Hello,
Has anyone got any photos of the inside of this preamp? Not the modular newer version but the big one that matches the power amps? I just need them for a comparision really, as I think some of my hardware are replacements not original. I've attached my preamp here.
Many thanks
Joe
Has anyone got any photos of the inside of this preamp? Not the modular newer version but the big one that matches the power amps? I just need them for a comparision really, as I think some of my hardware are replacements not original. I've attached my preamp here.
Many thanks
Joe
Attachments
Never seen this but willing to bet those silmics were not originally there. Does it matter? The originals would be due for replacement anyway.
Hi many thanks for the reply - it was more the volume pot and on off switch I was interested in - the silmics replaced some roedensteins (poor spelling), which were original and as you say - well up for replacing.
Joe
Joe
Unless the youtube video is of your preamp i would say the volume pot is original. Hard to be sure any two of these were ever made identical.
Yes the youtube video is from the guy who owned it before me, so its a handy reference. But the volume pot is in very poor shape so I'd like to replace it with a stepped attenuator - the problem is locating the correct ground with no schematic or circuit diagram. The original pot would be working backwards if the tabs that ground it were connected. Old stuff eh?
Regards
Joe
Regards
Joe
Attachments
Locating the ground should be straightforward. Drawing a schematic from the board too as it is such a simple board without even a solder mask.
RCA jacks outer terminal, power supply gnd, pot gnd are all tied up together. There is a screw tying up the star ground to the casing. The opposing side of the pot goes to the high level input or phono stage output and the wiper to the actual circuit input.
It seems the PS is unipolar and so probably is the entire circuit. In this way it is more similar to a Naim from that era rather than a Japanese circuit.
RCA jacks outer terminal, power supply gnd, pot gnd are all tied up together. There is a screw tying up the star ground to the casing. The opposing side of the pot goes to the high level input or phono stage output and the wiper to the actual circuit input.
It seems the PS is unipolar and so probably is the entire circuit. In this way it is more similar to a Naim from that era rather than a Japanese circuit.
Hi,
you make it sound easy - but I've no transferrable skills from my previous work life 🙂
Still, I'll follow your advice and see if I can locate it so I can change this pot. I tried this before and all it did was blow the mains fuse, but the point I attached the ground to was showing continuity to output and chassis ground, which is why I posed the question on the actual pot. The preamp itself is fed a supply (AC) from the power amp.
As Luck would have it..replacement with the old volume pot restored behaviour thank goodness.
Regards
Joe
you make it sound easy - but I've no transferrable skills from my previous work life 🙂
Still, I'll follow your advice and see if I can locate it so I can change this pot. I tried this before and all it did was blow the mains fuse, but the point I attached the ground to was showing continuity to output and chassis ground, which is why I posed the question on the actual pot. The preamp itself is fed a supply (AC) from the power amp.
As Luck would have it..replacement with the old volume pot restored behaviour thank goodness.
Regards
Joe
Well thats similar, I haven't seen another one of these for a while.
So your PCB is slightly different, you have a selector knob for functions on the side. Is the Volume pot 25K log? it looks exactly the same as mine - just less battered. - if so which of the tabs is going to your ground? I can work back on my one based on the units being the same (hopefully).
Thats in lovely condition.
Regards
Joe
So your PCB is slightly different, you have a selector knob for functions on the side. Is the Volume pot 25K log? it looks exactly the same as mine - just less battered. - if so which of the tabs is going to your ground? I can work back on my one based on the units being the same (hopefully).
Thats in lovely condition.
Regards
Joe
This picture is from a completed sale.
You could trace ground on the board with an ohmmeter using RCA
ground as the other pole and compare, it would be the wires in the
upright connections of the pot as seen in this last picture when it is
connected in usual style.
It seems the input of the pot, lower connections, is routed from the
balance control.
The pattern on the board does not look like a standard pot layout.
You could trace ground on the board with an ohmmeter using RCA
ground as the other pole and compare, it would be the wires in the
upright connections of the pot as seen in this last picture when it is
connected in usual style.
It seems the input of the pot, lower connections, is routed from the
balance control.
The pattern on the board does not look like a standard pot layout.
Hi, by way of an update the stepped attenuator has been fitted and is working. I've also managed to swap out the selector switches which were causing some signal problems.
Just as an aside - the difference between Phono MC and CD inputs on the volume control is HUGE. I can hear the difference between the MM/MC switch so I know its working, but to get comparable volumes between them, the CD is a couple of clicks from off and the MC is over halfway round!
The manual states the following input sensitivity for full output at 0.35V from the preamp:
MC 250uV RMS and for Tape (my CD input) 85mV. Can anyone explain this in laymans terms? All my CD players output around 2V ( I guess as a maximum signal), so I'd like to include suitably calculated inline attenuation in the connection or at the pre amp? Before I do this I'd like to understand this 'sensitivity' value a bit better.
Thanks in advance
Joe
Just as an aside - the difference between Phono MC and CD inputs on the volume control is HUGE. I can hear the difference between the MM/MC switch so I know its working, but to get comparable volumes between them, the CD is a couple of clicks from off and the MC is over halfway round!
The manual states the following input sensitivity for full output at 0.35V from the preamp:
MC 250uV RMS and for Tape (my CD input) 85mV. Can anyone explain this in laymans terms? All my CD players output around 2V ( I guess as a maximum signal), so I'd like to include suitably calculated inline attenuation in the connection or at the pre amp? Before I do this I'd like to understand this 'sensitivity' value a bit better.
Thanks in advance
Joe
Gain of the tape input to output is about 4, 12 dB, this is standard,
but the level of CD may be too high. Remember that many people
drive their power amp directly with CD.
Is there a means to adjust output volume of your player ?
but the level of CD may be too high. Remember that many people
drive their power amp directly with CD.
Is there a means to adjust output volume of your player ?