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Old 20th April 2017, 01:08 PM   #3001
Dave S is offline Dave S  United Kingdom
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Quote:
Originally Posted by ClaveFremen View Post
Nice build

I suppose you like what you hear...
1st impression is that it sounds fast and tight, with clear separation of instruments. Excellent harmonic structure with brass etc. Maybe it's a touch lightweight, but that could be the toroids (used with several amps previously and tend to have this character), or maybe it needs to some use for the parts to settle down.

Actually this was quite a tricky build:
- the 1/4" terminals are rather close to the rectifier diodes and require sleeving and careful fitting
- access to a screw to fasten the 3886 is blocked by other components and it's not possible to use an ally bar to clamp it, for the same reason.

I will probably change it to R-cores and Rev A and a nice box if it become my favourite amp.

Just checking... for Rev A (changing from FE):
- change R3 from 0.5R to 0.33R
- delete C10 and R39

Is that right?
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Old 20th April 2017, 01:12 PM   #3002
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Hi Bas,

When I read post #2988, I think rgaudio is saying that it is quiet with shorted input, but makes white noise when he connects to a signal source. If I understand correctly, then he could also have a ground loop issue.

Jac
You are correct!
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Old 20th April 2017, 11:26 PM   #3003
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Quote:
Originally Posted by Dave S View Post
1st impression is that it sounds fast and tight, with clear separation of instruments. Excellent harmonic structure with brass etc. Maybe it's a touch lightweight, but that could be the toroids (used with several amps previously and tend to have this character), or maybe it needs to some use for the parts to settle down.
Lightweight? Weird... did you observe suggested orientation for all parts?

Also input cabling could have a role, it seems you recicled pairs from an ethernet cable, isn't it?

VA rating of transformers?


Quote:
Originally Posted by Dave S View Post
Actually this was quite a tricky build:
- the 1/4" terminals are rather close to the rectifier diodes and require sleeving and careful fitting
- access to a screw to fasten the 3886 is blocked by other components and it's not possible to use an ally bar to clamp it, for the same reason.
Never had problems with faston tabs... they're a bit tight with 35mm caps, though.

The LM3886 should be fixed by a nut over a M3 grub screw:

Click the image to open in full size.

Click the image to open in full size.

Quote:
Originally Posted by Dave S View Post
I will probably change it to R-cores and Rev A and a nice box if it become my favourite amp.
Rev A is an improvement, as r-cores if you can find them now that Selectronic is no longer in activity...

Quote:
Originally Posted by Dave S View Post
Just checking... for Rev A (changing from FE):
- change R3 from 0.5R to 0.33R
- delete C10 and R39

Is that right?
Correct
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File Type: jpg Socket-Screws-2_billboard.jpg (40.2 KB, 226 views)
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Old 21st April 2017, 12:21 AM   #3004
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Quote:
Originally Posted by Dave S View Post
Maybe it's a touch lightweight, but that could be the toroids (used with several amps previously and tend to have this character), or maybe it needs to some use for the parts to settle down.
Hi Dave,

Like Dario, I'm a little surprised to hear lightweight. Of course, I out of touch using an older version, but I think the same things probably affect bass (Dario, please jump in and correct me). I see that you are already using the Mundorf power supply caps. That's good and was found to help the bass in early testing.

As Dario implies, with Toroids, a higher VA rating seemed to help bass as well. I've been using 300 VA Antek toroids, which is overkill, but a bigger VA is an option if you can't find R-core.

The other thing I noticed is that it appears you are running a DC coupled input (no input capacitor blocking DC). Normally, that cap and the input impedance resistor define the bass corner frequency of the bandwidth as well as affects the sound character a bit. When you are DC coupled, I'm not sure what defines the low end of the bandwidth, but I think the characteristics of the source device output impedance become part of the equation. I hope someone smarter can explain this phenomenon.

Anyway, I hope you enjoy it, I have.

Jac
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Old 21st April 2017, 01:48 AM   #3005
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Originally Posted by lehmanhill View Post
The other thing I noticed is that it appears you are running a DC coupled input (no input capacitor blocking DC). Normally, that cap and the input impedance resistor define the bass corner frequency of the bandwidth as well as affects the sound character a bit. When you are DC coupled, I'm not sure what defines the low end of the bandwidth, but I think the characteristics of the source device output impedance become part of the equation. I hope someone smarter can explain this phenomenon.
The low frequency bandwidth will be defined by the feedback cap C9.

I run without an input cap, and the low frequency weight is superb. I also use 300va torroids, but also some non standard mods which probably help.

i'd suggest to get used to it for a while, and let your (Dave's) amp/ears burn in.
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Old 21st April 2017, 07:36 AM   #3006
Dave S is offline Dave S  United Kingdom
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The lightweight sound was not the amp!!!!
I don't need an input cap for a very good reason!

Here's what happened:
- after my usual bench tests to check stability and correct operation I put the amp in my system and took and posted the picture
- after 1/2 hour of listening Dario posted asking for my thoughts on the sound
- I made the schoolboy error of commenting immediately
- after further listening I realised something was really not right. I then looked againa the the schematic and realised the gain of the FE is significantly higher than my usual amp(s)
- I turned up the bass level on my active XO so that the <100Hz matches the main speakers - leanness instantly fixed!

Anyway, apologies for the false alarm. I will not be commenting again on SQ until the amp has clocked up some decent hours and I have done some proper comparisions.

Last edited by Dave S; 21st April 2017 at 07:39 AM.
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Old 21st April 2017, 07:42 AM   #3007
Reality first!
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Quote:
Originally Posted by Dave S View Post
The lightweight sound was not the amp!!!!
I don't need an input cap for a very good reason!
(...)
Anyway, apologies for the false alarm. I will not be commenting again on SQ until the amp has clocked up some decent hours and I have done some proper comparisions.
Don't worry, the important thing is that you fixed the 'problem'

Keep us informed
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Old 21st April 2017, 12:41 PM   #3008
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Quote:
Originally Posted by Dave S View Post
The lightweight sound was not the amp!!!!
I don't need an input cap for a very good reason!

- I turned up the bass level on my active XO so that the <100Hz matches the main speakers - leanness instantly fixed!
A
Dave,

I'm sorry. I didn't mean to suggest that you need an input cap. I was just rambling on about things that were different from standard and possibilities that would affect bass.

And Spartacus is right about the low end cutoff frequency in a direct coupled FE amp. I knew that, but wasn't thinking clearly. I should think before typing next time.

Anyway, I'm glad you found the source of the issue. Enjoy your experiments.

Jac
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Old 21st April 2017, 02:57 PM   #3009
Dave S is offline Dave S  United Kingdom
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Jac,

I also didn't mean to sound aggressive in my reply. Anyway I am confident to run without an input cap because:
1) The FE doesn't receive any signal at LF
2) I am confident my XO does not output dc (at least <2mV)
3) The DC protection will hopefully save the day if it's ever needed

Interim report (can't resist) after a few hours of listening:- Wow! This is a very, very good amp!
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Old 21st April 2017, 03:11 PM   #3010
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Quote:
Originally Posted by Dave S View Post
I also didn't mean to sound aggressive in my reply.

Interim report (can't resist) after a few hours of listening:- Wow! This is a very, very good amp!
Dave,

You didn't sound too aggressive. I just wanted to make sure I wasn't sticking my nose in where it wasn't wanted. We're fine.

As for your interim report, Oh Yeah!

Jac
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