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oceanobsession
06-10-2019, 16:37
Just wondered if these would work with a pair of dave slagle auto formers , would these mono circuit board have gain and would I need 2 transformers
oh and do they look like they could sound great . will be using a sieden pot cheers phil.


https://www.ebay.co.uk/itm/2pcs-Pass-ALEPH-P-rev-1-7-Full-balance-Hife-fever-Pre-amplifier-finished-Board/283405250684?hash=item41fc44f07c:g:OtwAAOSwXoJcfkD q

Bigman80
06-10-2019, 17:50
Just wondered if these would work with a pair of dave slagle auto formers , would these mono circuit board have gain and would I need 2 transformers
oh and do they look like they could sound great . will be using a sieden pot cheers phil.


https://www.ebay.co.uk/itm/2pcs-Pass-ALEPH-P-rev-1-7-Full-balance-Hife-fever-Pre-amplifier-finished-Board/283405250684?hash=item41fc44f07c:g:OtwAAOSwXoJcfkD qWith at least 8 polyester caps on each board, it wouldn't make the cut here.

Why not get a DCB1 board?

If you don't need gain, it could be perfect for you.

oceanobsession
06-10-2019, 18:29
Hi bigman . I suppose I could do with a little gain , saying that it can still be to loud , but doesn't the sound quality suffer closer to full volume as in
distortion. hardly registers on the power amp meters but it would if there were about 18db of gain . I never thought about the caps if there for the power supply it doesn't matter I don't think , but otherwise yes they could/would smear detail. im building the slagle with seiden switch anyway just
thinking about more gain , I know you can switch in and out with the slagles to get a bit more oomph . I thought being a pass labs design they would be good and independent . phil.

Bigman80
06-10-2019, 18:41
Hi bigman . I suppose I could do with a little gain , saying that it can still be to loud , but doesn't the sound quality suffer closer to full volume as in
distortion. hardly registers on the power amp meters but it would if there were about 18db of gain . I never thought about the caps if there for the power supply it doesn't matter I don't think , but otherwise yes they could/would smear detail. im building the slagle with seiden switch anyway just
thinking about more gain , I know you can switch in and out with the slagles to get a bit more oomph . I thought being a pass labs design they would be good and independent . phil.Phil,

A pass labs design it may be, but this is a Chinese clone and whilst it may be very close to the original (wouldn't know personally) they rarely use high quality parts.

You could try and find the bare PCBs and populate them with parts bought from a more reputable source. If I was set on the design, that's what I would do.

It will be more time consumingand and more expensive but you'd have a custom filled pcb of known origin.

I'm not saying it won't be good but I think polyester caps are not the best for this application.

Also, I think most of the film caps are likely to be in the signal path as the chinese rarely put them in the PSU, as you can see with the electrolitics being on the same board.

Usually, the more gain you use, the more distortion is present. However, the DCB1 doesn't have gain so this is a non issue in that aspect.

oceanobsession
06-10-2019, 19:14
I take your point thanks for your advice cheers phil.

oceanobsession
06-10-2019, 20:36
Hi again , just reading about the dcb1 and found this post where they have moved the bias from 130 to 180 creating gain without any sacrifices

After reading this presentation I got the idea that one can search for an optimum bias for a push pull buffer so I decided to play a bit with the bias and increased it slightly from 130 to 180mA.

Measurements showed a real improvement... squares look like squares until 50kHz and faze shift is also greatly reduced in both extremes.

The major improvement is in bandwidth that now extends to 580khz at -3dB and starts at 1.4Hz at -3dB.

I could not believe in my measurements so I repeated them several times with consistent results.

Quite dazzled I connected the amp to my main system and now it sings !!!

Treble is now really extended and clear. Image grew a lot laterally as well as in depth. Bass is perfectly integrated, going low with very good control.

is this possible , cheers phil.

Bigman80
06-10-2019, 20:58
Hi again , just reading about the dcb1 and found this post where they have moved the bias from 130 to 180 creating gain without any sacrifices

After reading this presentation I got the idea that one can search for an optimum bias for a push pull buffer so I decided to play a bit with the bias and increased it slightly from 130 to 180mA.

Measurements showed a real improvement... squares look like squares until 50kHz and faze shift is also greatly reduced in both extremes.

The major improvement is in bandwidth that now extends to 580khz at -3dB and starts at 1.4Hz at -3dB.

I could not believe in my measurements so I repeated them several times with consistent results.

Quite dazzled I connected the amp to my main system and now it sings !!!

Treble is now really extended and clear. Image grew a lot laterally as well as in depth. Bass is perfectly integrated, going low with very good control.

is this possible , cheers phil.I don't see why not but I'm no expert on this level lol.

Where is the post?

oceanobsession
06-10-2019, 21:08
Diy audio ,

After reading this presentation I got the idea that one can search for an optimum bias for a push pull buffer so I decided to play a bit with the bias and increased it slightly from 130 to 180mA.

Measurements showed a real improvement... squares look like squares until 50kHz and faze shift is also greatly reduced in both extremes.

The major improvement is in bandwidth that now extends to 580khz at -3dB and starts at 1.4Hz at -3dB.

I could not believe in my measurements so I repeated them several times with consistent results.

Quite dazzled I connected the amp to my main system and now it sings !!!

Treble is now really extended and clear. Image grew a lot laterally as well as in depth. Bass is perfectly integrated, going low with very good control.

Voices are true and cymbals have real slam.

The amp is really quiet and I find the 19dB gain adequate in my system.

I plotted my measurements that I post here hoping for some edificant comments.

PS: I now consider this amp very good and the only drawbacks I can find are related with the opamp input .... maybe it is possible to use a suitable discrete jfet input ?
Attached Images

180mA bias.png (53.2 KB, 131 views)