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Post by PinkFloyd on Sept 6, 2013 9:54:37 GMT
Gonna reduce the gain today..... more to follow
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Post by PinkFloyd on Sept 6, 2013 19:09:42 GMT
Completed at last! I decided to reduce the input gain to adopt a standard 1.5V sensitivity and also to improve the signal to noise ratio.... in fact, the gain reduction mod actually brings the S/N ratio very close to the Quad 606! Initial impressions are better detail, a more organic / realistic presentation and a wider, spacier soundstage...... Sam was complaining about a slight roll off in the bass but that was thanks to me cocking up by fitting two x 3.3uF films caps as bypass caps onto 2 x 100nF film caps...... I managed to roll the bass off @ around 50Hz Sometimes it helps to concentrate when you're working on an amp Anyhoo.... no harm done, bass has been restored and I must say this is a totally better amp now...... there is now "fizz and energy" to the mids, space around instruments, "air" (in the sense that there is literally a walkaround type of soundstage), you can now pick out the individual instruments instead of listening to them as one congealed mass. The mids and highs have been improved substantially, no doubt about that at all! I'll have to await Sam's report on the real low octave stuff as I don't listen to the same kind of "organ" music that he listens to..... where I talk about grunt and toe curling bass he talks organ pipes and low bass extension / octaves etc...... he's a lot more eloquent than "I" with his descriptions...... I tend to talk grunt / slam / Prat and scrotum tightening eargasms. Anyhoo, once again, (why do I keep on saying "anyhoo"?) that's the amp completed and I will batten down the hatches on it..... I fitted the proper 4 amp slow blow (T) fuses into those flimsy copper fuse holders and also flooded a bit of solder between fuse ends and copper prongs..... I'm not keen on flimsy connections. The gain mods were simple...... it's a case of removing R6 and replacing it with a 100K resistor..... remove the 100uF non polar (C2) and replace it with a 33uF non polar / bypassed with a 100nF film cap..... the final thing to do is replace the 470nF (C4) film cap with a 150nF film cap and that's you good to go...... fantastic results for a few pence. I just hope that Sam has got his lower octaves back I trust he will report on the SQ as soon as he has had a good chance to listen to the "completed" amp. Here are a couple of pics of the completed 405/1: Sure does look perty I hope sam doesn't Squeal like a pig when he hears it: I hope he grins like a Cheshire Cat
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Post by PinkFloyd on Sept 6, 2013 20:52:37 GMT
I just LOVE this photo..... It shows traditional British workmanship at it's best...... so colourful, it looks like a licquorice allsort..... an absolute work of art..... no wonder these amps have gained "classic" status...... a shame I have bastardised the colour scheme but, hey, when Pinkie goes to work he doesn't give a fekk..... he wants to add MORE colour and show that true British workmanship is still alive, albeit from a kitchen table....... maybe a nice tone of pink wire would blend in Keith snook........ eat your hat mate!
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Post by PinkFloyd on Sept 12, 2013 22:13:30 GMT
Lump of lead or lead balloon? how's it's going Sam? these places ONLY exist by input or feedback..... any comments are most appreciated.
Mike.
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pingu
Been here a while!
Reallising what has been taken on with the GB
Posts: 332
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Post by pingu on Sept 13, 2013 11:07:57 GMT
Hi Mike, Nice work on the Amp and yes they are pretty colourful and neat inside. Even more so after those neat mods you did. Britain at it's best swinging 60's free festivals and all that They do sound good too. I have two of these mono blocked. I think the circuit board mods may be a little beyond me at the moment but the PSU caps definitely need replacing. I have had 4 Vishays similar to yours for a while, but never got around to replacing them. Now I know you said "Definitely No Kits" but do you have any spare bypass caps that you used on the Vishays, the 1 x polypropylene, 1 x polystyrene, 1 x paper in oil (Russian) and one silvered Mica? (for both amps) Finally what caps did you use to bypass on top of the Txs? Any help appreciated Martin
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Post by PinkFloyd on Sept 13, 2013 22:42:43 GMT
Hi Mike, Nice work on the Amp and yes they are pretty colourful and neat inside. Even more so after those neat mods you did. Britain at it's best swinging 60's free festivals and all that They do sound good too. I have two of these mono blocked. I think the circuit board mods may be a little beyond me at the moment but the PSU caps definitely need replacing. I have had 4 Vishays similar to yours for a while, but never got around to replacing them. Now I know you said "Definitely No Kits" but do you have any spare bypass caps that you used on the Vishays, the 1 x polypropylene, 1 x polystyrene, 1 x paper in oil (Russian) and one silvered Mica? (for both amps) Finally what caps did you use to bypass on top of the Txs? Any help appreciated Martin Hi Pingu. I think I've exhausted most of those caps but CAN supply you with the polyprops, the polystyrenes and the Russians....... I'm right out of silvered Mica..... if you have smaller (X4) vishay caps in yours I can supply even better "bigger" Russians which will fit the bill nicely...... can you show me a photo of your innards and I'll sort something nice out for you? Bypass caps on the transformer are 400V rated / 100nF EVOX polyprops..... I have plenty of them in stock..... Open the lid, let's see what you've got in there already. Mike.
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pingu
Been here a while!
Reallising what has been taken on with the GB
Posts: 332
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Post by pingu on Sept 14, 2013 20:20:54 GMT
Hi Mike, give me a day or so to get work sorted and I'll whip the cover off one of the amps and post some pix and give you the dims of the caps I have. Thanks Martin
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