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Old 23rd September 2012, 05:08 AM   #61
mikelm is offline mikelm  England
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Quote:
Originally Posted by Salas View Post
@Mikelm

There are C4,C5 470n bypasses on C2,C3 AC/DC split gain feedback electrolytics. Did you experiment on those too? Starting without any direct bypasses and then compare bypass solutions maybe its an acceptable practice also. I remember when I had been suggested to bypass my LCR 15000uF PSU capacitors in a JLH 80W amp with MKPs. The tone got pinched and I ditched them very soon. Snubbing is best but needs original PCB space. Your constantan wire does the trick neater though.
Hi Salas,

I will check the FB cap in spice later but I suspect they will not suffer from this problem because they only have very low impedance on the ground side whereas the rail caps have low impedance environment on both terminals which allows very high Q at resonance - but I will report for sure on this later. However I suspect that just upping the FB bypass cap from .47uF to 4.7uF might give other sonic benefits. The epcos open frame stacked film range are great because they are so small.

Quote:
P.S. What speakers you got and how is bass with TSSA at ~20dB feedback?
My current speakers are quite modest but actually I really like them. They are Modified B&W 602 S3 ( redesigned X-overs & cabinets )

Google Image Result for http://i157.photobucket.com/albums/t69/lyntonfitt/Bild200021.jpg

They give a clear insight to the music. The bass is fast & tight but may not be the best speakers to assess extreme low bass ( there isn't any ! ) 200mm cones . . . 90db / W / M.

Nelson Pass reports that subwoofers do need low impedance to drive them well otherwise he often prefers the sound of higher impedance o/p.

This amp has about 0.3R o/p impedance and with my speakers the bass there is, is fast, tight & very well defined
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Old 23rd September 2012, 05:18 AM   #62
Salas is offline Salas  Greece
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My diy speakers have tight S shaped double pleated rubber surrounds and they enjoyed my tube amp with 0.6R so it will be OK I guess since I will surely need your gain setting due to my vinyl source and buffer pre. Your info is enlightening, thanks for paving the road.
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Old 23rd September 2012, 05:22 AM   #63
Salas is offline Salas  Greece
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P.S. Can you link the vendor's Epcos listing? Cheers.
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Old 23rd September 2012, 05:36 AM   #64
mikelm is offline mikelm  England
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mmm - when sonny said my o/p Z was around 0.3 I'm not sure if he realised I had gain of 23 so I will have to do a test to check this - but I think will not much higher o/p Z that your ones.

check this:

B32562J1475K - EPCOS - CAPACITOR, 4.7UF, 100V | Farnell United Kingdom

or this:

B32560J475K - EPCOS - CAPACITOR, 4.7UF, 63V | Farnell United Kingdom

( The pics are incorrect for these values )
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Old 23rd September 2012, 05:41 AM   #65
mikelm is offline mikelm  England
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Quote:
Originally Posted by Salas View Post
thanks for paving the road.
you're welcome
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Old 23rd September 2012, 05:52 AM   #66
Salas is offline Salas  Greece
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Those caps remind me of the Siemens branded silver ones in the 90s. I still have 2-3 in a bin. Transparent, silver innards, you could see the stacking at the sides where the leads are running half height externally. They were good HF decoupling caps.
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Old 23rd September 2012, 06:28 AM   #67
mikelm is offline mikelm  England
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I think we have to thank mostly thank Andrej & Sonny and not forgetting Nelson who as far as I know was where the original idea sprang from
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Old 23rd September 2012, 06:30 AM   #68
Salas is offline Salas  Greece
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Maybe Hiraga too.
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Old 23rd September 2012, 07:34 AM   #69
mikelm is offline mikelm  England
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Yes, but I think that it's having the VAS as the O/P stage which is the most radical element in TSSA design.

So far I have only compared my SE 3 stage CFB with this Symmetrical 2 stage so it is not 100% clear to me what change causes what effect. So I would very interested to hear impressions for those who have built and listened to:

SSA - 3 stage with follower O/P stage
vs
TSSA - 2 stage with with VAS O/P stage

The other logical option would be a SE two stage with VAS as O/P but that would probably have a current ceiling of 2 x O/P stage bias so would have to be another heat monster

I must take another look at Nelson's 2 stage JLH - that could be another contester in this arena.
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Old 23rd September 2012, 09:38 AM   #70
mikelm is offline mikelm  England
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Please find photos of my TSSA built, the mod & the PSU here:

https://www.dropbox.com/sh/0i0l4krbr2b8zhs/mc1yVtWBmZ
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