equipment without mains switches, or with them hidden round the back.

But the ESL and QuadII are holy cows, so taking pot shots at them doesn't go down well, even when accurate.

David
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