Audio Research SP3
Hi,
I would like to replace the volume control and source switch of my SP3A-1 preamplifier. I am not an expert, just an old newbie. Any help, suggestions and recommendations will be greatly appreciated.
This is the list I was able to put together according to the suggestions I found on DIYaudio.
Goldpoint V47 [$246], TKD 2CP-2511 motorized [$114] this model is used in Kondo, Lamm and Audio Note, the Elma 2 pole 47 way switch [$231]. Switchable attenuators: ELMA 04-2264 [$101] and Seiden 32012 [$80].
There is a new ALPS HQPro but the price is out of the question, too expensive for me.
I do not know if I should get a 2 pole 6 way or a 4 pole 6 way switch. What's the degree of difficulty?
On another note, how about bypassing caps with Mundorfs or Jupiters, etc?
Thanks much in advance.
Hi,
I would like to replace the volume control and source switch of my SP3A-1 preamplifier. I am not an expert, just an old newbie. Any help, suggestions and recommendations will be greatly appreciated.
This is the list I was able to put together according to the suggestions I found on DIYaudio.
Goldpoint V47 [$246], TKD 2CP-2511 motorized [$114] this model is used in Kondo, Lamm and Audio Note, the Elma 2 pole 47 way switch [$231]. Switchable attenuators: ELMA 04-2264 [$101] and Seiden 32012 [$80].
There is a new ALPS HQPro but the price is out of the question, too expensive for me.
I do not know if I should get a 2 pole 6 way or a 4 pole 6 way switch. What's the degree of difficulty?
On another note, how about bypassing caps with Mundorfs or Jupiters, etc?
Thanks much in advance.
Attachments
Last edited:
It's a single ended circuit, so just two poles total are needed, one per channel. The grounds are not switched.
The Elma switches are excellent, but making up your own stepped volume control is not for the faint hearted.
The volume control choice is up to you, but the total panel/chassis thickness could cause some problems
with mounting if the bushings have a shorter length, or a different diameter.
The electrolytic capacitors in the power supply may be a weak link at this point in time, nearly 50 years old.
Unless the controls are causing problems, or there is poor channel balance, starting by replacing all the
Mylar coupling capacitors would be the easiest and most effective step.
The Elma switches are excellent, but making up your own stepped volume control is not for the faint hearted.
The volume control choice is up to you, but the total panel/chassis thickness could cause some problems
with mounting if the bushings have a shorter length, or a different diameter.
The electrolytic capacitors in the power supply may be a weak link at this point in time, nearly 50 years old.
Unless the controls are causing problems, or there is poor channel balance, starting by replacing all the
Mylar coupling capacitors would be the easiest and most effective step.
Last edited:
Thanks Rayma, always being so helpful.
If it was for you regardless of mounting problems, which attenuator would you choose?
Please take a look at this supplier in the UK. a friend of mine down under was very satisfied with them.
Potentiometers | Hifi Collective
If it was for you regardless of mounting problems, which attenuator would you choose?
Please take a look at this supplier in the UK. a friend of mine down under was very satisfied with them.
Potentiometers | Hifi Collective
Of those shown, I'd get the Alps, but have no experience of the other controls.
If you frequently use the volume control, a stepped one may be difficult to get used to,
especially if it takes significant force to turn it, like some switches do. For a selector switch,
that is not so important.
If you use the phono stage, keep the same impedance volume control, as it will load the
phono circuit more with a lower value. Otherwise, the volume control could be lower in impedance.
If you frequently use the volume control, a stepped one may be difficult to get used to,
especially if it takes significant force to turn it, like some switches do. For a selector switch,
that is not so important.
If you use the phono stage, keep the same impedance volume control, as it will load the
phono circuit more with a lower value. Otherwise, the volume control could be lower in impedance.
Last edited:
355F1, what brand/type of volume control/pot did you ended up getting?
I have just acquired a SP-3-A1 and it has a severe tracking issue with the original volume control. The control has a central adjustment but after fiddling with with a screwdriver I wasn't able to get a consistent balance between channels. It's a shame since the control is otherwise noise free.
I was checking the manual for the unit that includes the schematic and servicing information. It lists the volume control (LEVEL) as a 500K dual log potentiometer with their part number 45015.
Did you replace it with the same value? I have read some folks using 250K. Dunno if this is acceptable.
The TKD seems like the best choice, quality wise, but they don't make 500K anymore. I have a TOCOS (Tokyo Cosmos) 500K unit here, recent manufacture. However, these are known to have less that ideal tracking, so it's a crap shoot..
I have just acquired a SP-3-A1 and it has a severe tracking issue with the original volume control. The control has a central adjustment but after fiddling with with a screwdriver I wasn't able to get a consistent balance between channels. It's a shame since the control is otherwise noise free.
I was checking the manual for the unit that includes the schematic and servicing information. It lists the volume control (LEVEL) as a 500K dual log potentiometer with their part number 45015.
Did you replace it with the same value? I have read some folks using 250K. Dunno if this is acceptable.
The TKD seems like the best choice, quality wise, but they don't make 500K anymore. I have a TOCOS (Tokyo Cosmos) 500K unit here, recent manufacture. However, these are known to have less that ideal tracking, so it's a crap shoot..
Last edited:
A lower value is ok, it will just alter the action of the balance control somewhat.
You can check the tracking of your replacement volume control with a signal source and a DVM.
Input the same signal to both sections, and measure the outputs at the wipers (all wrt the lower ends).
A 10% difference is about 1dB, and a 20% difference is about 2dB. Expect worse near the low end of the range.
If you want better tracking, use a switched resistor control.
You can check the tracking of your replacement volume control with a signal source and a DVM.
Input the same signal to both sections, and measure the outputs at the wipers (all wrt the lower ends).
A 10% difference is about 1dB, and a 20% difference is about 2dB. Expect worse near the low end of the range.
If you want better tracking, use a switched resistor control.
Last edited:
Thanks rayma.
I will probably use 250K and I will measure the TOCOS as well with the DMM as you have indicated.
The finest attenuator I've heard is the Khozmo shunt with 48 steps. I use one on my original Marantz 7 and it's leagues beyond anything conventional. Extremely transparent.
I suppose I could use a Khozmo on the Audio Research, but I want to keep it as original possible, since I may sell it in the future.
I will probably use 250K and I will measure the TOCOS as well with the DMM as you have indicated.
The finest attenuator I've heard is the Khozmo shunt with 48 steps. I use one on my original Marantz 7 and it's leagues beyond anything conventional. Extremely transparent.
I suppose I could use a Khozmo on the Audio Research, but I want to keep it as original possible, since I may sell it in the future.
Last edited:
Hello I’m new here. I have an SP3. I mostly listen to records. The volume pot is not good, especially at low volume, so I would like to upgrade it. The schematic calls for a 500k pot which are difficult to find like stated above. There are however several nice 250k options that will fit the chassis. I sent ARC an email asking them if a 250k pot could be used without having to make any modifications. ARC replied: “If you replace the original pot with a 250K pot you will need to make further modifications to the unit but as we do not use those parts as subs we cannot advise on which part or what values you would need to change. It would be some caps in the power supply and possibly some resistors.” I believe ARC sells an ALPS 100k as its substitute part. I asked them that with their substitute part, what needs to be modified. I haven’t received a response.
Is ARC just trying to push me into buying the substitute part from them or can we actually use a 250k volume pot without having to make any modifications?