BA output caps

Support for JLM Audio Kits

Moderator: Joe Malone

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: BA output caps

Post by greenmanhumming »

you are suggesting a 5k resistor in series with the BA output? I'll try it...

I'd be delighted to get away from large expensive polyprop valve hifi caps for low volt circuits like the BA but i just need to know what to try instead... I'll see what I can find in line with your suggestions.

the claritycap SA is not extreme high end, the 4.7uF only costs around £5, which is as much as I am willing to spend on a cap... but its generally regarded as very good sound for the price.. it is bulky though, and unnecessarily high voltage at 630V. it was certainly an big improvement on the polyesters and the small polyprops I had for guitar amps. I haven't compared it with its immediate competitors. I have some russian paper caps which are nearly as good. (and some other russian paper caps which are totally coloured!)

my valve pres should have an output Z in the low hundreds of ohms, my own design has a 12at7 or 12av7 parallel cathode follower for output, and that is inside a global nfb loop which should lower the output z further, the mila uses a parallel 12av7 plate loaded stage which is also low Z, the one bottle is higher z out, and that may be the cause of my reservations about it, I will probably convert those to two bottles.

yep we were misunderstanding each other about the -out cap, i was talking about the -out cap you thought i meant something else...

and another misunderstanding - i wasnt talking about the bandwidth cap either, but the main output cap, for which I am/was looking to substitute a film type

about keeping the rolloff point below 5hz, 4.7uF into 10k gives 3.4hz doesn't it?, unless the output impedance of the preceding stage is affecting it... how do I calculate that?

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: BA output caps

Post by greenmanhumming »

I tried the 5k resistor in series, it does tame the harshness and top end edge, it may also make the sound a little fuzzy/imprecise, I'll have to listen more.

so far I'm sstill prefferring the alve pres, although its getting closer.

cap substitutions have not made as much difference in the BAs as they do in the valve pres. Maybe Hi Z hi V circuits are more sensitive to cap characteristics?

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: BA output caps

Post by greenmanhumming »

well I've decided after some listening that the caps are not really the source of my dissatisfaction, rather the transformers are more relevant....

neither the OEP nor the JLM 14 were really doing it for me so-

I've changed from 4 channels with JLM14 to 2 channels with lundahl LL12538, and 2 channels of BAN, and I'm much happier with the sounds available...

heres the BA with the LL1538:

Image

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: BA output caps

Post by greenmanhumming »

BTW is it really necessary to load a LL1538 withh 440pF across the secondary? seems a bit excessive to me, and if i were to criticise the sound I'm now getting from the BA it would be a tiny lack of air.... i guess i'll try with just 220pF, or a zobel of 22k and 220pF which is what i have on these transformers with my valve pres...

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