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#16 Re: Cole lcr phono stage rebuild

Posted: Thu Oct 22, 2020 6:30 pm
by Ant
These 7308s are interesting, sort of in the middle of the brimars and the pcc88s, but they apparently have matched triodes in them according to the blurb i can find about them. And its pretty noticeable in the channel balance and soundstage, which is better than either of the others. The brimars are sweeter than these but not very open at the top, the pcc88s are much more open than the brimars and abit leaner and less rose tinted than the brimars.
These 7308s are almost as open at the top as the pccs, a little fuller, but much more detailed than either of the other two
In terms of compatibility, the only notable difference i can find in the ecc88 data sheet and the sylvania datasheet for these is that the heater current is a little higher at 335ma as opposed to 300ma. The curves look very similar too. The tx that nick put in has a 10v 1a winding for the heater supply, so should have plenty of capacity for the extra, the reg itsself im not sure, i havent looked at what the device is, although i assume it would be specced with some extra current capacity over and above the required for ecc88s

#17 Re: Cole lcr phono stage rebuild

Posted: Thu Oct 22, 2020 7:42 pm
by JohnG
I am not any good with the Math, but I have took part in Two Separate E88CC Tube Rolling Sessions with a Valve Output Stage on a DAC and a Phonostage.

These have been very good experiences and had offered for my level of understanding a good opportunity to pick up on how different Valves Interface with a Device.

Interestingly the DAC has offered a very attractive Sound Quality with a Valve that was selected out of a Line Up of Six Brand Types.
I did not expect to hear such a broad range of presentations when the Valves to be used for the comparisons were being discussed.

I went into the Phonostage comparisons a little wiser, but got served a Curve Ball,
as when the Valve selected for the DAC was used on the Phonostage, it was put down the ratings and other Valves were a referred to as the better selection.

There are some great Valve Selections to be compared, it takes time to get a chance to discover and trial them.

#18 Re: Cole lcr phono stage rebuild

Posted: Thu Oct 22, 2020 8:33 pm
by Nick
Two things to remember.

1. The RIAA curve may be being changed by the valves changes. Measurement will show that, but without that we can't decide if what is a simple change in response as down to something in the valve.

2. The first valve in a phono stage will be getting 10 times the high frequency and a tenth of the low frequencies to the last valve so what may be a small and attractive change in a flat device like a DAC may be over the top in a phono (and vice versa).

I measured the FR of the Cole with the original valves in, the channels were matched to less that 1dB, and the frequency response was also flat to less that 1dB. Also the FR of the two channels were very closely matched.

The original circuit seemed to want the anode current adjusting to give 65v on the anodes. But without an original manual I have no way of knowing if that’s to be set after every valve swap or just a first time setup.

#19 Re: Cole lcr phono stage rebuild

Posted: Fri Oct 30, 2020 4:20 pm
by Andrew
izzy wizzy wrote: Wed Oct 21, 2020 10:45 am In following phono stage design over the years, one constant seems to always come up. When someone has or hears an LCR phono, they all say there's something right about it; a natural presentation that they can't quite figure out but they know it when they hear it. Many DIYers seem to stop building phonos once they have one. I have not heard one.
There's a good mathematical reason why LCR sounds right, if implemented correctly, the phase should be correct across the frequency band, you can't do that with just RC, right?

#20 Re: Cole lcr phono stage rebuild

Posted: Sat Oct 31, 2020 7:44 am
by Dave the bass
Aaaah, is correct phase across the AF range the main reason why LCR stages sound so 'good' mostly? I've heard a few over the years at Owston, home meets and shows. I like what I've heard.

It's still on my list of things to learn about and build.

It's a flippin' long list BTW.

#21 Re: Cole lcr phono stage rebuild

Posted: Sat Oct 31, 2020 10:48 am
by pre65
Dave the bass wrote: Sat Oct 31, 2020 7:44 am
It's still on my list of things to learn about and build.

It's a flippin' long list BTW.
You need to master on amp building first. :lol: :lol: :lol:

Just jesting Dave.

#22 Re: Cole lcr phono stage rebuild

Posted: Sat Oct 31, 2020 12:21 pm
by JamesD
Hi Andrew,

Andrew said
There's a good mathematical reason why LCR sounds right, if implemented correctly, the phase should be correct across the frequency band, you can't do that with just RC, right?
I don't think I agree with that as phase is a reflection of frequency response so with the same response achieved via the same generic filter design an LR and a CR filter of identical frequency response should have the same phase response...

I have two simulations of an LR RIAA pre (inspired by Pete Milletts design) and a CR RIAA equivalent using discrete CFPs and once I tweak the same frequency response from them I get the same phase response... attached are the LTspice files using generic 2N4401 and 2N4403 transistors for the sim.

I'll post the diagrams once I have got them as images too.

#23 Re: Cole lcr phono stage rebuild

Posted: Sat Oct 31, 2020 12:22 pm
by Nick
pre65 wrote: Sat Oct 31, 2020 10:48 am
Dave the bass wrote: Sat Oct 31, 2020 7:44 am
It's still on my list of things to learn about and build.

It's a flippin' long list BTW.
You need to master on amp building first. :lol: :lol: :lol:

Just jesting Dave.
Amps are easy. Phono stages are far more fun.

#24 Re: Cole lcr phono stage rebuild

Posted: Mon Nov 02, 2020 1:27 pm
by Andrew
JamesD wrote: Sat Oct 31, 2020 12:21 pm Hi Andrew,

Andrew said
There's a good mathematical reason why LCR sounds right, if implemented correctly, the phase should be correct across the frequency band, you can't do that with just RC, right?
I don't think I agree with that as phase is a reflection of frequency response so with the same response achieved via the same generic filter design an LR and a CR filter of identical frequency response should have the same phase response...

I have two simulations of an LR RIAA pre (inspired by Pete Milletts design) and a CR RIAA equivalent using discrete CFPs and once I tweak the same frequency response from them I get the same phase response... attached are the LTspice files using generic 2N4401 and 2N4403 transistors for the sim.

I'll post the diagrams once I have got them as images too.
All my RC simulations exhibit a bass phase shift. I'll take a look at yours, thanks James.

#25 Re: Cole lcr phono stage rebuild

Posted: Sat Nov 21, 2020 10:34 am
by Ant
Finally got round to listening to the zakhir hussain lp we listened to when we a/b'd the phono stages.
At that time, the source was the prototype type 2 lenco, r200 arm and goldring e3 cart.
Amp was simons 2a3, speakers mi dads fanes.
System this time, is the type 3 lenco with air bearing arm and at33sa.
Amp is the b1/f5 combo, plus nicks ha1 head amp. speakers are my big fanes.
Its just fabulous.
More fabulous than it was before which is unsurprising, given the arm and cart, i can hear the traits of the cart, and the speakers but i cant pick out the arm, or the phono stage. Apart from the 'rightness' if that makes sense. The f5 and b1 dont really sound of anything identifiable as it is.
So the amps, arm, head amp and phono are doing a disappearing act.
Whatever that rightness is, its still there in spades.
It continues to surprise.
I had some iron maiden on the other day (number of the beast) and the amount of clarity that was there was stunning.
To be honest, that record has always tended to degenerate into a screechy amorphous blob of glorious noise that is difficult to pick apart and follow if you want to, whatever equipment ive had before. now, it is just all there laid out and cohesive, and right. And still a glorious racket thats lost none of its shouty headbanging qualities.
Everything that comes out of it now is cohesive without being clinical

#26 Re: Cole lcr phono stage rebuild

Posted: Sat Nov 21, 2020 4:21 pm
by JamesD
Wonderful descriptions - really gives an insight into how it sounds in its own right and how it compares to what you had... many thanks for sharing this - its inspiring me to get on and complete my CR and LR phono versions so I can hear the difference in my system...

#27 Re: Cole lcr phono stage rebuild

Posted: Fri Feb 05, 2021 4:32 pm
by Ant
Oh dear.
It has another problem now, its suddenly very quiet on one channel.

First eliminated the deck and cart by plugging nicks step up into the benedict audio phono stage, all fine so not that.

Then eliminated the cables by plugging those into the cd player instead, all fine, so not the cables.

Then swapped the valves for the original brimars. Same problem so not the valves..

So its something else.

The quiet channel isnt distorted, its just really quiet compared to the other channel. My initial thought was a blown cathode bypass cap, but i dont even know at this stage if its got bypasses on it, ill have to look at the circuit diagram.

Probably not that, but i have just pulled it out in disgust. Again.

Stupid bloody thing.

#28 Re: Cole lcr phono stage rebuild

Posted: Fri Feb 05, 2021 4:47 pm
by Nick
check the voltages on the valve anodes. There are no cathode caps.

#29 Re: Cole lcr phono stage rebuild

Posted: Fri Feb 05, 2021 5:03 pm
by Ant
It'll have to wait until the kids go back to school, cant have it open with them bouncing round the house.
I'll get round to it eventually. It'll just have to get put again away for now

#30 Re: Cole lcr phono stage rebuild

Posted: Fri Feb 05, 2021 5:20 pm
by Nick
Don't they sleep? :-)