What is on your workbench right now?

[LTig]

The one thing I'm not happy with yet is the Phono stage, as it seems particularly noisy. It's based on BC549, BC559, BC556 and BC546.
View attachment 132709

There is probably not much you can do here WRT noise. I would bridge it with a small piggy back PCB with an Opamp based phono stage using NE5532. Beware that you need to reduce the PS voltage, +/- 23V is too high.

 

[sabristol]

There is probably not much you can do here WRT noise. I would bridge it with a small piggy back PCB with an Opamp based phono stage using NE5532. Beware that you need to reduce the PS voltage, +/- 23V is too high.

@LTig Thats a good call as it would be easy to design replacement phono boards as the current pair are vertically mounted daughter boards. I'll have a listen to see how it sounds before deciding if it's worth the effort as I don't intend to keep it.

 

[sabristol]

Refurbished Tannoy Devon (HPD315 drive refoamed). Frequency response at ca. 1m (not bad for almost half century old loudspeakers)
View attachment 128477

What setup do you use to measure speaker response?

 

[Vuki]

What setup do you use to measure speaker response?

It was measured in-room at ca 1m. Loudspeaker drive unit center at ca. 1m height. Controls set to rolloff 0, energy -1. Audiomatica Clio microphone, terratec dmx 6fire usb soundcard, rew sw. Mic level was uncalibrated, level was probably around 80db.
It would probably look nicer if I used mmm technique...

 

[sabristol]

Next project... service this Linn Intek amp that I've owned from new since ~1990. Nicely made kit. All Rubycon caps. It has a slight power on thump on the left channel and higher measured DC offset on that channel (15.4mV vs. 1.9mV).

 

[Andysu]

Taking a break between soldering Dolby cat 109 meter frequency filter card, feeding Magic a meaty stick.

 

[restorer-john]

Taking a break between soldering Dolby cat 109 meter frequency filter card, feeding Magic a meaty stick.

Magic is a cutey. He looks a bit like our cat Julio.

 

[restorer-john]

Next project... service this Linn Intek amp that I've owned from new since ~1990. Nicely made kit.

You know it's UK built when the heatsink is either the casework, or way, way too small. Run that thing in Australia in summer and it would self destruct in one afternoon. @50wpc (rated) that heatsink is a joke. And the flag heatsinks on the regulators? They riveted them to the PCB and riveted the TO-220? Tell me they are captive nuts. Please.

But yes, the overall component quality seems decent.

 

[egellings]

I did taw a puddy tat!

 

[sabristol]

You know it's UK built when the heatsink is either the casework, or way, way too small. Run that thing in Australia in summer and it would self destruct in one afternoon. @50wpc (rated) that heatsink is a joke. And the flag heatsinks on the regulators? They riveted them to the PCB and riveted the TO-220? Tell me they are captive nuts. Please.

But yes, the overall component quality seems decent.

You're right @restorer-john piddly arsed heatsink. However on closer inspection it looks the aluminium flag heatsinks are actually screwed in with some sort of self-tapper / captive nut arrangement - I'll have a better look once I've got the pcb out.

On a positive note, they have segregated the differential and VAS supplies from the output, used decent constant current and current mirrors. Interesting arrangement with the drivers using 3x ZTX653 / ZTX753. What do you think @pma?

 

[pma]

What do you think @pma?

Well - I am not sure. I suppose that three 653/753 parts would be limited in power dissipation. But, the output stage is connected as a CFP. Frankly, I do not like too much this variant of the output stage. How do they manage thermal stability? Where are those 653/753 packages, on the heatsink?

 

[restorer-john]

Frankly, I do not like too much this variant of the output stage. How do they manage thermal stability? Where are those 653/753 packages, on the heatsink?

On their own heatsink, not the main heatsink. See the pic above.

I do not like it either. No DC offset adjustment, no boas adjustment and TO92s driving a1306/c2519s? 1W per device.

Am I missing something, there's not enough V to drive those drivers it'll be limited by the fornt end swing.

 

[sabristol]

Well - I am not sure. I suppose that three 653/753 parts would be limited in power dissipation. But, the output stage is connected as a CFP. Frankly, I do not like too much this variant of the output stage. How do they manage thermal stability? Where are those 653/753 packages, on the heatsink?

No, the ZTX653/753 are clipped on separate strips of heatsink - can be seen in the pic above and below the main reservoir caps. There are 9 transistors mounted so I presume in addition to the drivers, one is the bias spreader and the other the VAS. From what I can see there doesn't appear to be any form of thermal feedback from that inadequate main heatsink :-(

 

[pma]

No, the ZTX653/753 are clipped on separate strips of heatsink - can be seen in the pic above and below the main reservoir caps. There are 9 transistors mounted so I presume in addition to the drivers, one is the bias spreader and the other the VAS. From what I can see there doesn't appear to be any form of thermal feedback from that inadequate main heatsink :-(

Not exactly. Q287 and 218 are VAS. Q211, 212, 213 and their PNP mirrors are a part of the output stage. Output stage here is CFP (not 2EF). Thermal stability of such output stage depends on Q211 etc Vbe.

 

[sabristol]

You know it's UK built when the heatsink is either the casework, or way, way too small. Run that thing in Australia in summer and it would self destruct in one afternoon. @50wpc (rated) that heatsink is a joke. And the flag heatsinks on the regulators? They riveted them to the PCB and riveted the TO-220? Tell me they are captive nuts. Please.

But yes, the overall component quality seems decent.

Phew not a pop-rivet, it's some sort of Allen headed self tapper.....

Pretty tight, it twisted the legs of the regulator.