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Post subject: Roc Pro 1000 combo - volume and pop problems
Posted: Wed Oct 07, 2015 12:15 pm
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Hello my forumite friends, I need some help figuring out these problems I have with my Roc Pro 1000.

Before I go on let me tell you I already searched the forum about this amp and understood this is a usual issue with Roc Pro/Performer series. But let me explain...

I bought this amp used, it's manufactured on early 90's I think.
When I first powered it, I noticed that:

1- It's a loud amp. I mean LOUD! Also get a huge volume jump only touching the volume knob a bit, making it difficult to find any "in between" settings - and I live in a apartment, which makes this a real issue...
2- The controls were scratchy as hell.
3- When reverb is on, it "humms" a lot.
4- When turned OFF it makes such a loud POP, whatever the volume is at the time. I mean, the first time this happened I almos had a heart atack!! Scared th $hit out of me and my cat! Never saw him running so fast to hide under the bed. :shock:

So I was searching for a solution for these issues and found this to be the right place to ask for help.
I already read almost all there is on "Roc pro problems" topics I think, and already took apart the amp to check values and components with the help of official schematic (http://support.fender.com/schematics/gu ... ematic.pdf).
This is what I found/did:

- All the traces and solder points seemed OK. Nonetheless I did some resoldering/reflowing on valve socket, input/output jacks, opamp pins and everything else I felt could be "better" soldered, just to make sure...
- No leaking/swollen electrolitics, no burnouts below power resitors also. I measured the cap values, namely C71-72-73-74 and they are reading ok.
- Sprayed the pots, jacks, switches (including ON/OFF switch and reverb connectors) and valve socket with contact cleaner.
- Changed the tube for a lower gain JJ 5751.
- Also noticed that the Volume Pots are log type (A), so my idea of changing them for this type so the volume could be more smooth and controlable is out the window...

Now, after all this done, I reassembled the amp and the shutoff POP is still present (my cat is also hiding everytime I get close to this amp :lol: )!
The reverb "hummm" is still there also.
Good news is that control pots "scratchiness" is GONE.


Now, please I need more advices.
- what else could I check??
- can I sub the A50K volume pots to say A500K and expect to get a smoother volume raise?

Thank you so much for your time!

Cheers!!


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Fri Oct 09, 2015 10:00 am
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If the pop occurs just as the switch is thrown, a .01uF 200volt cap across the switch might help.
If it occurs a second or two later, it's from the power supplies collapsing unevenly.
In this case, you might get a speaker protection module from Ebay. This will disconnect the speaker before it can pop.

The gain problem..... well, I gotta take off right now for a road trip. I'll think about that one and get back to ya.


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Fri Oct 09, 2015 2:06 pm
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TimsAudio wrote:
If the pop occurs just as the switch is thrown, a .01uF 200volt cap across the switch might help.
If it occurs a second or two later, it's from the power supplies collapsing unevenly.
In this case, you might get a speaker protection module from Ebay. This will disconnect the speaker before it can pop.

The gain problem..... well, I gotta take off right now for a road trip. I'll think about that one and get back to ya.


Hi Tims!
Thank you for your reply!

The POP occurs about half a second later (or even less) after I switch it off...
I think I will record a short movie about these issues and post it so it's more understandable what is happening.

About the gain, do you think lowering R88 (470k gain resistor on U5A opamp, after reverb section) would help?

Thank a lot, hoping to hear from you soon! :D


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Sat Oct 10, 2015 9:28 am
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Yes, you can tack another resistor right in parallel to drop the gain. I'd start with another 470K across R88.

Sounds like you need the speaker protection module. It's a common problem with many SS amps


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Sun Oct 11, 2015 8:08 pm
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Ok, so I just shot a video trying to explain the issues and what I did to solve the volume problem.
Again, sorry for my english. I don't practice a lot these days, very "rusty"... :?





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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Mon Oct 12, 2015 9:07 am
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Your english is fine.
The Feedback mod at R88 is going to be the best bet. Keep leads short as this is a sensitive circuit and is prone to picking up hum.

Adding series resistance at r89 is not as effective in attenuation and adds noise to dull the tone. Reducing the value of R91 47K would do the same job without the added noise


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Mon Oct 12, 2015 10:53 am
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TimsAudio wrote:
Your english is fine.


Thank you Tim!! You are too kind! My brain struggles to translate what i want to say from my native language to english and speak at the same time, real time I mean...

TimsAudio wrote:
The Feedback mod at R88 is going to be the best bet. Keep leads short as this is a sensitive circuit and is prone to picking up hum. Adding series resistance at r89 is not as effective in attenuation and adds noise to dull the tone. Reducing the value of R91 47K would do the same job without the added noise


You are absolutely right, and that's exactly what I did :D
After I shot this couple of vídeos, I messed around both mods and concluded that R89 mod gives a dull tone compared to R88// mod.
My main concern about this is that I I wanted to have the option to get the original value (470k) using a knob. I could accomplish this with a switch to break the parallel connection, but instead I modified the 500K pot. Opened it and used nail varnish on one end of the wiper so it would break the connection when it's fully CW.
Works like a charm!

The POP and "humm" is still there, the later I suspect it's caused by bad grounding issues...
I will post a follow-up video on this soon.

Again thank you Tim! :)


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Mon Oct 12, 2015 11:17 am
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zedsnotdead wrote:
...but instead I modified the 500K pot. Opened it and used nail varnish on one end of the wiper so it would break the connection when it's fully CW.
Works like a charm!


That's quite ingenious!

8)

Rawk on!

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Mon Oct 12, 2015 12:11 pm
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Retroverbial wrote:

That's quite ingenious!

8)

Rawk on!

Arjay


Thank you!
Well, it's just a "DIY no-load" pot... 8)


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Post subject: Re: Roc Pro 1000 combo - volume and pop problems
Posted: Mon Oct 12, 2015 1:15 pm
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Precisely.

:mrgreen:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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