It is currently Sun Jun 24, 2018 7:33 pm

Home brew HIFI

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Home brew HIFI

Post by PYE625 » Sat Mar 07, 2015 10:48 am

Hi, just thought I would share with anyone interested in building their own valve amplifiers my circuits that I have constructed.
I use this lot to drive a pair of Quad ESL57 with excellent results.
Each circuit is housed in a grey enclosure from RS, photos of which I will post shortly.

I make absolutely no claim to anything original, the circuits are merely variations of standard designs copied from various publications and slightly modified to suit my needs. The pre-amp PSU transformer I had made to my specification to suit the circuit, but the others were sourced from Sowter (Type U064 for the output stage of the power amp.)

First two are the pre-amp, then it's own PSU, followed by the power amp and it's PSU.
The pre-amp PSU is perhaps just a little over-the-top for a pre-amp, but it was fun to build and is EXTREMELY stable !!
Something like 0.01 volt variation of output for 20 volt change in mains.
Attachments
LINE LEVEL STAGE.jpg
PHONO STAGE.jpg
PRE AMP PSU.jpg
POWER AMP.jpg
PWR AMP PSU.jpg

 
Posts: 59
Joined: Tue Feb 28, 2012 3:07 pm
Location: Stevenage

Re: Home brew HIFI

Post by wd40addict » Sat Mar 07, 2015 5:11 pm

Hi Andrew,

Looks very interesting, a few comments:

Are you using the miller capacitance of the first triode to form the cartridge load capacitor? This looks like a good way of making something bad do something useful!

How accurate is the RIAA EQ?

I've never actually tried biasing the heater voltage - what effect does it have?

Am I right in thinking you have two balance controls so any cartridge imbalance can be corrected pre the recording output? This is also a nice feature because the main balance control won't (potentially) need adjusting when changing from CD to Gram.

I should think this should very good. What cartridge do you use?

Regards,

Paul

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Sat Mar 07, 2015 6:01 pm

Hi Paul, thanks for your interest.

I use a Shure M75 and the length of the turntable leads plus the miller effect give a capacitance approximately suitable.

I incorporated variable 2watt pre-set cermet resistors in the anode feed to balance the slight difference in gain you always get between valve sections.
I got fed up with trying to find valves with matched sections, and this was my idea of compensating for it.
Once set of course, it needs no alteration until you replace a valve.
The RIAA accuracy is very good and is only dependent of the component stability. It is purely a passive between-stage affair.
I found it in an RCA tube manual and made use of it with slight modification to the gain.
I tried various feedback types of phono stage designs, but i find this one to be the most natural sounding and the RIAA response does not change with varying valve characteristics.

The line stage is a pretty bog-standard cathode follower, but with two sets of outputs for different power amp sensitivity plus of course the recorder output.
I also found that the PSU played a big part in sound quality, hence my rather over-the top adaptation of a Philips stabilized power supply design. The PSU needs to be stable as mains variations cause quite an adverse effect with high gain valve stages. Of course a much simpler design could easily be used, but I rather fancied this one.

Best regards,
Andrew

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Sat Mar 07, 2015 6:33 pm

Here are some pics of my "den" and further down, the assembled amplifiers....
I will take some internal pics when I get time :qq1

Paul, I forgot to say that my reason for biasing the heaters to about +50vdc was to minimize the heater to cathode voltage for the line-stage cathode follower.
It is probably not needed as the cathode voltage is now about 75 volts.
(It was much higher until I altered the first stage from DC-coupled to as it is now.)
Attachments
rsz_img_1575.jpg
rsz_img_1574.jpg
rsz_img_1566.jpg
rsz_img_1576.jpg
rsz_img_1577.jpg

 
Posts: 1450
Joined: Wed Jul 27, 2011 10:14 am
Location: gloucestershire

Re: Home brew HIFI

Post by rob t » Sat Mar 07, 2015 11:14 pm

nice pair of QUAD11 in one of the pics .
I have built 4 valve amps 3 mullard designs and a single ended el34 based on a pye circuit.
I loved the sound of all of them .I like the idea of your complex psu does it alter the sound that much?
what speakers do you use?
the reason I ask is that in the 80's I bought some mission speakers after hearing a mates a disaster for low power valve amps so changed to solid state ending up with an audiolab 8000a .then in 2000 I got hold of a pair of 15" tannoy lancasters very cheap because they both needed reconing but through the audiolab the midrange sounded shoutey so dug out my long forgotten quad 11's fed by a beard Ca506 best sound ever.now I wish I had kept the home made amps .
Rob T

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Sat Mar 07, 2015 11:44 pm

Hi Rob,

I use the ESL57's as pictured. I have been using the Quad II's to drive them but have decided to give them a rest and use my own amp for a while. I have a Quad 405, but don't like the sound through the 57's. To me, it is rather lacking in detail. Plus it's WAY too powerful for them.

I did use a normal non-stabilized psu for the pre-amp, but was surprised how much the phono stage was affected by noise and fluctuations of the mains supply. Looking on the 'scope, the signal was bouncing all over the place rather akin to very low frequency turntable rumble.
I then decided to build a stabilized supply and found that the quality of sound improved dramatically with much greater detail and depth.

 
Posts: 1450
Joined: Wed Jul 27, 2011 10:14 am
Location: gloucestershire

Re: Home brew HIFI

Post by rob t » Sun Mar 08, 2015 12:21 am

thanks for that reply
I did borrow a pair of els67 but did not like the sound with the audiodlab maybe I should of tried the quad 11's
Rob T

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Sun Mar 08, 2015 12:25 am

The 57's are an awkward load plus they need to be positioned with care, ie away from corners and rear wall.
I have never heard such realism from a speaker until these.

 
Posts: 59
Joined: Tue Feb 28, 2012 3:07 pm
Location: Stevenage

Re: Home brew HIFI

Post by wd40addict » Sun Mar 08, 2015 6:43 pm

Rob,

Did you try the halfway house of Audiolab as pre-amp with QuadII power?

I currently use an 8000A, sometimes as a preamp to a Radford STA15 and sometimes on its own. I am interested in the phono amp described here as I still think there's more trapped in the grooves. I can also relate to your 'shouty' comment.

Regards,

Paul

 
Posts: 1450
Joined: Wed Jul 27, 2011 10:14 am
Location: gloucestershire

Re: Home brew HIFI

Post by rob t » Sun Mar 08, 2015 7:07 pm

hi paul no I didn't mainly because I have the beard valve preamp.
Rob T

 
Posts: 59
Joined: Tue Feb 28, 2012 3:07 pm
Location: Stevenage

Re: Home brew HIFI

Post by wd40addict » Mon Mar 09, 2015 11:39 pm

Hi Andrew,

I've been doing a bit of Spice on the RIAA response and there seems to be an issue with the values shown: The 2M2 grid resistor is causing a 2.5dB lift in the bass. See below

2meg2.gif


I dug out my RCA manual and in the original circuit the grid resistor is 680k. Plot below. A similar, but not as good result can also be obtained by leaving the grid resistor at 2M2 and dropping the 470k to approx 300k.

680k.gif


An alternative is maybe to reduce the 0.1uf feeding the 470k to 10n and introduce a little bass rolloff to help with warps (-1.5dB @10Hz).

However there is still some droop at the top end (-2dB @ 20kHz), reducing the anode capacitor from 180pf to 18pf gives the following:

18pf.gif


Note the small scale, errors are now well below 1dB.

Well that's the analysis, now I think I'd like to try building one - thanks for the inspiration :-)

Regards,

Paul

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Tue Mar 10, 2015 8:25 am

Hi Paul, that's excellent :qq1

I will try adjusting the value to 680k, I can't remember why I fitted a 2m2 resistor.
It also gives me a good excuse to take some pic's of the actual build.

Many thanks indeed.

 
Posts: 59
Joined: Tue Feb 28, 2012 3:07 pm
Location: Stevenage

Re: Home brew HIFI

Post by wd40addict » Tue Mar 10, 2015 2:27 pm

Hi Andrew,

Whilst you're in there, if you have a suitable signal generator and AC meter, it would be interesting to know if the response really is 2dB out at 20kHz due to the 180pf. The ideal response would be -19.62dB relative to 1kHz so I think it's actually going to measure around -21.6dB.

It does sound correct because the Ecc83 Ra // 100K will give an output impedance of ~38.5k. 1/(2*pi*38.5e3*180e-12) = 23kHz! Why RCA wanted this early roll off is a mystery. If the capacitor is missed out completely there is some peaking, 18pf seems to give the best result as seen in the last graph.

Regards,

Paul

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Tue Mar 10, 2015 7:43 pm

Hi Paul,
I have found by measurement that with the 180pf fitted the response at 20khz relative to 1khz is -24.4db !
With it removed, I get -21.4 db.
I would imagine there is some stray capacitance to take into account too.
I have also altered the 2m2 to 680k and the lower roll off is better.

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Tue Mar 10, 2015 9:40 pm

As promised, here are some extra pics.
First four are of the pre-amp, last four of it's PSU.
Attachments
rsz_img_1624.jpg
rsz_img_1614.jpg
rsz_img_1615.jpg
rsz_img_1622.jpg
rsz_img_1626.jpg
rsz_img_1625.jpg
rsz_img_1627.jpg
rsz_img_1623.jpg

 
Posts: 1450
Joined: Wed Jul 27, 2011 10:14 am
Location: gloucestershire

Re: Home brew HIFI

Post by rob t » Tue Mar 10, 2015 10:01 pm

What a fantastic job not at all what I was expecting from the description puts my efforts to shame
Rob T

 
Posts: 59
Joined: Tue Feb 28, 2012 3:07 pm
Location: Stevenage

Re: Home brew HIFI

Post by wd40addict » Tue Mar 10, 2015 10:02 pm

Looks really good Andrew!

Very thick cabling, is it something special?

Regards,

Paul

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Tue Mar 10, 2015 10:14 pm

Many thanks for the compliments. :qq1
It's nothing really, just a bit of hard work and patience lol, with application of readily available circuits (RCA and Philips).
The cable is left over bits I "acquired" from work. It is Van-Den-Hul silver plated.
Most of the signal capacitors are Russian paper in oil type and motor-run capacitors for the HT.

 
Posts: 715
Joined: Tue Jan 27, 2015 2:02 pm
Location: Chatteris, Cambs

Re: Home brew HIFI

Post by PYE625 » Fri Mar 13, 2015 10:13 am

Paul,

It would seem that the layout of cables and components around the ECC83 of the phono stage and indeed different ECC83's affect the upper roll-off to a small degree. I found a variation of +/- 1db at 20khz was possible with moving things around slightly.

So it proves that care and attention to the circuit layout is important, and the choice of components too.

I'm very grateful to your previous post as it has highlighted my rather casual assumption that all was well.
I should have been more particular and took the time to make the measurements to begin with. :ccb

 
Posts: 59
Joined: Tue Feb 28, 2012 3:07 pm
Location: Stevenage

Re: Home brew HIFI

Post by wd40addict » Fri Mar 13, 2015 6:05 pm

Andrew,

My pleasure, thanks for such a stimulating project!

It all goes to show measurements are necessary in Hi-Fi whatever some reviewers might think :-)

In case anyone's reading all this wondering "why are they worrying about the odd dB when vinyl isn't flat in the first place" below is the measured frequency response of my Denon DL-304 moving coil cartridge playing Decca LXT5346 test record. The response from 30Hz-18kHz is well within +/-1dB.

LXT5346.gif


Regards,

Paul

 
Posts: 2665
Joined: Sun Sep 01, 2013 6:19 pm
Location: Behind the sofa

Re: Home brew HIFI

Post by Cathovisor » Fri Mar 13, 2015 6:09 pm

wd40addict wrote:Andrew,

My pleasure, thanks for such a stimulating project!

It all goes to show measurements are necessary in Hi-Fi whatever some reviewers might think :-)

In case anyone's reading all this wondering "why are they worrying about the odd dB when vinyl isn't flat in the first place" below is the measured frequency response of my Denon DL-304 moving coil cartridge playing Decca LXT5346 test record. The response from 30Hz-18kHz is well within +/-1dB.
Regards,

Paul

When I bought my Goldring G900IGC back in 1980 (!!) they came with individual calibration and response charts. Similarly, mine was astonishingly flat - I wonder what it's like with the Expert "Paratrace" stylus it now has...? :aaq


Return to General Work Shop Discussion



Who is online

Users browsing this forum: No registered users and 4 guests