Pioneer SPEC-1/SPEC-4 Function Switch Noise

[Joe Nardy]

I have a very nice SPEC-1/SPEC-4 system that was refurbed (caps, transistors, relays, trimmers) in 2016. It works great with one small issue. The function switch has some noise (static/pop) when switched to phono 1 or phono 2. I cleaned the selector switch a couple days ago but didn't hear any noticeable improvement. I gave it a very thorough cleaning today, disconnecting the board from the chassis and cleaning the contacts with DeoxIT and Faderlube (the squeeze bottle types) along with white eraser and toothbrush. The contacts are as clean as I can get them. The noise isn't as loud as before but is still there.

I'm wondering if the noise is due to the higher gain of the phono inputs. I have also had other gear (Sony STR-6800SD) that had some RCA 'shorting' plugs that the Owner's manual states "Insert the shorting plugs (supplied) into the PHONO terminals when these inputs are not in use. Never insert the shorting plugs in the input and output jacks other than PHONO". Since Sony mentions 'shorting' in the description, are these just plugs with the signal and ground shorted together? If so, it would be easy to make some plugs but I wouldn't want to do that unless I know it's safe. Could there be something more to the plugs?

Please let me know if you've had any similar issues and offer any suggestions.

Thanks,
Joe

 

[markthefixer]

one channel or both channels, same on both channels or different on each channel?

Headphones help...

What transistors in the 2016 refurb were changed in the phono amps?

The +48v and -48v run the preamp, EXCEPT in the noise sensitive first stage, that has a pair (left / right) of 24v zener regulators for very clean DC.

You need to check if the +/- 48v power supplies are behaving. If all PS transistors are new...

 

[Joe Nardy]

Mark,

Thanks for the reply.

The noise is the same on both channels and about the same for both phono inputs. Phono 2 has a level adjustment so it varies but when centered the noise level is about the same as Phono 1.

I'm not sure what transistors were replaced in the refurb. I didn't do the work, it was done by the PO who is an AK member. I'll reach out to him to see if he has a list of what he replaced.

I'll check voltages tomorrow and report back.

One thing I just noticed when I was checking the channels. If there's no phono connected, the input selector is quiet on the other inputs (Tuner, Aux 1, Aux 2). If a turntable is connected to either Phono 1 or Phono 2, the other input positions are quiet unless switching from Phono 1. When switching from Phono 1, there is a small pop on the other inputs which decreases in amplitude over a few seconds. I'm not sure if this helps diagnose but thought it would be worth mentioning.

Thanks again,
Joe

 

[markthefixer]

the headphone test? if exactly the same on both channels it will sound like it's in the middle of your skull.This commonality indicts the power supply

I missed this... you HAVE it in front of you, what transistor part numbers are in the phono amp?

You working on it? or is it YOURS now??

 

[Joe Nardy]

the headphone test? if exactly the same on both channels it will sound like it's in the middle of your skull.This commonality indicts the power supply

I missed this... you HAVE it in front of you, what transistor part numbers are in the phono amp?

You working on it? or is it YOURS now??

Mark,

I don't have any headphones to test but can see both power meters jump at the same time when switching between inputs. I also tested with balance full left and full right and both pop at what to my ears seems to be the same level. I think I have a headphone adapter that I can use to test with some earbuds. I'll see if I can find it tomorrow and test to verify.

Sorry, I misunderstood your question about the transistors. I'll put together a list tomorrow.

Yes, the gear is mine. The refurb was done by the previous owner that I purchased it from. I have messaged him to see if he has a list of components he replaced.

Thanks,
Joe

 

[Joe Nardy]

Update 4/27/23:

Could not find headphone adapter so placed two speakers facing each other, head width apart. Pop is definitely in both speakers.

Compiled list of Input Circuit Assembly AWF-017 transistors.
Measured voltages on Input Circuit Assembly AWF-017.
Measured voltages on Power Supply AW094.

Results:


Thanks,
Joe

 

[markthefixer]

THANK YOU, that will give me something to chew on.

Also, calling pops "noise" gives me a mental train wreck (needle ripped across groves "sound")

The pops only happen upon switching, correct?

We aren't dealing with a preamp that's hissing like a snake, or popping bubbles like a boiling pot of water, correct?
Hands off is quiet, twisting a switch gets the pop, right?

 

[onwardjames]

Good luck, Joe.

Mark will get you to the promised land.

 

[Joe Nardy]

THANK YOU, that will give me something to chew on.

Also, calling pops "noise" gives me a mental train wreck (needle ripped across groves "sound")

The pops only happen upon switching, correct?

We aren't dealing with a preamp that's hissing like a snake, or popping bubbles like a boiling pot of water, correct?
Hands off is quiet, twisting a switch gets the pop, right?

Yes, the pops happen only when switching. Otherwise the preamp works and sounds fine.

Good luck, Joe.

Mark will get you to the promised land.

I have no doubt about Marks abilities. I only hope to pick up a bit of understanding and knowledge along the way.

Joe

 

[markthefixer]

find the phono amp C27 & C28, record the manufacturer and data codes off the components. Note their installation orientation.

Then measure the voltage (operating) with no incoming audio on both capacitor leads ( + & - ) referenced to ground.

 

[Joe Nardy]

find the phono amp C27 & C28, record the manufacturer and data codes off the components. Note their installation orientation.

Then measure the voltage (operating) with no incoming audio on both capacitor leads ( + & - ) referenced to ground.

Mark,

Will do. For what it's worth, I got the BOM the previous owner used for the refurb. Both C27 and C28 are on the list. I'll report back the voltage readings tomorrow.

Thanks,
Joe

 

[Joe Nardy]

Mark,

There is no polarity, see below message from previous owner:

"Mark may have something with C27/28. Original CEANL caps are low leakage parts. The list that I used replaced them with UES bipolars which may not be low leakage. UKL would be a better choice".

Capacitor markings are:

Nichicon
22uF 25V
BP
Muse
B1410
85(degree symbol) C(M)

Voltage readings:

C27 + (based on Service Manual board diagram) to ground = -.003Vdc
C27 - (based on Service Manual board diagram) to ground = Roughly -.46Vdc but fluctuates between -.45V and -.48V

C28 + (based on Service Manual board diagram) to ground = .00Vdc
C28 - (based on Service Manual board diagram) to ground = Roughly -.51Vdc but fluctuates between -.50V and -.52V

These readings are with no turntable connected. Readings are steady when switched to Tuner, Aux 1, or Aux 2. When switched from Tuner to Phono 1, the readings on the - side of C27 stay steady but the -side of C28 jumps to about -.63v then settles down to -.50v.

When switched from Phono 1 to Phono 2, the readings jump more, as high as -1.8v on C27 and -1.6v on C28, and then settle down to the -.46v and -.50v respectively.

When switched from Phono 2 to Phono 1, the readings drop, down to less than -.1v on both C27 and C28, then rise back to -.46v and -.50v respectively.

* Realizing these are all negative values, by rise or lower, I mean in value, as in -1.8v is higher (in value) than .50v.

In all cases, the pop is still there and noticeable if the amp is powered on and volume isn't at 0.

Thanks,
Joe

 

[markthefixer]

edit:
It has been brought to my attention there are some variations in what was used for the input capacitors C1 & C2. We need to visually verify what type of caps are doing duty at C1 & C2 in your unit..

phono 2 has a volume control, evaluate pops at minimum and maximum settings compared to the other channel.
Also try the switching more slowly, allowing time for a charge to build up to make the pop.


OK, I have a small experiment:

try disconnecting C27 & C28 from circuit, say, lift the + leg... then see if it continues with the pops.

now, looking at the circuit, we have a 330k ohm resistor to ground at the cap's "output"
then there's 500 ohms, a 10k pot and a 10k resistor - so it's loading down ~21k
it really shouldn't have much voltage there to upset things.
If it doesn't stop - well we then know to look elsewhere.

do you have some non-polar film caps.
The large value of the cap is due to the Pioneer Engineer's desire to be able to drive some really low impedance inputs outside of the preamp. (2.2k @ 20hz)

So, we also can try a 1uf(+) Film Cap in that position and see what happens

 

[Joe Nardy]

Mark,

I'll get you some answers shortly. While I was looking at the unit earlier I decided to check the AWF-017 voltages. I found some discrepancies that may or may not be consequential. Here's a crappy scan of the schematic and a spreadsheet with the suspect voltages in red.





Thanks,
Joe

 

[Joe Nardy]

Mark,

Here's a pic of C1 and C2:



Volume of pops does not seem to be affected by level of Phono 2 volume control. Volume of pops also does not seem to be affected by waiting longer between switching.

I will try lifting the + leg of C27 and C28 but it will take some time. There's a fair amount of disassembly involved to get the input board disconnected to access the foil side. My wife and I have plans for tomorrow and next week is full of appointments for my elderly parents. I'll try to work on it Sunday. I'll report back as soon as I can.

I have a few WIMA film caps, 1uF/50v and .22uF/63V.

Thanks for your help,
Joe

 

[Joe Nardy]

Update 5/1/23:

I did not get a chance to work on this yesterday. I ended up spending the day at the ER with my elderly father. It was nothing life threatening but just a mentally exhausting ordeal. I hope to have some time late this week or this weekend to disconnect C27 & C28 and test. I'll report back then.

Joe

 

[markthefixer]

Don't sweat it.

 

[Joe Nardy]

I finally had some time to look into this again. I lifted the + side of C27 and C28. Input selector switch is dead quiet. Tuner, Aux 1 and Aux 2 inputs work as expected. There is no output on Phono 1 or Phono 2.

Thanks for your patience!

Joe

 

[Joe Nardy]

edit:
It has been brought to my attention there are some variations in what was used for the input capacitors C1 & C2. We need to visually verify what type of caps are doing duty at C1 & C2 in your unit..

phono 2 has a volume control, evaluate pops at minimum and maximum settings compared to the other channel.
Also try the switching more slowly, allowing time for a charge to build up to make the pop.


OK, I have a small experiment:

try disconnecting C27 & C28 from circuit, say, lift the + leg... then see if it continues with the pops.

now, looking at the circuit, we have a 330k ohm resistor to ground at the cap's "output"
then there's 500 ohms, a 10k pot and a 10k resistor - so it's loading down ~21k
it really shouldn't have much voltage there to upset things.
If it doesn't stop - well we then know to look elsewhere.

do you have some non-polar film caps.
The large value of the cap is due to the Pioneer Engineer's desire to be able to drive some really low impedance inputs outside of the preamp. (2.2k @ 20hz)

So, we also can try a 1uf(+) Film Cap in that position and see what happens

Mark,

Before proceeding with component replacement, I want to clarify the above statement (So, we also can try a 1uf(+) Film Cap in that position and see what happens). Do you mean to swap C27 and C28 with the WIMA 1uF film caps I have on hand?

Thanks,
Joe

 

[markthefixer]

Mark,

Before proceeding with component replacement, I want to clarify the above statement (So, we also can try a 1uf(+) Film Cap in that position and see what happens). Do you mean to swap C27 and C28 with the WIMA 1uF film caps I have on hand?

Thanks,
Joe

Yes, C27 & C28 WIMA 1 uF film caps.
it will not have deep bass response at the lower (2.2k) impedances if hooked to an external preamp, but it would be a good test for the problem.