As it says....on the hunt for a pre-amp to go with my JLH Monoblocks project!
In the short term, I still have my Crimson Pre that I assembled from a kit back in the 80's.
Seems to be so much choice out there, not sure what to focus on.😕
I'm hoping that I might get some help in narrowing the field somewhat!!
Whether it be an assembly job, from a kit of parts....or selecting suitable PCBs and going for a straight build...I'm up for a challenge🙂
BTW...Don't have access to a scope...but have a good DMM (FWIW!)
Any pointers would be much appreciated.
In the short term, I still have my Crimson Pre that I assembled from a kit back in the 80's.
Seems to be so much choice out there, not sure what to focus on.😕
I'm hoping that I might get some help in narrowing the field somewhat!!
Whether it be an assembly job, from a kit of parts....or selecting suitable PCBs and going for a straight build...I'm up for a challenge🙂
BTW...Don't have access to a scope...but have a good DMM (FWIW!)
Any pointers would be much appreciated.
With over 200 views here, it occurs that I'm asking the wrong question
(too broad??)....😱
After doing a bit of searching, I think I can say that I'm not after a Passive solution.
At this point, not too concerned about having a MM/MC input, as I could add that later.
Suppose that leaves me with CD (line?) level inputs....🙂
Really just hoping for any ideas on where to start here.....and not wishing to start WWIII......😉
(too broad??)....😱
After doing a bit of searching, I think I can say that I'm not after a Passive solution.
At this point, not too concerned about having a MM/MC input, as I could add that later.
Suppose that leaves me with CD (line?) level inputs....🙂
Really just hoping for any ideas on where to start here.....and not wishing to start WWIII......😉
Most people who are into DIY seem to be looking for something that off-the-shelf components cannot provide for one reason or another (or at least not within the given budget). In any case they seem to have rather specific ideas about what they want (whether for good reason or not is another matter), whether in terms of circuitry, features or looks. Yours appear to be rather fuzzy, and it doesn't seem like you want anything special at all.
What are your sources, what are your loudspeakers, what are the features you would want?
You can still buy individual boards (assembled or in kit form) and cases / parts of varying quality, and it probably has never been easier to roll your own boards and have them fabricated, but the market for whole unit kits (Heathkit style) has pretty much disappeared, so don't expect too much from that side. Wiring everything up without turning it into an RF-prone tangle of ground loops is left to you.
BTW, which Crimson preamp would that be? Their history lists a few models. Schematics for some of their stuff from that time and notes from the folks who designed them exist. Seemingly a rather small-scale operation.
What are your sources, what are your loudspeakers, what are the features you would want?
You can still buy individual boards (assembled or in kit form) and cases / parts of varying quality, and it probably has never been easier to roll your own boards and have them fabricated, but the market for whole unit kits (Heathkit style) has pretty much disappeared, so don't expect too much from that side. Wiring everything up without turning it into an RF-prone tangle of ground loops is left to you.
BTW, which Crimson preamp would that be? Their history lists a few models. Schematics for some of their stuff from that time and notes from the folks who designed them exist. Seemingly a rather small-scale operation.
With CD input signal level, this amplifier has enough gain to reach clipping.
Try just a 10k volume control, at least as a start.
Try just a 10k volume control, at least as a start.
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Thanks for the replies🙂
Take it that quality of pot is going to be important here!!
Yeah...can see where you're coming from there.😱
Sources : CD (Analogue and/or Digital), AV pre-outs (which most likely will bypass the preamp and be routed through it) ...plus (min.1) Aux inputs. MM input possibly added later
Aware of the likes of the Velleman kit as a starting point.....but as for anything else, was looking for suggestions!
It's the CPR2 board.... which also appeared in the Crimson 610 Pre...I think!
May well play with this...despite what I said earlier🙂
Take it that quality of pot is going to be important here!!
Choose what you like, a 10k will work for anything you decide on. Here's a very nice yet inexpensive option.
DACT Type 21 Stepped Attenuator / Volume Control (Hi Fi Grade) * D shape Shaft * | eBay
....so....combined with a suitable 'selector'....the AV pre-outs could bypass the volume control...going straight to pwr amps?? (Volume for this option, being controlled at the AVR??)🙂
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Just occurs to me that introducing a 'selector' of some kind is going to defeat the object of a 'potentiometer only' solution, by adding degradation into the signal pathway???!!😡
If you only have one line level source, all that is needed is a volume control.
Preferably, install it inside the amplifier. Otherwise you'll need a box with two pairs of RCA jacks,
as well as the volume control.
Preferably, install it inside the amplifier. Otherwise you'll need a box with two pairs of RCA jacks,
as well as the volume control.
A set of monoblocks would only allow for input trim but not a convenient volume control.
The downside of an all-passive solution is pot impedance invariably being a compromise between input impedance and output impedance (~Rpot/4, worst-case). You also have a rather big Rpot/4 (max) node that may be subject to the effect of cable capacitance (you generally don't have monoblocks placed right next to each other) or electrostatic coupling. Hence why having at least a buffer stage (to keep output impedance down to no more than a few hundred ohms) is generally preferred.
10 kOhm is a value that makes a decent compromise in practice. Unfortunately, channel tracking still tends to be best on the more traditional 50k and 100k values. Mind you, with no preamp gain you are far less likely to require the critical lower reaches to begin with. Either of the sources listed should provide enough level to drive a typical JLH (10 W @ 8 ohms, gain 23.7 dB) into clipping as-is.
There's nothing too fundamentally wrong with selector switches. They are somewhat prone to capacitive crosstalk though, or rather the longish PCB traces to go along with them. Buffering each input individually would reduce source impedance on unused ones dramatically, so they would be much less prone to crosstalk. Wiring things up with shielded cables would already help as well.
The downside of an all-passive solution is pot impedance invariably being a compromise between input impedance and output impedance (~Rpot/4, worst-case). You also have a rather big Rpot/4 (max) node that may be subject to the effect of cable capacitance (you generally don't have monoblocks placed right next to each other) or electrostatic coupling. Hence why having at least a buffer stage (to keep output impedance down to no more than a few hundred ohms) is generally preferred.
10 kOhm is a value that makes a decent compromise in practice. Unfortunately, channel tracking still tends to be best on the more traditional 50k and 100k values. Mind you, with no preamp gain you are far less likely to require the critical lower reaches to begin with. Either of the sources listed should provide enough level to drive a typical JLH (10 W @ 8 ohms, gain 23.7 dB) into clipping as-is.
There's nothing too fundamentally wrong with selector switches. They are somewhat prone to capacitive crosstalk though, or rather the longish PCB traces to go along with them. Buffering each input individually would reduce source impedance on unused ones dramatically, so they would be much less prone to crosstalk. Wiring things up with shielded cables would already help as well.
If you only have one source, a selector switch is unnecessary. High quality switches are also rather expensive.