Glen's 700 series II build

[laatsch55]

No load connected, inputs shorted, Pots all the way....

 

[grapplesaw]

Hello everyone
its been a while now since my last post so I wanted say I am very happy with the amp as it has preformed flawlessly.
Many things have been going on with me so time has been short to do much building but I am happy to say my upside down biuild is underway and I will show that off soon. I will clear up your question's Upside Down WTF in a new thread.

Over the past few weeks l have rebuild my HP 334a distortion tester only to be disappointed with the results and finally replaced it with a Keithley 2015 thd+n tester so I could see how clean this puppy is.
The Keithly, made in the USA, is a great unit and good enough for my needs. We have .018 thd at 45 volts

Now to the present question "high pass input filter"

You may or maynot know the 700's have a high pass filter while the 400's do not

After a lot of running time the sound of the amp has changed remarkably. Now I have still some noticeable difference in sound when played with the high pass input filter engaged(normal setting) and with it set bypass (direct coupled) mode. I have read a lot on low pass capacitors as an outcome of this.
From mkp caps, which is what is installed, to exodic Teflon , Russian, oil filled, paper rapped, honey coated, etc. all have differences in sound quality and more over price. Maybe all I need is more hours on it but this leads to more discussion

I think the best choice for sound is no low pass filter, but I could very wrong on this so please follow along as this gives no DC protection in this setting.

Well (light goes on) we have Don's DCP board on the output side, so my first question is is that sufficient for speaker side? What about the amp itself after all it was build to be a DC output amp for motor control before ever being concidered to power speakers?

The 400's don't have any high pass filter then can we eliminate it now on the 700's is my question?

if I do remove the cap on the input does the remaining 220k resistor have any good or bad effect or should it go to?

I plan to try issoaltion transformers on the input which also convert the higher + 1v and -1v input XLR voltage to standard 0-+1 line input from my soon to be installed Sunfire preamp.
Amazingly Transformers will not pass DC current so there is the safety high pass filter.
Not so fast I have discovered. As you apply near DC voltage to a transformer close to full line voltage we get satiation of the transformer core resulting in high low end distortion . This could cause big problems so it is recommended to add a high pass cat on the input to the transformer. I should have quite before I started.!!!!!!

So now I have come full circle with the Dam high pass filter not sadly leaving the application.
I think I may proceed without any high pass filter anyway .

So Does anyone have thoughts on this?


By the way Joe you rock! This stuff works !!!!!!!

 

[laatsch55]

I've never had a pre-amp go DC on me. Joe has but under severe circumstances. My personal 700's no longer have the options for Normal/Direct coupling. I'm naked on the inputs. The 400's don't suffer from naked inputs , and neither do the 700's....just my 2 cents worth...

 

[grapplesaw]

I've never had a pre-amp go DC on me. Joe has but under severe circumstances. My personal 700's no longer have the options for Normal/Direct coupling. I'm naked on the inputs. The 400's don't suffer from naked inputs , and neither do the 700's....just my 2 cents worth...

I am going this way to I think

 

[laatsch55]

Glen , I think any decent pre-amp is all that's needed...

 

[grapplesaw]

Glen , I think any decent pre-amp is all that's needed...

Thanks
Yes I agree
this should reduce the cost by at least 50 cents by dropping it off the build

 

[Gepetto]

Hello everyone
its been a while now since my last post so I wanted say I am very happy with the amp as it has preformed flawlessly.
Many things have been going on with me so time has been short to do much building but I am happy to say my upside down biuild is underway and I will show that off soon. I will clear up your question's Upside Down WTF in a new thread.

Over the past few weeks l have rebuild my HP 334a distortion tester only to be disappointed with the results and finally replaced it with a Keithley 2015 thd+n tester so I could see how clean this puppy is.
The Keithly, made in the USA, is a great unit and good enough for my needs. We have .018 thd at 45 volts

Now to the present question "high pass input filter"

You may or maynot know the 700's have a high pass filter while the 400's do not

After a lot of running time the sound of the amp has changed remarkably. Now I have still some noticeable difference in sound when played with the high pass input filter engaged(normal setting) and with it set bypass (direct coupled) mode. I have read a lot on low pass capacitors as an outcome of this.
From mkp caps, which is what is installed, to exodic Teflon , Russian, oil filled, paper rapped, honey coated, etc. all have differences in sound quality and more over price. Maybe all I need is more hours on it but this leads to more discussion

I think the best choice for sound is no low pass filter, but I could very wrong on this so please follow along as this gives no DC protection in this setting.

Well (light goes on) we have Don's DCP board on the output side, so my first question is is that sufficient for speaker side? What about the amp itself after all it was build to be a DC output amp for motor control before ever being concidered to power speakers?

The 400's don't have any high pass filter then can we eliminate it now on the 700's is my question?

if I do remove the cap on the input does the remaining 220k resistor have any good or bad effect or should it go to?

I plan to try issoaltion transformers on the input which also convert the higher + 1v and -1v input XLR voltage to standard 0-+1 line input from my soon to be installed Sunfire preamp.
Amazingly Transformers will not pass DC current so there is the safety high pass filter.
Not so fast I have discovered. As you apply near DC voltage to a transformer close to full line voltage we get satiation of the transformer core resulting in high low end distortion . This could cause big problems so it is recommended to add a high pass cat on the input to the transformer. I should have quite before I started.!!!!!!

So now I have come full circle with the Dam high pass filter not sadly leaving the application.
I think I may proceed without any high pass filter anyway .

So Does anyone have thoughts on this?


By the way Joe you rock! This stuff works !!!!!!!

I run mine in direct mode Glenn...

My pre did not really go DC, what it did was the final output push-pull stage before the large output blocking cap failed and pushed the internal power supply rail voltage on the input side of the output cap. Thus I had a huge signal that persisted for seconds before the charge on the output cap dissipated. It blew one of the rail fuses in the amp and the line fuses to my speakers.

After fuse replacement, all was well but it was one hell of a noise when it went. In that case, the normal/direct switch position would have had little effect since that input cap would have also passed that transient.

 

[laatsch55]

At least....

 

[laatsch55]

Ok, get all technical on me...a 48khz square wave ACTS like DC ...kinda....sorta....maybe....

 

[Gepetto]

Ok, get all technical on me...a 48khz square wave ACTS like DC ...kinda....sorta....maybe....

It wasn't my PL4000 that did that Lee although that was exciting too. My Yamaha C-2a crapped out with the output stage failure, noise like a lightning bolt going off when that happened. I am surprised the speakers survived it.

 

[laatsch55]

Ah... I vaguely remember you mentioning that......years ago..

 

[grapplesaw]

I have been using this amp for about a year now and found it had more bottom end when bypassing the high pass filters using the direct coupled setting. I pulled it out this weekend to replace the face plate and do the upgrade to the Navo's power caps. I replaced it with my last 700 I did using the revission E board. Wow there was a big sonic difference. Lot more punch in the bottom end.

So so I decided to replace the descreet component rev D for a new rev E op amp board while I put in the new power caps. I also put on one of my new faceplates with Sainless Steel handles as I the attasged photo's.

All ll went straight forward, other than tapping out the gable holes for 1/4 NC bolts.

After firing wirh with the dim bulb and 2 amp fuses without an trouble I moved to5 am fuses and straight out from the varic

I had good output and hit the 56 volt range on both Chanel's The hydro was hot tonight with 119 main voltage and 214 across the caps.

So here is the twist. Using the THD test on 2k over 5 octaves I got a respectable .039 % total harmonic distortion at full and half power out in the left channel. The right was higher at .06-.07 % through the same test settings. I tried to increase bias to .4 v without change. I buttoned it back together so I test the sound quality again tomorrow but this little increase in distortion is bugging me as to what is causing the spread between channels.

Any ideas are welcomb as to what may cause the difference. My lowest measurement for this test criteria is measured on a stock Phase linear full comp unit at just .02 % THD
Thanks
Glen

 

[laatsch55]

I've never measured two channels that were the same...

 

[grapplesaw]

Just put my black face plate on Stainless steel covered back plate. Still need to polish some knobs to match.

 

[NavLinear]

That looks sexy Glen. I like that contrast between the black face plate and the stainless back plate.

 

[grapplesaw]

That looks sexy Glen. I like that contrast between the black face plate and the stainless back plate.

Thanks Dennis

it is first one so will work on improving the overall look , like painting the buttons and mirror polishing some knobs.

I have couple of black face plates available if anyone wants to PM me

 

[laatsch55]

Sexy as hell.....

 

[WOPL Sniffer]

Very NICE, I like the contrast of the SS.

 

[grapplesaw]

Very NICE, I like the contrast of the SS.

Perry the knobs mirror off the stainless. I am going to order some black knobs like you use and see how that looks.

 

[WOPL Sniffer]

The black knobs look good too with the black faces...

I should show you how I resto'd my originals, thy look really nice. I'll post a pic later