Quad 303 pop on switch on - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

mikes08 · 3rd Jul 2022, 4:26 pm

Could I be that unlucky...worth a try I guess..

PJL · 3rd Jul 2022, 11:22 pm

Electrolytic capacitors that have been stored for a few years may need reforming.

mikes08 · 4th Jul 2022, 7:43 am

Many thanks
I will order a couple of new caps to replace the Epcos ones and give that a go.
If i replaced the possible defective one with the known good I took out would it create a problem to have one 10,000mf and one 12,000mf in the amp just for testing purposes?
Sorry for all the questions - just learning as i go along.

stevehertz · 4th Jul 2022, 7:50 am

No, they're separate circuits.

mikes08 · 4th Jul 2022, 7:51 am

Thanks Steve
Will try that and if it solves it i know i need to order a couple of new caps.

vidjoman · 4th Jul 2022, 8:58 am

I thought the original 303 used 2,000 mfd caps. Surely increasing to 5 times the capacitance will increase the switch-on charging current and possibly lead to a thump as the cap is charged.

radio69 · 4th Jul 2022, 11:01 am

Yes, the original used two in number, 2,000uF caps.

So are you using two 10,000uF in parallel ? That's insane. Especially with a regulator downstream.

I take it this relates to the modern obsession of so-called 'upgrades' to everything. Many of which are not.

Peter Walker and Mike Albinson knew what they were doing, leave it as it was.

My own 303 works perfectly well as it was when it left the factory.

mikes08 · 4th Jul 2022, 11:15 am

Many thanks - That is standard upgrade with Dada kit and works fine in my other two 303's that I have done. It is just problem with one channel here. I could reduce them to 4700mf if replacing. Not a thump but more of a higher frequency 'pop/crack' the thumps i can live with but this is slightly different. The difference once done is audible noticeable.

Goldieoldie · 4th Jul 2022, 11:24 am

If the amp is working fine except for this problem could you fit a simple 555 with a very short delay circuit triggered on switch on with a relay in series with the speakers ?

Radio Wrangler · 4th Jul 2022, 12:46 pm

It might be the only audible clue that something bad is happening, like the burst of spurious oscillation mentioned earlier as a possibility. Calling it "A higher frequency pop/crack" seems to play towards this possibility.

I'd want to look with a scope and see what's going on.

David

mikes08 · 4th Jul 2022, 1:00 pm

Thanks David
I can take it out of service as i have others. Just strange symptoms i have not had with the other two. All my quiescent voltages check out fine.
I have ordered two new 4700mf Epcos caps for the output side just in case it is that .
The odd thing is that the 'pop' changed from right to left channel yesterday after swapping the existing caps over. The amp is on now and works fine after the initial problem and if turned off and on again once fired up for the day it doesn't create any noise. I am assuming that is due to the capacitors charging up and not depleting say overnight.
Unfortunately no scope unless there is a member on here close to Canterbury who could assist. I could also look and see if any audio repairs near here.

PJL · 4th Jul 2022, 3:02 pm

There is more energy stored in the output capacitors than the PSU which sounds like a recipe for instability.

stevehertz · 4th Jul 2022, 3:55 pm

Sounds to me like the value of the caps is too high. Generally it's not advisable to 'improve' on smoothing cap values by too much, especially in valve circuits which ok, is not the case here. But you're increasing the value five-fold? I'd stick with stock or maybe double at most. It may well be a 'quirk' of the circuitry that nine times out of ten the combination will work, but maybe it's a case of the exception proving the rule, as what you are experiencing?

mikes08 · 5th Jul 2022, 7:51 am

Thanks Steve and all.
I have ordered some 4700mf caps to replace the current ones so will try those. As you note it could just be an anomaly with this particular amp. Will report back when they arrive and have been fitted. I have taken out of service for now. More concerned about my BC1 bass units going pop....still it is keeping me occupied.

stevehertz · 5th Jul 2022, 8:53 am

Do not damage a BC1! That is a punishable offence!

mikes08 · 5th Jul 2022, 1:01 pm

Quote:

Originally Posted by stevehertz

Do not damage a BC1! That is a punishable offence!

I know....

mikes08 · 24th Jul 2022, 9:14 am

A quick update now - i have replaced TR1 with a spare genuine RCA one I had and have now replaced the output capacitors with 4700mf - it still pops in one channel(left) on first turn on but is more muted now so I guess related to the capacitors. It is less alarming now so will leave at that but still curious why it should be an anomaly with this amp and not the others. In the interim i have acquired some high end Dada boards via e bay. One board has a fault which i am working through but will start another thread on that.

Craig Sawyers · 24th Jul 2022, 9:33 am

Since DADA say "Completely tested & calibrated with professional lab-equipment" and "1 year full warrantee", surely that is your first port of call if there is a fault with one board?

Craig

mikes08 · 24th Jul 2022, 9:37 am

Hi Craig
Bought second hand and listed as one resistor will need replacing - it had burnt out but there appears to be more than this.
I don't know how old they are though - no serial numbers either.

I will start a separate thread on this.

mikes08 · 29th Jul 2022, 7:50 am

Now resolved - having replaced the boards - see my other thread - with Dada high end boards the pop on turn on has now gone.
I had replaced TR1 to no effect so wonder if it might be on the regulator board after all so will investigate that further. Odd though as only affected one channel.

3rd Jul 2022, 4:26 pm	#41
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Could I be that unlucky...worth a try I guess..

3rd Jul 2022, 11:22 pm	#42
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,937	Re: Quad 303 pop on switch on Electrolytic capacitors that have been stored for a few years may need reforming.

4th Jul 2022, 7:43 am	#43
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Many thanks I will order a couple of new caps to replace the Epcos ones and give that a go. If i replaced the possible defective one with the known good I took out would it create a problem to have one 10,000mf and one 12,000mf in the amp just for testing purposes? Sorry for all the questions - just learning as i go along.

4th Jul 2022, 7:50 am	#44
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,653	Re: Quad 303 pop on switch on No, they're separate circuits. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

4th Jul 2022, 7:51 am	#45
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Thanks Steve Will try that and if it solves it i know i need to order a couple of new caps.

4th Jul 2022, 8:58 am	#46
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,210	Re: Quad 303 pop on switch on I thought the original 303 used 2,000 mfd caps. Surely increasing to 5 times the capacitance will increase the switch-on charging current and possibly lead to a thump as the cap is charged.

4th Jul 2022, 11:01 am	#47
radio69 Tetrode Join Date: May 2022 Location: Hangleton, (Hove) East Sussex. UK. Posts: 61	Re: Quad 303 pop on switch on Yes, the original used two in number, 2,000uF caps. So are you using two 10,000uF in parallel ? That's insane. Especially with a regulator downstream. I take it this relates to the modern obsession of so-called 'upgrades' to everything. Many of which are not. Peter Walker and Mike Albinson knew what they were doing, leave it as it was. My own 303 works perfectly well as it was when it left the factory.

4th Jul 2022, 11:15 am	#48
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Many thanks - That is standard upgrade with Dada kit and works fine in my other two 303's that I have done. It is just problem with one channel here. I could reduce them to 4700mf if replacing. Not a thump but more of a higher frequency 'pop/crack' the thumps i can live with but this is slightly different. The difference once done is audible noticeable.

4th Jul 2022, 11:24 am	#49
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,036	Re: Quad 303 pop on switch on If the amp is working fine except for this problem could you fit a simple 555 with a very short delay circuit triggered on switch on with a relay in series with the speakers ?

4th Jul 2022, 12:46 pm	#50
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,239	Re: Quad 303 pop on switch on It might be the only audible clue that something bad is happening, like the burst of spurious oscillation mentioned earlier as a possibility. Calling it "A higher frequency pop/crack" seems to play towards this possibility. I'd want to look with a scope and see what's going on. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

4th Jul 2022, 1:00 pm	#51
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Thanks David I can take it out of service as i have others. Just strange symptoms i have not had with the other two. All my quiescent voltages check out fine. I have ordered two new 4700mf Epcos caps for the output side just in case it is that . The odd thing is that the 'pop' changed from right to left channel yesterday after swapping the existing caps over. The amp is on now and works fine after the initial problem and if turned off and on again once fired up for the day it doesn't create any noise. I am assuming that is due to the capacitors charging up and not depleting say overnight. Unfortunately no scope unless there is a member on here close to Canterbury who could assist. I could also look and see if any audio repairs near here.

4th Jul 2022, 3:02 pm	#52
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,937	Re: Quad 303 pop on switch on There is more energy stored in the output capacitors than the PSU which sounds like a recipe for instability.

4th Jul 2022, 3:55 pm	#53
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,653	Re: Quad 303 pop on switch on Sounds to me like the value of the caps is too high. Generally it's not advisable to 'improve' on smoothing cap values by too much, especially in valve circuits which ok, is not the case here. But you're increasing the value five-fold? I'd stick with stock or maybe double at most. It may well be a 'quirk' of the circuitry that nine times out of ten the combination will work, but maybe it's a case of the exception proving the rule, as what you are experiencing? __________________ A digital radio is the latest thing, but a vintage wireless is forever..

5th Jul 2022, 7:51 am	#54
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Thanks Steve and all. I have ordered some 4700mf caps to replace the current ones so will try those. As you note it could just be an anomaly with this particular amp. Will report back when they arrive and have been fitted. I have taken out of service for now. More concerned about my BC1 bass units going pop....still it is keeping me occupied.

5th Jul 2022, 8:53 am	#55
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,653	Re: Quad 303 pop on switch on Do not damage a BC1! That is a punishable offence! __________________ A digital radio is the latest thing, but a vintage wireless is forever..

24th Jul 2022, 9:14 am	#57
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on A quick update now - i have replaced TR1 with a spare genuine RCA one I had and have now replaced the output capacitors with 4700mf - it still pops in one channel(left) on first turn on but is more muted now so I guess related to the capacitors. It is less alarming now so will leave at that but still curious why it should be an anomaly with this amp and not the others. In the interim i have acquired some high end Dada boards via e bay. One board has a fault which i am working through but will start another thread on that. Attached Thumbnails

24th Jul 2022, 9:33 am	#58
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,864	Re: Quad 303 pop on switch on Since DADA say "Completely tested & calibrated with professional lab-equipment" and "1 year full warrantee", surely that is your first port of call if there is a fault with one board? Craig __________________ Doomed for a certain term to walk the night

24th Jul 2022, 9:37 am	#59
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Hi Craig Bought second hand and listed as one resistor will need replacing - it had burnt out but there appears to be more than this. I don't know how old they are though - no serial numbers either. I will start a separate thread on this.

29th Jul 2022, 7:50 am	#60
mikes08 Pentode Join Date: Dec 2021 Location: Canterbury, Kent, UK. Posts: 131	Re: Quad 303 pop on switch on Now resolved - having replaced the boards - see my other thread - with Dada high end boards the pop on turn on has now gone. I had replaced TR1 to no effect so wonder if it might be on the regulator board after all so will investigate that further. Odd though as only affected one channel.