Monoblocking Quad 303

[Goochtoucher]

Hi all,

I am purchasing another Quad 303 so that I have one for each speaker and I will need to monoblock them to do this. However, as I am a newbie, I have absolutely no idea how to monoblock a power amp, what I will need etc.

My questions to you fine gentlemen are:

Do I need something particular to this amp to do this?
How do I connect both amps to my receiver? Is it a simple Y-Splitter? Or does that degrade the signal?

Thanks in advance, any other information you think I might need will be welcomed.

 

[ImcLoud]

My Quad 303's only had 1 line input and one speaker output, does yours have more than one set? I had 2 of them one for the left and one for right...

 

[fuzz092888]

Hi all,

I am purchasing another Quad 303 so that I have one for each speaker and I will need to monoblock them to do this. However, as I am a newbie, I have absolutely no idea how to monoblock a power amp, what I will need etc.

My questions to you fine gentlemen are:

Do I need something particular to this amp to do this?
How do I connect both amps to my receiver? Is it a simple Y-Splitter? Or does that degrade the signal?

Thanks in advance, any other information you think I might need will be welcomed.

As far as I can tell there are no special settings. Simply attach one RCA and one set of speaker outputs to each amp and they are now mono blocks

 

[fuzz092888]

My Quad 303's only had 1 line input and one speaker output, does yours have more than one set? I had 2 of them one for the left and one for right...

If his look like this, then they have two.

 

[ImcLoud]

Wow thats different than mine, mine had 1 rca and 1 set of speaker terminals... weird, 303's too...

 

[macddmac]

I saw a 303 J model on eBay that looks the same other than the single in-out thing

 

[markw]

This would be one for the other Mark here. He loves this Brit stuff.

 

[fuzz092888]

This would be one for the other Mark here. He loves this Brit stuff.

I believe he is actually in England right meow.

 

[Grador]

Briarsfield Hi-Fi - Quad 303 overview

This might be of help, I cannot attest to it's validity, but check the section on "bridging"

 

[TLS Guy]

Hi all,

I am purchasing another Quad 303 so that I have one for each speaker and I will need to monoblock them to do this. However, as I am a newbie, I have absolutely no idea how to monoblock a power amp, what I will need etc.

My questions to you fine gentlemen are:

Do I need something particular to this amp to do this?
How do I connect both amps to my receiver? Is it a simple Y-Splitter? Or does that degrade the signal?

Thanks in advance, any other information you think I might need will be welcomed.

Can you be certain what the impedance of your speakers is? If they are four ohm, you can parallel bridge them. You will need a couple of 5Kohm potentiometers. Set the amps to a null of output, and then parallel the outputs. You will get 90 watts into a four ohm speaker.

If anyone is contemplating doing this with any other amp, don't. The Quad 303 is probably the most bullet proof amp of all time. It was a resounding achievement given its date.

If your speakers are 8 ohm, you will need to series bridge it. For this you will need a phase splitter, which can be a center tap transformer. However a better solution is to build an op amp circuit. If you do this correctly you will get 90 watts into 8 ohms. You must be very careful to balance the op amp phase splitter, or you will have distortion. The positive and negative sides of the cycle must e perfectly symmetrical. Ideally you really need a scope to do this.

 

[Grador]

So TLS Guy is seems to be validating the information on the link I posted so you can use it for reference.

 

[Goochtoucher]

Hi, sorry for the slow reply.
Yes it has 2 output channels, I assume I will need to join both channels together.
They are 6 ohm speakers...does that make it more complex?

 

[markw]

I don't know the particulars about bridging that particular amp, but i do know that all bridged amps "see" the load (speaker impedance) presented to them as one half of their rated impedance.

So, it will see your six ohm speakers as a three ohm load. I don't know how those bridged amps will react to that.

 

[Grador]

Hi, sorry for the slow reply.
Yes it has 2 output channels, I assume I will need to join both channels together.
They are 6 ohm speakers...does that make it more complex?

Treat them as 4 ohm per the instructions in the link I posted earlier.

 

[TLS Guy]

Treat them as 4 ohm per the instructions in the link I posted earlier.

You will need two of the 5 kOhm pots as per previous post and the diagram. It is not as simple as you think.

Since the Quad 303 is about the only amp I can think of that can be bridged parallel, (that is very unusual) the half impedance rule does not apply. So your amp will see you speakers as 6ohm, and not three like the usual bridging situation.

Make sure you understand the diagrams and the procedure or you will cause trouble.

 

[Goochtoucher]

You will need two of the 5 kOhm pots as per previous post and the diagram. It is not as simple as you think.

Since the Quad 303 is about the only amp I can think of that can be bridged parallel, (that is very unusual) the half impedance rule does not apply. So your amp will see you speakers as 6ohm, and not three like the usual bridging situation.

Make sure you understand the diagrams and the procedure or you will cause trouble.

I need to send one of them to have a channel repaired and have RCA ports put in, do you reckon they would set up the bridge for me? At an extra cost of course.

 

[Grador]

TLSguy

Given the means of "bridging" this amplifier it seems to me that there could be some pretty strong deleterious effects on sound quality do to differences between the channels.

Are these an issue in practice or just on paper/in my head.

 

[TLS Guy]

TLSguy

Given the means of "bridging" this amplifier it seems to me that there could be some pretty strong deleterious effects on sound quality do to differences between the channels.

Are these an issue in practice or just on paper/in my head.

I'm sure Quad will bridge the amp if he wants.

However Peter Walker was against bridging. He did offer mono blocks to special order. However very close tolerance parts were used, and the amps very carefully set up. Unless any type of bridging is done very carefully, then distortion increases. Everything must be in perfect balance between the channels, or else results are bad.

I think bridging is high risk for just 3 db more output.

I would advise the OP discuss the issue with Bob Flain at Quad. He is a very nice guy and will give the OP a thoughtful answer and he should follow it.

I have never used any type of amp in bridged mode, and I'm fundamentally opposed to the idea.

 

[lsiberian]

3db is not worth the trouble of bridging IMO. It just isn't worth the trade of IMO.